`): use regular link syntax instead (`[http://localhost:3000](http://localhost:3000)`)
+- HTML syntax (``): use JSX instead (`
`)
+- Unescaped `{` and `<`: escape them with `\` instead (`\{` and `\<`)
+
+:::danger Experimental CommonMark support
+
+Docusaurus v3 makes it possible to opt-in for a less strict, standard [CommonMark](https://commonmark.org/) support with the following options:
+
+- The `mdx.format: md` front matter
+- The `.md` file extension combined with the `siteConfig.markdown.format: "detect"` configuration
+
+This feature is **experimental** and currently has a few [limitations](https://github.com/facebook/docusaurus/issues/9092).
+
+:::
+
+## Importing code snippets {/* #importing-code-snippets */}
+
+You can not only import a file containing a component definition, but also import any code file as raw text, and then insert it in a code block, thanks to [Webpack raw-loader](https://webpack.js.org/loaders/raw-loader/). In order to use `raw-loader`, you first need to install it in your project:
+
+```bash npm2yarn
+npm install --save raw-loader
+```
+
+Now you can import code snippets from another file as it is:
+
+{/* prettier-ignore */}
+```jsx title="myMarkdownFile.mdx"
+import CodeBlock from '@theme/CodeBlock';
+import MyComponentSource from '!!raw-loader!./myComponent';
+
+{MyComponentSource}
+```
+
+```mdx-code-block
+import CodeBlock from '@theme/CodeBlock';
+import MyComponentSource from '!!raw-loader!@site/src/pages/examples/_myComponent';
+
+
+
+{MyComponentSource}
+
+
+```
+
+See [using code blocks in JSX](./markdown-features-code-blocks.mdx#usage-in-jsx) for more details of the `` component.
+
+:::note
+
+You have to use `` rather than the Markdown triple-backtick ` ``` `, because the latter will ship out any of its content as-is, but you want to interpolate the imported text here.
+
+:::
+
+:::warning
+
+This feature is experimental and might be subject to breaking API changes in the future.
+
+:::
+
+## Importing Markdown {/* #importing-markdown */}
+
+You can use Markdown files as components and import them elsewhere, either in Markdown files or in React pages. Each MDX file default-exports its page content as a React component. In the `import` statement, you can default-import this component with any name, but it must be capitalized following React's naming rules.
+
+By convention, using the **`_` filename prefix** will not create any doc page and means the Markdown file is a **"partial"**, to be imported by other files.
+
+```md title="_markdown-partial-example.mdx"
+Hello {props.name}
+
+This is text some content from `_markdown-partial-example.mdx`.
+```
+
+{/* prettier-ignore */}
+```jsx title="someOtherDoc.mdx"
+import PartialExample from './_markdown-partial-example.mdx';
+
+
+```
+
+```mdx-code-block
+import PartialExample from './_markdown-partial-example.mdx';
+
+
+
+
+```
+
+This way, you can reuse content among multiple pages and avoid duplicating materials.
+
+## Available exports {/* #available-exports */}
+
+Within the MDX page, the following variables are available as globals:
+
+- `frontMatter`: the front matter as a record of string keys and values;
+- `toc`: the table of contents, as a tree of headings. See also [Inline TOC](./markdown-features-toc.mdx#inline-table-of-contents) for a more concrete use-case.
+- `contentTitle`: the Markdown title, which is the first `h1` heading in the Markdown text. It's `undefined` if there isn't one (e.g. title specified in the front matter).
+
+```jsx
+import TOCInline from '@theme/TOCInline';
+import CodeBlock from '@theme/CodeBlock';
+
+The table of contents for this page, serialized:
+
+{JSON.stringify(toc, null, 2)}
+
+The front matter of this page:
+
+
+ {Object.entries(frontMatter).map(([key, value]) => - {key}: {value}
)}
+
+
+The title of this page is: {contentTitle}
+```
+
+```mdx-code-block
+import TOCInline from '@theme/TOCInline';
+
+
+
+The table of contents for this page, serialized:
+
+{JSON.stringify(toc, null, 2)}
+
+The front matter of this page:
+
+
+ {Object.entries(frontMatter).map(([key, value]) => - {key}: {value}
)}
+
+
+The title of this page is: {contentTitle}
+
+
+```
diff --git a/documents/markdown/docusaurus/markdown-features-tabs.md b/documents/markdown/docusaurus/markdown-features-tabs.md
new file mode 100644
index 0000000..b878104
--- /dev/null
+++ b/documents/markdown/docusaurus/markdown-features-tabs.md
@@ -0,0 +1,378 @@
+---
+id: tabs
+description: Using tabs inside Docusaurus Markdown
+slug: /markdown-features/tabs
+---
+
+# Tabs
+
+```mdx-code-block
+import BrowserWindow from '@site/src/components/BrowserWindow';
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+import styles from './markdown-features-tabs-styles.module.css';
+```
+
+Docusaurus provides the `` component that you can use in Markdown thanks to [MDX](./markdown-features-react.mdx):
+
+{/* prettier-ignore */}
+```jsx
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+
+
+
+ This is an apple 🍎
+
+
+ This is an orange 🍊
+
+
+ This is a banana 🍌
+
+
+```
+
+```mdx-code-block
+
+
+ This is an apple 🍎
+ This is an orange 🍊
+ This is a banana 🍌
+
+
+```
+
+---
+
+It is also possible to provide `values` and `defaultValue` props to `Tabs`:
+
+```jsx
+
+ This is an apple 🍎
+ This is an orange 🍊
+ This is a banana 🍌
+
+```
+
+```mdx-code-block
+
+
+ This is an apple 🍎
+ This is an orange 🍊
+ This is a banana 🍌
+
+
+```
+
+
+ Tabs props take precedence over the TabItem props:
+
+```jsx
+
+
+ This is an apple 🍎
+
+
+ This is an orange 🍊
+
+
+ This is a banana 🍌
+
+
+```
+
+```mdx-code-block
+
+
+ This is an apple 🍎
+ This is an orange 🍊
+ This is a banana 🍌
+
+
+```
+
+
+
+:::tip
+
+By default, all tabs are rendered eagerly during the build process, and search engines can index hidden tabs.
+
+It is possible to only render the default tab with ``.
+
+:::
+
+## Displaying a default tab {/* #displaying-a-default-tab */}
+
+The first tab is displayed by default, and to override this behavior, you can specify a default tab by adding `default` to one of the tab items. You can also set the `defaultValue` prop of the `Tabs` component to the label value of your choice. For example, in the example above, either setting `default` for the `value="apple"` tab or setting `defaultValue="apple"` for the tabs forces the "Apple" tab to be open by default.
+
+Docusaurus will throw an error if a `defaultValue` is provided for the `Tabs` but it refers to a non-existing value. If you want none of the tabs to be shown by default, use `defaultValue={null}`.
+
+## Syncing tab choices {/* #syncing-tab-choices */}
+
+You may want choices of the same kind of tabs to sync with each other. For example, you might want to provide different instructions for users on Windows vs users on macOS, and you want to change all OS-specific instructions tabs in one click. To achieve that, you can give all related tabs the same `groupId` prop. Note that doing this will persist the choice in `localStorage` and all `` instances with the same `groupId` will update automatically when the value of one of them is changed. Note that group IDs are globally namespaced.
+
+```jsx
+// highlight-next-line
+
+ Use Ctrl + C to copy.
+ Use Command + C to copy.
+
+
+// highlight-next-line
+
+ Use Ctrl + V to paste.
+ Use Command + V to paste.
+
+```
+
+```mdx-code-block
+
+
+ Use Ctrl + C to copy.
+ Use Command + C to copy.
+
+
+
+ Use Ctrl + V to paste.
+ Use Command + V to paste.
+
+
+```
+
+For all tab groups that have the same `groupId`, the possible values do not need to be the same. If one tab group is chosen a value that does not exist in another tab group with the same `groupId`, the tab group with the missing value won't change its tab. You can see that from the following example. Try to select Linux, and the above tab groups don't change.
+
+```jsx
+
+
+ I am Windows.
+
+
+ I am macOS.
+
+
+ I am Linux.
+
+
+```
+
+```mdx-code-block
+
+
+ I am Windows.
+ I am macOS.
+ I am Linux.
+
+
+```
+
+---
+
+Tab choices with different group IDs will not interfere with each other:
+
+```jsx
+// highlight-next-line
+
+ Windows in windows.
+ macOS is macOS.
+
+
+// highlight-next-line
+
+ Windows is windows.
+ Unix is unix.
+
+```
+
+```mdx-code-block
+
+
+ Windows in windows.
+ macOS is macOS.
+
+
+
+ Windows is windows.
+ Unix is unix.
+
+
+```
+
+## Customizing tabs {/* #customizing-tabs */}
+
+You might want to customize the appearance of a certain set of tabs. You can pass the string in `className` prop, and the specified CSS class will be added to the `Tabs` component:
+
+```jsx
+// highlight-next-line
+
+ This is an apple 🍎
+ This is an orange 🍊
+ This is a banana 🍌
+
+```
+
+```mdx-code-block
+
+
+ This is an apple 🍎
+ This is an orange 🍊
+ This is a banana 🍌
+
+
+```
+
+### Customizing tab headings {/* #customizing-tab-headings */}
+
+You can also customize each tab heading independently by using the `attributes` field. The extra props can be passed to the headings either through the `values` prop in `Tabs`, or props of each `TabItem`—in the same way as you declare `label`.
+
+{/* prettier-ignore */}
+```jsx title="some-doc.mdx"
+import styles from './styles.module.css';
+
+
+
+ This is an apple 🍎
+
+
+ This is an orange 🍊
+
+
+ This is a banana 🍌
+
+
+```
+
+```css title="styles.module.css"
+.red {
+ color: red;
+}
+.red[aria-selected='true'] {
+ border-bottom-color: red;
+}
+
+.orange {
+ color: orange;
+}
+.orange[aria-selected='true'] {
+ border-bottom-color: orange;
+}
+
+.yellow {
+ color: yellow;
+}
+.yellow[aria-selected='true'] {
+ border-bottom-color: yellow;
+}
+```
+
+```mdx-code-block
+
+
+
+ This is an apple 🍎
+
+
+ This is an orange 🍊
+
+
+ This is a banana 🍌
+
+
+
+```
+
+:::tip
+
+`className` would be merged with other default class names. You may also use a custom `data-value` field (`{'data-value': 'apple'}`) paired with CSS attribute selectors:
+
+```css title="styles.module.css"
+li[role='tab'][data-value='apple'] {
+ color: red;
+}
+```
+
+:::
+
+## Query string {/* #query-string */}
+
+It is possible to persist the selected tab into the url search parameters. This enables you to share a link to a page which pre-selects the tab - linking from your Android app to documentation with the Android tabs pre-selected. This feature does not provide an anchor link - the browser will not scroll to the tab.
+
+Use the `queryString` prop to enable this feature and define the search param name to use.
+
+```tsx
+// highlight-next-line
+
+
+ Android
+
+
+ iOS
+
+
+```
+
+```mdx-code-block
+
+
+ Android
+ iOS
+
+
+```
+
+As soon as a tab is clicked, a search parameter is added at the end of the url: `?current-os=android` or `?current-os=ios`.
+
+:::tip
+
+`queryString` can be used together with `groupId`.
+
+For convenience, when the `queryString` prop is `true`, the `groupId` value will be used as a fallback.
+
+```tsx
+// highlight-next-line
+
+
+ Android
+
+
+ iOS
+
+
+```
+
+```mdx-code-block
+
+
+ Android
+ iOS
+
+
+```
+
+When the page loads, the tab query string choice will be restored in priority over the `groupId` choice (using `localStorage`).
+
+:::
diff --git a/documents/markdown/rust-book/appendix-00.md b/documents/markdown/rust-book/appendix-00.md
new file mode 100644
index 0000000..83a7e91
--- /dev/null
+++ b/documents/markdown/rust-book/appendix-00.md
@@ -0,0 +1,4 @@
+# Appendix
+
+The following sections contain reference material you may find useful in your
+Rust journey.
diff --git a/documents/markdown/rust-book/appendix-01-keywords.md b/documents/markdown/rust-book/appendix-01-keywords.md
new file mode 100644
index 0000000..5d4716b
--- /dev/null
+++ b/documents/markdown/rust-book/appendix-01-keywords.md
@@ -0,0 +1,140 @@
+## Appendix A: Keywords
+
+The following lists contain keywords that are reserved for current or future
+use by the Rust language. As such, they cannot be used as identifiers (except
+as raw identifiers, as we discuss in the [“Raw
+Identifiers”][raw-identifiers] section). _Identifiers_ are names
+of functions, variables, parameters, struct fields, modules, crates, constants,
+macros, static values, attributes, types, traits, or lifetimes.
+
+[raw-identifiers]: #raw-identifiers
+
+### Keywords Currently in Use
+
+The following is a list of keywords currently in use, with their functionality
+described.
+
+- **`as`**: Perform primitive casting, disambiguate the specific trait
+ containing an item, or rename items in `use` statements.
+- **`async`**: Return a `Future` instead of blocking the current thread.
+- **`await`**: Suspend execution until the result of a `Future` is ready.
+- **`break`**: Exit a loop immediately.
+- **`const`**: Define constant items or constant raw pointers.
+- **`continue`**: Continue to the next loop iteration.
+- **`crate`**: In a module path, refers to the crate root.
+- **`dyn`**: Dynamic dispatch to a trait object.
+- **`else`**: Fallback for `if` and `if let` control flow constructs.
+- **`enum`**: Define an enumeration.
+- **`extern`**: Link an external function or variable.
+- **`false`**: Boolean false literal.
+- **`fn`**: Define a function or the function pointer type.
+- **`for`**: Loop over items from an iterator, implement a trait, or specify a
+ higher ranked lifetime.
+- **`if`**: Branch based on the result of a conditional expression.
+- **`impl`**: Implement inherent or trait functionality.
+- **`in`**: Part of `for` loop syntax.
+- **`let`**: Bind a variable.
+- **`loop`**: Loop unconditionally.
+- **`match`**: Match a value to patterns.
+- **`mod`**: Define a module.
+- **`move`**: Make a closure take ownership of all its captures.
+- **`mut`**: Denote mutability in references, raw pointers, or pattern bindings.
+- **`pub`**: Denote public visibility in struct fields, `impl` blocks, or
+ modules.
+- **`ref`**: Bind by reference.
+- **`return`**: Return from function.
+- **`Self`**: A type alias for the type we are defining or implementing.
+- **`self`**: Method subject or current module.
+- **`static`**: Global variable or lifetime lasting the entire program
+ execution.
+- **`struct`**: Define a structure.
+- **`super`**: Parent module of the current module.
+- **`trait`**: Define a trait.
+- **`true`**: Boolean true literal.
+- **`type`**: Define a type alias or associated type.
+- **`union`**: Define a [union][union]; is a keyword only when
+ used in a union declaration.
+- **`unsafe`**: Denote unsafe code, functions, traits, or implementations.
+- **`use`**: Bring symbols into scope.
+- **`where`**: Denote clauses that constrain a type.
+- **`while`**: Loop conditionally based on the result of an expression.
+
+[union]: ../reference/items/unions.html
+
+### Keywords Reserved for Future Use
+
+The following keywords do not yet have any functionality but are reserved by
+Rust for potential future use:
+
+- `abstract`
+- `become`
+- `box`
+- `do`
+- `final`
+- `gen`
+- `macro`
+- `override`
+- `priv`
+- `try`
+- `typeof`
+- `unsized`
+- `virtual`
+- `yield`
+
+### Raw Identifiers
+
+_Raw identifiers_ are the syntax that lets you use keywords where they wouldn’t
+normally be allowed. You use a raw identifier by prefixing a keyword with `r#`.
+
+For example, `match` is a keyword. If you try to compile the following function
+that uses `match` as its name:
+
+Filename: src/main.rs
+
+```rust,ignore,does_not_compile
+fn match(needle: &str, haystack: &str) -> bool {
+ haystack.contains(needle)
+}
+```
+
+you’ll get this error:
+
+```text
+error: expected identifier, found keyword `match`
+ --> src/main.rs:4:4
+ |
+4 | fn match(needle: &str, haystack: &str) -> bool {
+ | ^^^^^ expected identifier, found keyword
+```
+
+The error shows that you can’t use the keyword `match` as the function
+identifier. To use `match` as a function name, you need to use the raw
+identifier syntax, like this:
+
+Filename: src/main.rs
+
+```rust
+fn r#match(needle: &str, haystack: &str) -> bool {
+ haystack.contains(needle)
+}
+
+fn main() {
+ assert!(r#match("foo", "foobar"));
+}
+```
+
+This code will compile without any errors. Note the `r#` prefix on the function
+name in its definition as well as where the function is called in `main`.
+
+Raw identifiers allow you to use any word you choose as an identifier, even if
+that word happens to be a reserved keyword. This gives us more freedom to choose
+identifier names, as well as lets us integrate with programs written in a
+language where these words aren’t keywords. In addition, raw identifiers allow
+you to use libraries written in a different Rust edition than your crate uses.
+For example, `try` isn’t a keyword in the 2015 edition but is in the 2018, 2021,
+and 2024 editions. If you depend on a library that is written using the 2015
+edition and has a `try` function, you’ll need to use the raw identifier syntax,
+`r#try` in this case, to call that function from your code on later editions.
+See [Appendix E][appendix-e] for more information on editions.
+
+[appendix-e]: appendix-05-editions.html
diff --git a/documents/markdown/rust-book/appendix-02-operators.md b/documents/markdown/rust-book/appendix-02-operators.md
new file mode 100644
index 0000000..e938b5e
--- /dev/null
+++ b/documents/markdown/rust-book/appendix-02-operators.md
@@ -0,0 +1,206 @@
+## Appendix B: Operators and Symbols
+
+This appendix contains a glossary of Rust’s syntax, including operators and
+other symbols that appear by themselves or in the context of paths, generics,
+trait bounds, macros, attributes, comments, tuples, and brackets.
+
+### Operators
+
+Table B-1 contains the operators in Rust, an example of how the operator would
+appear in context, a short explanation, and whether that operator is
+overloadable. If an operator is overloadable, the relevant trait to use to
+overload that operator is listed.
+
+Table B-1: Operators
+
+| Operator | Example | Explanation | Overloadable? |
+| ------------------------- | ------------------------------------------------------- | --------------------------------------------------------------------- | -------------- |
+| `!` | `ident!(...)`, `ident!{...}`, `ident![...]` | Macro expansion | |
+| `!` | `!expr` | Bitwise or logical complement | `Not` |
+| `!=` | `expr != expr` | Nonequality comparison | `PartialEq` |
+| `%` | `expr % expr` | Arithmetic remainder | `Rem` |
+| `%=` | `var %= expr` | Arithmetic remainder and assignment | `RemAssign` |
+| `&` | `&expr`, `&mut expr` | Borrow | |
+| `&` | `&type`, `&mut type`, `&'a type`, `&'a mut type` | Borrowed pointer type | |
+| `&` | `expr & expr` | Bitwise AND | `BitAnd` |
+| `&=` | `var &= expr` | Bitwise AND and assignment | `BitAndAssign` |
+| `&&` | `expr && expr` | Short-circuiting logical AND | |
+| `*` | `expr * expr` | Arithmetic multiplication | `Mul` |
+| `*=` | `var *= expr` | Arithmetic multiplication and assignment | `MulAssign` |
+| `*` | `*expr` | Dereference | `Deref` |
+| `*` | `*const type`, `*mut type` | Raw pointer | |
+| `+` | `trait + trait`, `'a + trait` | Compound type constraint | |
+| `+` | `expr + expr` | Arithmetic addition | `Add` |
+| `+=` | `var += expr` | Arithmetic addition and assignment | `AddAssign` |
+| `,` | `expr, expr` | Argument and element separator | |
+| `-` | `- expr` | Arithmetic negation | `Neg` |
+| `-` | `expr - expr` | Arithmetic subtraction | `Sub` |
+| `-=` | `var -= expr` | Arithmetic subtraction and assignment | `SubAssign` |
+| `->` | `fn(...) -> type`, |...| -> type | Function and closure return type | |
+| `.` | `expr.ident` | Field access | |
+| `.` | `expr.ident(expr, ...)` | Method call | |
+| `.` | `expr.0`, `expr.1`, and so on | Tuple indexing | |
+| `..` | `..`, `expr..`, `..expr`, `expr..expr` | Right-exclusive range literal | `PartialOrd` |
+| `..=` | `..=expr`, `expr..=expr` | Right-inclusive range literal | `PartialOrd` |
+| `..` | `..expr` | Struct literal update syntax | |
+| `..` | `variant(x, ..)`, `struct_type { x, .. }` | “And the rest” pattern binding | |
+| `...` | `expr...expr` | (Deprecated, use `..=` instead) In a pattern: inclusive range pattern | |
+| `/` | `expr / expr` | Arithmetic division | `Div` |
+| `/=` | `var /= expr` | Arithmetic division and assignment | `DivAssign` |
+| `:` | `pat: type`, `ident: type` | Constraints | |
+| `:` | `ident: expr` | Struct field initializer | |
+| `:` | `'a: loop {...}` | Loop label | |
+| `;` | `expr;` | Statement and item terminator | |
+| `;` | `[...; len]` | Part of fixed-size array syntax | |
+| `<<` | `expr << expr` | Left-shift | `Shl` |
+| `<<=` | `var <<= expr` | Left-shift and assignment | `ShlAssign` |
+| `<` | `expr < expr` | Less than comparison | `PartialOrd` |
+| `<=` | `expr <= expr` | Less than or equal to comparison | `PartialOrd` |
+| `=` | `var = expr`, `ident = type` | Assignment/equivalence | |
+| `==` | `expr == expr` | Equality comparison | `PartialEq` |
+| `=>` | `pat => expr` | Part of match arm syntax | |
+| `>` | `expr > expr` | Greater than comparison | `PartialOrd` |
+| `>=` | `expr >= expr` | Greater than or equal to comparison | `PartialOrd` |
+| `>>` | `expr >> expr` | Right-shift | `Shr` |
+| `>>=` | `var >>= expr` | Right-shift and assignment | `ShrAssign` |
+| `@` | `ident @ pat` | Pattern binding | |
+| `^` | `expr ^ expr` | Bitwise exclusive OR | `BitXor` |
+| `^=` | `var ^= expr` | Bitwise exclusive OR and assignment | `BitXorAssign` |
+| | | pat | pat | Pattern alternatives | |
+| | | expr | expr | Bitwise OR | `BitOr` |
+| |= | var |= expr | Bitwise OR and assignment | `BitOrAssign` |
+| || | expr || expr | Short-circuiting logical OR | |
+| `?` | `expr?` | Error propagation | |
+
+### Non-operator Symbols
+
+The following tables contain all symbols that don’t function as operators; that
+is, they don’t behave like a function or method call.
+
+Table B-2 shows symbols that appear on their own and are valid in a variety of
+locations.
+
+Table B-2: Stand-alone Syntax
+
+| Symbol | Explanation |
+| ---------------------------------------------------------------------- | ---------------------------------------------------------------------- |
+| `'ident` | Named lifetime or loop label |
+| Digits immediately followed by `u8`, `i32`, `f64`, `usize`, and so on | Numeric literal of specific type |
+| `"..."` | String literal |
+| `r"..."`, `r#"..."#`, `r##"..."##`, and so on | Raw string literal; escape characters not processed |
+| `b"..."` | Byte string literal; constructs an array of bytes instead of a string |
+| `br"..."`, `br#"..."#`, `br##"..."##`, and so on | Raw byte string literal; combination of raw and byte string literal |
+| `'...'` | Character literal |
+| `b'...'` | ASCII byte literal |
+| |...| expr | Closure |
+| `!` | Always-empty bottom type for diverging functions |
+| `_` | “Ignored” pattern binding; also used to make integer literals readable |
+
+Table B-3 shows symbols that appear in the context of a path through the module
+hierarchy to an item.
+
+Table B-3: Path-Related Syntax
+
+| Symbol | Explanation |
+| --------------------------------------- | -------------------------------------------------------------------------------------------------------------|
+| `ident::ident` | Namespace path |
+| `::path` | Path relative to the crate root (that is, an explicitly absolute path) |
+| `self::path` | Path relative to the current module (that is, an explicitly relative path) |
+| `super::path` | Path relative to the parent of the current module |
+| `type::ident`, `::ident` | Associated constants, functions, and types |
+| `::...` | Associated item for a type that cannot be directly named (for example, `<&T>::...`, `<[T]>::...`, and so on) |
+| `trait::method(...)` | Disambiguating a method call by naming the trait that defines it |
+| `type::method(...)` | Disambiguating a method call by naming the type for which it’s defined |
+| `::method(...)` | Disambiguating a method call by naming the trait and type |
+
+Table B-4 shows symbols that appear in the context of using generic type
+parameters.
+
+Table B-4: Generics
+
+| Symbol | Explanation |
+| ------------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------- |
+| `path<...>` | Specifies parameters to a generic type in a type (for example, `Vec`) |
+| `path::<...>`, `method::<...>` | Specifies parameters to a generic type, function, or method in an expression; often referred to as _turbofish_ (for example, `"42".parse::()`) |
+| `fn ident<...> ...` | Define generic function |
+| `struct ident<...> ...` | Define generic structure |
+| `enum ident<...> ...` | Define generic enumeration |
+| `impl<...> ...` | Define generic implementation |
+| `for<...> type` | Higher ranked lifetime bounds |
+| `type` | A generic type where one or more associated types have specific assignments (for example, `Iterator`) |
+
+Table B-5 shows symbols that appear in the context of constraining generic type
+parameters with trait bounds.
+
+Table B-5: Trait Bound Constraints
+
+| Symbol | Explanation |
+| ----------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------ |
+| `T: U` | Generic parameter `T` constrained to types that implement `U` |
+| `T: 'a` | Generic type `T` must outlive lifetime `'a` (meaning the type cannot transitively contain any references with lifetimes shorter than `'a`) |
+| `T: 'static` | Generic type `T` contains no borrowed references other than `'static` ones |
+| `'b: 'a` | Generic lifetime `'b` must outlive lifetime `'a` |
+| `T: ?Sized` | Allow generic type parameter to be a dynamically sized type |
+| `'a + trait`, `trait + trait` | Compound type constraint |
+
+Table B-6 shows symbols that appear in the context of calling or defining
+macros and specifying attributes on an item.
+
+Table B-6: Macros and Attributes
+
+| Symbol | Explanation |
+| ------------------------------------------- | ------------------ |
+| `#[meta]` | Outer attribute |
+| `#![meta]` | Inner attribute |
+| `$ident` | Macro substitution |
+| `$ident:kind` | Macro metavariable |
+| `$(...)...` | Macro repetition |
+| `ident!(...)`, `ident!{...}`, `ident![...]` | Macro invocation |
+
+Table B-7 shows symbols that create comments.
+
+Table B-7: Comments
+
+| Symbol | Explanation |
+| ---------- | ----------------------- |
+| `//` | Line comment |
+| `//!` | Inner line doc comment |
+| `///` | Outer line doc comment |
+| `/*...*/` | Block comment |
+| `/*!...*/` | Inner block doc comment |
+| `/**...*/` | Outer block doc comment |
+
+Table B-8 shows the contexts in which parentheses are used.
+
+Table B-8: Parentheses
+
+| Symbol | Explanation |
+| ------------------------ | ------------------------------------------------------------------------------------------- |
+| `()` | Empty tuple (aka unit), both literal and type |
+| `(expr)` | Parenthesized expression |
+| `(expr,)` | Single-element tuple expression |
+| `(type,)` | Single-element tuple type |
+| `(expr, ...)` | Tuple expression |
+| `(type, ...)` | Tuple type |
+| `expr(expr, ...)` | Function call expression; also used to initialize tuple `struct`s and tuple `enum` variants |
+
+Table B-9 shows the contexts in which curly brackets are used.
+
+Table B-9: Curly Brackets
+
+| Context | Explanation |
+| ------------ | ---------------- |
+| `{...}` | Block expression |
+| `Type {...}` | Struct literal |
+
+Table B-10 shows the contexts in which square brackets are used.
+
+Table B-10: Square Brackets
+
+| Context | Explanation |
+| -------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------- |
+| `[...]` | Array literal |
+| `[expr; len]` | Array literal containing `len` copies of `expr` |
+| `[type; len]` | Array type containing `len` instances of `type` |
+| `expr[expr]` | Collection indexing; overloadable (`Index`, `IndexMut`) |
+| `expr[..]`, `expr[a..]`, `expr[..b]`, `expr[a..b]` | Collection indexing pretending to be collection slicing, using `Range`, `RangeFrom`, `RangeTo`, or `RangeFull` as the “index” |
diff --git a/documents/markdown/rust-book/appendix-03-derivable-traits.md b/documents/markdown/rust-book/appendix-03-derivable-traits.md
new file mode 100644
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--- /dev/null
+++ b/documents/markdown/rust-book/appendix-03-derivable-traits.md
@@ -0,0 +1,185 @@
+## Appendix C: Derivable Traits
+
+In various places in the book, we’ve discussed the `derive` attribute, which
+you can apply to a struct or enum definition. The `derive` attribute generates
+code that will implement a trait with its own default implementation on the
+type you’ve annotated with the `derive` syntax.
+
+In this appendix, we provide a reference of all the traits in the standard
+library that you can use with `derive`. Each section covers:
+
+- What operators and methods deriving this trait will enable
+- What the implementation of the trait provided by `derive` does
+- What implementing the trait signifies about the type
+- The conditions in which you’re allowed or not allowed to implement the trait
+- Examples of operations that require the trait
+
+If you want different behavior from that provided by the `derive` attribute,
+consult the [standard library documentation](../std/index.html)
+for each trait for details on how to manually implement them.
+
+The traits listed here are the only ones defined by the standard library that
+can be implemented on your types using `derive`. Other traits defined in the
+standard library don’t have sensible default behavior, so it’s up to you to
+implement them in the way that makes sense for what you’re trying to accomplish.
+
+An example of a trait that can’t be derived is `Display`, which handles
+formatting for end users. You should always consider the appropriate way to
+display a type to an end user. What parts of the type should an end user be
+allowed to see? What parts would they find relevant? What format of the data
+would be most relevant to them? The Rust compiler doesn’t have this insight, so
+it can’t provide appropriate default behavior for you.
+
+The list of derivable traits provided in this appendix is not comprehensive:
+Libraries can implement `derive` for their own traits, making the list of
+traits you can use `derive` with truly open ended. Implementing `derive`
+involves using a procedural macro, which is covered in the [“Custom `derive`
+Macros”][custom-derive-macros] section in Chapter 20.
+
+### `Debug` for Programmer Output
+
+The `Debug` trait enables debug formatting in format strings, which you
+indicate by adding `:?` within `{}` placeholders.
+
+The `Debug` trait allows you to print instances of a type for debugging
+purposes, so you and other programmers using your type can inspect an instance
+at a particular point in a program’s execution.
+
+The `Debug` trait is required, for example, in the use of the `assert_eq!`
+macro. This macro prints the values of instances given as arguments if the
+equality assertion fails so that programmers can see why the two instances
+weren’t equal.
+
+### `PartialEq` and `Eq` for Equality Comparisons
+
+The `PartialEq` trait allows you to compare instances of a type to check for
+equality and enables use of the `==` and `!=` operators.
+
+Deriving `PartialEq` implements the `eq` method. When `PartialEq` is derived on
+structs, two instances are equal only if _all_ fields are equal, and the
+instances are not equal if _any_ fields are not equal. When derived on enums,
+each variant is equal to itself and not equal to the other variants.
+
+The `PartialEq` trait is required, for example, with the use of the
+`assert_eq!` macro, which needs to be able to compare two instances of a type
+for equality.
+
+The `Eq` trait has no methods. Its purpose is to signal that for every value of
+the annotated type, the value is equal to itself. The `Eq` trait can only be
+applied to types that also implement `PartialEq`, although not all types that
+implement `PartialEq` can implement `Eq`. One example of this is floating-point
+number types: The implementation of floating-point numbers states that two
+instances of the not-a-number (`NaN`) value are not equal to each other.
+
+An example of when `Eq` is required is for keys in a `HashMap` so that
+the `HashMap` can tell whether two keys are the same.
+
+### `PartialOrd` and `Ord` for Ordering Comparisons
+
+The `PartialOrd` trait allows you to compare instances of a type for sorting
+purposes. A type that implements `PartialOrd` can be used with the `<`, `>`,
+`<=`, and `>=` operators. You can only apply the `PartialOrd` trait to types
+that also implement `PartialEq`.
+
+Deriving `PartialOrd` implements the `partial_cmp` method, which returns an
+`Option` that will be `None` when the values given don’t produce an
+ordering. An example of a value that doesn’t produce an ordering, even though
+most values of that type can be compared, is the `NaN` floating point value.
+Calling `partial_cmp` with any floating-point number and the `NaN`
+floating-point value will return `None`.
+
+When derived on structs, `PartialOrd` compares two instances by comparing the
+value in each field in the order in which the fields appear in the struct
+definition. When derived on enums, variants of the enum declared earlier in the
+enum definition are considered less than the variants listed later.
+
+The `PartialOrd` trait is required, for example, for the `gen_range` method
+from the `rand` crate that generates a random value in the range specified by a
+range expression.
+
+The `Ord` trait allows you to know that for any two values of the annotated
+type, a valid ordering will exist. The `Ord` trait implements the `cmp` method,
+which returns an `Ordering` rather than an `Option` because a valid
+ordering will always be possible. You can only apply the `Ord` trait to types
+that also implement `PartialOrd` and `Eq` (and `Eq` requires `PartialEq`). When
+derived on structs and enums, `cmp` behaves the same way as the derived
+implementation for `partial_cmp` does with `PartialOrd`.
+
+An example of when `Ord` is required is when storing values in a `BTreeSet`,
+a data structure that stores data based on the sort order of the values.
+
+### `Clone` and `Copy` for Duplicating Values
+
+The `Clone` trait allows you to explicitly create a deep copy of a value, and
+the duplication process might involve running arbitrary code and copying heap
+data. See the [“Variables and Data Interacting with
+Clone”][variables-and-data-interacting-with-clone] section in
+Chapter 4 for more information on `Clone`.
+
+Deriving `Clone` implements the `clone` method, which when implemented for the
+whole type, calls `clone` on each of the parts of the type. This means all the
+fields or values in the type must also implement `Clone` to derive `Clone`.
+
+An example of when `Clone` is required is when calling the `to_vec` method on a
+slice. The slice doesn’t own the type instances it contains, but the vector
+returned from `to_vec` will need to own its instances, so `to_vec` calls
+`clone` on each item. Thus, the type stored in the slice must implement `Clone`.
+
+The `Copy` trait allows you to duplicate a value by only copying bits stored on
+the stack; no arbitrary code is necessary. See the [“Stack-Only Data:
+Copy”][stack-only-data-copy] section in Chapter 4 for more
+information on `Copy`.
+
+The `Copy` trait doesn’t define any methods to prevent programmers from
+overloading those methods and violating the assumption that no arbitrary code
+is being run. That way, all programmers can assume that copying a value will be
+very fast.
+
+You can derive `Copy` on any type whose parts all implement `Copy`. A type that
+implements `Copy` must also implement `Clone` because a type that implements
+`Copy` has a trivial implementation of `Clone` that performs the same task as
+`Copy`.
+
+The `Copy` trait is rarely required; types that implement `Copy` have
+optimizations available, meaning you don’t have to call `clone`, which makes
+the code more concise.
+
+Everything possible with `Copy` you can also accomplish with `Clone`, but the
+code might be slower or have to use `clone` in places.
+
+### `Hash` for Mapping a Value to a Value of Fixed Size
+
+The `Hash` trait allows you to take an instance of a type of arbitrary size and
+map that instance to a value of fixed size using a hash function. Deriving
+`Hash` implements the `hash` method. The derived implementation of the `hash`
+method combines the result of calling `hash` on each of the parts of the type,
+meaning all fields or values must also implement `Hash` to derive `Hash`.
+
+An example of when `Hash` is required is in storing keys in a `HashMap`
+to store data efficiently.
+
+### `Default` for Default Values
+
+The `Default` trait allows you to create a default value for a type. Deriving
+`Default` implements the `default` function. The derived implementation of the
+`default` function calls the `default` function on each part of the type,
+meaning all fields or values in the type must also implement `Default` to
+derive `Default`.
+
+The `Default::default` function is commonly used in combination with the struct
+update syntax discussed in the [“Creating Instances from Other Instances with
+Struct Update
+Syntax”][creating-instances-from-other-instances-with-struct-update-syntax] section in Chapter 5. You can customize a few fields of a struct and
+then set and use a default value for the rest of the fields by using
+`..Default::default()`.
+
+The `Default` trait is required when you use the method `unwrap_or_default` on
+`Option` instances, for example. If the `Option` is `None`, the method
+`unwrap_or_default` will return the result of `Default::default` for the type
+`T` stored in the `Option`.
+
+[creating-instances-from-other-instances-with-struct-update-syntax]: ch05-01-defining-structs.html#creating-instances-from-other-instances-with-struct-update-syntax
+[stack-only-data-copy]: ch04-01-what-is-ownership.html#stack-only-data-copy
+[variables-and-data-interacting-with-clone]: ch04-01-what-is-ownership.html#variables-and-data-interacting-with-clone
+[custom-derive-macros]: ch20-05-macros.html#custom-derive-macros
diff --git a/documents/markdown/rust-book/appendix-04-useful-development-tools.md b/documents/markdown/rust-book/appendix-04-useful-development-tools.md
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+## Appendix D: Useful Development Tools
+
+In this appendix, we talk about some useful development tools that the Rust
+project provides. We’ll look at automatic formatting, quick ways to apply
+warning fixes, a linter, and integrating with IDEs.
+
+### Automatic Formatting with `rustfmt`
+
+The `rustfmt` tool reformats your code according to the community code style.
+Many collaborative projects use `rustfmt` to prevent arguments about which
+style to use when writing Rust: Everyone formats their code using the tool.
+
+Rust installations include `rustfmt` by default, so you should already have the
+programs `rustfmt` and `cargo-fmt` on your system. These two commands are
+analogous to `rustc` and `cargo` in that `rustfmt` allows finer grained control
+and `cargo-fmt` understands conventions of a project that uses Cargo. To format
+any Cargo project, enter the following:
+
+```console
+$ cargo fmt
+```
+
+Running this command reformats all the Rust code in the current crate. This
+should only change the code style, not the code semantics. For more information
+on `rustfmt`, see [its documentation][rustfmt].
+
+### Fix Your Code with `rustfix`
+
+The `rustfix` tool is included with Rust installations and can automatically
+fix compiler warnings that have a clear way to correct the problem that’s
+likely what you want. You’ve probably seen compiler warnings before. For
+example, consider this code:
+
+Filename: src/main.rs
+
+```rust
+fn main() {
+ let mut x = 42;
+ println!("{x}");
+}
+```
+
+Here, we’re defining the variable `x` as mutable, but we never actually mutate
+it. Rust warns us about that:
+
+```console
+$ cargo build
+ Compiling myprogram v0.1.0 (file:///projects/myprogram)
+warning: variable does not need to be mutable
+ --> src/main.rs:2:9
+ |
+2 | let mut x = 0;
+ | ----^
+ | |
+ | help: remove this `mut`
+ |
+ = note: `#[warn(unused_mut)]` on by default
+```
+
+The warning suggests that we remove the `mut` keyword. We can automatically
+apply that suggestion using the `rustfix` tool by running the command `cargo
+fix`:
+
+```console
+$ cargo fix
+ Checking myprogram v0.1.0 (file:///projects/myprogram)
+ Fixing src/main.rs (1 fix)
+ Finished dev [unoptimized + debuginfo] target(s) in 0.59s
+```
+
+When we look at _src/main.rs_ again, we’ll see that `cargo fix` has changed the
+code:
+
+Filename: src/main.rs
+
+```rust
+fn main() {
+ let x = 42;
+ println!("{x}");
+}
+```
+
+The variable `x` is now immutable, and the warning no longer appears.
+
+You can also use the `cargo fix` command to transition your code between
+different Rust editions. Editions are covered in [Appendix E][editions].
+
+### More Lints with Clippy
+
+The Clippy tool is a collection of lints to analyze your code so that you can
+catch common mistakes and improve your Rust code. Clippy is included with
+standard Rust installations.
+
+To run Clippy’s lints on any Cargo project, enter the following:
+
+```console
+$ cargo clippy
+```
+
+For example, say you write a program that uses an approximation of a
+mathematical constant, such as pi, as this program does:
+
+
+
+```rust
+fn main() {
+ let x = 3.1415;
+ let r = 8.0;
+ println!("the area of the circle is {}", x * r * r);
+}
+```
+
+
+
+Running `cargo clippy` on this project results in this error:
+
+```text
+error: approximate value of `f{32, 64}::consts::PI` found
+ --> src/main.rs:2:13
+ |
+2 | let x = 3.1415;
+ | ^^^^^^
+ |
+ = note: `#[deny(clippy::approx_constant)]` on by default
+ = help: consider using the constant directly
+ = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#approx_constant
+```
+
+This error lets you know that Rust already has a more precise `PI` constant
+defined, and that your program would be more correct if you used the constant
+instead. You would then change your code to use the `PI` constant.
+
+The following code doesn’t result in any errors or warnings from Clippy:
+
+
+
+```rust
+fn main() {
+ let x = std::f64::consts::PI;
+ let r = 8.0;
+ println!("the area of the circle is {}", x * r * r);
+}
+```
+
+
+
+For more information on Clippy, see [its documentation][clippy].
+
+### IDE Integration Using `rust-analyzer`
+
+To help with IDE integration, the Rust community recommends using
+[`rust-analyzer`][rust-analyzer]. This tool is a set of
+compiler-centric utilities that speak [Language Server Protocol][lsp], which is a specification for IDEs and programming languages to
+communicate with each other. Different clients can use `rust-analyzer`, such as
+[the Rust analyzer plug-in for Visual Studio Code][vscode].
+
+Visit the `rust-analyzer` project’s [home page][rust-analyzer]
+for installation instructions, then install the language server support in your
+particular IDE. Your IDE will gain capabilities such as autocompletion, jump to
+definition, and inline errors.
+
+[rustfmt]: https://github.com/rust-lang/rustfmt
+[editions]: appendix-05-editions.md
+[clippy]: https://github.com/rust-lang/rust-clippy
+[rust-analyzer]: https://rust-analyzer.github.io
+[lsp]: http://langserver.org/
+[vscode]: https://marketplace.visualstudio.com/items?itemName=rust-lang.rust-analyzer
diff --git a/documents/markdown/rust-book/appendix-05-editions.md b/documents/markdown/rust-book/appendix-05-editions.md
new file mode 100644
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--- /dev/null
+++ b/documents/markdown/rust-book/appendix-05-editions.md
@@ -0,0 +1,59 @@
+## Appendix E: Editions
+
+In Chapter 1, you saw that `cargo new` adds a bit of metadata to your
+_Cargo.toml_ file about an edition. This appendix talks about what that means!
+
+The Rust language and compiler have a six-week release cycle, meaning users get
+a constant stream of new features. Other programming languages release larger
+changes less often; Rust releases smaller updates more frequently. After a
+while, all of these tiny changes add up. But from release to release, it can be
+difficult to look back and say, “Wow, between Rust 1.10 and Rust 1.31, Rust has
+changed a lot!”
+
+Every three years or so, the Rust team produces a new Rust _edition_. Each
+edition brings together the features that have landed into a clear package with
+fully updated documentation and tooling. New editions ship as part of the usual
+six-week release process.
+
+Editions serve different purposes for different people:
+
+- For active Rust users, a new edition brings together incremental changes into
+ an easy-to-understand package.
+- For non-users, a new edition signals that some major advancements have
+ landed, which might make Rust worth another look.
+- For those developing Rust, a new edition provides a rallying point for the
+ project as a whole.
+
+At the time of this writing, four Rust editions are available: Rust 2015, Rust
+2018, Rust 2021, and Rust 2024. This book is written using Rust 2024 edition
+idioms.
+
+The `edition` key in _Cargo.toml_ indicates which edition the compiler should
+use for your code. If the key doesn’t exist, Rust uses `2015` as the edition
+value for backward compatibility reasons.
+
+Each project can opt in to an edition other than the default 2015 edition.
+Editions can contain incompatible changes, such as including a new keyword that
+conflicts with identifiers in code. However, unless you opt in to those
+changes, your code will continue to compile even as you upgrade the Rust
+compiler version you use.
+
+All Rust compiler versions support any edition that existed prior to that
+compiler’s release, and they can link crates of any supported editions
+together. Edition changes only affect the way the compiler initially parses
+code. Therefore, if you’re using Rust 2015 and one of your dependencies uses
+Rust 2018, your project will compile and be able to use that dependency. The
+opposite situation, where your project uses Rust 2018 and a dependency uses
+Rust 2015, works as well.
+
+To be clear: Most features will be available on all editions. Developers using
+any Rust edition will continue to see improvements as new stable releases are
+made. However, in some cases, mainly when new keywords are added, some new
+features might only be available in later editions. You will need to switch
+editions if you want to take advantage of such features.
+
+For more details, see [_The Rust Edition Guide_][edition-guide]. This is a
+complete book that enumerates the differences between editions and explains how
+to automatically upgrade your code to a new edition via `cargo fix`.
+
+[edition-guide]: https://doc.rust-lang.org/stable/edition-guide
diff --git a/documents/markdown/rust-book/appendix-06-translation.md b/documents/markdown/rust-book/appendix-06-translation.md
new file mode 100644
index 0000000..0933907
--- /dev/null
+++ b/documents/markdown/rust-book/appendix-06-translation.md
@@ -0,0 +1,32 @@
+## Appendix F: Translations of the Book
+
+For resources in languages other than English. Most are still in progress; see
+[the Translations label][label] to help or let us know about a new translation!
+
+[label]: https://github.com/rust-lang/book/issues?q=is%3Aopen+is%3Aissue+label%3ATranslations
+
+- [Português](https://github.com/rust-br/rust-book-pt-br) (BR)
+- [Português](https://github.com/nunojesus/rust-book-pt-pt) (PT)
+- 简体中文: [KaiserY/trpl-zh-cn](https://github.com/KaiserY/trpl-zh-cn), [gnu4cn/rust-lang-Zh_CN](https://github.com/gnu4cn/rust-lang-Zh_CN)
+- [正體中文](https://github.com/rust-tw/book-tw)
+- [Українська](https://rust-lang-ua.github.io/rustbook_ukrainian)
+- [Español](https://github.com/thecodix/book), [alternate](https://github.com/ManRR/rust-book-es), [Español por RustLangES](https://github.com/RustLangES/rust-book-es)
+- [Русский](https://github.com/rust-lang-ru/book)
+- [한국어](https://github.com/rust-kr/doc.rust-kr.org)
+- [日本語](https://github.com/rust-lang-ja/book-ja)
+- [Français](https://github.com/Jimskapt/rust-book-fr)
+- [Polski](https://github.com/paytchoo/book-pl)
+- [Cebuano](https://github.com/agentzero1/book)
+- [Tagalog](https://github.com/josephace135/book)
+- [Esperanto](https://github.com/psychoslave/Rust-libro)
+- [ελληνική](https://github.com/TChatzigiannakis/rust-book-greek)
+- [Svenska](https://github.com/sebras/book)
+- [Farsi](https://github.com/RustFarsi/book), [Persian (FA)](https://github.com/persian-rust/book)
+- [Deutsch](https://github.com/rust-lang-de/rustbook-de)
+- [हिंदी](https://github.com/venkatarun95/rust-book-hindi)
+- [ไทย](https://github.com/rust-lang-th/book-th)
+- [Danske](https://github.com/DanKHansen/book-dk)
+- [O'zbek](https://github.com/rust-lang-uz/book)
+- [Tiếng Việt](https://github.com/tuanemdev/rust-book-vn)
+- [Italiano](https://nixxo.github.io/rust-lang-book-it/)
+- [বাংলা](https://github.com/IsmailHosenIsmailJames/rust-book-bn)
diff --git a/documents/markdown/rust-book/appendix-07-nightly-rust.md b/documents/markdown/rust-book/appendix-07-nightly-rust.md
new file mode 100644
index 0000000..7108441
--- /dev/null
+++ b/documents/markdown/rust-book/appendix-07-nightly-rust.md
@@ -0,0 +1,206 @@
+## Appendix G - How Rust is Made and “Nightly Rust”
+
+This appendix is about how Rust is made and how that affects you as a Rust
+developer.
+
+### Stability Without Stagnation
+
+As a language, Rust cares a _lot_ about the stability of your code. We want
+Rust to be a rock-solid foundation you can build on, and if things were
+constantly changing, that would be impossible. At the same time, if we can’t
+experiment with new features, we may not find out important flaws until after
+their release, when we can no longer change things.
+
+Our solution to this problem is what we call “stability without stagnation”,
+and our guiding principle is this: you should never have to fear upgrading to a
+new version of stable Rust. Each upgrade should be painless, but should also
+bring you new features, fewer bugs, and faster compile times.
+
+### Choo, Choo! Release Channels and Riding the Trains
+
+Rust development operates on a _train schedule_. That is, all development is
+done in the main branch of the Rust repository. Releases follow a software
+release train model, which has been used by Cisco IOS and other software
+projects. There are three _release channels_ for Rust:
+
+- Nightly
+- Beta
+- Stable
+
+Most Rust developers primarily use the stable channel, but those who want to
+try out experimental new features may use nightly or beta.
+
+Here’s an example of how the development and release process works: let’s
+assume that the Rust team is working on the release of Rust 1.5. That release
+happened in December of 2015, but it will provide us with realistic version
+numbers. A new feature is added to Rust: a new commit lands on the main
+branch. Each night, a new nightly version of Rust is produced. Every day is a
+release day, and these releases are created by our release infrastructure
+automatically. So as time passes, our releases look like this, once a night:
+
+```text
+nightly: * - - * - - *
+```
+
+Every six weeks, it’s time to prepare a new release! The `beta` branch of the
+Rust repository branches off from the main branch used by nightly. Now,
+there are two releases:
+
+```text
+nightly: * - - * - - *
+ |
+beta: *
+```
+
+Most Rust users do not use beta releases actively, but test against beta in
+their CI system to help Rust discover possible regressions. In the meantime,
+there’s still a nightly release every night:
+
+```text
+nightly: * - - * - - * - - * - - *
+ |
+beta: *
+```
+
+Let’s say a regression is found. Good thing we had some time to test the beta
+release before the regression snuck into a stable release! The fix is applied
+to the main branch, so that nightly is fixed, and then the fix is backported to
+the `beta` branch, and a new release of beta is produced:
+
+```text
+nightly: * - - * - - * - - * - - * - - *
+ |
+beta: * - - - - - - - - *
+```
+
+Six weeks after the first beta was created, it’s time for a stable release! The
+`stable` branch is produced from the `beta` branch:
+
+```text
+nightly: * - - * - - * - - * - - * - - * - * - *
+ |
+beta: * - - - - - - - - *
+ |
+stable: *
+```
+
+Hooray! Rust 1.5 is done! However, we’ve forgotten one thing: because the six
+weeks have gone by, we also need a new beta of the _next_ version of Rust, 1.6.
+So after `stable` branches off of `beta`, the next version of `beta` branches
+off of `nightly` again:
+
+```text
+nightly: * - - * - - * - - * - - * - - * - * - *
+ | |
+beta: * - - - - - - - - * *
+ |
+stable: *
+```
+
+This is called the “train model” because every six weeks, a release “leaves the
+station”, but still has to take a journey through the beta channel before it
+arrives as a stable release.
+
+Rust releases every six weeks, like clockwork. If you know the date of one Rust
+release, you can know the date of the next one: it’s six weeks later. A nice
+aspect of having releases scheduled every six weeks is that the next train is
+coming soon. If a feature happens to miss a particular release, there’s no need
+to worry: another one is happening in a short time! This helps reduce pressure
+to sneak possibly unpolished features in close to the release deadline.
+
+Thanks to this process, you can always check out the next build of Rust and
+verify for yourself that it’s easy to upgrade to: if a beta release doesn’t
+work as expected, you can report it to the team and get it fixed before the
+next stable release happens! Breakage in a beta release is relatively rare, but
+`rustc` is still a piece of software, and bugs do exist.
+
+### Maintenance time
+
+The Rust project supports the most recent stable version. When a new stable
+version is released, the old version reaches its end of life (EOL). This means
+each version is supported for six weeks.
+
+### Unstable Features
+
+There’s one more catch with this release model: unstable features. Rust uses a
+technique called “feature flags” to determine what features are enabled in a
+given release. If a new feature is under active development, it lands on the
+main branch, and therefore, in nightly, but behind a _feature flag_. If you, as
+a user, wish to try out the work-in-progress feature, you can, but you must be
+using a nightly release of Rust and annotate your source code with the
+appropriate flag to opt in.
+
+If you’re using a beta or stable release of Rust, you can’t use any feature
+flags. This is the key that allows us to get practical use with new features
+before we declare them stable forever. Those who wish to opt into the bleeding
+edge can do so, and those who want a rock-solid experience can stick with
+stable and know that their code won’t break. Stability without stagnation.
+
+This book only contains information about stable features, as in-progress
+features are still changing, and surely they’ll be different between when this
+book was written and when they get enabled in stable builds. You can find
+documentation for nightly-only features online.
+
+### Rustup and the Role of Rust Nightly
+
+Rustup makes it easy to change between different release channels of Rust, on a
+global or per-project basis. By default, you’ll have stable Rust installed. To
+install nightly, for example:
+
+```console
+$ rustup toolchain install nightly
+```
+
+You can see all of the _toolchains_ (releases of Rust and associated
+components) you have installed with `rustup` as well. Here’s an example on one
+of your authors’ Windows computer:
+
+```powershell
+> rustup toolchain list
+stable-x86_64-pc-windows-msvc (default)
+beta-x86_64-pc-windows-msvc
+nightly-x86_64-pc-windows-msvc
+```
+
+As you can see, the stable toolchain is the default. Most Rust users use stable
+most of the time. You might want to use stable most of the time, but use
+nightly on a specific project, because you care about a cutting-edge feature.
+To do so, you can use `rustup override` in that project’s directory to set the
+nightly toolchain as the one `rustup` should use when you’re in that directory:
+
+```console
+$ cd ~/projects/needs-nightly
+$ rustup override set nightly
+```
+
+Now, every time you call `rustc` or `cargo` inside of
+_~/projects/needs-nightly_, `rustup` will make sure that you are using nightly
+Rust, rather than your default of stable Rust. This comes in handy when you
+have a lot of Rust projects!
+
+### The RFC Process and Teams
+
+So how do you learn about these new features? Rust’s development model follows
+a _Request For Comments (RFC) process_. If you’d like an improvement in Rust,
+you can write up a proposal, called an RFC.
+
+Anyone can write RFCs to improve Rust, and the proposals are reviewed and
+discussed by the Rust team, which is comprised of many topic subteams. There’s
+a full list of the teams [on Rust’s website](https://www.rust-lang.org/governance), which includes teams for
+each area of the project: language design, compiler implementation,
+infrastructure, documentation, and more. The appropriate team reads the
+proposal and the comments, writes some comments of their own, and eventually,
+there’s consensus to accept or reject the feature.
+
+If the feature is accepted, an issue is opened on the Rust repository, and
+someone can implement it. The person who implements it very well may not be the
+person who proposed the feature in the first place! When the implementation is
+ready, it lands on the main branch behind a feature gate, as we discussed in
+the [“Unstable Features”](#unstable-features) section.
+
+After some time, once Rust developers who use nightly releases have been able
+to try out the new feature, team members will discuss the feature, how it’s
+worked out on nightly, and decide if it should make it into stable Rust or not.
+If the decision is to move forward, the feature gate is removed, and the
+feature is now considered stable! It rides the trains into a new stable release
+of Rust.
diff --git a/documents/markdown/rust-book/ch00-00-introduction.md b/documents/markdown/rust-book/ch00-00-introduction.md
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+# Introduction
+
+> Note: This edition of the book is the same as [The Rust Programming
+> Language][nsprust] available in print and ebook format from [No Starch
+> Press][nsp].
+
+[nsprust]: https://nostarch.com/rust-programming-language-3rd-edition
+[nsp]: https://nostarch.com/
+
+Welcome to _The Rust Programming Language_, an introductory book about Rust.
+The Rust programming language helps you write faster, more reliable software.
+High-level ergonomics and low-level control are often at odds in programming
+language design; Rust challenges that conflict. Through balancing powerful
+technical capacity and a great developer experience, Rust gives you the option
+to control low-level details (such as memory usage) without all the hassle
+traditionally associated with such control.
+
+## Who Rust Is For
+
+Rust is ideal for many people for a variety of reasons. Let’s look at a few of
+the most important groups.
+
+### Teams of Developers
+
+Rust is proving to be a productive tool for collaborating among large teams of
+developers with varying levels of systems programming knowledge. Low-level code
+is prone to various subtle bugs, which in most other languages can only be
+caught through extensive testing and careful code review by experienced
+developers. In Rust, the compiler plays a gatekeeper role by refusing to
+compile code with these elusive bugs, including concurrency bugs. By working
+alongside the compiler, the team can spend its time focusing on the program’s
+logic rather than chasing down bugs.
+
+Rust also brings contemporary developer tools to the systems programming world:
+
+- Cargo, the included dependency manager and build tool, makes adding,
+ compiling, and managing dependencies painless and consistent across the Rust
+ ecosystem.
+- The `rustfmt` formatting tool ensures a consistent coding style across
+ developers.
+- The Rust Language Server powers integrated development environment (IDE)
+ integration for code completion and inline error messages.
+
+By using these and other tools in the Rust ecosystem, developers can be
+productive while writing systems-level code.
+
+### Students
+
+Rust is for students and those who are interested in learning about systems
+concepts. Using Rust, many people have learned about topics like operating
+systems development. The community is very welcoming and happy to answer
+students’ questions. Through efforts such as this book, the Rust teams want to
+make systems concepts more accessible to more people, especially those new to
+programming.
+
+### Companies
+
+Hundreds of companies, large and small, use Rust in production for a variety of
+tasks, including command line tools, web services, DevOps tooling, embedded
+devices, audio and video analysis and transcoding, cryptocurrencies,
+bioinformatics, search engines, Internet of Things applications, machine
+learning, and even major parts of the Firefox web browser.
+
+### Open Source Developers
+
+Rust is for people who want to build the Rust programming language, community,
+developer tools, and libraries. We’d love to have you contribute to the Rust
+language.
+
+### People Who Value Speed and Stability
+
+Rust is for people who crave speed and stability in a language. By speed, we
+mean both how quickly Rust code can run and the speed at which Rust lets you
+write programs. The Rust compiler’s checks ensure stability through feature
+additions and refactoring. This is in contrast to the brittle legacy code in
+languages without these checks, which developers are often afraid to modify. By
+striving for zero-cost abstractions—higher-level features that compile to
+lower-level code as fast as code written manually—Rust endeavors to make safe
+code be fast code as well.
+
+The Rust language hopes to support many other users as well; those mentioned
+here are merely some of the biggest stakeholders. Overall, Rust’s greatest
+ambition is to eliminate the trade-offs that programmers have accepted for
+decades by providing safety _and_ productivity, speed _and_ ergonomics. Give
+Rust a try, and see if its choices work for you.
+
+## Who This Book Is For
+
+This book assumes that you’ve written code in another programming language, but
+it doesn’t make any assumptions about which one. We’ve tried to make the
+material broadly accessible to those from a wide variety of programming
+backgrounds. We don’t spend a lot of time talking about what programming _is_
+or how to think about it. If you’re entirely new to programming, you would be
+better served by reading a book that specifically provides an introduction to
+programming.
+
+## How to Use This Book
+
+In general, this book assumes that you’re reading it in sequence from front to
+back. Later chapters build on concepts in earlier chapters, and earlier
+chapters might not delve into details on a particular topic but will revisit
+the topic in a later chapter.
+
+You’ll find two kinds of chapters in this book: concept chapters and project
+chapters. In concept chapters, you’ll learn about an aspect of Rust. In project
+chapters, we’ll build small programs together, applying what you’ve learned so
+far. Chapter 2, Chapter 12, and Chapter 21 are project chapters; the rest are
+concept chapters.
+
+**Chapter 1** explains how to install Rust, how to write a “Hello, world!”
+program, and how to use Cargo, Rust’s package manager and build tool. **Chapter
+2** is a hands-on introduction to writing a program in Rust, having you build
+up a number-guessing game. Here, we cover concepts at a high level, and later
+chapters will provide additional detail. If you want to get your hands dirty
+right away, Chapter 2 is the place for that. If you’re a particularly
+meticulous learner who prefers to learn every detail before moving on to the
+next, you might want to skip Chapter 2 and go straight to **Chapter 3**, which
+covers Rust features that are similar to those of other programming languages;
+then, you can return to Chapter 2 when you’d like to work on a project applying
+the details you’ve learned.
+
+In **Chapter 4**, you’ll learn about Rust’s ownership system. **Chapter 5**
+discusses structs and methods. **Chapter 6** covers enums, `match` expressions,
+and the `if let` and `let...else` control flow constructs. You’ll use structs
+and enums to make custom types.
+
+In **Chapter 7**, you’ll learn about Rust’s module system and about privacy
+rules for organizing your code and its public application programming interface
+(API). **Chapter 8** discusses some common collection data structures that the
+standard library provides: vectors, strings, and hash maps. **Chapter 9**
+explores Rust’s error-handling philosophy and techniques.
+
+**Chapter 10** digs into generics, traits, and lifetimes, which give you the
+power to define code that applies to multiple types. **Chapter 11** is all
+about testing, which even with Rust’s safety guarantees is necessary to ensure
+that your program’s logic is correct. In **Chapter 12**, we’ll build our own
+implementation of a subset of functionality from the `grep` command line tool
+that searches for text within files. For this, we’ll use many of the concepts
+we discussed in the previous chapters.
+
+**Chapter 13** explores closures and iterators: features of Rust that come from
+functional programming languages. In **Chapter 14**, we’ll examine Cargo in
+more depth and talk about best practices for sharing your libraries with
+others. **Chapter 15** discusses smart pointers that the standard library
+provides and the traits that enable their functionality.
+
+In **Chapter 16**, we’ll walk through different models of concurrent
+programming and talk about how Rust helps you program in multiple threads
+fearlessly. In **Chapter 17**, we build on that by exploring Rust’s async and
+await syntax, along with tasks, futures, and streams, and the lightweight
+concurrency model they enable.
+
+**Chapter 18** looks at how Rust idioms compare to object-oriented programming
+principles you might be familiar with. **Chapter 19** is a reference on
+patterns and pattern matching, which are powerful ways of expressing ideas
+throughout Rust programs. **Chapter 20** contains a smorgasbord of advanced
+topics of interest, including unsafe Rust, macros, and more about lifetimes,
+traits, types, functions, and closures.
+
+In **Chapter 21**, we’ll complete a project in which we’ll implement a
+low-level multithreaded web server!
+
+Finally, some appendixes contain useful information about the language in a
+more reference-like format. **Appendix A** covers Rust’s keywords, **Appendix
+B** covers Rust’s operators and symbols, **Appendix C** covers derivable traits
+provided by the standard library, **Appendix D** covers some useful development
+tools, and **Appendix E** explains Rust editions. In **Appendix F**, you can
+find translations of the book, and in **Appendix G** we’ll cover how Rust is
+made and what nightly Rust is.
+
+There is no wrong way to read this book: If you want to skip ahead, go for it!
+You might have to jump back to earlier chapters if you experience any
+confusion. But do whatever works for you.
+
+
+
+An important part of the process of learning Rust is learning how to read the
+error messages the compiler displays: These will guide you toward working code.
+As such, we’ll provide many examples that don’t compile along with the error
+message the compiler will show you in each situation. Know that if you enter
+and run a random example, it may not compile! Make sure you read the
+surrounding text to see whether the example you’re trying to run is meant to
+error. In most situations, we’ll lead you to the correct version of any code
+that doesn’t compile. Ferris will also help you distinguish code that isn’t
+meant to work:
+
+| Ferris | Meaning |
+| ---------------------------------------------------------------------------------------------------------------- | ------------------------------------------------ |
+| 
| This code does not compile! |
+| 
| This code panics! |
+| 
| This code does not produce the desired behavior. |
+
+In most situations, we’ll lead you to the correct version of any code that
+doesn’t compile.
+
+## Source Code
+
+The source files from which this book is generated can be found on
+[GitHub][book].
+
+[book]: https://github.com/rust-lang/book/tree/main/src
diff --git a/documents/markdown/rust-book/ch01-00-getting-started.md b/documents/markdown/rust-book/ch01-00-getting-started.md
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+# Getting Started
+
+Let’s start your Rust journey! There’s a lot to learn, but every journey starts
+somewhere. In this chapter, we’ll discuss:
+
+- Installing Rust on Linux, macOS, and Windows
+- Writing a program that prints `Hello, world!`
+- Using `cargo`, Rust’s package manager and build system
diff --git a/documents/markdown/rust-book/ch01-01-installation.md b/documents/markdown/rust-book/ch01-01-installation.md
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+## Installation
+
+The first step is to install Rust. We’ll download Rust through `rustup`, a
+command line tool for managing Rust versions and associated tools. You’ll need
+an internet connection for the download.
+
+> Note: If you prefer not to use `rustup` for some reason, please see the
+> [Other Rust Installation Methods page][otherinstall] for more options.
+
+The following steps install the latest stable version of the Rust compiler.
+Rust’s stability guarantees ensure that all the examples in the book that
+compile will continue to compile with newer Rust versions. The output might
+differ slightly between versions because Rust often improves error messages and
+warnings. In other words, any newer, stable version of Rust you install using
+these steps should work as expected with the content of this book.
+
+> ### Command Line Notation
+>
+> In this chapter and throughout the book, we’ll show some commands used in the
+> terminal. Lines that you should enter in a terminal all start with `$`. You
+> don’t need to type the `$` character; it’s the command line prompt shown to
+> indicate the start of each command. Lines that don’t start with `$` typically
+> show the output of the previous command. Additionally, PowerShell-specific
+> examples will use `>` rather than `$`.
+
+### Installing `rustup` on Linux or macOS
+
+If you’re using Linux or macOS, open a terminal and enter the following command:
+
+```console
+$ curl --proto '=https' --tlsv1.2 https://sh.rustup.rs -sSf | sh
+```
+
+The command downloads a script and starts the installation of the `rustup`
+tool, which installs the latest stable version of Rust. You might be prompted
+for your password. If the install is successful, the following line will appear:
+
+```text
+Rust is installed now. Great!
+```
+
+You will also need a _linker_, which is a program that Rust uses to join its
+compiled outputs into one file. It is likely you already have one. If you get
+linker errors, you should install a C compiler, which will typically include a
+linker. A C compiler is also useful because some common Rust packages depend on
+C code and will need a C compiler.
+
+On macOS, you can get a C compiler by running:
+
+```console
+$ xcode-select --install
+```
+
+Linux users should generally install GCC or Clang, according to their
+distribution’s documentation. For example, if you use Ubuntu, you can install
+the `build-essential` package.
+
+### Installing `rustup` on Windows
+
+On Windows, go to [https://www.rust-lang.org/tools/install][install] and follow the instructions for installing Rust. At some point in the
+installation, you’ll be prompted to install Visual Studio. This provides a
+linker and the native libraries needed to compile programs. If you need more
+help with this step, see
+[https://rust-lang.github.io/rustup/installation/windows-msvc.html][msvc].
+
+The rest of this book uses commands that work in both _cmd.exe_ and PowerShell.
+If there are specific differences, we’ll explain which to use.
+
+### Troubleshooting
+
+To check whether you have Rust installed correctly, open a shell and enter this
+line:
+
+```console
+$ rustc --version
+```
+
+You should see the version number, commit hash, and commit date for the latest
+stable version that has been released, in the following format:
+
+```text
+rustc x.y.z (abcabcabc yyyy-mm-dd)
+```
+
+If you see this information, you have installed Rust successfully! If you don’t
+see this information, check that Rust is in your `%PATH%` system variable as
+follows.
+
+In Windows CMD, use:
+
+```console
+> echo %PATH%
+```
+
+In PowerShell, use:
+
+```powershell
+> echo $env:Path
+```
+
+In Linux and macOS, use:
+
+```console
+$ echo $PATH
+```
+
+If that’s all correct and Rust still isn’t working, there are a number of
+places you can get help. Find out how to get in touch with other Rustaceans (a
+silly nickname we call ourselves) on [the community page][community].
+
+### Updating and Uninstalling
+
+Once Rust is installed via `rustup`, updating to a newly released version is
+easy. From your shell, run the following update script:
+
+```console
+$ rustup update
+```
+
+To uninstall Rust and `rustup`, run the following uninstall script from your
+shell:
+
+```console
+$ rustup self uninstall
+```
+
+
+
+
+### Reading the Local Documentation
+
+The installation of Rust also includes a local copy of the documentation so
+that you can read it offline. Run `rustup doc` to open the local documentation
+in your browser.
+
+Any time a type or function is provided by the standard library and you’re not
+sure what it does or how to use it, use the application programming interface
+(API) documentation to find out!
+
+
+
+
+### Using Text Editors and IDEs
+
+This book makes no assumptions about what tools you use to author Rust code.
+Just about any text editor will get the job done! However, many text editors and
+integrated development environments (IDEs) have built-in support for Rust. You
+can always find a fairly current list of many editors and IDEs on [the tools
+page][tools] on the Rust website.
+
+### Working Offline with This Book
+
+In several examples, we will use Rust packages beyond the standard library. To
+work through those examples, you will either need to have an internet connection
+or to have downloaded those dependencies ahead of time. To download the
+dependencies ahead of time, you can run the following commands. (We’ll explain
+what `cargo` is and what each of these commands does in detail later.)
+
+```console
+$ cargo new get-dependencies
+$ cd get-dependencies
+$ cargo add rand@0.8.5 trpl@0.2.0
+```
+
+This will cache the downloads for these packages so you will not need to
+download them later. Once you have run this command, you do not need to keep the
+`get-dependencies` folder. If you have run this command, you can use the
+`--offline` flag with all `cargo` commands in the rest of the book to use these
+cached versions instead of attempting to use the network.
+
+[otherinstall]: https://forge.rust-lang.org/infra/other-installation-methods.html
+[install]: https://www.rust-lang.org/tools/install
+[msvc]: https://rust-lang.github.io/rustup/installation/windows-msvc.html
+[community]: https://www.rust-lang.org/community
+[tools]: https://www.rust-lang.org/tools
diff --git a/documents/markdown/rust-book/ch01-02-hello-world.md b/documents/markdown/rust-book/ch01-02-hello-world.md
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+## Hello, World!
+
+Now that you’ve installed Rust, it’s time to write your first Rust program.
+It’s traditional when learning a new language to write a little program that
+prints the text `Hello, world!` to the screen, so we’ll do the same here!
+
+> Note: This book assumes basic familiarity with the command line. Rust makes
+> no specific demands about your editing or tooling or where your code lives, so
+> if you prefer to use an IDE instead of the command line, feel free to use your
+> favorite IDE. Many IDEs now have some degree of Rust support; check the IDE’s
+> documentation for details. The Rust team has been focusing on enabling great
+> IDE support via `rust-analyzer`. See [Appendix D][devtools]
+> for more details.
+
+
+
+
+### Project Directory Setup
+
+You’ll start by making a directory to store your Rust code. It doesn’t matter
+to Rust where your code lives, but for the exercises and projects in this book,
+we suggest making a _projects_ directory in your home directory and keeping all
+your projects there.
+
+Open a terminal and enter the following commands to make a _projects_ directory
+and a directory for the “Hello, world!” project within the _projects_ directory.
+
+For Linux, macOS, and PowerShell on Windows, enter this:
+
+```console
+$ mkdir ~/projects
+$ cd ~/projects
+$ mkdir hello_world
+$ cd hello_world
+```
+
+For Windows CMD, enter this:
+
+```cmd
+> mkdir "%USERPROFILE%\projects"
+> cd /d "%USERPROFILE%\projects"
+> mkdir hello_world
+> cd hello_world
+```
+
+
+
+
+### Rust Program Basics
+
+Next, make a new source file and call it _main.rs_. Rust files always end with
+the _.rs_ extension. If you’re using more than one word in your filename, the
+convention is to use an underscore to separate them. For example, use
+_hello_world.rs_ rather than _helloworld.rs_.
+
+Now open the _main.rs_ file you just created and enter the code in Listing 1-1.
+
+
+
+```rust
+fn main() {
+ println!("Hello, world!");
+}
+```
+
+
+
+Save the file and go back to your terminal window in the
+_~/projects/hello_world_ directory. On Linux or macOS, enter the following
+commands to compile and run the file:
+
+```console
+$ rustc main.rs
+$ ./main
+Hello, world!
+```
+
+On Windows, enter the command `.\main` instead of `./main`:
+
+```powershell
+> rustc main.rs
+> .\main
+Hello, world!
+```
+
+Regardless of your operating system, the string `Hello, world!` should print to
+the terminal. If you don’t see this output, refer back to the
+[“Troubleshooting”][troubleshooting] part of the Installation
+section for ways to get help.
+
+If `Hello, world!` did print, congratulations! You’ve officially written a Rust
+program. That makes you a Rust programmer—welcome!
+
+
+
+
+
+### The Anatomy of a Rust Program
+
+Let’s review this “Hello, world!” program in detail. Here’s the first piece of
+the puzzle:
+
+```rust
+fn main() {
+
+}
+```
+
+These lines define a function named `main`. The `main` function is special: It
+is always the first code that runs in every executable Rust program. Here, the
+first line declares a function named `main` that has no parameters and returns
+nothing. If there were parameters, they would go inside the parentheses (`()`).
+
+The function body is wrapped in `{}`. Rust requires curly brackets around all
+function bodies. It’s good style to place the opening curly bracket on the same
+line as the function declaration, adding one space in between.
+
+> Note: If you want to stick to a standard style across Rust projects, you can
+> use an automatic formatter tool called `rustfmt` to format your code in a
+> particular style (more on `rustfmt` in
+> [Appendix D][devtools]). The Rust team has included this tool
+> with the standard Rust distribution, as `rustc` is, so it should already be
+> installed on your computer!
+
+The body of the `main` function holds the following code:
+
+```rust
+println!("Hello, world!");
+```
+
+This line does all the work in this little program: It prints text to the
+screen. There are three important details to notice here.
+
+First, `println!` calls a Rust macro. If it had called a function instead, it
+would be entered as `println` (without the `!`). Rust macros are a way to write
+code that generates code to extend Rust syntax, and we’ll discuss them in more
+detail in [Chapter 20][ch20-macros]. For now, you just need to
+know that using a `!` means that you’re calling a macro instead of a normal
+function and that macros don’t always follow the same rules as functions.
+
+Second, you see the `"Hello, world!"` string. We pass this string as an argument
+to `println!`, and the string is printed to the screen.
+
+Third, we end the line with a semicolon (`;`), which indicates that this
+expression is over, and the next one is ready to begin. Most lines of Rust code
+end with a semicolon.
+
+
+
+
+### Compilation and Execution
+
+You’ve just run a newly created program, so let’s examine each step in the
+process.
+
+Before running a Rust program, you must compile it using the Rust compiler by
+entering the `rustc` command and passing it the name of your source file, like
+this:
+
+```console
+$ rustc main.rs
+```
+
+If you have a C or C++ background, you’ll notice that this is similar to `gcc`
+or `clang`. After compiling successfully, Rust outputs a binary executable.
+
+On Linux, macOS, and PowerShell on Windows, you can see the executable by
+entering the `ls` command in your shell:
+
+```console
+$ ls
+main main.rs
+```
+
+On Linux and macOS, you’ll see two files. With PowerShell on Windows, you’ll
+see the same three files that you would see using CMD. With CMD on Windows, you
+would enter the following:
+
+```cmd
+> dir /B %= the /B option says to only show the file names =%
+main.exe
+main.pdb
+main.rs
+```
+
+This shows the source code file with the _.rs_ extension, the executable file
+(_main.exe_ on Windows, but _main_ on all other platforms), and, when using
+Windows, a file containing debugging information with the _.pdb_ extension.
+From here, you run the _main_ or _main.exe_ file, like this:
+
+```console
+$ ./main # or .\main on Windows
+```
+
+If your _main.rs_ is your “Hello, world!” program, this line prints `Hello,
+world!` to your terminal.
+
+If you’re more familiar with a dynamic language, such as Ruby, Python, or
+JavaScript, you might not be used to compiling and running a program as
+separate steps. Rust is an _ahead-of-time compiled_ language, meaning you can
+compile a program and give the executable to someone else, and they can run it
+even without having Rust installed. If you give someone a _.rb_, _.py_, or
+_.js_ file, they need to have a Ruby, Python, or JavaScript implementation
+installed (respectively). But in those languages, you only need one command to
+compile and run your program. Everything is a trade-off in language design.
+
+Just compiling with `rustc` is fine for simple programs, but as your project
+grows, you’ll want to manage all the options and make it easy to share your
+code. Next, we’ll introduce you to the Cargo tool, which will help you write
+real-world Rust programs.
+
+[troubleshooting]: ch01-01-installation.html#troubleshooting
+[devtools]: appendix-04-useful-development-tools.html
+[ch20-macros]: ch20-05-macros.html
diff --git a/documents/markdown/rust-book/ch01-03-hello-cargo.md b/documents/markdown/rust-book/ch01-03-hello-cargo.md
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--- /dev/null
+++ b/documents/markdown/rust-book/ch01-03-hello-cargo.md
@@ -0,0 +1,261 @@
+## Hello, Cargo!
+
+Cargo is Rust’s build system and package manager. Most Rustaceans use this tool
+to manage their Rust projects because Cargo handles a lot of tasks for you,
+such as building your code, downloading the libraries your code depends on, and
+building those libraries. (We call the libraries that your code needs
+_dependencies_.)
+
+The simplest Rust programs, like the one we’ve written so far, don’t have any
+dependencies. If we had built the “Hello, world!” project with Cargo, it would
+only use the part of Cargo that handles building your code. As you write more
+complex Rust programs, you’ll add dependencies, and if you start a project
+using Cargo, adding dependencies will be much easier to do.
+
+Because the vast majority of Rust projects use Cargo, the rest of this book
+assumes that you’re using Cargo too. Cargo comes installed with Rust if you
+used the official installers discussed in the
+[“Installation”][installation] section. If you installed Rust
+through some other means, check whether Cargo is installed by entering the
+following in your terminal:
+
+```console
+$ cargo --version
+```
+
+If you see a version number, you have it! If you see an error, such as `command
+not found`, look at the documentation for your method of installation to
+determine how to install Cargo separately.
+
+### Creating a Project with Cargo
+
+Let’s create a new project using Cargo and look at how it differs from our
+original “Hello, world!” project. Navigate back to your _projects_ directory
+(or wherever you decided to store your code). Then, on any operating system,
+run the following:
+
+```console
+$ cargo new hello_cargo
+$ cd hello_cargo
+```
+
+The first command creates a new directory and project called _hello_cargo_.
+We’ve named our project _hello_cargo_, and Cargo creates its files in a
+directory of the same name.
+
+Go into the _hello_cargo_ directory and list the files. You’ll see that Cargo
+has generated two files and one directory for us: a _Cargo.toml_ file and a
+_src_ directory with a _main.rs_ file inside.
+
+It has also initialized a new Git repository along with a _.gitignore_ file.
+Git files won’t be generated if you run `cargo new` within an existing Git
+repository; you can override this behavior by using `cargo new --vcs=git`.
+
+> Note: Git is a common version control system. You can change `cargo new` to
+> use a different version control system or no version control system by using
+> the `--vcs` flag. Run `cargo new --help` to see the available options.
+
+Open _Cargo.toml_ in your text editor of choice. It should look similar to the
+code in Listing 1-2.
+
+
+
+```toml
+[package]
+name = "hello_cargo"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+```
+
+
+
+This file is in the [_TOML_][toml] (_Tom’s Obvious, Minimal
+Language_) format, which is Cargo’s configuration format.
+
+The first line, `[package]`, is a section heading that indicates that the
+following statements are configuring a package. As we add more information to
+this file, we’ll add other sections.
+
+The next three lines set the configuration information Cargo needs to compile
+your program: the name, the version, and the edition of Rust to use. We’ll talk
+about the `edition` key in [Appendix E][appendix-e].
+
+The last line, `[dependencies]`, is the start of a section for you to list any
+of your project’s dependencies. In Rust, packages of code are referred to as
+_crates_. We won’t need any other crates for this project, but we will in the
+first project in Chapter 2, so we’ll use this dependencies section then.
+
+Now open _src/main.rs_ and take a look:
+
+Filename: src/main.rs
+
+```rust
+fn main() {
+ println!("Hello, world!");
+}
+```
+
+Cargo has generated a “Hello, world!” program for you, just like the one we
+wrote in Listing 1-1! So far, the differences between our project and the
+project Cargo generated are that Cargo placed the code in the _src_ directory,
+and we have a _Cargo.toml_ configuration file in the top directory.
+
+Cargo expects your source files to live inside the _src_ directory. The
+top-level project directory is just for README files, license information,
+configuration files, and anything else not related to your code. Using Cargo
+helps you organize your projects. There’s a place for everything, and
+everything is in its place.
+
+If you started a project that doesn’t use Cargo, as we did with the “Hello,
+world!” project, you can convert it to a project that does use Cargo. Move the
+project code into the _src_ directory and create an appropriate _Cargo.toml_
+file. One easy way to get that _Cargo.toml_ file is to run `cargo init`, which
+will create it for you automatically.
+
+### Building and Running a Cargo Project
+
+Now let’s look at what’s different when we build and run the “Hello, world!”
+program with Cargo! From your _hello_cargo_ directory, build your project by
+entering the following command:
+
+```console
+$ cargo build
+ Compiling hello_cargo v0.1.0 (file:///projects/hello_cargo)
+ Finished dev [unoptimized + debuginfo] target(s) in 2.85 secs
+```
+
+This command creates an executable file in _target/debug/hello_cargo_ (or
+_target\debug\hello_cargo.exe_ on Windows) rather than in your current
+directory. Because the default build is a debug build, Cargo puts the binary in
+a directory named _debug_. You can run the executable with this command:
+
+```console
+$ ./target/debug/hello_cargo # or .\target\debug\hello_cargo.exe on Windows
+Hello, world!
+```
+
+If all goes well, `Hello, world!` should print to the terminal. Running `cargo
+build` for the first time also causes Cargo to create a new file at the top
+level: _Cargo.lock_. This file keeps track of the exact versions of
+dependencies in your project. This project doesn’t have dependencies, so the
+file is a bit sparse. You won’t ever need to change this file manually; Cargo
+manages its contents for you.
+
+We just built a project with `cargo build` and ran it with
+`./target/debug/hello_cargo`, but we can also use `cargo run` to compile the
+code and then run the resultant executable all in one command:
+
+```console
+$ cargo run
+ Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
+ Running `target/debug/hello_cargo`
+Hello, world!
+```
+
+Using `cargo run` is more convenient than having to remember to run `cargo
+build` and then use the whole path to the binary, so most developers use `cargo
+run`.
+
+Notice that this time we didn’t see output indicating that Cargo was compiling
+`hello_cargo`. Cargo figured out that the files hadn’t changed, so it didn’t
+rebuild but just ran the binary. If you had modified your source code, Cargo
+would have rebuilt the project before running it, and you would have seen this
+output:
+
+```console
+$ cargo run
+ Compiling hello_cargo v0.1.0 (file:///projects/hello_cargo)
+ Finished dev [unoptimized + debuginfo] target(s) in 0.33 secs
+ Running `target/debug/hello_cargo`
+Hello, world!
+```
+
+Cargo also provides a command called `cargo check`. This command quickly checks
+your code to make sure it compiles but doesn’t produce an executable:
+
+```console
+$ cargo check
+ Checking hello_cargo v0.1.0 (file:///projects/hello_cargo)
+ Finished dev [unoptimized + debuginfo] target(s) in 0.32 secs
+```
+
+Why would you not want an executable? Often, `cargo check` is much faster than
+`cargo build` because it skips the step of producing an executable. If you’re
+continually checking your work while writing the code, using `cargo check` will
+speed up the process of letting you know if your project is still compiling! As
+such, many Rustaceans run `cargo check` periodically as they write their
+program to make sure it compiles. Then, they run `cargo build` when they’re
+ready to use the executable.
+
+Let’s recap what we’ve learned so far about Cargo:
+
+- We can create a project using `cargo new`.
+- We can build a project using `cargo build`.
+- We can build and run a project in one step using `cargo run`.
+- We can build a project without producing a binary to check for errors using
+ `cargo check`.
+- Instead of saving the result of the build in the same directory as our code,
+ Cargo stores it in the _target/debug_ directory.
+
+An additional advantage of using Cargo is that the commands are the same no
+matter which operating system you’re working on. So, at this point, we’ll no
+longer provide specific instructions for Linux and macOS versus Windows.
+
+### Building for Release
+
+When your project is finally ready for release, you can use `cargo build
+--release` to compile it with optimizations. This command will create an
+executable in _target/release_ instead of _target/debug_. The optimizations
+make your Rust code run faster, but turning them on lengthens the time it takes
+for your program to compile. This is why there are two different profiles: one
+for development, when you want to rebuild quickly and often, and another for
+building the final program you’ll give to a user that won’t be rebuilt
+repeatedly and that will run as fast as possible. If you’re benchmarking your
+code’s running time, be sure to run `cargo build --release` and benchmark with
+the executable in _target/release_.
+
+
+
+
+### Leveraging Cargo’s Conventions
+
+With simple projects, Cargo doesn’t provide a lot of value over just using
+`rustc`, but it will prove its worth as your programs become more intricate.
+Once programs grow to multiple files or need a dependency, it’s much easier to
+let Cargo coordinate the build.
+
+Even though the `hello_cargo` project is simple, it now uses much of the real
+tooling you’ll use in the rest of your Rust career. In fact, to work on any
+existing projects, you can use the following commands to check out the code
+using Git, change to that project’s directory, and build:
+
+```console
+$ git clone example.org/someproject
+$ cd someproject
+$ cargo build
+```
+
+For more information about Cargo, check out [its documentation][cargo].
+
+## Summary
+
+You’re already off to a great start on your Rust journey! In this chapter, you
+learned how to:
+
+- Install the latest stable version of Rust using `rustup`.
+- Update to a newer Rust version.
+- Open locally installed documentation.
+- Write and run a “Hello, world!” program using `rustc` directly.
+- Create and run a new project using the conventions of Cargo.
+
+This is a great time to build a more substantial program to get used to reading
+and writing Rust code. So, in Chapter 2, we’ll build a guessing game program.
+If you would rather start by learning how common programming concepts work in
+Rust, see Chapter 3 and then return to Chapter 2.
+
+[installation]: ch01-01-installation.html#installation
+[toml]: https://toml.io
+[appendix-e]: appendix-05-editions.html
+[cargo]: https://doc.rust-lang.org/cargo/
diff --git a/documents/markdown/rust-book/ch02-00-guessing-game-tutorial.md b/documents/markdown/rust-book/ch02-00-guessing-game-tutorial.md
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+# Programming a Guessing Game
+
+Let’s jump into Rust by working through a hands-on project together! This
+chapter introduces you to a few common Rust concepts by showing you how to use
+them in a real program. You’ll learn about `let`, `match`, methods, associated
+functions, external crates, and more! In the following chapters, we’ll explore
+these ideas in more detail. In this chapter, you’ll just practice the
+fundamentals.
+
+We’ll implement a classic beginner programming problem: a guessing game. Here’s
+how it works: The program will generate a random integer between 1 and 100. It
+will then prompt the player to enter a guess. After a guess is entered, the
+program will indicate whether the guess is too low or too high. If the guess is
+correct, the game will print a congratulatory message and exit.
+
+## Setting Up a New Project
+
+To set up a new project, go to the _projects_ directory that you created in
+Chapter 1 and make a new project using Cargo, like so:
+
+```console
+$ cargo new guessing_game
+$ cd guessing_game
+```
+
+The first command, `cargo new`, takes the name of the project (`guessing_game`)
+as the first argument. The second command changes to the new project’s
+directory.
+
+Look at the generated _Cargo.toml_ file:
+
+
+
+Filename: Cargo.toml
+
+```toml
+{{#include ../listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/Cargo.toml}}
+```
+
+As you saw in Chapter 1, `cargo new` generates a “Hello, world!” program for
+you. Check out the _src/main.rs_ file:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/src/main.rs}}
+```
+
+Now let’s compile this “Hello, world!” program and run it in the same step
+using the `cargo run` command:
+
+```console
+{{#include ../listings/ch02-guessing-game-tutorial/no-listing-01-cargo-new/output.txt}}
+```
+
+The `run` command comes in handy when you need to rapidly iterate on a project,
+as we’ll do in this game, quickly testing each iteration before moving on to
+the next one.
+
+Reopen the _src/main.rs_ file. You’ll be writing all the code in this file.
+
+## Processing a Guess
+
+The first part of the guessing game program will ask for user input, process
+that input, and check that the input is in the expected form. To start, we’ll
+allow the player to input a guess. Enter the code in Listing 2-1 into
+_src/main.rs_.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:all}}
+```
+
+
+
+This code contains a lot of information, so let’s go over it line by line. To
+obtain user input and then print the result as output, we need to bring the
+`io` input/output library into scope. The `io` library comes from the standard
+library, known as `std`:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:io}}
+```
+
+By default, Rust has a set of items defined in the standard library that it
+brings into the scope of every program. This set is called the _prelude_, and
+you can see everything in it [in the standard library documentation][prelude].
+
+If a type you want to use isn’t in the prelude, you have to bring that type
+into scope explicitly with a `use` statement. Using the `std::io` library
+provides you with a number of useful features, including the ability to accept
+user input.
+
+As you saw in Chapter 1, the `main` function is the entry point into the
+program:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:main}}
+```
+
+The `fn` syntax declares a new function; the parentheses, `()`, indicate there
+are no parameters; and the curly bracket, `{`, starts the body of the function.
+
+As you also learned in Chapter 1, `println!` is a macro that prints a string to
+the screen:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:print}}
+```
+
+This code is printing a prompt stating what the game is and requesting input
+from the user.
+
+### Storing Values with Variables
+
+Next, we’ll create a _variable_ to store the user input, like this:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:string}}
+```
+
+Now the program is getting interesting! There’s a lot going on in this little
+line. We use the `let` statement to create the variable. Here’s another example:
+
+```rust,ignore
+let apples = 5;
+```
+
+This line creates a new variable named `apples` and binds it to the value `5`.
+In Rust, variables are immutable by default, meaning once we give the variable
+a value, the value won’t change. We’ll be discussing this concept in detail in
+the [“Variables and Mutability”][variables-and-mutability]
+section in Chapter 3. To make a variable mutable, we add `mut` before the
+variable name:
+
+```rust,ignore
+let apples = 5; // immutable
+let mut bananas = 5; // mutable
+```
+
+> Note: The `//` syntax starts a comment that continues until the end of the
+> line. Rust ignores everything in comments. We’ll discuss comments in more
+> detail in [Chapter 3][comments].
+
+Returning to the guessing game program, you now know that `let mut guess` will
+introduce a mutable variable named `guess`. The equal sign (`=`) tells Rust we
+want to bind something to the variable now. On the right of the equal sign is
+the value that `guess` is bound to, which is the result of calling
+`String::new`, a function that returns a new instance of a `String`.
+[`String`][string] is a string type provided by the standard
+library that is a growable, UTF-8 encoded bit of text.
+
+The `::` syntax in the `::new` line indicates that `new` is an associated
+function of the `String` type. An _associated function_ is a function that’s
+implemented on a type, in this case `String`. This `new` function creates a
+new, empty string. You’ll find a `new` function on many types because it’s a
+common name for a function that makes a new value of some kind.
+
+In full, the `let mut guess = String::new();` line has created a mutable
+variable that is currently bound to a new, empty instance of a `String`. Whew!
+
+### Receiving User Input
+
+Recall that we included the input/output functionality from the standard
+library with `use std::io;` on the first line of the program. Now we’ll call
+the `stdin` function from the `io` module, which will allow us to handle user
+input:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:read}}
+```
+
+If we hadn’t imported the `io` module with `use std::io;` at the beginning of
+the program, we could still use the function by writing this function call as
+`std::io::stdin`. The `stdin` function returns an instance of
+[`std::io::Stdin`][iostdin], which is a type that represents a
+handle to the standard input for your terminal.
+
+Next, the line `.read_line(&mut guess)` calls the [`read_line`][read_line] method on the standard input handle to get input from the user.
+We’re also passing `&mut guess` as the argument to `read_line` to tell it what
+string to store the user input in. The full job of `read_line` is to take
+whatever the user types into standard input and append that into a string
+(without overwriting its contents), so we therefore pass that string as an
+argument. The string argument needs to be mutable so that the method can change
+the string’s content.
+
+The `&` indicates that this argument is a _reference_, which gives you a way to
+let multiple parts of your code access one piece of data without needing to
+copy that data into memory multiple times. References are a complex feature,
+and one of Rust’s major advantages is how safe and easy it is to use
+references. You don’t need to know a lot of those details to finish this
+program. For now, all you need to know is that, like variables, references are
+immutable by default. Hence, you need to write `&mut guess` rather than
+`&guess` to make it mutable. (Chapter 4 will explain references more
+thoroughly.)
+
+
+
+
+
+### Handling Potential Failure with `Result`
+
+We’re still working on this line of code. We’re now discussing a third line of
+text, but note that it’s still part of a single logical line of code. The next
+part is this method:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:expect}}
+```
+
+We could have written this code as:
+
+```rust,ignore
+io::stdin().read_line(&mut guess).expect("Failed to read line");
+```
+
+However, one long line is difficult to read, so it’s best to divide it. It’s
+often wise to introduce a newline and other whitespace to help break up long
+lines when you call a method with the `.method_name()` syntax. Now let’s
+discuss what this line does.
+
+As mentioned earlier, `read_line` puts whatever the user enters into the string
+we pass to it, but it also returns a `Result` value. [`Result`][result] is an [_enumeration_][enums], often called an _enum_,
+which is a type that can be in one of multiple possible states. We call each
+possible state a _variant_.
+
+[Chapter 6][enums] will cover enums in more detail. The purpose
+of these `Result` types is to encode error-handling information.
+
+`Result`’s variants are `Ok` and `Err`. The `Ok` variant indicates the
+operation was successful, and it contains the successfully generated value.
+The `Err` variant means the operation failed, and it contains information
+about how or why the operation failed.
+
+Values of the `Result` type, like values of any type, have methods defined on
+them. An instance of `Result` has an [`expect` method][expect]
+that you can call. If this instance of `Result` is an `Err` value, `expect`
+will cause the program to crash and display the message that you passed as an
+argument to `expect`. If the `read_line` method returns an `Err`, it would
+likely be the result of an error coming from the underlying operating system.
+If this instance of `Result` is an `Ok` value, `expect` will take the return
+value that `Ok` is holding and return just that value to you so that you can
+use it. In this case, that value is the number of bytes in the user’s input.
+
+If you don’t call `expect`, the program will compile, but you’ll get a warning:
+
+```console
+{{#include ../listings/ch02-guessing-game-tutorial/no-listing-02-without-expect/output.txt}}
+```
+
+Rust warns that you haven’t used the `Result` value returned from `read_line`,
+indicating that the program hasn’t handled a possible error.
+
+The right way to suppress the warning is to actually write error-handling code,
+but in our case we just want to crash this program when a problem occurs, so we
+can use `expect`. You’ll learn about recovering from errors in [Chapter
+9][recover].
+
+### Printing Values with `println!` Placeholders
+
+Aside from the closing curly bracket, there’s only one more line to discuss in
+the code so far:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-01/src/main.rs:print_guess}}
+```
+
+This line prints the string that now contains the user’s input. The `{}` set of
+curly brackets is a placeholder: Think of `{}` as little crab pincers that hold
+a value in place. When printing the value of a variable, the variable name can
+go inside the curly brackets. When printing the result of evaluating an
+expression, place empty curly brackets in the format string, then follow the
+format string with a comma-separated list of expressions to print in each empty
+curly bracket placeholder in the same order. Printing a variable and the result
+of an expression in one call to `println!` would look like this:
+
+```rust
+let x = 5;
+let y = 10;
+
+println!("x = {x} and y + 2 = {}", y + 2);
+```
+
+This code would print `x = 5 and y + 2 = 12`.
+
+### Testing the First Part
+
+Let’s test the first part of the guessing game. Run it using `cargo run`:
+
+
+
+```console
+$ cargo run
+ Compiling guessing_game v0.1.0 (file:///projects/guessing_game)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 6.44s
+ Running `target/debug/guessing_game`
+Guess the number!
+Please input your guess.
+6
+You guessed: 6
+```
+
+At this point, the first part of the game is done: We’re getting input from the
+keyboard and then printing it.
+
+## Generating a Secret Number
+
+Next, we need to generate a secret number that the user will try to guess. The
+secret number should be different every time so that the game is fun to play
+more than once. We’ll use a random number between 1 and 100 so that the game
+isn’t too difficult. Rust doesn’t yet include random number functionality in
+its standard library. However, the Rust team does provide a [`rand`
+crate][randcrate] with said functionality.
+
+
+
+
+### Increasing Functionality with a Crate
+
+Remember that a crate is a collection of Rust source code files. The project
+we’ve been building is a binary crate, which is an executable. The `rand` crate
+is a library crate, which contains code that is intended to be used in other
+programs and can’t be executed on its own.
+
+Cargo’s coordination of external crates is where Cargo really shines. Before we
+can write code that uses `rand`, we need to modify the _Cargo.toml_ file to
+include the `rand` crate as a dependency. Open that file now and add the
+following line to the bottom, beneath the `[dependencies]` section header that
+Cargo created for you. Be sure to specify `rand` exactly as we have here, with
+this version number, or the code examples in this tutorial may not work:
+
+
+
+Filename: Cargo.toml
+
+```toml
+{{#include ../listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.toml:8:}}
+```
+
+In the _Cargo.toml_ file, everything that follows a header is part of that
+section that continues until another section starts. In `[dependencies]`, you
+tell Cargo which external crates your project depends on and which versions of
+those crates you require. In this case, we specify the `rand` crate with the
+semantic version specifier `0.8.5`. Cargo understands [Semantic
+Versioning][semver] (sometimes called _SemVer_), which is a
+standard for writing version numbers. The specifier `0.8.5` is actually
+shorthand for `^0.8.5`, which means any version that is at least 0.8.5 but
+below 0.9.0.
+
+Cargo considers these versions to have public APIs compatible with version
+0.8.5, and this specification ensures that you’ll get the latest patch release
+that will still compile with the code in this chapter. Any version 0.9.0 or
+greater is not guaranteed to have the same API as what the following examples
+use.
+
+Now, without changing any of the code, let’s build the project, as shown in
+Listing 2-2.
+
+
+
+
+
+```console
+$ cargo build
+ Updating crates.io index
+ Locking 15 packages to latest Rust 1.85.0 compatible versions
+ Adding rand v0.8.5 (available: v0.9.0)
+ Compiling proc-macro2 v1.0.93
+ Compiling unicode-ident v1.0.17
+ Compiling libc v0.2.170
+ Compiling cfg-if v1.0.0
+ Compiling byteorder v1.5.0
+ Compiling getrandom v0.2.15
+ Compiling rand_core v0.6.4
+ Compiling quote v1.0.38
+ Compiling syn v2.0.98
+ Compiling zerocopy-derive v0.7.35
+ Compiling zerocopy v0.7.35
+ Compiling ppv-lite86 v0.2.20
+ Compiling rand_chacha v0.3.1
+ Compiling rand v0.8.5
+ Compiling guessing_game v0.1.0 (file:///projects/guessing_game)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 2.48s
+```
+
+
+
+You may see different version numbers (but they will all be compatible with the
+code, thanks to SemVer!) and different lines (depending on the operating
+system), and the lines may be in a different order.
+
+When we include an external dependency, Cargo fetches the latest versions of
+everything that dependency needs from the _registry_, which is a copy of data
+from [Crates.io][cratesio]. Crates.io is where people in the Rust ecosystem
+post their open source Rust projects for others to use.
+
+After updating the registry, Cargo checks the `[dependencies]` section and
+downloads any crates listed that aren’t already downloaded. In this case,
+although we only listed `rand` as a dependency, Cargo also grabbed other crates
+that `rand` depends on to work. After downloading the crates, Rust compiles
+them and then compiles the project with the dependencies available.
+
+If you immediately run `cargo build` again without making any changes, you
+won’t get any output aside from the `Finished` line. Cargo knows it has already
+downloaded and compiled the dependencies, and you haven’t changed anything
+about them in your _Cargo.toml_ file. Cargo also knows that you haven’t changed
+anything about your code, so it doesn’t recompile that either. With nothing to
+do, it simply exits.
+
+If you open the _src/main.rs_ file, make a trivial change, and then save it and
+build again, you’ll only see two lines of output:
+
+
+
+```console
+$ cargo build
+ Compiling guessing_game v0.1.0 (file:///projects/guessing_game)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.13s
+```
+
+These lines show that Cargo only updates the build with your tiny change to the
+_src/main.rs_ file. Your dependencies haven’t changed, so Cargo knows it can
+reuse what it has already downloaded and compiled for those.
+
+
+
+
+#### Ensuring Reproducible Builds
+
+Cargo has a mechanism that ensures that you can rebuild the same artifact every
+time you or anyone else builds your code: Cargo will use only the versions of
+the dependencies you specified until you indicate otherwise. For example, say
+that next week version 0.8.6 of the `rand` crate comes out, and that version
+contains an important bug fix, but it also contains a regression that will
+break your code. To handle this, Rust creates the _Cargo.lock_ file the first
+time you run `cargo build`, so we now have this in the _guessing_game_
+directory.
+
+When you build a project for the first time, Cargo figures out all the versions
+of the dependencies that fit the criteria and then writes them to the
+_Cargo.lock_ file. When you build your project in the future, Cargo will see
+that the _Cargo.lock_ file exists and will use the versions specified there
+rather than doing all the work of figuring out versions again. This lets you
+have a reproducible build automatically. In other words, your project will
+remain at 0.8.5 until you explicitly upgrade, thanks to the _Cargo.lock_ file.
+Because the _Cargo.lock_ file is important for reproducible builds, it’s often
+checked into source control with the rest of the code in your project.
+
+#### Updating a Crate to Get a New Version
+
+When you _do_ want to update a crate, Cargo provides the command `update`,
+which will ignore the _Cargo.lock_ file and figure out all the latest versions
+that fit your specifications in _Cargo.toml_. Cargo will then write those
+versions to the _Cargo.lock_ file. Otherwise, by default, Cargo will only look
+for versions greater than 0.8.5 and less than 0.9.0. If the `rand` crate has
+released the two new versions 0.8.6 and 0.999.0, you would see the following if
+you ran `cargo update`:
+
+
+
+```console
+$ cargo update
+ Updating crates.io index
+ Locking 1 package to latest Rust 1.85.0 compatible version
+ Updating rand v0.8.5 -> v0.8.6 (available: v0.999.0)
+```
+
+Cargo ignores the 0.999.0 release. At this point, you would also notice a
+change in your _Cargo.lock_ file noting that the version of the `rand` crate
+you are now using is 0.8.6. To use `rand` version 0.999.0 or any version in the
+0.999._x_ series, you’d have to update the _Cargo.toml_ file to look like this
+instead (don’t actually make this change because the following examples assume
+you’re using `rand` 0.8):
+
+```toml
+[dependencies]
+rand = "0.999.0"
+```
+
+The next time you run `cargo build`, Cargo will update the registry of crates
+available and reevaluate your `rand` requirements according to the new version
+you have specified.
+
+There’s a lot more to say about [Cargo][doccargo] and [its
+ecosystem][doccratesio], which we’ll discuss in Chapter 14, but
+for now, that’s all you need to know. Cargo makes it very easy to reuse
+libraries, so Rustaceans are able to write smaller projects that are assembled
+from a number of packages.
+
+### Generating a Random Number
+
+Let’s start using `rand` to generate a number to guess. The next step is to
+update _src/main.rs_, as shown in Listing 2-3.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-03/src/main.rs:all}}
+```
+
+
+
+First, we add the line `use rand::Rng;`. The `Rng` trait defines methods that
+random number generators implement, and this trait must be in scope for us to
+use those methods. Chapter 10 will cover traits in detail.
+
+Next, we’re adding two lines in the middle. In the first line, we call the
+`rand::thread_rng` function that gives us the particular random number
+generator we’re going to use: one that is local to the current thread of
+execution and is seeded by the operating system. Then, we call the `gen_range`
+method on the random number generator. This method is defined by the `Rng`
+trait that we brought into scope with the `use rand::Rng;` statement. The
+`gen_range` method takes a range expression as an argument and generates a
+random number in the range. The kind of range expression we’re using here takes
+the form `start..=end` and is inclusive on the lower and upper bounds, so we
+need to specify `1..=100` to request a number between 1 and 100.
+
+> Note: You won’t just know which traits to use and which methods and functions
+> to call from a crate, so each crate has documentation with instructions for
+> using it. Another neat feature of Cargo is that running the `cargo doc
+> --open` command will build documentation provided by all your dependencies
+> locally and open it in your browser. If you’re interested in other
+> functionality in the `rand` crate, for example, run `cargo doc --open` and
+> click `rand` in the sidebar on the left.
+
+The second new line prints the secret number. This is useful while we’re
+developing the program to be able to test it, but we’ll delete it from the
+final version. It’s not much of a game if the program prints the answer as soon
+as it starts!
+
+Try running the program a few times:
+
+
+
+```console
+$ cargo run
+ Compiling guessing_game v0.1.0 (file:///projects/guessing_game)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
+ Running `target/debug/guessing_game`
+Guess the number!
+The secret number is: 7
+Please input your guess.
+4
+You guessed: 4
+
+$ cargo run
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.02s
+ Running `target/debug/guessing_game`
+Guess the number!
+The secret number is: 83
+Please input your guess.
+5
+You guessed: 5
+```
+
+You should get different random numbers, and they should all be numbers between
+1 and 100. Great job!
+
+## Comparing the Guess to the Secret Number
+
+Now that we have user input and a random number, we can compare them. That step
+is shown in Listing 2-4. Note that this code won’t compile just yet, as we will
+explain.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-04/src/main.rs:here}}
+```
+
+
+
+First, we add another `use` statement, bringing a type called
+`std::cmp::Ordering` into scope from the standard library. The `Ordering` type
+is another enum and has the variants `Less`, `Greater`, and `Equal`. These are
+the three outcomes that are possible when you compare two values.
+
+Then, we add five new lines at the bottom that use the `Ordering` type. The
+`cmp` method compares two values and can be called on anything that can be
+compared. It takes a reference to whatever you want to compare with: Here, it’s
+comparing `guess` to `secret_number`. Then, it returns a variant of the
+`Ordering` enum we brought into scope with the `use` statement. We use a
+[`match`][match] expression to decide what to do next based on
+which variant of `Ordering` was returned from the call to `cmp` with the values
+in `guess` and `secret_number`.
+
+A `match` expression is made up of _arms_. An arm consists of a _pattern_ to
+match against, and the code that should be run if the value given to `match`
+fits that arm’s pattern. Rust takes the value given to `match` and looks
+through each arm’s pattern in turn. Patterns and the `match` construct are
+powerful Rust features: They let you express a variety of situations your code
+might encounter, and they make sure you handle them all. These features will be
+covered in detail in Chapter 6 and Chapter 19, respectively.
+
+Let’s walk through an example with the `match` expression we use here. Say that
+the user has guessed 50 and the randomly generated secret number this time is
+38.
+
+When the code compares 50 to 38, the `cmp` method will return
+`Ordering::Greater` because 50 is greater than 38. The `match` expression gets
+the `Ordering::Greater` value and starts checking each arm’s pattern. It looks
+at the first arm’s pattern, `Ordering::Less`, and sees that the value
+`Ordering::Greater` does not match `Ordering::Less`, so it ignores the code in
+that arm and moves to the next arm. The next arm’s pattern is
+`Ordering::Greater`, which _does_ match `Ordering::Greater`! The associated
+code in that arm will execute and print `Too big!` to the screen. The `match`
+expression ends after the first successful match, so it won’t look at the last
+arm in this scenario.
+
+However, the code in Listing 2-4 won’t compile yet. Let’s try it:
+
+
+
+```console
+{{#include ../listings/ch02-guessing-game-tutorial/listing-02-04/output.txt}}
+```
+
+The core of the error states that there are _mismatched types_. Rust has a
+strong, static type system. However, it also has type inference. When we wrote
+`let mut guess = String::new()`, Rust was able to infer that `guess` should be
+a `String` and didn’t make us write the type. The `secret_number`, on the other
+hand, is a number type. A few of Rust’s number types can have a value between 1
+and 100: `i32`, a 32-bit number; `u32`, an unsigned 32-bit number; `i64`, a
+64-bit number; as well as others. Unless otherwise specified, Rust defaults to
+an `i32`, which is the type of `secret_number` unless you add type information
+elsewhere that would cause Rust to infer a different numerical type. The reason
+for the error is that Rust cannot compare a string and a number type.
+
+Ultimately, we want to convert the `String` the program reads as input into a
+number type so that we can compare it numerically to the secret number. We do
+so by adding this line to the `main` function body:
+
+Filename: src/main.rs
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/no-listing-03-convert-string-to-number/src/main.rs:here}}
+```
+
+The line is:
+
+```rust,ignore
+let guess: u32 = guess.trim().parse().expect("Please type a number!");
+```
+
+We create a variable named `guess`. But wait, doesn’t the program already have
+a variable named `guess`? It does, but helpfully Rust allows us to shadow the
+previous value of `guess` with a new one. _Shadowing_ lets us reuse the `guess`
+variable name rather than forcing us to create two unique variables, such as
+`guess_str` and `guess`, for example. We’ll cover this in more detail in
+[Chapter 3][shadowing], but for now, know that this feature is
+often used when you want to convert a value from one type to another type.
+
+We bind this new variable to the expression `guess.trim().parse()`. The `guess`
+in the expression refers to the original `guess` variable that contained the
+input as a string. The `trim` method on a `String` instance will eliminate any
+whitespace at the beginning and end, which we must do before we can convert the
+string to a `u32`, which can only contain numerical data. The user must press
+enter to satisfy `read_line` and input their guess, which adds a
+newline character to the string. For example, if the user types 5 and
+presses enter, `guess` looks like this: `5\n`. The `\n` represents
+“newline.” (On Windows, pressing enter results in a carriage return
+and a newline, `\r\n`.) The `trim` method eliminates `\n` or `\r\n`, resulting
+in just `5`.
+
+The [`parse` method on strings][parse] converts a string to
+another type. Here, we use it to convert from a string to a number. We need to
+tell Rust the exact number type we want by using `let guess: u32`. The colon
+(`:`) after `guess` tells Rust we’ll annotate the variable’s type. Rust has a
+few built-in number types; the `u32` seen here is an unsigned, 32-bit integer.
+It’s a good default choice for a small positive number. You’ll learn about
+other number types in [Chapter 3][integers].
+
+Additionally, the `u32` annotation in this example program and the comparison
+with `secret_number` means Rust will infer that `secret_number` should be a
+`u32` as well. So, now the comparison will be between two values of the same
+type!
+
+The `parse` method will only work on characters that can logically be converted
+into numbers and so can easily cause errors. If, for example, the string
+contained `A👍%`, there would be no way to convert that to a number. Because it
+might fail, the `parse` method returns a `Result` type, much as the `read_line`
+method does (discussed earlier in [“Handling Potential Failure with
+`Result`”](#handling-potential-failure-with-result)). We’ll treat
+this `Result` the same way by using the `expect` method again. If `parse`
+returns an `Err` `Result` variant because it couldn’t create a number from the
+string, the `expect` call will crash the game and print the message we give it.
+If `parse` can successfully convert the string to a number, it will return the
+`Ok` variant of `Result`, and `expect` will return the number that we want from
+the `Ok` value.
+
+Let’s run the program now:
+
+
+
+```console
+$ cargo run
+ Compiling guessing_game v0.1.0 (file:///projects/guessing_game)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.26s
+ Running `target/debug/guessing_game`
+Guess the number!
+The secret number is: 58
+Please input your guess.
+ 76
+You guessed: 76
+Too big!
+```
+
+Nice! Even though spaces were added before the guess, the program still figured
+out that the user guessed 76. Run the program a few times to verify the
+different behavior with different kinds of input: Guess the number correctly,
+guess a number that is too high, and guess a number that is too low.
+
+We have most of the game working now, but the user can make only one guess.
+Let’s change that by adding a loop!
+
+## Allowing Multiple Guesses with Looping
+
+The `loop` keyword creates an infinite loop. We’ll add a loop to give users
+more chances at guessing the number:
+
+Filename: src/main.rs
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/no-listing-04-looping/src/main.rs:here}}
+```
+
+As you can see, we’ve moved everything from the guess input prompt onward into
+a loop. Be sure to indent the lines inside the loop another four spaces each
+and run the program again. The program will now ask for another guess forever,
+which actually introduces a new problem. It doesn’t seem like the user can quit!
+
+The user could always interrupt the program by using the keyboard shortcut
+ctrl-C. But there’s another way to escape this insatiable
+monster, as mentioned in the `parse` discussion in [“Comparing the Guess to the
+Secret Number”](#comparing-the-guess-to-the-secret-number): If
+the user enters a non-number answer, the program will crash. We can take
+advantage of that to allow the user to quit, as shown here:
+
+
+
+```console
+$ cargo run
+ Compiling guessing_game v0.1.0 (file:///projects/guessing_game)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.23s
+ Running `target/debug/guessing_game`
+Guess the number!
+The secret number is: 59
+Please input your guess.
+45
+You guessed: 45
+Too small!
+Please input your guess.
+60
+You guessed: 60
+Too big!
+Please input your guess.
+59
+You guessed: 59
+You win!
+Please input your guess.
+quit
+
+thread 'main' panicked at src/main.rs:28:47:
+Please type a number!: ParseIntError { kind: InvalidDigit }
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+```
+
+Typing `quit` will quit the game, but as you’ll notice, so will entering any
+other non-number input. This is suboptimal, to say the least; we want the game
+to also stop when the correct number is guessed.
+
+### Quitting After a Correct Guess
+
+Let’s program the game to quit when the user wins by adding a `break` statement:
+
+Filename: src/main.rs
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/no-listing-05-quitting/src/main.rs:here}}
+```
+
+Adding the `break` line after `You win!` makes the program exit the loop when
+the user guesses the secret number correctly. Exiting the loop also means
+exiting the program, because the loop is the last part of `main`.
+
+### Handling Invalid Input
+
+To further refine the game’s behavior, rather than crashing the program when
+the user inputs a non-number, let’s make the game ignore a non-number so that
+the user can continue guessing. We can do that by altering the line where
+`guess` is converted from a `String` to a `u32`, as shown in Listing 2-5.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-05/src/main.rs:here}}
+```
+
+
+
+We switch from an `expect` call to a `match` expression to move from crashing
+on an error to handling the error. Remember that `parse` returns a `Result`
+type and `Result` is an enum that has the variants `Ok` and `Err`. We’re using
+a `match` expression here, as we did with the `Ordering` result of the `cmp`
+method.
+
+If `parse` is able to successfully turn the string into a number, it will
+return an `Ok` value that contains the resultant number. That `Ok` value will
+match the first arm’s pattern, and the `match` expression will just return the
+`num` value that `parse` produced and put inside the `Ok` value. That number
+will end up right where we want it in the new `guess` variable we’re creating.
+
+If `parse` is _not_ able to turn the string into a number, it will return an
+`Err` value that contains more information about the error. The `Err` value
+does not match the `Ok(num)` pattern in the first `match` arm, but it does
+match the `Err(_)` pattern in the second arm. The underscore, `_`, is a
+catch-all value; in this example, we’re saying we want to match all `Err`
+values, no matter what information they have inside them. So, the program will
+execute the second arm’s code, `continue`, which tells the program to go to the
+next iteration of the `loop` and ask for another guess. So, effectively, the
+program ignores all errors that `parse` might encounter!
+
+Now everything in the program should work as expected. Let’s try it:
+
+
+
+```console
+$ cargo run
+ Compiling guessing_game v0.1.0 (file:///projects/guessing_game)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.13s
+ Running `target/debug/guessing_game`
+Guess the number!
+The secret number is: 61
+Please input your guess.
+10
+You guessed: 10
+Too small!
+Please input your guess.
+99
+You guessed: 99
+Too big!
+Please input your guess.
+foo
+Please input your guess.
+61
+You guessed: 61
+You win!
+```
+
+Awesome! With one tiny final tweak, we will finish the guessing game. Recall
+that the program is still printing the secret number. That worked well for
+testing, but it ruins the game. Let’s delete the `println!` that outputs the
+secret number. Listing 2-6 shows the final code.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-06/src/main.rs}}
+```
+
+
+
+At this point, you’ve successfully built the guessing game. Congratulations!
+
+## Summary
+
+This project was a hands-on way to introduce you to many new Rust concepts:
+`let`, `match`, functions, the use of external crates, and more. In the next
+few chapters, you’ll learn about these concepts in more detail. Chapter 3
+covers concepts that most programming languages have, such as variables, data
+types, and functions, and shows how to use them in Rust. Chapter 4 explores
+ownership, a feature that makes Rust different from other languages. Chapter 5
+discusses structs and method syntax, and Chapter 6 explains how enums work.
+
+[prelude]: ../std/prelude/index.html
+[variables-and-mutability]: ch03-01-variables-and-mutability.html#variables-and-mutability
+[comments]: ch03-04-comments.html
+[string]: ../std/string/struct.String.html
+[iostdin]: ../std/io/struct.Stdin.html
+[read_line]: ../std/io/struct.Stdin.html#method.read_line
+[result]: ../std/result/enum.Result.html
+[enums]: ch06-00-enums.html
+[expect]: ../std/result/enum.Result.html#method.expect
+[recover]: ch09-02-recoverable-errors-with-result.html
+[randcrate]: https://crates.io/crates/rand
+[semver]: http://semver.org
+[cratesio]: https://crates.io/
+[doccargo]: https://doc.rust-lang.org/cargo/
+[doccratesio]: https://doc.rust-lang.org/cargo/reference/publishing.html
+[match]: ch06-02-match.html
+[shadowing]: ch03-01-variables-and-mutability.html#shadowing
+[parse]: ../std/primitive.str.html#method.parse
+[integers]: ch03-02-data-types.html#integer-types
diff --git a/documents/markdown/rust-book/ch03-00-common-programming-concepts.md b/documents/markdown/rust-book/ch03-00-common-programming-concepts.md
new file mode 100644
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--- /dev/null
+++ b/documents/markdown/rust-book/ch03-00-common-programming-concepts.md
@@ -0,0 +1,23 @@
+# Common Programming Concepts
+
+This chapter covers concepts that appear in almost every programming language
+and how they work in Rust. Many programming languages have much in common at
+their core. None of the concepts presented in this chapter are unique to Rust,
+but we’ll discuss them in the context of Rust and explain the conventions
+around using them.
+
+Specifically, you’ll learn about variables, basic types, functions, comments,
+and control flow. These foundations will be in every Rust program, and learning
+them early will give you a strong core to start from.
+
+> #### Keywords
+>
+> The Rust language has a set of _keywords_ that are reserved for use by the
+> language only, much as in other languages. Keep in mind that you cannot use
+> these words as names of variables or functions. Most of the keywords have
+> special meanings, and you’ll be using them to do various tasks in your Rust
+> programs; a few have no current functionality associated with them but have
+> been reserved for functionality that might be added to Rust in the future. You
+> can find the list of the keywords in [Appendix A][appendix_a].
+
+[appendix_a]: appendix-01-keywords.md
diff --git a/documents/markdown/rust-book/ch03-01-variables-and-mutability.md b/documents/markdown/rust-book/ch03-01-variables-and-mutability.md
new file mode 100644
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--- /dev/null
+++ b/documents/markdown/rust-book/ch03-01-variables-and-mutability.md
@@ -0,0 +1,192 @@
+## Variables and Mutability
+
+As mentioned in the [“Storing Values with
+Variables”][storing-values-with-variables] section, by default,
+variables are immutable. This is one of many nudges Rust gives you to write
+your code in a way that takes advantage of the safety and easy concurrency that
+Rust offers. However, you still have the option to make your variables mutable.
+Let’s explore how and why Rust encourages you to favor immutability and why
+sometimes you might want to opt out.
+
+When a variable is immutable, once a value is bound to a name, you can’t change
+that value. To illustrate this, generate a new project called _variables_ in
+your _projects_ directory by using `cargo new variables`.
+
+Then, in your new _variables_ directory, open _src/main.rs_ and replace its
+code with the following code, which won’t compile just yet:
+
+Filename: src/main.rs
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-01-variables-are-immutable/src/main.rs}}
+```
+
+Save and run the program using `cargo run`. You should receive an error message
+regarding an immutability error, as shown in this output:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-01-variables-are-immutable/output.txt}}
+```
+
+This example shows how the compiler helps you find errors in your programs.
+Compiler errors can be frustrating, but really they only mean your program
+isn’t safely doing what you want it to do yet; they do _not_ mean that you’re
+not a good programmer! Experienced Rustaceans still get compiler errors.
+
+You received the error message `` cannot assign twice to immutable variable `x` `` because you tried to assign a second value to the immutable `x` variable.
+
+It’s important that we get compile-time errors when we attempt to change a
+value that’s designated as immutable, because this very situation can lead to
+bugs. If one part of our code operates on the assumption that a value will
+never change and another part of our code changes that value, it’s possible
+that the first part of the code won’t do what it was designed to do. The cause
+of this kind of bug can be difficult to track down after the fact, especially
+when the second piece of code changes the value only _sometimes_. The Rust
+compiler guarantees that when you state that a value won’t change, it really
+won’t change, so you don’t have to keep track of it yourself. Your code is thus
+easier to reason through.
+
+But mutability can be very useful and can make code more convenient to write.
+Although variables are immutable by default, you can make them mutable by
+adding `mut` in front of the variable name as you did in [Chapter
+2][storing-values-with-variables]. Adding `mut` also conveys
+intent to future readers of the code by indicating that other parts of the code
+will be changing this variable’s value.
+
+For example, let’s change _src/main.rs_ to the following:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-02-adding-mut/src/main.rs}}
+```
+
+When we run the program now, we get this:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-02-adding-mut/output.txt}}
+```
+
+We’re allowed to change the value bound to `x` from `5` to `6` when `mut` is
+used. Ultimately, deciding whether to use mutability or not is up to you and
+depends on what you think is clearest in that particular situation.
+
+
+
+
+### Declaring Constants
+
+Like immutable variables, _constants_ are values that are bound to a name and
+are not allowed to change, but there are a few differences between constants
+and variables.
+
+First, you aren’t allowed to use `mut` with constants. Constants aren’t just
+immutable by default—they’re always immutable. You declare constants using the
+`const` keyword instead of the `let` keyword, and the type of the value _must_
+be annotated. We’ll cover types and type annotations in the next section,
+[“Data Types”][data-types], so don’t worry about the details
+right now. Just know that you must always annotate the type.
+
+Constants can be declared in any scope, including the global scope, which makes
+them useful for values that many parts of code need to know about.
+
+The last difference is that constants may be set only to a constant expression,
+not the result of a value that could only be computed at runtime.
+
+Here’s an example of a constant declaration:
+
+```rust
+const THREE_HOURS_IN_SECONDS: u32 = 60 * 60 * 3;
+```
+
+The constant’s name is `THREE_HOURS_IN_SECONDS`, and its value is set to the
+result of multiplying 60 (the number of seconds in a minute) by 60 (the number
+of minutes in an hour) by 3 (the number of hours we want to count in this
+program). Rust’s naming convention for constants is to use all uppercase with
+underscores between words. The compiler is able to evaluate a limited set of
+operations at compile time, which lets us choose to write out this value in a
+way that’s easier to understand and verify, rather than setting this constant
+to the value 10,800. See the [Rust Reference’s section on constant
+evaluation][const-eval] for more information on what operations can be used
+when declaring constants.
+
+Constants are valid for the entire time a program runs, within the scope in
+which they were declared. This property makes constants useful for values in
+your application domain that multiple parts of the program might need to know
+about, such as the maximum number of points any player of a game is allowed to
+earn, or the speed of light.
+
+Naming hardcoded values used throughout your program as constants is useful in
+conveying the meaning of that value to future maintainers of the code. It also
+helps to have only one place in your code that you would need to change if the
+hardcoded value needed to be updated in the future.
+
+### Shadowing
+
+As you saw in the guessing game tutorial in [Chapter
+2][comparing-the-guess-to-the-secret-number], you can declare a
+new variable with the same name as a previous variable. Rustaceans say that the
+first variable is _shadowed_ by the second, which means that the second
+variable is what the compiler will see when you use the name of the variable.
+In effect, the second variable overshadows the first, taking any uses of the
+variable name to itself until either it itself is shadowed or the scope ends.
+We can shadow a variable by using the same variable’s name and repeating the
+use of the `let` keyword as follows:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-03-shadowing/src/main.rs}}
+```
+
+This program first binds `x` to a value of `5`. Then, it creates a new variable
+`x` by repeating `let x =`, taking the original value and adding `1` so that
+the value of `x` is `6`. Then, within an inner scope created with the curly
+brackets, the third `let` statement also shadows `x` and creates a new
+variable, multiplying the previous value by `2` to give `x` a value of `12`.
+When that scope is over, the inner shadowing ends and `x` returns to being `6`.
+When we run this program, it will output the following:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-03-shadowing/output.txt}}
+```
+
+Shadowing is different from marking a variable as `mut` because we’ll get a
+compile-time error if we accidentally try to reassign to this variable without
+using the `let` keyword. By using `let`, we can perform a few transformations
+on a value but have the variable be immutable after those transformations have
+completed.
+
+The other difference between `mut` and shadowing is that because we’re
+effectively creating a new variable when we use the `let` keyword again, we can
+change the type of the value but reuse the same name. For example, say our
+program asks a user to show how many spaces they want between some text by
+inputting space characters, and then we want to store that input as a number:
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-04-shadowing-can-change-types/src/main.rs:here}}
+```
+
+The first `spaces` variable is a string type, and the second `spaces` variable
+is a number type. Shadowing thus spares us from having to come up with
+different names, such as `spaces_str` and `spaces_num`; instead, we can reuse
+the simpler `spaces` name. However, if we try to use `mut` for this, as shown
+here, we’ll get a compile-time error:
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-05-mut-cant-change-types/src/main.rs:here}}
+```
+
+The error says we’re not allowed to mutate a variable’s type:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-05-mut-cant-change-types/output.txt}}
+```
+
+Now that we’ve explored how variables work, let’s look at more data types they
+can have.
+
+[comparing-the-guess-to-the-secret-number]: ch02-00-guessing-game-tutorial.html#comparing-the-guess-to-the-secret-number
+[data-types]: ch03-02-data-types.html#data-types
+[storing-values-with-variables]: ch02-00-guessing-game-tutorial.html#storing-values-with-variables
+[const-eval]: ../reference/const_eval.html
diff --git a/documents/markdown/rust-book/ch03-02-data-types.md b/documents/markdown/rust-book/ch03-02-data-types.md
new file mode 100644
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@@ -0,0 +1,385 @@
+## Data Types
+
+Every value in Rust is of a certain _data type_, which tells Rust what kind of
+data is being specified so that it knows how to work with that data. We’ll look
+at two data type subsets: scalar and compound.
+
+Keep in mind that Rust is a _statically typed_ language, which means that it
+must know the types of all variables at compile time. The compiler can usually
+infer what type we want to use based on the value and how we use it. In cases
+when many types are possible, such as when we converted a `String` to a numeric
+type using `parse` in the [“Comparing the Guess to the Secret
+Number”][comparing-the-guess-to-the-secret-number] section in
+Chapter 2, we must add a type annotation, like this:
+
+```rust
+let guess: u32 = "42".parse().expect("Not a number!");
+```
+
+If we don’t add the `: u32` type annotation shown in the preceding code, Rust
+will display the following error, which means the compiler needs more
+information from us to know which type we want to use:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/output-only-01-no-type-annotations/output.txt}}
+```
+
+You’ll see different type annotations for other data types.
+
+### Scalar Types
+
+A _scalar_ type represents a single value. Rust has four primary scalar types:
+integers, floating-point numbers, Booleans, and characters. You may recognize
+these from other programming languages. Let’s jump into how they work in Rust.
+
+#### Integer Types
+
+An _integer_ is a number without a fractional component. We used one integer
+type in Chapter 2, the `u32` type. This type declaration indicates that the
+value it’s associated with should be an unsigned integer (signed integer types
+start with `i` instead of `u`) that takes up 32 bits of space. Table 3-1 shows
+the built-in integer types in Rust. We can use any of these variants to declare
+the type of an integer value.
+
+Table 3-1: Integer Types in Rust
+
+| Length | Signed | Unsigned |
+| ------- | ------- | -------- |
+| 8-bit | `i8` | `u8` |
+| 16-bit | `i16` | `u16` |
+| 32-bit | `i32` | `u32` |
+| 64-bit | `i64` | `u64` |
+| 128-bit | `i128` | `u128` |
+| Architecture-dependent | `isize` | `usize` |
+
+Each variant can be either signed or unsigned and has an explicit size.
+_Signed_ and _unsigned_ refer to whether it’s possible for the number to be
+negative—in other words, whether the number needs to have a sign with it
+(signed) or whether it will only ever be positive and can therefore be
+represented without a sign (unsigned). It’s like writing numbers on paper: When
+the sign matters, a number is shown with a plus sign or a minus sign; however,
+when it’s safe to assume the number is positive, it’s shown with no sign.
+Signed numbers are stored using [two’s complement][twos-complement] representation.
+
+Each signed variant can store numbers from −(2n − 1) to 2n −
+1 − 1 inclusive, where _n_ is the number of bits that variant uses. So, an
+`i8` can store numbers from −(27) to 27 − 1, which equals
+−128 to 127. Unsigned variants can store numbers from 0 to 2n − 1,
+so a `u8` can store numbers from 0 to 28 − 1, which equals 0 to 255.
+
+Additionally, the `isize` and `usize` types depend on the architecture of the
+computer your program is running on: 64 bits if you’re on a 64-bit architecture
+and 32 bits if you’re on a 32-bit architecture.
+
+You can write integer literals in any of the forms shown in Table 3-2. Note
+that number literals that can be multiple numeric types allow a type suffix,
+such as `57u8`, to designate the type. Number literals can also use `_` as a
+visual separator to make the number easier to read, such as `1_000`, which will
+have the same value as if you had specified `1000`.
+
+Table 3-2: Integer Literals in Rust
+
+| Number literals | Example |
+| ---------------- | ------------- |
+| Decimal | `98_222` |
+| Hex | `0xff` |
+| Octal | `0o77` |
+| Binary | `0b1111_0000` |
+| Byte (`u8` only) | `b'A'` |
+
+So how do you know which type of integer to use? If you’re unsure, Rust’s
+defaults are generally good places to start: Integer types default to `i32`.
+The primary situation in which you’d use `isize` or `usize` is when indexing
+some sort of collection.
+
+> ##### Integer Overflow
+>
+> Let’s say you have a variable of type `u8` that can hold values between 0 and
+> 255. If you try to change the variable to a value outside that range, such as
+> 256, _integer overflow_ will occur, which can result in one of two behaviors.
+> When you’re compiling in debug mode, Rust includes checks for integer overflow
+> that cause your program to _panic_ at runtime if this behavior occurs. Rust
+> uses the term _panicking_ when a program exits with an error; we’ll discuss
+> panics in more depth in the [“Unrecoverable Errors with
+> `panic!`”][unrecoverable-errors-with-panic] section in Chapter
+> 9.
+>
+> When you’re compiling in release mode with the `--release` flag, Rust does
+> _not_ include checks for integer overflow that cause panics. Instead, if
+> overflow occurs, Rust performs _two’s complement wrapping_. In short, values
+> greater than the maximum value the type can hold “wrap around” to the minimum
+> of the values the type can hold. In the case of a `u8`, the value 256 becomes
+> 0, the value 257 becomes 1, and so on. The program won’t panic, but the
+> variable will have a value that probably isn’t what you were expecting it to
+> have. Relying on integer overflow’s wrapping behavior is considered an error.
+>
+> To explicitly handle the possibility of overflow, you can use these families
+> of methods provided by the standard library for primitive numeric types:
+>
+> - Wrap in all modes with the `wrapping_*` methods, such as `wrapping_add`.
+> - Return the `None` value if there is overflow with the `checked_*` methods.
+> - Return the value and a Boolean indicating whether there was overflow with
+> the `overflowing_*` methods.
+> - Saturate at the value’s minimum or maximum values with the `saturating_*`
+> methods.
+
+#### Floating-Point Types
+
+Rust also has two primitive types for _floating-point numbers_, which are
+numbers with decimal points. Rust’s floating-point types are `f32` and `f64`,
+which are 32 bits and 64 bits in size, respectively. The default type is `f64`
+because on modern CPUs, it’s roughly the same speed as `f32` but is capable of
+more precision. All floating-point types are signed.
+
+Here’s an example that shows floating-point numbers in action:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-06-floating-point/src/main.rs}}
+```
+
+Floating-point numbers are represented according to the IEEE-754 standard.
+
+#### Numeric Operations
+
+Rust supports the basic mathematical operations you’d expect for all the number
+types: addition, subtraction, multiplication, division, and remainder. Integer
+division truncates toward zero to the nearest integer. The following code shows
+how you’d use each numeric operation in a `let` statement:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-07-numeric-operations/src/main.rs}}
+```
+
+Each expression in these statements uses a mathematical operator and evaluates
+to a single value, which is then bound to a variable. [Appendix
+B][appendix_b] contains a list of all operators that Rust
+provides.
+
+#### The Boolean Type
+
+As in most other programming languages, a Boolean type in Rust has two possible
+values: `true` and `false`. Booleans are one byte in size. The Boolean type in
+Rust is specified using `bool`. For example:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-08-boolean/src/main.rs}}
+```
+
+The main way to use Boolean values is through conditionals, such as an `if`
+expression. We’ll cover how `if` expressions work in Rust in the [“Control
+Flow”][control-flow] section.
+
+#### The Character Type
+
+Rust’s `char` type is the language’s most primitive alphabetic type. Here are
+some examples of declaring `char` values:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-09-char/src/main.rs}}
+```
+
+Note that we specify `char` literals with single quotation marks, as opposed to
+string literals, which use double quotation marks. Rust’s `char` type is 4
+bytes in size and represents a Unicode scalar value, which means it can
+represent a lot more than just ASCII. Accented letters; Chinese, Japanese, and
+Korean characters; emojis; and zero-width spaces are all valid `char` values in
+Rust. Unicode scalar values range from `U+0000` to `U+D7FF` and `U+E000` to
+`U+10FFFF` inclusive. However, a “character” isn’t really a concept in Unicode,
+so your human intuition for what a “character” is may not match up with what a
+`char` is in Rust. We’ll discuss this topic in detail in [“Storing UTF-8
+Encoded Text with Strings”][strings] in Chapter 8.
+
+### Compound Types
+
+_Compound types_ can group multiple values into one type. Rust has two
+primitive compound types: tuples and arrays.
+
+#### The Tuple Type
+
+A _tuple_ is a general way of grouping together a number of values with a
+variety of types into one compound type. Tuples have a fixed length: Once
+declared, they cannot grow or shrink in size.
+
+We create a tuple by writing a comma-separated list of values inside
+parentheses. Each position in the tuple has a type, and the types of the
+different values in the tuple don’t have to be the same. We’ve added optional
+type annotations in this example:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-10-tuples/src/main.rs}}
+```
+
+The variable `tup` binds to the entire tuple because a tuple is considered a
+single compound element. To get the individual values out of a tuple, we can
+use pattern matching to destructure a tuple value, like this:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-11-destructuring-tuples/src/main.rs}}
+```
+
+This program first creates a tuple and binds it to the variable `tup`. It then
+uses a pattern with `let` to take `tup` and turn it into three separate
+variables, `x`, `y`, and `z`. This is called _destructuring_ because it breaks
+the single tuple into three parts. Finally, the program prints the value of
+`y`, which is `6.4`.
+
+We can also access a tuple element directly by using a period (`.`) followed by
+the index of the value we want to access. For example:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-12-tuple-indexing/src/main.rs}}
+```
+
+This program creates the tuple `x` and then accesses each element of the tuple
+using their respective indices. As with most programming languages, the first
+index in a tuple is 0.
+
+The tuple without any values has a special name, _unit_. This value and its
+corresponding type are both written `()` and represent an empty value or an
+empty return type. Expressions implicitly return the unit value if they don’t
+return any other value.
+
+#### The Array Type
+
+Another way to have a collection of multiple values is with an _array_. Unlike
+a tuple, every element of an array must have the same type. Unlike arrays in
+some other languages, arrays in Rust have a fixed length.
+
+We write the values in an array as a comma-separated list inside square
+brackets:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-13-arrays/src/main.rs}}
+```
+
+Arrays are useful when you want your data allocated on the stack, the same as
+the other types we have seen so far, rather than the heap (we will discuss the
+stack and the heap more in [Chapter 4][stack-and-heap]) or when
+you want to ensure that you always have a fixed number of elements. An array
+isn’t as flexible as the vector type, though. A vector is a similar collection
+type provided by the standard library that _is_ allowed to grow or shrink in
+size because its contents live on the heap. If you’re unsure whether to use an
+array or a vector, chances are you should use a vector. [Chapter
+8][vectors] discusses vectors in more detail.
+
+However, arrays are more useful when you know the number of elements will not
+need to change. For example, if you were using the names of the month in a
+program, you would probably use an array rather than a vector because you know
+it will always contain 12 elements:
+
+```rust
+let months = ["January", "February", "March", "April", "May", "June", "July",
+ "August", "September", "October", "November", "December"];
+```
+
+You write an array’s type using square brackets with the type of each element,
+a semicolon, and then the number of elements in the array, like so:
+
+```rust
+let a: [i32; 5] = [1, 2, 3, 4, 5];
+```
+
+Here, `i32` is the type of each element. After the semicolon, the number `5`
+indicates the array contains five elements.
+
+You can also initialize an array to contain the same value for each element by
+specifying the initial value, followed by a semicolon, and then the length of
+the array in square brackets, as shown here:
+
+```rust
+let a = [3; 5];
+```
+
+The array named `a` will contain `5` elements that will all be set to the value
+`3` initially. This is the same as writing `let a = [3, 3, 3, 3, 3];` but in a
+more concise way.
+
+
+
+
+#### Array Element Access
+
+An array is a single chunk of memory of a known, fixed size that can be
+allocated on the stack. You can access elements of an array using indexing,
+like this:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-14-array-indexing/src/main.rs}}
+```
+
+In this example, the variable named `first` will get the value `1` because that
+is the value at index `[0]` in the array. The variable named `second` will get
+the value `2` from index `[1]` in the array.
+
+#### Invalid Array Element Access
+
+Let’s see what happens if you try to access an element of an array that is past
+the end of the array. Say you run this code, similar to the guessing game in
+Chapter 2, to get an array index from the user:
+
+Filename: src/main.rs
+
+```rust,ignore,panics
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-15-invalid-array-access/src/main.rs}}
+```
+
+This code compiles successfully. If you run this code using `cargo run` and
+enter `0`, `1`, `2`, `3`, or `4`, the program will print out the corresponding
+value at that index in the array. If you instead enter a number past the end of
+the array, such as `10`, you’ll see output like this:
+
+
+
+```console
+thread 'main' panicked at src/main.rs:19:19:
+index out of bounds: the len is 5 but the index is 10
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+```
+
+The program resulted in a runtime error at the point of using an invalid
+value in the indexing operation. The program exited with an error message and
+didn’t execute the final `println!` statement. When you attempt to access an
+element using indexing, Rust will check that the index you’ve specified is less
+than the array length. If the index is greater than or equal to the length,
+Rust will panic. This check has to happen at runtime, especially in this case,
+because the compiler can’t possibly know what value a user will enter when they
+run the code later.
+
+This is an example of Rust’s memory safety principles in action. In many
+low-level languages, this kind of check is not done, and when you provide an
+incorrect index, invalid memory can be accessed. Rust protects you against this
+kind of error by immediately exiting instead of allowing the memory access and
+continuing. Chapter 9 discusses more of Rust’s error handling and how you can
+write readable, safe code that neither panics nor allows invalid memory access.
+
+[comparing-the-guess-to-the-secret-number]: ch02-00-guessing-game-tutorial.html#comparing-the-guess-to-the-secret-number
+[twos-complement]: https://en.wikipedia.org/wiki/Two%27s_complement
+[control-flow]: ch03-05-control-flow.html#control-flow
+[strings]: ch08-02-strings.html#storing-utf-8-encoded-text-with-strings
+[stack-and-heap]: ch04-01-what-is-ownership.html#the-stack-and-the-heap
+[vectors]: ch08-01-vectors.html
+[unrecoverable-errors-with-panic]: ch09-01-unrecoverable-errors-with-panic.html
+[appendix_b]: appendix-02-operators.md
diff --git a/documents/markdown/rust-book/ch03-03-how-functions-work.md b/documents/markdown/rust-book/ch03-03-how-functions-work.md
new file mode 100644
index 0000000..5f9e512
--- /dev/null
+++ b/documents/markdown/rust-book/ch03-03-how-functions-work.md
@@ -0,0 +1,253 @@
+## Functions
+
+Functions are prevalent in Rust code. You’ve already seen one of the most
+important functions in the language: the `main` function, which is the entry
+point of many programs. You’ve also seen the `fn` keyword, which allows you to
+declare new functions.
+
+Rust code uses _snake case_ as the conventional style for function and variable
+names, in which all letters are lowercase and underscores separate words.
+Here’s a program that contains an example function definition:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-16-functions/src/main.rs}}
+```
+
+We define a function in Rust by entering `fn` followed by a function name and a
+set of parentheses. The curly brackets tell the compiler where the function
+body begins and ends.
+
+We can call any function we’ve defined by entering its name followed by a set
+of parentheses. Because `another_function` is defined in the program, it can be
+called from inside the `main` function. Note that we defined `another_function`
+_after_ the `main` function in the source code; we could have defined it before
+as well. Rust doesn’t care where you define your functions, only that they’re
+defined somewhere in a scope that can be seen by the caller.
+
+Let’s start a new binary project named _functions_ to explore functions
+further. Place the `another_function` example in _src/main.rs_ and run it. You
+should see the following output:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-16-functions/output.txt}}
+```
+
+The lines execute in the order in which they appear in the `main` function.
+First the “Hello, world!” message prints, and then `another_function` is called
+and its message is printed.
+
+### Parameters
+
+We can define functions to have _parameters_, which are special variables that
+are part of a function’s signature. When a function has parameters, you can
+provide it with concrete values for those parameters. Technically, the concrete
+values are called _arguments_, but in casual conversation, people tend to use
+the words _parameter_ and _argument_ interchangeably for either the variables
+in a function’s definition or the concrete values passed in when you call a
+function.
+
+In this version of `another_function` we add a parameter:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-17-functions-with-parameters/src/main.rs}}
+```
+
+Try running this program; you should get the following output:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-17-functions-with-parameters/output.txt}}
+```
+
+The declaration of `another_function` has one parameter named `x`. The type of
+`x` is specified as `i32`. When we pass `5` in to `another_function`, the
+`println!` macro puts `5` where the pair of curly brackets containing `x` was
+in the format string.
+
+In function signatures, you _must_ declare the type of each parameter. This is
+a deliberate decision in Rust’s design: Requiring type annotations in function
+definitions means the compiler almost never needs you to use them elsewhere in
+the code to figure out what type you mean. The compiler is also able to give
+more-helpful error messages if it knows what types the function expects.
+
+When defining multiple parameters, separate the parameter declarations with
+commas, like this:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-18-functions-with-multiple-parameters/src/main.rs}}
+```
+
+This example creates a function named `print_labeled_measurement` with two
+parameters. The first parameter is named `value` and is an `i32`. The second is
+named `unit_label` and is type `char`. The function then prints text containing
+both the `value` and the `unit_label`.
+
+Let’s try running this code. Replace the program currently in your _functions_
+project’s _src/main.rs_ file with the preceding example and run it using `cargo
+run`:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-18-functions-with-multiple-parameters/output.txt}}
+```
+
+Because we called the function with `5` as the value for `value` and `'h'` as
+the value for `unit_label`, the program output contains those values.
+
+### Statements and Expressions
+
+Function bodies are made up of a series of statements optionally ending in an
+expression. So far, the functions we’ve covered haven’t included an ending
+expression, but you have seen an expression as part of a statement. Because
+Rust is an expression-based language, this is an important distinction to
+understand. Other languages don’t have the same distinctions, so let’s look at
+what statements and expressions are and how their differences affect the bodies
+of functions.
+
+- _Statements_ are instructions that perform some action and do not return
+ a value.
+- _Expressions_ evaluate to a resultant value.
+
+Let’s look at some examples.
+
+We’ve actually already used statements and expressions. Creating a variable and
+assigning a value to it with the `let` keyword is a statement. In Listing 3-1,
+`let y = 6;` is a statement.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/listing-03-01/src/main.rs}}
+```
+
+
+
+Function definitions are also statements; the entire preceding example is a
+statement in itself. (As we’ll see shortly, calling a function is not a
+statement, though.)
+
+Statements do not return values. Therefore, you can’t assign a `let` statement
+to another variable, as the following code tries to do; you’ll get an error:
+
+Filename: src/main.rs
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-19-statements-vs-expressions/src/main.rs}}
+```
+
+When you run this program, the error you’ll get looks like this:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-19-statements-vs-expressions/output.txt}}
+```
+
+The `let y = 6` statement does not return a value, so there isn’t anything for
+`x` to bind to. This is different from what happens in other languages, such as
+C and Ruby, where the assignment returns the value of the assignment. In those
+languages, you can write `x = y = 6` and have both `x` and `y` have the value
+`6`; that is not the case in Rust.
+
+Expressions evaluate to a value and make up most of the rest of the code that
+you’ll write in Rust. Consider a math operation, such as `5 + 6`, which is an
+expression that evaluates to the value `11`. Expressions can be part of
+statements: In Listing 3-1, the `6` in the statement `let y = 6;` is an
+expression that evaluates to the value `6`. Calling a function is an
+expression. Calling a macro is an expression. A new scope block created with
+curly brackets is an expression, for example:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-20-blocks-are-expressions/src/main.rs}}
+```
+
+This expression:
+
+```rust,ignore
+{
+ let x = 3;
+ x + 1
+}
+```
+
+is a block that, in this case, evaluates to `4`. That value gets bound to `y`
+as part of the `let` statement. Note the `x + 1` line without a semicolon at
+the end, which is unlike most of the lines you’ve seen so far. Expressions do
+not include ending semicolons. If you add a semicolon to the end of an
+expression, you turn it into a statement, and it will then not return a value.
+Keep this in mind as you explore function return values and expressions next.
+
+### Functions with Return Values
+
+Functions can return values to the code that calls them. We don’t name return
+values, but we must declare their type after an arrow (`->`). In Rust, the
+return value of the function is synonymous with the value of the final
+expression in the block of the body of a function. You can return early from a
+function by using the `return` keyword and specifying a value, but most
+functions return the last expression implicitly. Here’s an example of a
+function that returns a value:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-21-function-return-values/src/main.rs}}
+```
+
+There are no function calls, macros, or even `let` statements in the `five`
+function—just the number `5` by itself. That’s a perfectly valid function in
+Rust. Note that the function’s return type is specified too, as `-> i32`. Try
+running this code; the output should look like this:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-21-function-return-values/output.txt}}
+```
+
+The `5` in `five` is the function’s return value, which is why the return type
+is `i32`. Let’s examine this in more detail. There are two important bits:
+First, the line `let x = five();` shows that we’re using the return value of a
+function to initialize a variable. Because the function `five` returns a `5`,
+that line is the same as the following:
+
+```rust
+let x = 5;
+```
+
+Second, the `five` function has no parameters and defines the type of the
+return value, but the body of the function is a lonely `5` with no semicolon
+because it’s an expression whose value we want to return.
+
+Let’s look at another example:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-22-function-parameter-and-return/src/main.rs}}
+```
+
+Running this code will print `The value of x is: 6`. But what happens if we
+place a semicolon at the end of the line containing `x + 1`, changing it from
+an expression to a statement?
+
+Filename: src/main.rs
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/src/main.rs}}
+```
+
+Compiling this code will produce an error, as follows:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-23-statements-dont-return-values/output.txt}}
+```
+
+The main error message, `mismatched types`, reveals the core issue with this
+code. The definition of the function `plus_one` says that it will return an
+`i32`, but statements don’t evaluate to a value, which is expressed by `()`,
+the unit type. Therefore, nothing is returned, which contradicts the function
+definition and results in an error. In this output, Rust provides a message to
+possibly help rectify this issue: It suggests removing the semicolon, which
+would fix the error.
diff --git a/documents/markdown/rust-book/ch03-04-comments.md b/documents/markdown/rust-book/ch03-04-comments.md
new file mode 100644
index 0000000..fdcdbd4
--- /dev/null
+++ b/documents/markdown/rust-book/ch03-04-comments.md
@@ -0,0 +1,45 @@
+## Comments
+
+All programmers strive to make their code easy to understand, but sometimes
+extra explanation is warranted. In these cases, programmers leave _comments_ in
+their source code that the compiler will ignore but that people reading the
+source code may find useful.
+
+Here’s a simple comment:
+
+```rust
+// hello, world
+```
+
+In Rust, the idiomatic comment style starts a comment with two slashes, and the
+comment continues until the end of the line. For comments that extend beyond a
+single line, you’ll need to include `//` on each line, like this:
+
+```rust
+// So we're doing something complicated here, long enough that we need
+// multiple lines of comments to do it! Whew! Hopefully, this comment will
+// explain what's going on.
+```
+
+Comments can also be placed at the end of lines containing code:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-24-comments-end-of-line/src/main.rs}}
+```
+
+But you’ll more often see them used in this format, with the comment on a
+separate line above the code it’s annotating:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-25-comments-above-line/src/main.rs}}
+```
+
+Rust also has another kind of comment, documentation comments, which we’ll
+discuss in the [“Publishing a Crate to Crates.io”][publishing]
+section of Chapter 14.
+
+[publishing]: ch14-02-publishing-to-crates-io.html
diff --git a/documents/markdown/rust-book/ch03-05-control-flow.md b/documents/markdown/rust-book/ch03-05-control-flow.md
new file mode 100644
index 0000000..6bde674
--- /dev/null
+++ b/documents/markdown/rust-book/ch03-05-control-flow.md
@@ -0,0 +1,397 @@
+## Control Flow
+
+The ability to run some code depending on whether a condition is `true` and the
+ability to run some code repeatedly while a condition is `true` are basic
+building blocks in most programming languages. The most common constructs that
+let you control the flow of execution of Rust code are `if` expressions and
+loops.
+
+### `if` Expressions
+
+An `if` expression allows you to branch your code depending on conditions. You
+provide a condition and then state, “If this condition is met, run this block
+of code. If the condition is not met, do not run this block of code.”
+
+Create a new project called _branches_ in your _projects_ directory to explore
+the `if` expression. In the _src/main.rs_ file, input the following:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-26-if-true/src/main.rs}}
+```
+
+All `if` expressions start with the keyword `if`, followed by a condition. In
+this case, the condition checks whether or not the variable `number` has a
+value less than 5. We place the block of code to execute if the condition is
+`true` immediately after the condition inside curly brackets. Blocks of code
+associated with the conditions in `if` expressions are sometimes called _arms_,
+just like the arms in `match` expressions that we discussed in the [“Comparing
+the Guess to the Secret Number”][comparing-the-guess-to-the-secret-number] section of Chapter 2.
+
+Optionally, we can also include an `else` expression, which we chose to do
+here, to give the program an alternative block of code to execute should the
+condition evaluate to `false`. If you don’t provide an `else` expression and
+the condition is `false`, the program will just skip the `if` block and move on
+to the next bit of code.
+
+Try running this code; you should see the following output:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-26-if-true/output.txt}}
+```
+
+Let’s try changing the value of `number` to a value that makes the condition
+`false` to see what happens:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-27-if-false/src/main.rs:here}}
+```
+
+Run the program again, and look at the output:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-27-if-false/output.txt}}
+```
+
+It’s also worth noting that the condition in this code _must_ be a `bool`. If
+the condition isn’t a `bool`, we’ll get an error. For example, try running the
+following code:
+
+Filename: src/main.rs
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-28-if-condition-must-be-bool/src/main.rs}}
+```
+
+The `if` condition evaluates to a value of `3` this time, and Rust throws an
+error:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-28-if-condition-must-be-bool/output.txt}}
+```
+
+The error indicates that Rust expected a `bool` but got an integer. Unlike
+languages such as Ruby and JavaScript, Rust will not automatically try to
+convert non-Boolean types to a Boolean. You must be explicit and always provide
+`if` with a Boolean as its condition. If we want the `if` code block to run
+only when a number is not equal to `0`, for example, we can change the `if`
+expression to the following:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-29-if-not-equal-0/src/main.rs}}
+```
+
+Running this code will print `number was something other than zero`.
+
+#### Handling Multiple Conditions with `else if`
+
+You can use multiple conditions by combining `if` and `else` in an `else if`
+expression. For example:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-30-else-if/src/main.rs}}
+```
+
+This program has four possible paths it can take. After running it, you should
+see the following output:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-30-else-if/output.txt}}
+```
+
+When this program executes, it checks each `if` expression in turn and executes
+the first body for which the condition evaluates to `true`. Note that even
+though 6 is divisible by 2, we don’t see the output `number is divisible by 2`,
+nor do we see the `number is not divisible by 4, 3, or 2` text from the `else`
+block. That’s because Rust only executes the block for the first `true`
+condition, and once it finds one, it doesn’t even check the rest.
+
+Using too many `else if` expressions can clutter your code, so if you have more
+than one, you might want to refactor your code. Chapter 6 describes a powerful
+Rust branching construct called `match` for these cases.
+
+#### Using `if` in a `let` Statement
+
+Because `if` is an expression, we can use it on the right side of a `let`
+statement to assign the outcome to a variable, as in Listing 3-2.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/listing-03-02/src/main.rs}}
+```
+
+
+
+The `number` variable will be bound to a value based on the outcome of the `if`
+expression. Run this code to see what happens:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/listing-03-02/output.txt}}
+```
+
+Remember that blocks of code evaluate to the last expression in them, and
+numbers by themselves are also expressions. In this case, the value of the
+whole `if` expression depends on which block of code executes. This means the
+values that have the potential to be results from each arm of the `if` must be
+the same type; in Listing 3-2, the results of both the `if` arm and the `else`
+arm were `i32` integers. If the types are mismatched, as in the following
+example, we’ll get an error:
+
+Filename: src/main.rs
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-31-arms-must-return-same-type/src/main.rs}}
+```
+
+When we try to compile this code, we’ll get an error. The `if` and `else` arms
+have value types that are incompatible, and Rust indicates exactly where to
+find the problem in the program:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/no-listing-31-arms-must-return-same-type/output.txt}}
+```
+
+The expression in the `if` block evaluates to an integer, and the expression in
+the `else` block evaluates to a string. This won’t work, because variables must
+have a single type, and Rust needs to know definitively at compile time what
+type the `number` variable is. Knowing the type of `number` lets the compiler
+verify the type is valid everywhere we use `number`. Rust wouldn’t be able to
+do that if the type of `number` was only determined at runtime; the compiler
+would be more complex and would make fewer guarantees about the code if it had
+to keep track of multiple hypothetical types for any variable.
+
+### Repetition with Loops
+
+It’s often useful to execute a block of code more than once. For this task,
+Rust provides several _loops_, which will run through the code inside the loop
+body to the end and then start immediately back at the beginning. To experiment
+with loops, let’s make a new project called _loops_.
+
+Rust has three kinds of loops: `loop`, `while`, and `for`. Let’s try each one.
+
+#### Repeating Code with `loop`
+
+The `loop` keyword tells Rust to execute a block of code over and over again
+either forever or until you explicitly tell it to stop.
+
+As an example, change the _src/main.rs_ file in your _loops_ directory to look
+like this:
+
+Filename: src/main.rs
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-32-loop/src/main.rs}}
+```
+
+When we run this program, we’ll see `again!` printed over and over continuously
+until we stop the program manually. Most terminals support the keyboard shortcut
+ctrl-C to interrupt a program that is stuck in a continual
+loop. Give it a try:
+
+
+
+```console
+$ cargo run
+ Compiling loops v0.1.0 (file:///projects/loops)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.08s
+ Running `target/debug/loops`
+again!
+again!
+again!
+again!
+^Cagain!
+```
+
+The symbol `^C` represents where you pressed ctrl-C.
+
+You may or may not see the word `again!` printed after the `^C`, depending on
+where the code was in the loop when it received the interrupt signal.
+
+Fortunately, Rust also provides a way to break out of a loop using code. You
+can place the `break` keyword within the loop to tell the program when to stop
+executing the loop. Recall that we did this in the guessing game in the
+[“Quitting After a Correct Guess”][quitting-after-a-correct-guess] section of Chapter 2 to exit the program when the user won the game by
+guessing the correct number.
+
+We also used `continue` in the guessing game, which in a loop tells the program
+to skip over any remaining code in this iteration of the loop and go to the
+next iteration.
+
+#### Returning Values from Loops
+
+One of the uses of a `loop` is to retry an operation you know might fail, such
+as checking whether a thread has completed its job. You might also need to pass
+the result of that operation out of the loop to the rest of your code. To do
+this, you can add the value you want returned after the `break` expression you
+use to stop the loop; that value will be returned out of the loop so that you
+can use it, as shown here:
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-33-return-value-from-loop/src/main.rs}}
+```
+
+Before the loop, we declare a variable named `counter` and initialize it to
+`0`. Then, we declare a variable named `result` to hold the value returned from
+the loop. On every iteration of the loop, we add `1` to the `counter` variable,
+and then check whether the `counter` is equal to `10`. When it is, we use the
+`break` keyword with the value `counter * 2`. After the loop, we use a
+semicolon to end the statement that assigns the value to `result`. Finally, we
+print the value in `result`, which in this case is `20`.
+
+You can also `return` from inside a loop. While `break` only exits the current
+loop, `return` always exits the current function.
+
+
+
+
+#### Disambiguating with Loop Labels
+
+If you have loops within loops, `break` and `continue` apply to the innermost
+loop at that point. You can optionally specify a _loop label_ on a loop that
+you can then use with `break` or `continue` to specify that those keywords
+apply to the labeled loop instead of the innermost loop. Loop labels must begin
+with a single quote. Here’s an example with two nested loops:
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/src/main.rs}}
+```
+
+The outer loop has the label `'counting_up`, and it will count up from 0 to 2.
+The inner loop without a label counts down from 10 to 9. The first `break` that
+doesn’t specify a label will exit the inner loop only. The `break
+'counting_up;` statement will exit the outer loop. This code prints:
+
+```console
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-32-5-loop-labels/output.txt}}
+```
+
+
+
+
+#### Streamlining Conditional Loops with while
+
+A program will often need to evaluate a condition within a loop. While the
+condition is `true`, the loop runs. When the condition ceases to be `true`, the
+program calls `break`, stopping the loop. It’s possible to implement behavior
+like this using a combination of `loop`, `if`, `else`, and `break`; you could
+try that now in a program, if you’d like. However, this pattern is so common
+that Rust has a built-in language construct for it, called a `while` loop. In
+Listing 3-3, we use `while` to loop the program three times, counting down each
+time, and then, after the loop, to print a message and exit.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/listing-03-03/src/main.rs}}
+```
+
+
+
+This construct eliminates a lot of nesting that would be necessary if you used
+`loop`, `if`, `else`, and `break`, and it’s clearer. While a condition
+evaluates to `true`, the code runs; otherwise, it exits the loop.
+
+#### Looping Through a Collection with `for`
+
+You can choose to use the `while` construct to loop over the elements of a
+collection, such as an array. For example, the loop in Listing 3-4 prints each
+element in the array `a`.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/listing-03-04/src/main.rs}}
+```
+
+
+
+Here, the code counts up through the elements in the array. It starts at index
+`0` and then loops until it reaches the final index in the array (that is,
+when `index < 5` is no longer `true`). Running this code will print every
+element in the array:
+
+```console
+{{#include ../listings/ch03-common-programming-concepts/listing-03-04/output.txt}}
+```
+
+All five array values appear in the terminal, as expected. Even though `index`
+will reach a value of `5` at some point, the loop stops executing before trying
+to fetch a sixth value from the array.
+
+However, this approach is error-prone; we could cause the program to panic if
+the index value or test condition is incorrect. For example, if you changed the
+definition of the `a` array to have four elements but forgot to update the
+condition to `while index < 4`, the code would panic. It’s also slow, because
+the compiler adds runtime code to perform the conditional check of whether the
+index is within the bounds of the array on every iteration through the loop.
+
+As a more concise alternative, you can use a `for` loop and execute some code
+for each item in a collection. A `for` loop looks like the code in Listing 3-5.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/listing-03-05/src/main.rs}}
+```
+
+
+
+When we run this code, we’ll see the same output as in Listing 3-4. More
+importantly, we’ve now increased the safety of the code and eliminated the
+chance of bugs that might result from going beyond the end of the array or not
+going far enough and missing some items. Machine code generated from `for`
+loops can be more efficient as well because the index doesn’t need to be
+compared to the length of the array at every iteration.
+
+Using the `for` loop, you wouldn’t need to remember to change any other code if
+you changed the number of values in the array, as you would with the method
+used in Listing 3-4.
+
+The safety and conciseness of `for` loops make them the most commonly used loop
+construct in Rust. Even in situations in which you want to run some code a
+certain number of times, as in the countdown example that used a `while` loop
+in Listing 3-3, most Rustaceans would use a `for` loop. The way to do that
+would be to use a `Range`, provided by the standard library, which generates
+all numbers in sequence starting from one number and ending before another
+number.
+
+Here’s what the countdown would look like using a `for` loop and another method
+we’ve not yet talked about, `rev`, to reverse the range:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch03-common-programming-concepts/no-listing-34-for-range/src/main.rs}}
+```
+
+This code is a bit nicer, isn’t it?
+
+## Summary
+
+You made it! This was a sizable chapter: You learned about variables, scalar
+and compound data types, functions, comments, `if` expressions, and loops! To
+practice with the concepts discussed in this chapter, try building programs to
+do the following:
+
+- Convert temperatures between Fahrenheit and Celsius.
+- Generate the *n*th Fibonacci number.
+- Print the lyrics to the Christmas carol “The Twelve Days of Christmas,”
+ taking advantage of the repetition in the song.
+
+When you’re ready to move on, we’ll talk about a concept in Rust that _doesn’t_
+commonly exist in other programming languages: ownership.
+
+[comparing-the-guess-to-the-secret-number]: ch02-00-guessing-game-tutorial.html#comparing-the-guess-to-the-secret-number
+[quitting-after-a-correct-guess]: ch02-00-guessing-game-tutorial.html#quitting-after-a-correct-guess
diff --git a/documents/markdown/rust-book/ch04-00-understanding-ownership.md b/documents/markdown/rust-book/ch04-00-understanding-ownership.md
new file mode 100644
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--- /dev/null
+++ b/documents/markdown/rust-book/ch04-00-understanding-ownership.md
@@ -0,0 +1,7 @@
+# Understanding Ownership
+
+Ownership is Rust’s most unique feature and has deep implications for the rest
+of the language. It enables Rust to make memory safety guarantees without
+needing a garbage collector, so it’s important to understand how ownership
+works. In this chapter, we’ll talk about ownership as well as several related
+features: borrowing, slices, and how Rust lays data out in memory.
diff --git a/documents/markdown/rust-book/ch04-01-what-is-ownership.md b/documents/markdown/rust-book/ch04-01-what-is-ownership.md
new file mode 100644
index 0000000..aa8fc61
--- /dev/null
+++ b/documents/markdown/rust-book/ch04-01-what-is-ownership.md
@@ -0,0 +1,522 @@
+## What Is Ownership?
+
+_Ownership_ is a set of rules that govern how a Rust program manages memory.
+All programs have to manage the way they use a computer’s memory while running.
+Some languages have garbage collection that regularly looks for no-longer-used
+memory as the program runs; in other languages, the programmer must explicitly
+allocate and free the memory. Rust uses a third approach: Memory is managed
+through a system of ownership with a set of rules that the compiler checks. If
+any of the rules are violated, the program won’t compile. None of the features
+of ownership will slow down your program while it’s running.
+
+Because ownership is a new concept for many programmers, it does take some time
+to get used to. The good news is that the more experienced you become with Rust
+and the rules of the ownership system, the easier you’ll find it to naturally
+develop code that is safe and efficient. Keep at it!
+
+When you understand ownership, you’ll have a solid foundation for understanding
+the features that make Rust unique. In this chapter, you’ll learn ownership by
+working through some examples that focus on a very common data structure:
+strings.
+
+> ### The Stack and the Heap
+>
+> Many programming languages don’t require you to think about the stack and the
+> heap very often. But in a systems programming language like Rust, whether a
+> value is on the stack or the heap affects how the language behaves and why
+> you have to make certain decisions. Parts of ownership will be described in
+> relation to the stack and the heap later in this chapter, so here is a brief
+> explanation in preparation.
+>
+> Both the stack and the heap are parts of memory available to your code to use
+> at runtime, but they are structured in different ways. The stack stores
+> values in the order it gets them and removes the values in the opposite
+> order. This is referred to as _last in, first out (LIFO)_. Think of a stack of
+> plates: When you add more plates, you put them on top of the pile, and when
+> you need a plate, you take one off the top. Adding or removing plates from
+> the middle or bottom wouldn’t work as well! Adding data is called _pushing
+> onto the stack_, and removing data is called _popping off the stack_. All
+> data stored on the stack must have a known, fixed size. Data with an unknown
+> size at compile time or a size that might change must be stored on the heap
+> instead.
+>
+> The heap is less organized: When you put data on the heap, you request a
+> certain amount of space. The memory allocator finds an empty spot in the heap
+> that is big enough, marks it as being in use, and returns a _pointer_, which
+> is the address of that location. This process is called _allocating on the
+> heap_ and is sometimes abbreviated as just _allocating_ (pushing values onto
+> the stack is not considered allocating). Because the pointer to the heap is a
+> known, fixed size, you can store the pointer on the stack, but when you want
+> the actual data, you must follow the pointer. Think of being seated at a
+> restaurant. When you enter, you state the number of people in your group, and
+> the host finds an empty table that fits everyone and leads you there. If
+> someone in your group comes late, they can ask where you’ve been seated to
+> find you.
+>
+> Pushing to the stack is faster than allocating on the heap because the
+> allocator never has to search for a place to store new data; that location is
+> always at the top of the stack. Comparatively, allocating space on the heap
+> requires more work because the allocator must first find a big enough space
+> to hold the data and then perform bookkeeping to prepare for the next
+> allocation.
+>
+> Accessing data in the heap is generally slower than accessing data on the
+> stack because you have to follow a pointer to get there. Contemporary
+> processors are faster if they jump around less in memory. Continuing the
+> analogy, consider a server at a restaurant taking orders from many tables.
+> It’s most efficient to get all the orders at one table before moving on to
+> the next table. Taking an order from table A, then an order from table B,
+> then one from A again, and then one from B again would be a much slower
+> process. By the same token, a processor can usually do its job better if it
+> works on data that’s close to other data (as it is on the stack) rather than
+> farther away (as it can be on the heap).
+>
+> When your code calls a function, the values passed into the function
+> (including, potentially, pointers to data on the heap) and the function’s
+> local variables get pushed onto the stack. When the function is over, those
+> values get popped off the stack.
+>
+> Keeping track of what parts of code are using what data on the heap,
+> minimizing the amount of duplicate data on the heap, and cleaning up unused
+> data on the heap so that you don’t run out of space are all problems that
+> ownership addresses. Once you understand ownership, you won’t need to think
+> about the stack and the heap very often. But knowing that the main purpose of
+> ownership is to manage heap data can help explain why it works the way it
+> does.
+
+### Ownership Rules
+
+First, let’s take a look at the ownership rules. Keep these rules in mind as we
+work through the examples that illustrate them:
+
+- Each value in Rust has an _owner_.
+- There can only be one owner at a time.
+- When the owner goes out of scope, the value will be dropped.
+
+### Variable Scope
+
+Now that we’re past basic Rust syntax, we won’t include all the `fn main() {`
+code in the examples, so if you’re following along, make sure to put the
+following examples inside a `main` function manually. As a result, our examples
+will be a bit more concise, letting us focus on the actual details rather than
+boilerplate code.
+
+As a first example of ownership, we’ll look at the scope of some variables. A
+_scope_ is the range within a program for which an item is valid. Take the
+following variable:
+
+```rust
+let s = "hello";
+```
+
+The variable `s` refers to a string literal, where the value of the string is
+hardcoded into the text of our program. The variable is valid from the point at
+which it’s declared until the end of the current scope. Listing 4-1 shows a
+program with comments annotating where the variable `s` would be valid.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-01/src/main.rs:here}}
+```
+
+
+
+In other words, there are two important points in time here:
+
+- When `s` comes _into_ scope, it is valid.
+- It remains valid until it goes _out of_ scope.
+
+At this point, the relationship between scopes and when variables are valid is
+similar to that in other programming languages. Now we’ll build on top of this
+understanding by introducing the `String` type.
+
+### The `String` Type
+
+To illustrate the rules of ownership, we need a data type that is more complex
+than those we covered in the [“Data Types”][data-types] section
+of Chapter 3. The types covered previously are of a known size, can be stored
+on the stack and popped off the stack when their scope is over, and can be
+quickly and trivially copied to make a new, independent instance if another
+part of code needs to use the same value in a different scope. But we want to
+look at data that is stored on the heap and explore how Rust knows when to
+clean up that data, and the `String` type is a great example.
+
+We’ll concentrate on the parts of `String` that relate to ownership. These
+aspects also apply to other complex data types, whether they are provided by
+the standard library or created by you. We’ll discuss non-ownership aspects of
+`String` in [Chapter 8][ch8].
+
+We’ve already seen string literals, where a string value is hardcoded into our
+program. String literals are convenient, but they aren’t suitable for every
+situation in which we may want to use text. One reason is that they’re
+immutable. Another is that not every string value can be known when we write
+our code: For example, what if we want to take user input and store it? It is
+for these situations that Rust has the `String` type. This type manages
+data allocated on the heap and as such is able to store an amount of text that
+is unknown to us at compile time. You can create a `String` from a string
+literal using the `from` function, like so:
+
+```rust
+let s = String::from("hello");
+```
+
+The double colon `::` operator allows us to namespace this particular `from`
+function under the `String` type rather than using some sort of name like
+`string_from`. We’ll discuss this syntax more in the [“Methods”][methods] section of Chapter 5, and when we talk about namespacing with
+modules in [“Paths for Referring to an Item in the Module
+Tree”][paths-module-tree] in Chapter 7.
+
+This kind of string _can_ be mutated:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-01-can-mutate-string/src/main.rs:here}}
+```
+
+So, what’s the difference here? Why can `String` be mutated but literals
+cannot? The difference is in how these two types deal with memory.
+
+### Memory and Allocation
+
+In the case of a string literal, we know the contents at compile time, so the
+text is hardcoded directly into the final executable. This is why string
+literals are fast and efficient. But these properties only come from the string
+literal’s immutability. Unfortunately, we can’t put a blob of memory into the
+binary for each piece of text whose size is unknown at compile time and whose
+size might change while running the program.
+
+With the `String` type, in order to support a mutable, growable piece of text,
+we need to allocate an amount of memory on the heap, unknown at compile time,
+to hold the contents. This means:
+
+- The memory must be requested from the memory allocator at runtime.
+- We need a way of returning this memory to the allocator when we’re done with
+ our `String`.
+
+That first part is done by us: When we call `String::from`, its implementation
+requests the memory it needs. This is pretty much universal in programming
+languages.
+
+However, the second part is different. In languages with a _garbage collector
+(GC)_, the GC keeps track of and cleans up memory that isn’t being used
+anymore, and we don’t need to think about it. In most languages without a GC,
+it’s our responsibility to identify when memory is no longer being used and to
+call code to explicitly free it, just as we did to request it. Doing this
+correctly has historically been a difficult programming problem. If we forget,
+we’ll waste memory. If we do it too early, we’ll have an invalid variable. If
+we do it twice, that’s a bug too. We need to pair exactly one `allocate` with
+exactly one `free`.
+
+Rust takes a different path: The memory is automatically returned once the
+variable that owns it goes out of scope. Here’s a version of our scope example
+from Listing 4-1 using a `String` instead of a string literal:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-02-string-scope/src/main.rs:here}}
+```
+
+There is a natural point at which we can return the memory our `String` needs
+to the allocator: when `s` goes out of scope. When a variable goes out of
+scope, Rust calls a special function for us. This function is called
+`drop`, and it’s where the author of `String` can put
+the code to return the memory. Rust calls `drop` automatically at the closing
+curly bracket.
+
+> Note: In C++, this pattern of deallocating resources at the end of an item’s
+> lifetime is sometimes called _Resource Acquisition Is Initialization (RAII)_.
+> The `drop` function in Rust will be familiar to you if you’ve used RAII
+> patterns.
+
+This pattern has a profound impact on the way Rust code is written. It may seem
+simple right now, but the behavior of code can be unexpected in more
+complicated situations when we want to have multiple variables use the data
+we’ve allocated on the heap. Let’s explore some of those situations now.
+
+
+
+
+
+#### Variables and Data Interacting with Move
+
+Multiple variables can interact with the same data in different ways in Rust.
+Listing 4-2 shows an example using an integer.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-02/src/main.rs:here}}
+```
+
+
+
+We can probably guess what this is doing: “Bind the value `5` to `x`; then, make
+a copy of the value in `x` and bind it to `y`.” We now have two variables, `x`
+and `y`, and both equal `5`. This is indeed what is happening, because integers
+are simple values with a known, fixed size, and these two `5` values are pushed
+onto the stack.
+
+Now let’s look at the `String` version:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-03-string-move/src/main.rs:here}}
+```
+
+This looks very similar, so we might assume that the way it works would be the
+same: That is, the second line would make a copy of the value in `s1` and bind
+it to `s2`. But this isn’t quite what happens.
+
+Take a look at Figure 4-1 to see what is happening to `String` under the
+covers. A `String` is made up of three parts, shown on the left: a pointer to
+the memory that holds the contents of the string, a length, and a capacity.
+This group of data is stored on the stack. On the right is the memory on the
+heap that holds the contents.
+
+
+
+Figure 4-1: The representation in memory of a `String`
+holding the value `"hello"` bound to `s1`
+
+The length is how much memory, in bytes, the contents of the `String` are
+currently using. The capacity is the total amount of memory, in bytes, that the
+`String` has received from the allocator. The difference between length and
+capacity matters, but not in this context, so for now, it’s fine to ignore the
+capacity.
+
+When we assign `s1` to `s2`, the `String` data is copied, meaning we copy the
+pointer, the length, and the capacity that are on the stack. We do not copy the
+data on the heap that the pointer refers to. In other words, the data
+representation in memory looks like Figure 4-2.
+
+![Three tables: tables s1 and s2 representing those strings on the
+stack, respectively, and both pointing to the same string data on the heap.]()
+
+Figure 4-2: The representation in memory of the variable
+`s2` that has a copy of the pointer, length, and capacity of `s1`
+
+The representation does _not_ look like Figure 4-3, which is what memory would
+look like if Rust instead copied the heap data as well. If Rust did this, the
+operation `s2 = s1` could be very expensive in terms of runtime performance if
+the data on the heap were large.
+
+![Four tables: two tables representing the stack data for s1 and s2,
+and each points to its own copy of string data on the heap.]()
+
+Figure 4-3: Another possibility for what `s2 = s1` might
+do if Rust copied the heap data as well
+
+Earlier, we said that when a variable goes out of scope, Rust automatically
+calls the `drop` function and cleans up the heap memory for that variable. But
+Figure 4-2 shows both data pointers pointing to the same location. This is a
+problem: When `s2` and `s1` go out of scope, they will both try to free the
+same memory. This is known as a _double free_ error and is one of the memory
+safety bugs we mentioned previously. Freeing memory twice can lead to memory
+corruption, which can potentially lead to security vulnerabilities.
+
+To ensure memory safety, after the line `let s2 = s1;`, Rust considers `s1` as
+no longer valid. Therefore, Rust doesn’t need to free anything when `s1` goes
+out of scope. Check out what happens when you try to use `s1` after `s2` is
+created; it won’t work:
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/src/main.rs:here}}
+```
+
+You’ll get an error like this because Rust prevents you from using the
+invalidated reference:
+
+```console
+{{#include ../listings/ch04-understanding-ownership/no-listing-04-cant-use-after-move/output.txt}}
+```
+
+If you’ve heard the terms _shallow copy_ and _deep copy_ while working with
+other languages, the concept of copying the pointer, length, and capacity
+without copying the data probably sounds like making a shallow copy. But
+because Rust also invalidates the first variable, instead of being called a
+shallow copy, it’s known as a _move_. In this example, we would say that `s1`
+was _moved_ into `s2`. So, what actually happens is shown in Figure 4-4.
+
+
+
+Figure 4-4: The representation in memory after `s1` has
+been invalidated
+
+That solves our problem! With only `s2` valid, when it goes out of scope it
+alone will free the memory, and we’re done.
+
+In addition, there’s a design choice that’s implied by this: Rust will never
+automatically create “deep” copies of your data. Therefore, any _automatic_
+copying can be assumed to be inexpensive in terms of runtime performance.
+
+#### Scope and Assignment
+
+The inverse of this is true for the relationship between scoping, ownership, and
+memory being freed via the `drop` function as well. When you assign a completely
+new value to an existing variable, Rust will call `drop` and free the original
+value’s memory immediately. Consider this code, for example:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-04b-replacement-drop/src/main.rs:here}}
+```
+
+We initially declare a variable `s` and bind it to a `String` with the value
+`"hello"`. Then, we immediately create a new `String` with the value `"ahoy"`
+and assign it to `s`. At this point, nothing is referring to the original value
+on the heap at all. Figure 4-5 illustrates the stack and heap data now:
+
+![One table representing the string value on the stack, pointing to
+the second piece of string data (ahoy) on the heap, with the original string
+data (hello) grayed out because it cannot be accessed anymore.]()
+
+Figure 4-5: The representation in memory after the initial
+value has been replaced in its entirety
+
+The original string thus immediately goes out of scope. Rust will run the `drop`
+function on it and its memory will be freed right away. When we print the value
+at the end, it will be `"ahoy, world!"`.
+
+
+
+
+
+#### Variables and Data Interacting with Clone
+
+If we _do_ want to deeply copy the heap data of the `String`, not just the
+stack data, we can use a common method called `clone`. We’ll discuss method
+syntax in Chapter 5, but because methods are a common feature in many
+programming languages, you’ve probably seen them before.
+
+Here’s an example of the `clone` method in action:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-05-clone/src/main.rs:here}}
+```
+
+This works just fine and explicitly produces the behavior shown in Figure 4-3,
+where the heap data _does_ get copied.
+
+When you see a call to `clone`, you know that some arbitrary code is being
+executed and that code may be expensive. It’s a visual indicator that something
+different is going on.
+
+#### Stack-Only Data: Copy
+
+There’s another wrinkle we haven’t talked about yet. This code using
+integers—part of which was shown in Listing 4-2—works and is valid:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-06-copy/src/main.rs:here}}
+```
+
+But this code seems to contradict what we just learned: We don’t have a call to
+`clone`, but `x` is still valid and wasn’t moved into `y`.
+
+The reason is that types such as integers that have a known size at compile
+time are stored entirely on the stack, so copies of the actual values are quick
+to make. That means there’s no reason we would want to prevent `x` from being
+valid after we create the variable `y`. In other words, there’s no difference
+between deep and shallow copying here, so calling `clone` wouldn’t do anything
+different from the usual shallow copying, and we can leave it out.
+
+Rust has a special annotation called the `Copy` trait that we can place on
+types that are stored on the stack, as integers are (we’ll talk more about
+traits in [Chapter 10][traits]). If a type implements the `Copy`
+trait, variables that use it do not move, but rather are trivially copied,
+making them still valid after assignment to another variable.
+
+Rust won’t let us annotate a type with `Copy` if the type, or any of its parts,
+has implemented the `Drop` trait. If the type needs something special to happen
+when the value goes out of scope and we add the `Copy` annotation to that type,
+we’ll get a compile-time error. To learn about how to add the `Copy` annotation
+to your type to implement the trait, see [“Derivable
+Traits”][derivable-traits] in Appendix C.
+
+So, what types implement the `Copy` trait? You can check the documentation for
+the given type to be sure, but as a general rule, any group of simple scalar
+values can implement `Copy`, and nothing that requires allocation or is some
+form of resource can implement `Copy`. Here are some of the types that
+implement `Copy`:
+
+- All the integer types, such as `u32`.
+- The Boolean type, `bool`, with values `true` and `false`.
+- All the floating-point types, such as `f64`.
+- The character type, `char`.
+- Tuples, if they only contain types that also implement `Copy`. For example,
+ `(i32, i32)` implements `Copy`, but `(i32, String)` does not.
+
+### Ownership and Functions
+
+The mechanics of passing a value to a function are similar to those when
+assigning a value to a variable. Passing a variable to a function will move or
+copy, just as assignment does. Listing 4-3 has an example with some annotations
+showing where variables go into and out of scope.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-03/src/main.rs}}
+```
+
+
+
+If we tried to use `s` after the call to `takes_ownership`, Rust would throw a
+compile-time error. These static checks protect us from mistakes. Try adding
+code to `main` that uses `s` and `x` to see where you can use them and where
+the ownership rules prevent you from doing so.
+
+### Return Values and Scope
+
+Returning values can also transfer ownership. Listing 4-4 shows an example of a
+function that returns some value, with similar annotations as those in Listing
+4-3.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-04/src/main.rs}}
+```
+
+
+
+The ownership of a variable follows the same pattern every time: Assigning a
+value to another variable moves it. When a variable that includes data on the
+heap goes out of scope, the value will be cleaned up by `drop` unless ownership
+of the data has been moved to another variable.
+
+While this works, taking ownership and then returning ownership with every
+function is a bit tedious. What if we want to let a function use a value but
+not take ownership? It’s quite annoying that anything we pass in also needs to
+be passed back if we want to use it again, in addition to any data resulting
+from the body of the function that we might want to return as well.
+
+Rust does let us return multiple values using a tuple, as shown in Listing 4-5.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-05/src/main.rs}}
+```
+
+
+
+But this is too much ceremony and a lot of work for a concept that should be
+common. Luckily for us, Rust has a feature for using a value without
+transferring ownership: references.
+
+[data-types]: ch03-02-data-types.html#data-types
+[ch8]: ch08-02-strings.html
+[traits]: ch10-02-traits.html
+[derivable-traits]: appendix-03-derivable-traits.html
+[methods]: ch05-03-method-syntax.html#methods
+[paths-module-tree]: ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html
diff --git a/documents/markdown/rust-book/ch04-02-references-and-borrowing.md b/documents/markdown/rust-book/ch04-02-references-and-borrowing.md
new file mode 100644
index 0000000..8c37601
--- /dev/null
+++ b/documents/markdown/rust-book/ch04-02-references-and-borrowing.md
@@ -0,0 +1,263 @@
+## References and Borrowing
+
+The issue with the tuple code in Listing 4-5 is that we have to return the
+`String` to the calling function so that we can still use the `String` after
+the call to `calculate_length`, because the `String` was moved into
+`calculate_length`. Instead, we can provide a reference to the `String` value.
+A reference is like a pointer in that it’s an address we can follow to access
+the data stored at that address; that data is owned by some other variable.
+Unlike a pointer, a reference is guaranteed to point to a valid value of a
+particular type for the life of that reference.
+
+Here is how you would define and use a `calculate_length` function that has a
+reference to an object as a parameter instead of taking ownership of the value:
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-07-reference/src/main.rs:all}}
+```
+
+
+
+First, notice that all the tuple code in the variable declaration and the
+function return value is gone. Second, note that we pass `&s1` into
+`calculate_length` and, in its definition, we take `&String` rather than
+`String`. These ampersands represent references, and they allow you to refer to
+some value without taking ownership of it. Figure 4-6 depicts this concept.
+
+
+
+Figure 4-6: A diagram of `&String` `s` pointing at
+`String` `s1`
+
+> Note: The opposite of referencing by using `&` is _dereferencing_, which is
+> accomplished with the dereference operator, `*`. We’ll see some uses of the
+> dereference operator in Chapter 8 and discuss details of dereferencing in
+> Chapter 15.
+
+Let’s take a closer look at the function call here:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-07-reference/src/main.rs:here}}
+```
+
+The `&s1` syntax lets us create a reference that _refers_ to the value of `s1`
+but does not own it. Because the reference does not own it, the value it points
+to will not be dropped when the reference stops being used.
+
+Likewise, the signature of the function uses `&` to indicate that the type of
+the parameter `s` is a reference. Let’s add some explanatory annotations:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-08-reference-with-annotations/src/main.rs:here}}
+```
+
+The scope in which the variable `s` is valid is the same as any function
+parameter’s scope, but the value pointed to by the reference is not dropped
+when `s` stops being used, because `s` doesn’t have ownership. When functions
+have references as parameters instead of the actual values, we won’t need to
+return the values in order to give back ownership, because we never had
+ownership.
+
+We call the action of creating a reference _borrowing_. As in real life, if a
+person owns something, you can borrow it from them. When you’re done, you have
+to give it back. You don’t own it.
+
+So, what happens if we try to modify something we’re borrowing? Try the code in
+Listing 4-6. Spoiler alert: It doesn’t work!
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-06/src/main.rs}}
+```
+
+
+
+Here’s the error:
+
+```console
+{{#include ../listings/ch04-understanding-ownership/listing-04-06/output.txt}}
+```
+
+Just as variables are immutable by default, so are references. We’re not
+allowed to modify something we have a reference to.
+
+### Mutable References
+
+We can fix the code from Listing 4-6 to allow us to modify a borrowed value
+with just a few small tweaks that use, instead, a _mutable reference_:
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-09-fixes-listing-04-06/src/main.rs}}
+```
+
+
+
+First, we change `s` to be `mut`. Then, we create a mutable reference with
+`&mut s` where we call the `change` function and update the function signature
+to accept a mutable reference with `some_string: &mut String`. This makes it
+very clear that the `change` function will mutate the value it borrows.
+
+Mutable references have one big restriction: If you have a mutable reference to
+a value, you can have no other references to that value. This code that
+attempts to create two mutable references to `s` will fail:
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/src/main.rs:here}}
+```
+
+
+
+Here’s the error:
+
+```console
+{{#include ../listings/ch04-understanding-ownership/no-listing-10-multiple-mut-not-allowed/output.txt}}
+```
+
+This error says that this code is invalid because we cannot borrow `s` as
+mutable more than once at a time. The first mutable borrow is in `r1` and must
+last until it’s used in the `println!`, but between the creation of that
+mutable reference and its usage, we tried to create another mutable reference
+in `r2` that borrows the same data as `r1`.
+
+The restriction preventing multiple mutable references to the same data at the
+same time allows for mutation but in a very controlled fashion. It’s something
+that new Rustaceans struggle with because most languages let you mutate
+whenever you’d like. The benefit of having this restriction is that Rust can
+prevent data races at compile time. A _data race_ is similar to a race
+condition and happens when these three behaviors occur:
+
+- Two or more pointers access the same data at the same time.
+- At least one of the pointers is being used to write to the data.
+- There’s no mechanism being used to synchronize access to the data.
+
+Data races cause undefined behavior and can be difficult to diagnose and fix
+when you’re trying to track them down at runtime; Rust prevents this problem by
+refusing to compile code with data races!
+
+As always, we can use curly brackets to create a new scope, allowing for
+multiple mutable references, just not _simultaneous_ ones:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-11-muts-in-separate-scopes/src/main.rs:here}}
+```
+
+Rust enforces a similar rule for combining mutable and immutable references.
+This code results in an error:
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/src/main.rs:here}}
+```
+
+Here’s the error:
+
+```console
+{{#include ../listings/ch04-understanding-ownership/no-listing-12-immutable-and-mutable-not-allowed/output.txt}}
+```
+
+Whew! We _also_ cannot have a mutable reference while we have an immutable one
+to the same value.
+
+Users of an immutable reference don’t expect the value to suddenly change out
+from under them! However, multiple immutable references are allowed because no
+one who is just reading the data has the ability to affect anyone else’s
+reading of the data.
+
+Note that a reference’s scope starts from where it is introduced and continues
+through the last time that reference is used. For instance, this code will
+compile because the last usage of the immutable references is in the `println!`,
+before the mutable reference is introduced:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-13-reference-scope-ends/src/main.rs:here}}
+```
+
+The scopes of the immutable references `r1` and `r2` end after the `println!`
+where they are last used, which is before the mutable reference `r3` is
+created. These scopes don’t overlap, so this code is allowed: The compiler can
+tell that the reference is no longer being used at a point before the end of
+the scope.
+
+Even though borrowing errors may be frustrating at times, remember that it’s
+the Rust compiler pointing out a potential bug early (at compile time rather
+than at runtime) and showing you exactly where the problem is. Then, you don’t
+have to track down why your data isn’t what you thought it was.
+
+### Dangling References
+
+In languages with pointers, it’s easy to erroneously create a _dangling
+pointer_—a pointer that references a location in memory that may have been
+given to someone else—by freeing some memory while preserving a pointer to that
+memory. In Rust, by contrast, the compiler guarantees that references will
+never be dangling references: If you have a reference to some data, the
+compiler will ensure that the data will not go out of scope before the
+reference to the data does.
+
+Let’s try to create a dangling reference to see how Rust prevents them with a
+compile-time error:
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-14-dangling-reference/src/main.rs}}
+```
+
+
+
+Here’s the error:
+
+```console
+{{#include ../listings/ch04-understanding-ownership/no-listing-14-dangling-reference/output.txt}}
+```
+
+This error message refers to a feature we haven’t covered yet: lifetimes. We’ll
+discuss lifetimes in detail in Chapter 10. But, if you disregard the parts
+about lifetimes, the message does contain the key to why this code is a problem:
+
+```text
+this function's return type contains a borrowed value, but there is no value
+for it to be borrowed from
+```
+
+Let’s take a closer look at exactly what’s happening at each stage of our
+`dangle` code:
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-15-dangling-reference-annotated/src/main.rs:here}}
+```
+
+
+
+Because `s` is created inside `dangle`, when the code of `dangle` is finished,
+`s` will be deallocated. But we tried to return a reference to it. That means
+this reference would be pointing to an invalid `String`. That’s no good! Rust
+won’t let us do this.
+
+The solution here is to return the `String` directly:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-16-no-dangle/src/main.rs:here}}
+```
+
+This works without any problems. Ownership is moved out, and nothing is
+deallocated.
+
+### The Rules of References
+
+Let’s recap what we’ve discussed about references:
+
+- At any given time, you can have _either_ one mutable reference _or_ any
+ number of immutable references.
+- References must always be valid.
+
+Next, we’ll look at a different kind of reference: slices.
diff --git a/documents/markdown/rust-book/ch04-03-slices.md b/documents/markdown/rust-book/ch04-03-slices.md
new file mode 100644
index 0000000..7f145ba
--- /dev/null
+++ b/documents/markdown/rust-book/ch04-03-slices.md
@@ -0,0 +1,334 @@
+## The Slice Type
+
+_Slices_ let you reference a contiguous sequence of elements in a
+[collection](ch08-00-common-collections.md). A slice is a kind
+of reference, so it does not have ownership.
+
+Here’s a small programming problem: Write a function that takes a string of
+words separated by spaces and returns the first word it finds in that string.
+If the function doesn’t find a space in the string, the whole string must be
+one word, so the entire string should be returned.
+
+> Note: For the purposes of introducing slices, we are assuming ASCII only in
+> this section; a more thorough discussion of UTF-8 handling is in the
+> [“Storing UTF-8 Encoded Text with Strings”][strings] section
+> of Chapter 8.
+
+Let’s work through how we’d write the signature of this function without using
+slices, to understand the problem that slices will solve:
+
+```rust,ignore
+fn first_word(s: &String) -> ?
+```
+
+The `first_word` function has a parameter of type `&String`. We don’t need
+ownership, so this is fine. (In idiomatic Rust, functions do not take ownership
+of their arguments unless they need to, and the reasons for that will become
+clear as we keep going.) But what should we return? We don’t really have a way
+to talk about *part* of a string. However, we could return the index of the end
+of the word, indicated by a space. Let’s try that, as shown in Listing 4-7.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-07/src/main.rs:here}}
+```
+
+
+
+Because we need to go through the `String` element by element and check whether
+a value is a space, we’ll convert our `String` to an array of bytes using the
+`as_bytes` method.
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-07/src/main.rs:as_bytes}}
+```
+
+Next, we create an iterator over the array of bytes using the `iter` method:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-07/src/main.rs:iter}}
+```
+
+We’ll discuss iterators in more detail in [Chapter 13][ch13].
+For now, know that `iter` is a method that returns each element in a collection
+and that `enumerate` wraps the result of `iter` and returns each element as
+part of a tuple instead. The first element of the tuple returned from
+`enumerate` is the index, and the second element is a reference to the element.
+This is a bit more convenient than calculating the index ourselves.
+
+Because the `enumerate` method returns a tuple, we can use patterns to
+destructure that tuple. We’ll be discussing patterns more in [Chapter
+6][ch6]. In the `for` loop, we specify a pattern that has `i`
+for the index in the tuple and `&item` for the single byte in the tuple.
+Because we get a reference to the element from `.iter().enumerate()`, we use
+`&` in the pattern.
+
+Inside the `for` loop, we search for the byte that represents the space by
+using the byte literal syntax. If we find a space, we return the position.
+Otherwise, we return the length of the string by using `s.len()`.
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-07/src/main.rs:inside_for}}
+```
+
+We now have a way to find out the index of the end of the first word in the
+string, but there’s a problem. We’re returning a `usize` on its own, but it’s
+only a meaningful number in the context of the `&String`. In other words,
+because it’s a separate value from the `String`, there’s no guarantee that it
+will still be valid in the future. Consider the program in Listing 4-8 that
+uses the `first_word` function from Listing 4-7.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-08/src/main.rs:here}}
+```
+
+
+
+This program compiles without any errors and would also do so if we used `word`
+after calling `s.clear()`. Because `word` isn’t connected to the state of `s`
+at all, `word` still contains the value `5`. We could use that value `5` with
+the variable `s` to try to extract the first word out, but this would be a bug
+because the contents of `s` have changed since we saved `5` in `word`.
+
+Having to worry about the index in `word` getting out of sync with the data in
+`s` is tedious and error-prone! Managing these indices is even more brittle if
+we write a `second_word` function. Its signature would have to look like this:
+
+```rust,ignore
+fn second_word(s: &String) -> (usize, usize) {
+```
+
+Now we’re tracking a starting _and_ an ending index, and we have even more
+values that were calculated from data in a particular state but aren’t tied to
+that state at all. We have three unrelated variables floating around that need
+to be kept in sync.
+
+Luckily, Rust has a solution to this problem: string slices.
+
+### String Slices
+
+A _string slice_ is a reference to a contiguous sequence of the elements of a
+`String`, and it looks like this:
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-17-slice/src/main.rs:here}}
+```
+
+Rather than a reference to the entire `String`, `hello` is a reference to a
+portion of the `String`, specified in the extra `[0..5]` bit. We create slices
+using a range within square brackets by specifying
+`[starting_index..ending_index]`, where _`starting_index`_ is the first
+position in the slice and _`ending_index`_ is one more than the last position
+in the slice. Internally, the slice data structure stores the starting position
+and the length of the slice, which corresponds to _`ending_index`_ minus
+_`starting_index`_. So, in the case of `let world = &s[6..11];`, `world` would
+be a slice that contains a pointer to the byte at index 6 of `s` with a length
+value of `5`.
+
+Figure 4-7 shows this in a diagram.
+
+![Three tables: a table representing the stack data of s, which points
+to the byte at index 0 in a table of the string data "hello world" on
+the heap. The third table represents the stack data of the slice world, which
+has a length value of 5 and points to byte 6 of the heap data table.]()
+
+Figure 4-7: A string slice referring to part of a
+`String`
+
+With Rust’s `..` range syntax, if you want to start at index 0, you can drop
+the value before the two periods. In other words, these are equal:
+
+```rust
+let s = String::from("hello");
+
+let slice = &s[0..2];
+let slice = &s[..2];
+```
+
+By the same token, if your slice includes the last byte of the `String`, you
+can drop the trailing number. That means these are equal:
+
+```rust
+let s = String::from("hello");
+
+let len = s.len();
+
+let slice = &s[3..len];
+let slice = &s[3..];
+```
+
+You can also drop both values to take a slice of the entire string. So, these
+are equal:
+
+```rust
+let s = String::from("hello");
+
+let len = s.len();
+
+let slice = &s[0..len];
+let slice = &s[..];
+```
+
+> Note: String slice range indices must occur at valid UTF-8 character
+> boundaries. If you attempt to create a string slice in the middle of a
+> multibyte character, your program will exit with an error.
+
+With all this information in mind, let’s rewrite `first_word` to return a
+slice. The type that signifies “string slice” is written as `&str`:
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-18-first-word-slice/src/main.rs:here}}
+```
+
+
+
+We get the index for the end of the word the same way we did in Listing 4-7, by
+looking for the first occurrence of a space. When we find a space, we return a
+string slice using the start of the string and the index of the space as the
+starting and ending indices.
+
+Now when we call `first_word`, we get back a single value that is tied to the
+underlying data. The value is made up of a reference to the starting point of
+the slice and the number of elements in the slice.
+
+Returning a slice would also work for a `second_word` function:
+
+```rust,ignore
+fn second_word(s: &String) -> &str {
+```
+
+We now have a straightforward API that’s much harder to mess up because the
+compiler will ensure that the references into the `String` remain valid.
+Remember the bug in the program in Listing 4-8, when we got the index to the
+end of the first word but then cleared the string so our index was invalid?
+That code was logically incorrect but didn’t show any immediate errors. The
+problems would show up later if we kept trying to use the first word index with
+an emptied string. Slices make this bug impossible and let us know much sooner
+that we have a problem with our code. Using the slice version of `first_word`
+will throw a compile-time error:
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch04-understanding-ownership/no-listing-19-slice-error/src/main.rs:here}}
+```
+
+
+
+Here’s the compiler error:
+
+```console
+{{#include ../listings/ch04-understanding-ownership/no-listing-19-slice-error/output.txt}}
+```
+
+Recall from the borrowing rules that if we have an immutable reference to
+something, we cannot also take a mutable reference. Because `clear` needs to
+truncate the `String`, it needs to get a mutable reference. The `println!`
+after the call to `clear` uses the reference in `word`, so the immutable
+reference must still be active at that point. Rust disallows the mutable
+reference in `clear` and the immutable reference in `word` from existing at the
+same time, and compilation fails. Not only has Rust made our API easier to use,
+but it has also eliminated an entire class of errors at compile time!
+
+
+
+
+
+#### String Literals as Slices
+
+Recall that we talked about string literals being stored inside the binary. Now
+that we know about slices, we can properly understand string literals:
+
+```rust
+let s = "Hello, world!";
+```
+
+The type of `s` here is `&str`: It’s a slice pointing to that specific point of
+the binary. This is also why string literals are immutable; `&str` is an
+immutable reference.
+
+#### String Slices as Parameters
+
+Knowing that you can take slices of literals and `String` values leads us to
+one more improvement on `first_word`, and that’s its signature:
+
+```rust,ignore
+fn first_word(s: &String) -> &str {
+```
+
+A more experienced Rustacean would write the signature shown in Listing 4-9
+instead because it allows us to use the same function on both `&String` values
+and `&str` values.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-09/src/main.rs:here}}
+```
+
+
+
+If we have a string slice, we can pass that directly. If we have a `String`, we
+can pass a slice of the `String` or a reference to the `String`. This
+flexibility takes advantage of deref coercions, a feature we will cover in
+the [“Using Deref Coercions in Functions and Methods”][deref-coercions] section of Chapter 15.
+
+Defining a function to take a string slice instead of a reference to a `String`
+makes our API more general and useful without losing any functionality:
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch04-understanding-ownership/listing-04-09/src/main.rs:usage}}
+```
+
+
+
+### Other Slices
+
+String slices, as you might imagine, are specific to strings. But there’s a
+more general slice type too. Consider this array:
+
+```rust
+let a = [1, 2, 3, 4, 5];
+```
+
+Just as we might want to refer to part of a string, we might want to refer to
+part of an array. We’d do so like this:
+
+```rust
+let a = [1, 2, 3, 4, 5];
+
+let slice = &a[1..3];
+
+assert_eq!(slice, &[2, 3]);
+```
+
+This slice has the type `&[i32]`. It works the same way as string slices do, by
+storing a reference to the first element and a length. You’ll use this kind of
+slice for all sorts of other collections. We’ll discuss these collections in
+detail when we talk about vectors in Chapter 8.
+
+## Summary
+
+The concepts of ownership, borrowing, and slices ensure memory safety in Rust
+programs at compile time. The Rust language gives you control over your memory
+usage in the same way as other systems programming languages. But having the
+owner of data automatically clean up that data when the owner goes out of scope
+means you don’t have to write and debug extra code to get this control.
+
+Ownership affects how lots of other parts of Rust work, so we’ll talk about
+these concepts further throughout the rest of the book. Let’s move on to
+Chapter 5 and look at grouping pieces of data together in a `struct`.
+
+[ch13]: ch13-02-iterators.html
+[ch6]: ch06-02-match.html#patterns-that-bind-to-values
+[strings]: ch08-02-strings.html#storing-utf-8-encoded-text-with-strings
+[deref-coercions]: ch15-02-deref.html#using-deref-coercions-in-functions-and-methods
diff --git a/documents/markdown/rust-book/ch05-00-structs.md b/documents/markdown/rust-book/ch05-00-structs.md
new file mode 100644
index 0000000..4c0f7d3
--- /dev/null
+++ b/documents/markdown/rust-book/ch05-00-structs.md
@@ -0,0 +1,14 @@
+# Using Structs to Structure Related Data
+
+A _struct_, or _structure_, is a custom data type that lets you package
+together and name multiple related values that make up a meaningful group. If
+you’re familiar with an object-oriented language, a struct is like an object’s
+data attributes. In this chapter, we’ll compare and contrast tuples with
+structs to build on what you already know and demonstrate when structs are a
+better way to group data.
+
+We’ll demonstrate how to define and instantiate structs. We’ll discuss how to
+define associated functions, especially the kind of associated functions called
+_methods_, to specify behavior associated with a struct type. Structs and enums
+(discussed in Chapter 6) are the building blocks for creating new types in your
+program’s domain to take full advantage of Rust’s compile-time type checking.
diff --git a/documents/markdown/rust-book/ch05-01-defining-structs.md b/documents/markdown/rust-book/ch05-01-defining-structs.md
new file mode 100644
index 0000000..66da938
--- /dev/null
+++ b/documents/markdown/rust-book/ch05-01-defining-structs.md
@@ -0,0 +1,313 @@
+## Defining and Instantiating Structs
+
+Structs are similar to tuples, discussed in [“The Tuple Type”][tuples] section, in that both hold multiple related values. Like tuples, the
+pieces of a struct can be different types. Unlike with tuples, in a struct
+you’ll name each piece of data so it’s clear what the values mean. Adding these
+names means that structs are more flexible than tuples: You don’t have to rely
+on the order of the data to specify or access the values of an instance.
+
+To define a struct, we enter the keyword `struct` and name the entire struct. A
+struct’s name should describe the significance of the pieces of data being
+grouped together. Then, inside curly brackets, we define the names and types of
+the pieces of data, which we call _fields_. For example, Listing 5-1 shows a
+struct that stores information about a user account.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-01/src/main.rs:here}}
+```
+
+
+
+To use a struct after we’ve defined it, we create an _instance_ of that struct
+by specifying concrete values for each of the fields. We create an instance by
+stating the name of the struct and then add curly brackets containing _`key:
+value`_ pairs, where the keys are the names of the fields and the values are the
+data we want to store in those fields. We don’t have to specify the fields in
+the same order in which we declared them in the struct. In other words, the
+struct definition is like a general template for the type, and instances fill
+in that template with particular data to create values of the type. For
+example, we can declare a particular user as shown in Listing 5-2.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-02/src/main.rs:here}}
+```
+
+
+
+To get a specific value from a struct, we use dot notation. For example, to
+access this user’s email address, we use `user1.email`. If the instance is
+mutable, we can change a value by using the dot notation and assigning into a
+particular field. Listing 5-3 shows how to change the value in the `email`
+field of a mutable `User` instance.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-03/src/main.rs:here}}
+```
+
+
+
+Note that the entire instance must be mutable; Rust doesn’t allow us to mark
+only certain fields as mutable. As with any expression, we can construct a new
+instance of the struct as the last expression in the function body to
+implicitly return that new instance.
+
+Listing 5-4 shows a `build_user` function that returns a `User` instance with
+the given email and username. The `active` field gets the value `true`, and the
+`sign_in_count` gets a value of `1`.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-04/src/main.rs:here}}
+```
+
+
+
+It makes sense to name the function parameters with the same name as the struct
+fields, but having to repeat the `email` and `username` field names and
+variables is a bit tedious. If the struct had more fields, repeating each name
+would get even more annoying. Luckily, there’s a convenient shorthand!
+
+
+
+
+
+### Using the Field Init Shorthand
+
+Because the parameter names and the struct field names are exactly the same in
+Listing 5-4, we can use the _field init shorthand_ syntax to rewrite
+`build_user` so that it behaves exactly the same but doesn’t have the
+repetition of `username` and `email`, as shown in Listing 5-5.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-05/src/main.rs:here}}
+```
+
+
+
+Here, we’re creating a new instance of the `User` struct, which has a field
+named `email`. We want to set the `email` field’s value to the value in the
+`email` parameter of the `build_user` function. Because the `email` field and
+the `email` parameter have the same name, we only need to write `email` rather
+than `email: email`.
+
+
+
+
+
+### Creating Instances with Struct Update Syntax
+
+It’s often useful to create a new instance of a struct that includes most of
+the values from another instance of the same type, but changes some of them.
+You can do this using struct update syntax.
+
+First, in Listing 5-6 we show how to create a new `User` instance in `user2` in
+the regular way, without the update syntax. We set a new value for `email` but
+otherwise use the same values from `user1` that we created in Listing 5-2.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-06/src/main.rs:here}}
+```
+
+
+
+Using struct update syntax, we can achieve the same effect with less code, as
+shown in Listing 5-7. The syntax `..` specifies that the remaining fields not
+explicitly set should have the same value as the fields in the given instance.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-07/src/main.rs:here}}
+```
+
+
+
+The code in Listing 5-7 also creates an instance in `user2` that has a
+different value for `email` but has the same values for the `username`,
+`active`, and `sign_in_count` fields from `user1`. The `..user1` must come last
+to specify that any remaining fields should get their values from the
+corresponding fields in `user1`, but we can choose to specify values for as
+many fields as we want in any order, regardless of the order of the fields in
+the struct’s definition.
+
+Note that the struct update syntax uses `=` like an assignment; this is because
+it moves the data, just as we saw in the [“Variables and Data Interacting with
+Move”][move] section. In this example, we can no longer use
+`user1` after creating `user2` because the `String` in the `username` field of
+`user1` was moved into `user2`. If we had given `user2` new `String` values for
+both `email` and `username`, and thus only used the `active` and `sign_in_count`
+values from `user1`, then `user1` would still be valid after creating `user2`.
+Both `active` and `sign_in_count` are types that implement the `Copy` trait, so
+the behavior we discussed in the [“Stack-Only Data: Copy”][copy]
+section would apply. We can also still use `user1.email` in this example,
+because its value was not moved out of `user1`.
+
+
+
+
+
+### Creating Different Types with Tuple Structs
+
+Rust also supports structs that look similar to tuples, called _tuple structs_.
+Tuple structs have the added meaning the struct name provides but don’t have
+names associated with their fields; rather, they just have the types of the
+fields. Tuple structs are useful when you want to give the whole tuple a name
+and make the tuple a different type from other tuples, and when naming each
+field as in a regular struct would be verbose or redundant.
+
+To define a tuple struct, start with the `struct` keyword and the struct name
+followed by the types in the tuple. For example, here we define and use two
+tuple structs named `Color` and `Point`:
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/no-listing-01-tuple-structs/src/main.rs}}
+```
+
+
+
+Note that the `black` and `origin` values are different types because they’re
+instances of different tuple structs. Each struct you define is its own type,
+even though the fields within the struct might have the same types. For
+example, a function that takes a parameter of type `Color` cannot take a
+`Point` as an argument, even though both types are made up of three `i32`
+values. Otherwise, tuple struct instances are similar to tuples in that you can
+destructure them into their individual pieces, and you can use a `.` followed
+by the index to access an individual value. Unlike tuples, tuple structs
+require you to name the type of the struct when you destructure them. For
+example, we would write `let Point(x, y, z) = origin;` to destructure the
+values in the `origin` point into variables named `x`, `y`, and `z`.
+
+
+
+
+
+### Defining Unit-Like Structs
+
+You can also define structs that don’t have any fields! These are called
+_unit-like structs_ because they behave similarly to `()`, the unit type that
+we mentioned in [“The Tuple Type”][tuples] section. Unit-like
+structs can be useful when you need to implement a trait on some type but don’t
+have any data that you want to store in the type itself. We’ll discuss traits
+in Chapter 10. Here’s an example of declaring and instantiating a unit struct
+named `AlwaysEqual`:
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/no-listing-04-unit-like-structs/src/main.rs}}
+```
+
+
+
+To define `AlwaysEqual`, we use the `struct` keyword, the name we want, and
+then a semicolon. No need for curly brackets or parentheses! Then, we can get
+an instance of `AlwaysEqual` in the `subject` variable in a similar way: using
+the name we defined, without any curly brackets or parentheses. Imagine that
+later we’ll implement behavior for this type such that every instance of
+`AlwaysEqual` is always equal to every instance of any other type, perhaps to
+have a known result for testing purposes. We wouldn’t need any data to
+implement that behavior! You’ll see in Chapter 10 how to define traits and
+implement them on any type, including unit-like structs.
+
+> ### Ownership of Struct Data
+>
+> In the `User` struct definition in Listing 5-1, we used the owned `String`
+> type rather than the `&str` string slice type. This is a deliberate choice
+> because we want each instance of this struct to own all of its data and for
+> that data to be valid for as long as the entire struct is valid.
+>
+> It’s also possible for structs to store references to data owned by something
+> else, but to do so requires the use of _lifetimes_, a Rust feature that we’ll
+> discuss in Chapter 10. Lifetimes ensure that the data referenced by a struct
+> is valid for as long as the struct is. Let’s say you try to store a reference
+> in a struct without specifying lifetimes, like the following in
+> *src/main.rs*; this won’t work:
+>
+>
+>
+>
+>
+> ```rust,ignore,does_not_compile
+> struct User {
+> active: bool,
+> username: &str,
+> email: &str,
+> sign_in_count: u64,
+> }
+>
+> fn main() {
+> let user1 = User {
+> active: true,
+> username: "someusername123",
+> email: "someone@example.com",
+> sign_in_count: 1,
+> };
+> }
+> ```
+>
+>
+>
+> The compiler will complain that it needs lifetime specifiers:
+>
+> ```console
+> $ cargo run
+> Compiling structs v0.1.0 (file:///projects/structs)
+> error[E0106]: missing lifetime specifier
+> --> src/main.rs:3:15
+> |
+> 3 | username: &str,
+> | ^ expected named lifetime parameter
+> |
+> help: consider introducing a named lifetime parameter
+> |
+> 1 ~ struct User<'a> {
+> 2 | active: bool,
+> 3 ~ username: &'a str,
+> |
+>
+> error[E0106]: missing lifetime specifier
+> --> src/main.rs:4:12
+> |
+> 4 | email: &str,
+> | ^ expected named lifetime parameter
+> |
+> help: consider introducing a named lifetime parameter
+> |
+> 1 ~ struct User<'a> {
+> 2 | active: bool,
+> 3 | username: &str,
+> 4 ~ email: &'a str,
+> |
+>
+> For more information about this error, try `rustc --explain E0106`.
+> error: could not compile `structs` (bin "structs") due to 2 previous errors
+> ```
+>
+> In Chapter 10, we’ll discuss how to fix these errors so that you can store
+> references in structs, but for now, we’ll fix errors like these using owned
+> types like `String` instead of references like `&str`.
+
+
+
+[tuples]: ch03-02-data-types.html#the-tuple-type
+[move]: ch04-01-what-is-ownership.html#variables-and-data-interacting-with-move
+[copy]: ch04-01-what-is-ownership.html#stack-only-data-copy
diff --git a/documents/markdown/rust-book/ch05-02-example-structs.md b/documents/markdown/rust-book/ch05-02-example-structs.md
new file mode 100644
index 0000000..fe59bb4
--- /dev/null
+++ b/documents/markdown/rust-book/ch05-02-example-structs.md
@@ -0,0 +1,252 @@
+## An Example Program Using Structs
+
+To understand when we might want to use structs, let’s write a program that
+calculates the area of a rectangle. We’ll start by using single variables and
+then refactor the program until we’re using structs instead.
+
+Let’s make a new binary project with Cargo called _rectangles_ that will take
+the width and height of a rectangle specified in pixels and calculate the area
+of the rectangle. Listing 5-8 shows a short program with one way of doing
+exactly that in our project’s _src/main.rs_.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-08/src/main.rs:all}}
+```
+
+
+
+Now, run this program using `cargo run`:
+
+```console
+{{#include ../listings/ch05-using-structs-to-structure-related-data/listing-05-08/output.txt}}
+```
+
+This code succeeds in figuring out the area of the rectangle by calling the
+`area` function with each dimension, but we can do more to make this code clear
+and readable.
+
+The issue with this code is evident in the signature of `area`:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-08/src/main.rs:here}}
+```
+
+The `area` function is supposed to calculate the area of one rectangle, but the
+function we wrote has two parameters, and it’s not clear anywhere in our
+program that the parameters are related. It would be more readable and more
+manageable to group width and height together. We’ve already discussed one way
+we might do that in [“The Tuple Type”][the-tuple-type] section
+of Chapter 3: by using tuples.
+
+### Refactoring with Tuples
+
+Listing 5-9 shows another version of our program that uses tuples.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-09/src/main.rs}}
+```
+
+
+
+In one way, this program is better. Tuples let us add a bit of structure, and
+we’re now passing just one argument. But in another way, this version is less
+clear: Tuples don’t name their elements, so we have to index into the parts of
+the tuple, making our calculation less obvious.
+
+Mixing up the width and height wouldn’t matter for the area calculation, but if
+we want to draw the rectangle on the screen, it would matter! We would have to
+keep in mind that `width` is the tuple index `0` and `height` is the tuple
+index `1`. This would be even harder for someone else to figure out and keep in
+mind if they were to use our code. Because we haven’t conveyed the meaning of
+our data in our code, it’s now easier to introduce errors.
+
+
+
+
+
+### Refactoring with Structs
+
+We use structs to add meaning by labeling the data. We can transform the tuple
+we’re using into a struct with a name for the whole as well as names for the
+parts, as shown in Listing 5-10.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-10/src/main.rs}}
+```
+
+
+
+Here, we’ve defined a struct and named it `Rectangle`. Inside the curly
+brackets, we defined the fields as `width` and `height`, both of which have
+type `u32`. Then, in `main`, we created a particular instance of `Rectangle`
+that has a width of `30` and a height of `50`.
+
+Our `area` function is now defined with one parameter, which we’ve named
+`rectangle`, whose type is an immutable borrow of a struct `Rectangle`
+instance. As mentioned in Chapter 4, we want to borrow the struct rather than
+take ownership of it. This way, `main` retains its ownership and can continue
+using `rect1`, which is the reason we use the `&` in the function signature and
+where we call the function.
+
+The `area` function accesses the `width` and `height` fields of the `Rectangle`
+instance (note that accessing fields of a borrowed struct instance does not
+move the field values, which is why you often see borrows of structs). Our
+function signature for `area` now says exactly what we mean: Calculate the area
+of `Rectangle`, using its `width` and `height` fields. This conveys that the
+width and height are related to each other, and it gives descriptive names to
+the values rather than using the tuple index values of `0` and `1`. This is a
+win for clarity.
+
+
+
+
+
+### Adding Functionality with Derived Traits
+
+It’d be useful to be able to print an instance of `Rectangle` while we’re
+debugging our program and see the values for all its fields. Listing 5-11 tries
+using the [`println!` macro][println] as we have used in
+previous chapters. This won’t work, however.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-11/src/main.rs}}
+```
+
+
+
+When we compile this code, we get an error with this core message:
+
+```text
+{{#include ../listings/ch05-using-structs-to-structure-related-data/listing-05-11/output.txt:3}}
+```
+
+The `println!` macro can do many kinds of formatting, and by default, the curly
+brackets tell `println!` to use formatting known as `Display`: output intended
+for direct end user consumption. The primitive types we’ve seen so far
+implement `Display` by default because there’s only one way you’d want to show
+a `1` or any other primitive type to a user. But with structs, the way
+`println!` should format the output is less clear because there are more
+display possibilities: Do you want commas or not? Do you want to print the
+curly brackets? Should all the fields be shown? Due to this ambiguity, Rust
+doesn’t try to guess what we want, and structs don’t have a provided
+implementation of `Display` to use with `println!` and the `{}` placeholder.
+
+If we continue reading the errors, we’ll find this helpful note:
+
+```text
+{{#include ../listings/ch05-using-structs-to-structure-related-data/listing-05-11/output.txt:9:10}}
+```
+
+Let’s try it! The `println!` macro call will now look like `println!("rect1 is
+{rect1:?}");`. Putting the specifier `:?` inside the curly brackets tells
+`println!` we want to use an output format called `Debug`. The `Debug` trait
+enables us to print our struct in a way that is useful for developers so that
+we can see its value while we’re debugging our code.
+
+Compile the code with this change. Drat! We still get an error:
+
+```text
+{{#include ../listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/output.txt:3}}
+```
+
+But again, the compiler gives us a helpful note:
+
+```text
+{{#include ../listings/ch05-using-structs-to-structure-related-data/output-only-01-debug/output.txt:9:10}}
+```
+
+Rust _does_ include functionality to print out debugging information, but we
+have to explicitly opt in to make that functionality available for our struct.
+To do that, we add the outer attribute `#[derive(Debug)]` just before the
+struct definition, as shown in Listing 5-12.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-12/src/main.rs}}
+```
+
+
+
+Now when we run the program, we won’t get any errors, and we’ll see the
+following output:
+
+```console
+{{#include ../listings/ch05-using-structs-to-structure-related-data/listing-05-12/output.txt}}
+```
+
+Nice! It’s not the prettiest output, but it shows the values of all the fields
+for this instance, which would definitely help during debugging. When we have
+larger structs, it’s useful to have output that’s a bit easier to read; in
+those cases, we can use `{:#?}` instead of `{:?}` in the `println!` string. In
+this example, using the `{:#?}` style will output the following:
+
+```console
+{{#include ../listings/ch05-using-structs-to-structure-related-data/output-only-02-pretty-debug/output.txt}}
+```
+
+Another way to print out a value using the `Debug` format is to use the [`dbg!`
+macro][dbg], which takes ownership of an expression (as opposed
+to `println!`, which takes a reference), prints the file and line number of
+where that `dbg!` macro call occurs in your code along with the resultant value
+of that expression, and returns ownership of the value.
+
+> Note: Calling the `dbg!` macro prints to the standard error console stream
+> (`stderr`), as opposed to `println!`, which prints to the standard output
+> console stream (`stdout`). We’ll talk more about `stderr` and `stdout` in the
+> [“Redirecting Errors to Standard Error” section in Chapter
+> 12][err].
+
+Here’s an example where we’re interested in the value that gets assigned to the
+`width` field, as well as the value of the whole struct in `rect1`:
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/src/main.rs}}
+```
+
+We can put `dbg!` around the expression `30 * scale` and, because `dbg!`
+returns ownership of the expression’s value, the `width` field will get the
+same value as if we didn’t have the `dbg!` call there. We don’t want `dbg!` to
+take ownership of `rect1`, so we use a reference to `rect1` in the next call.
+Here’s what the output of this example looks like:
+
+```console
+{{#include ../listings/ch05-using-structs-to-structure-related-data/no-listing-05-dbg-macro/output.txt}}
+```
+
+We can see the first bit of output came from _src/main.rs_ line 10 where we’re
+debugging the expression `30 * scale`, and its resultant value is `60` (the
+`Debug` formatting implemented for integers is to print only their value). The
+`dbg!` call on line 14 of _src/main.rs_ outputs the value of `&rect1`, which is
+the `Rectangle` struct. This output uses the pretty `Debug` formatting of the
+`Rectangle` type. The `dbg!` macro can be really helpful when you’re trying to
+figure out what your code is doing!
+
+In addition to the `Debug` trait, Rust has provided a number of traits for us
+to use with the `derive` attribute that can add useful behavior to our custom
+types. Those traits and their behaviors are listed in [Appendix C][app-c]. We’ll cover how to implement these traits with custom behavior as
+well as how to create your own traits in Chapter 10. There are also many
+attributes other than `derive`; for more information, see [the “Attributes”
+section of the Rust Reference][attributes].
+
+Our `area` function is very specific: It only computes the area of rectangles.
+It would be helpful to tie this behavior more closely to our `Rectangle` struct
+because it won’t work with any other type. Let’s look at how we can continue to
+refactor this code by turning the `area` function into an `area` method
+defined on our `Rectangle` type.
+
+[the-tuple-type]: ch03-02-data-types.html#the-tuple-type
+[app-c]: appendix-03-derivable-traits.md
+[println]: ../std/macro.println.html
+[dbg]: ../std/macro.dbg.html
+[err]: ch12-06-writing-to-stderr-instead-of-stdout.html
+[attributes]: ../reference/attributes.html
diff --git a/documents/markdown/rust-book/ch05-03-method-syntax.md b/documents/markdown/rust-book/ch05-03-method-syntax.md
new file mode 100644
index 0000000..fe0c7e3
--- /dev/null
+++ b/documents/markdown/rust-book/ch05-03-method-syntax.md
@@ -0,0 +1,260 @@
+## Methods
+
+Methods are similar to functions: We declare them with the `fn` keyword and a
+name, they can have parameters and a return value, and they contain some code
+that’s run when the method is called from somewhere else. Unlike functions,
+methods are defined within the context of a struct (or an enum or a trait
+object, which we cover in [Chapter 6][enums] and [Chapter
+18][trait-objects], respectively), and their first parameter is
+always `self`, which represents the instance of the struct the method is being
+called on.
+
+
+
+
+
+### Method Syntax
+
+Let’s change the `area` function that has a `Rectangle` instance as a parameter
+and instead make an `area` method defined on the `Rectangle` struct, as shown
+in Listing 5-13.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-13/src/main.rs}}
+```
+
+
+
+To define the function within the context of `Rectangle`, we start an `impl`
+(implementation) block for `Rectangle`. Everything within this `impl` block
+will be associated with the `Rectangle` type. Then, we move the `area` function
+within the `impl` curly brackets and change the first (and in this case, only)
+parameter to be `self` in the signature and everywhere within the body. In
+`main`, where we called the `area` function and passed `rect1` as an argument,
+we can instead use _method syntax_ to call the `area` method on our `Rectangle`
+instance. The method syntax goes after an instance: We add a dot followed by
+the method name, parentheses, and any arguments.
+
+In the signature for `area`, we use `&self` instead of `rectangle: &Rectangle`.
+The `&self` is actually short for `self: &Self`. Within an `impl` block, the
+type `Self` is an alias for the type that the `impl` block is for. Methods must
+have a parameter named `self` of type `Self` for their first parameter, so Rust
+lets you abbreviate this with only the name `self` in the first parameter spot.
+Note that we still need to use the `&` in front of the `self` shorthand to
+indicate that this method borrows the `Self` instance, just as we did in
+`rectangle: &Rectangle`. Methods can take ownership of `self`, borrow `self`
+immutably, as we’ve done here, or borrow `self` mutably, just as they can any
+other parameter.
+
+We chose `&self` here for the same reason we used `&Rectangle` in the function
+version: We don’t want to take ownership, and we just want to read the data in
+the struct, not write to it. If we wanted to change the instance that we’ve
+called the method on as part of what the method does, we’d use `&mut self` as
+the first parameter. Having a method that takes ownership of the instance by
+using just `self` as the first parameter is rare; this technique is usually
+used when the method transforms `self` into something else and you want to
+prevent the caller from using the original instance after the transformation.
+
+The main reason for using methods instead of functions, in addition to
+providing method syntax and not having to repeat the type of `self` in every
+method’s signature, is for organization. We’ve put all the things we can do
+with an instance of a type in one `impl` block rather than making future users
+of our code search for capabilities of `Rectangle` in various places in the
+library we provide.
+
+Note that we can choose to give a method the same name as one of the struct’s
+fields. For example, we can define a method on `Rectangle` that is also named
+`width`:
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/no-listing-06-method-field-interaction/src/main.rs:here}}
+```
+
+
+
+Here, we’re choosing to make the `width` method return `true` if the value in
+the instance’s `width` field is greater than `0` and `false` if the value is
+`0`: We can use a field within a method of the same name for any purpose. In
+`main`, when we follow `rect1.width` with parentheses, Rust knows we mean the
+method `width`. When we don’t use parentheses, Rust knows we mean the field
+`width`.
+
+Often, but not always, when we give a method the same name as a field we want
+it to only return the value in the field and do nothing else. Methods like this
+are called _getters_, and Rust does not implement them automatically for struct
+fields as some other languages do. Getters are useful because you can make the
+field private but the method public and thus enable read-only access to that
+field as part of the type’s public API. We will discuss what public and private
+are and how to designate a field or method as public or private in [Chapter
+7][public].
+
+> ### Where’s the `->` Operator?
+>
+> In C and C++, two different operators are used for calling methods: You use
+> `.` if you’re calling a method on the object directly and `->` if you’re
+> calling the method on a pointer to the object and need to dereference the
+> pointer first. In other words, if `object` is a pointer,
+> `object->something()` is similar to `(*object).something()`.
+>
+> Rust doesn’t have an equivalent to the `->` operator; instead, Rust has a
+> feature called _automatic referencing and dereferencing_. Calling methods is
+> one of the few places in Rust with this behavior.
+>
+> Here’s how it works: When you call a method with `object.something()`, Rust
+> automatically adds in `&`, `&mut`, or `*` so that `object` matches the
+> signature of the method. In other words, the following are the same:
+>
+>
+>
+> ```rust
+> # #[derive(Debug,Copy,Clone)]
+> # struct Point {
+> # x: f64,
+> # y: f64,
+> # }
+> #
+> # impl Point {
+> # fn distance(&self, other: &Point) -> f64 {
+> # let x_squared = f64::powi(other.x - self.x, 2);
+> # let y_squared = f64::powi(other.y - self.y, 2);
+> #
+> # f64::sqrt(x_squared + y_squared)
+> # }
+> # }
+> # let p1 = Point { x: 0.0, y: 0.0 };
+> # let p2 = Point { x: 5.0, y: 6.5 };
+> p1.distance(&p2);
+> (&p1).distance(&p2);
+> ```
+>
+> The first one looks much cleaner. This automatic referencing behavior works
+> because methods have a clear receiver—the type of `self`. Given the receiver
+> and name of a method, Rust can figure out definitively whether the method is
+> reading (`&self`), mutating (`&mut self`), or consuming (`self`). The fact
+> that Rust makes borrowing implicit for method receivers is a big part of
+> making ownership ergonomic in practice.
+
+### Methods with More Parameters
+
+Let’s practice using methods by implementing a second method on the `Rectangle`
+struct. This time we want an instance of `Rectangle` to take another instance
+of `Rectangle` and return `true` if the second `Rectangle` can fit completely
+within `self` (the first `Rectangle`); otherwise, it should return `false`.
+That is, once we’ve defined the `can_hold` method, we want to be able to write
+the program shown in Listing 5-14.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-14/src/main.rs}}
+```
+
+
+
+The expected output would look like the following because both dimensions of
+`rect2` are smaller than the dimensions of `rect1`, but `rect3` is wider than
+`rect1`:
+
+```text
+Can rect1 hold rect2? true
+Can rect1 hold rect3? false
+```
+
+We know we want to define a method, so it will be within the `impl Rectangle`
+block. The method name will be `can_hold`, and it will take an immutable borrow
+of another `Rectangle` as a parameter. We can tell what the type of the
+parameter will be by looking at the code that calls the method:
+`rect1.can_hold(&rect2)` passes in `&rect2`, which is an immutable borrow to
+`rect2`, an instance of `Rectangle`. This makes sense because we only need to
+read `rect2` (rather than write, which would mean we’d need a mutable borrow),
+and we want `main` to retain ownership of `rect2` so that we can use it again
+after calling the `can_hold` method. The return value of `can_hold` will be a
+Boolean, and the implementation will check whether the width and height of
+`self` are greater than the width and height of the other `Rectangle`,
+respectively. Let’s add the new `can_hold` method to the `impl` block from
+Listing 5-13, shown in Listing 5-15.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-15/src/main.rs:here}}
+```
+
+
+
+When we run this code with the `main` function in Listing 5-14, we’ll get our
+desired output. Methods can take multiple parameters that we add to the
+signature after the `self` parameter, and those parameters work just like
+parameters in functions.
+
+### Associated Functions
+
+All functions defined within an `impl` block are called _associated functions_
+because they’re associated with the type named after the `impl`. We can define
+associated functions that don’t have `self` as their first parameter (and thus
+are not methods) because they don’t need an instance of the type to work with.
+We’ve already used one function like this: the `String::from` function that’s
+defined on the `String` type.
+
+Associated functions that aren’t methods are often used for constructors that
+will return a new instance of the struct. These are often called `new`, but
+`new` isn’t a special name and isn’t built into the language. For example, we
+could choose to provide an associated function named `square` that would have
+one dimension parameter and use that as both width and height, thus making it
+easier to create a square `Rectangle` rather than having to specify the same
+value twice:
+
+Filename: src/main.rs
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/no-listing-03-associated-functions/src/main.rs:here}}
+```
+
+The `Self` keywords in the return type and in the body of the function are
+aliases for the type that appears after the `impl` keyword, which in this case
+is `Rectangle`.
+
+To call this associated function, we use the `::` syntax with the struct name;
+`let sq = Rectangle::square(3);` is an example. This function is namespaced by
+the struct: The `::` syntax is used for both associated functions and
+namespaces created by modules. We’ll discuss modules in [Chapter
+7][modules].
+
+### Multiple `impl` Blocks
+
+Each struct is allowed to have multiple `impl` blocks. For example, Listing
+5-15 is equivalent to the code shown in Listing 5-16, which has each method in
+its own `impl` block.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch05-using-structs-to-structure-related-data/listing-05-16/src/main.rs:here}}
+```
+
+
+
+There’s no reason to separate these methods into multiple `impl` blocks here,
+but this is valid syntax. We’ll see a case in which multiple `impl` blocks are
+useful in Chapter 10, where we discuss generic types and traits.
+
+## Summary
+
+Structs let you create custom types that are meaningful for your domain. By
+using structs, you can keep associated pieces of data connected to each other
+and name each piece to make your code clear. In `impl` blocks, you can define
+functions that are associated with your type, and methods are a kind of
+associated function that let you specify the behavior that instances of your
+structs have.
+
+But structs aren’t the only way you can create custom types: Let’s turn to
+Rust’s enum feature to add another tool to your toolbox.
+
+[enums]: ch06-00-enums.html
+[trait-objects]: ch18-02-trait-objects.md
+[public]: ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html#exposing-paths-with-the-pub-keyword
+[modules]: ch07-02-defining-modules-to-control-scope-and-privacy.html
diff --git a/documents/markdown/rust-book/ch06-00-enums.md b/documents/markdown/rust-book/ch06-00-enums.md
new file mode 100644
index 0000000..982e62c
--- /dev/null
+++ b/documents/markdown/rust-book/ch06-00-enums.md
@@ -0,0 +1,11 @@
+# Enums and Pattern Matching
+
+In this chapter, we’ll look at enumerations, also referred to as _enums_.
+Enums allow you to define a type by enumerating its possible variants. First
+we’ll define and use an enum to show how an enum can encode meaning along with
+data. Next, we’ll explore a particularly useful enum, called `Option`, which
+expresses that a value can be either something or nothing. Then, we’ll look at
+how pattern matching in the `match` expression makes it easy to run different
+code for different values of an enum. Finally, we’ll cover how the `if let`
+construct is another convenient and concise idiom available to handle enums in
+your code.
diff --git a/documents/markdown/rust-book/ch06-01-defining-an-enum.md b/documents/markdown/rust-book/ch06-01-defining-an-enum.md
new file mode 100644
index 0000000..74e460d
--- /dev/null
+++ b/documents/markdown/rust-book/ch06-01-defining-an-enum.md
@@ -0,0 +1,330 @@
+## Defining an Enum
+
+Where structs give you a way of grouping together related fields and data, like
+a `Rectangle` with its `width` and `height`, enums give you a way of saying a
+value is one of a possible set of values. For example, we may want to say that
+`Rectangle` is one of a set of possible shapes that also includes `Circle` and
+`Triangle`. To do this, Rust allows us to encode these possibilities as an enum.
+
+Let’s look at a situation we might want to express in code and see why enums
+are useful and more appropriate than structs in this case. Say we need to work
+with IP addresses. Currently, two major standards are used for IP addresses:
+version four and version six. Because these are the only possibilities for an
+IP address that our program will come across, we can _enumerate_ all possible
+variants, which is where enumeration gets its name.
+
+Any IP address can be either a version four or a version six address, but not
+both at the same time. That property of IP addresses makes the enum data
+structure appropriate because an enum value can only be one of its variants.
+Both version four and version six addresses are still fundamentally IP
+addresses, so they should be treated as the same type when the code is handling
+situations that apply to any kind of IP address.
+
+We can express this concept in code by defining an `IpAddrKind` enumeration and
+listing the possible kinds an IP address can be, `V4` and `V6`. These are the
+variants of the enum:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-01-defining-enums/src/main.rs:def}}
+```
+
+`IpAddrKind` is now a custom data type that we can use elsewhere in our code.
+
+### Enum Values
+
+We can create instances of each of the two variants of `IpAddrKind` like this:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-01-defining-enums/src/main.rs:instance}}
+```
+
+Note that the variants of the enum are namespaced under its identifier, and we
+use a double colon to separate the two. This is useful because now both values
+`IpAddrKind::V4` and `IpAddrKind::V6` are of the same type: `IpAddrKind`. We
+can then, for instance, define a function that takes any `IpAddrKind`:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-01-defining-enums/src/main.rs:fn}}
+```
+
+And we can call this function with either variant:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-01-defining-enums/src/main.rs:fn_call}}
+```
+
+Using enums has even more advantages. Thinking more about our IP address type,
+at the moment we don’t have a way to store the actual IP address _data_; we
+only know what _kind_ it is. Given that you just learned about structs in
+Chapter 5, you might be tempted to tackle this problem with structs as shown in
+Listing 6-1.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-01/src/main.rs:here}}
+```
+
+
+
+Here, we’ve defined a struct `IpAddr` that has two fields: a `kind` field that
+is of type `IpAddrKind` (the enum we defined previously) and an `address` field
+of type `String`. We have two instances of this struct. The first is `home`,
+and it has the value `IpAddrKind::V4` as its `kind` with associated address
+data of `127.0.0.1`. The second instance is `loopback`. It has the other
+variant of `IpAddrKind` as its `kind` value, `V6`, and has address `::1`
+associated with it. We’ve used a struct to bundle the `kind` and `address`
+values together, so now the variant is associated with the value.
+
+However, representing the same concept using just an enum is more concise:
+Rather than an enum inside a struct, we can put data directly into each enum
+variant. This new definition of the `IpAddr` enum says that both `V4` and `V6`
+variants will have associated `String` values:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-02-enum-with-data/src/main.rs:here}}
+```
+
+We attach data to each variant of the enum directly, so there is no need for an
+extra struct. Here, it’s also easier to see another detail of how enums work:
+The name of each enum variant that we define also becomes a function that
+constructs an instance of the enum. That is, `IpAddr::V4()` is a function call
+that takes a `String` argument and returns an instance of the `IpAddr` type. We
+automatically get this constructor function defined as a result of defining the
+enum.
+
+There’s another advantage to using an enum rather than a struct: Each variant
+can have different types and amounts of associated data. Version four IP
+addresses will always have four numeric components that will have values
+between 0 and 255. If we wanted to store `V4` addresses as four `u8` values but
+still express `V6` addresses as one `String` value, we wouldn’t be able to with
+a struct. Enums handle this case with ease:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-03-variants-with-different-data/src/main.rs:here}}
+```
+
+We’ve shown several different ways to define data structures to store version
+four and version six IP addresses. However, as it turns out, wanting to store
+IP addresses and encode which kind they are is so common that [the standard
+library has a definition we can use!][IpAddr] Let’s look at how
+the standard library defines `IpAddr`. It has the exact enum and variants that
+we’ve defined and used, but it embeds the address data inside the variants in
+the form of two different structs, which are defined differently for each
+variant:
+
+```rust
+struct Ipv4Addr {
+ // --snip--
+}
+
+struct Ipv6Addr {
+ // --snip--
+}
+
+enum IpAddr {
+ V4(Ipv4Addr),
+ V6(Ipv6Addr),
+}
+```
+
+This code illustrates that you can put any kind of data inside an enum variant:
+strings, numeric types, or structs, for example. You can even include another
+enum! Also, standard library types are often not much more complicated than
+what you might come up with.
+
+Note that even though the standard library contains a definition for `IpAddr`,
+we can still create and use our own definition without conflict because we
+haven’t brought the standard library’s definition into our scope. We’ll talk
+more about bringing types into scope in Chapter 7.
+
+Let’s look at another example of an enum in Listing 6-2: This one has a wide
+variety of types embedded in its variants.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-02/src/main.rs:here}}
+```
+
+
+
+This enum has four variants with different types:
+
+- `Quit`: Has no data associated with it at all
+- `Move`: Has named fields, like a struct does
+- `Write`: Includes a single `String`
+- `ChangeColor`: Includes three `i32` values
+
+Defining an enum with variants such as the ones in Listing 6-2 is similar to
+defining different kinds of struct definitions, except the enum doesn’t use the
+`struct` keyword and all the variants are grouped together under the `Message`
+type. The following structs could hold the same data that the preceding enum
+variants hold:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-04-structs-similar-to-message-enum/src/main.rs:here}}
+```
+
+But if we used the different structs, each of which has its own type, we
+couldn’t as easily define a function to take any of these kinds of messages as
+we could with the `Message` enum defined in Listing 6-2, which is a single type.
+
+There is one more similarity between enums and structs: Just as we’re able to
+define methods on structs using `impl`, we’re also able to define methods on
+enums. Here’s a method named `call` that we could define on our `Message` enum:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-05-methods-on-enums/src/main.rs:here}}
+```
+
+The body of the method would use `self` to get the value that we called the
+method on. In this example, we’ve created a variable `m` that has the value
+`Message::Write(String::from("hello"))`, and that is what `self` will be in the
+body of the `call` method when `m.call()` runs.
+
+Let’s look at another enum in the standard library that is very common and
+useful: `Option`.
+
+
+
+
+
+### The `Option` Enum
+
+This section explores a case study of `Option`, which is another enum defined
+by the standard library. The `Option` type encodes the very common scenario in
+which a value could be something, or it could be nothing.
+
+For example, if you request the first item in a non-empty list, you would get
+a value. If you request the first item in an empty list, you would get nothing.
+Expressing this concept in terms of the type system means the compiler can
+check whether you’ve handled all the cases you should be handling; this
+functionality can prevent bugs that are extremely common in other programming
+languages.
+
+Programming language design is often thought of in terms of which features you
+include, but the features you exclude are important too. Rust doesn’t have the
+null feature that many other languages have. _Null_ is a value that means there
+is no value there. In languages with null, variables can always be in one of
+two states: null or not-null.
+
+In his 2009 presentation “Null References: The Billion Dollar Mistake,” Tony
+Hoare, the inventor of null, had this to say:
+
+> I call it my billion-dollar mistake. At that time, I was designing the first
+> comprehensive type system for references in an object-oriented language. My
+> goal was to ensure that all use of references should be absolutely safe, with
+> checking performed automatically by the compiler. But I couldn’t resist the
+> temptation to put in a null reference, simply because it was so easy to
+> implement. This has led to innumerable errors, vulnerabilities, and system
+> crashes, which have probably caused a billion dollars of pain and damage in
+> the last forty years.
+
+The problem with null values is that if you try to use a null value as a
+not-null value, you’ll get an error of some kind. Because this null or not-null
+property is pervasive, it’s extremely easy to make this kind of error.
+
+However, the concept that null is trying to express is still a useful one: A
+null is a value that is currently invalid or absent for some reason.
+
+The problem isn’t really with the concept but with the particular
+implementation. As such, Rust does not have nulls, but it does have an enum
+that can encode the concept of a value being present or absent. This enum is
+`Option`, and it is [defined by the standard library][option]
+as follows:
+
+```rust
+enum Option {
+ None,
+ Some(T),
+}
+```
+
+The `Option` enum is so useful that it’s even included in the prelude; you
+don’t need to bring it into scope explicitly. Its variants are also included in
+the prelude: You can use `Some` and `None` directly without the `Option::`
+prefix. The `Option` enum is still just a regular enum, and `Some(T)` and
+`None` are still variants of type `Option`.
+
+The `` syntax is a feature of Rust we haven’t talked about yet. It’s a
+generic type parameter, and we’ll cover generics in more detail in Chapter 10.
+For now, all you need to know is that `` means that the `Some` variant of
+the `Option` enum can hold one piece of data of any type, and that each
+concrete type that gets used in place of `T` makes the overall `Option` type
+a different type. Here are some examples of using `Option` values to hold
+number types and char types:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-06-option-examples/src/main.rs:here}}
+```
+
+The type of `some_number` is `Option`. The type of `some_char` is
+`Option`, which is a different type. Rust can infer these types because
+we’ve specified a value inside the `Some` variant. For `absent_number`, Rust
+requires us to annotate the overall `Option` type: The compiler can’t infer the
+type that the corresponding `Some` variant will hold by looking only at a
+`None` value. Here, we tell Rust that we mean for `absent_number` to be of type
+`Option`.
+
+When we have a `Some` value, we know that a value is present, and the value is
+held within the `Some`. When we have a `None` value, in some sense it means the
+same thing as null: We don’t have a valid value. So, why is having `Option`
+any better than having null?
+
+In short, because `Option` and `T` (where `T` can be any type) are different
+types, the compiler won’t let us use an `Option` value as if it were
+definitely a valid value. For example, this code won’t compile, because it’s
+trying to add an `i8` to an `Option`:
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-07-cant-use-option-directly/src/main.rs:here}}
+```
+
+If we run this code, we get an error message like this one:
+
+```console
+{{#include ../listings/ch06-enums-and-pattern-matching/no-listing-07-cant-use-option-directly/output.txt}}
+```
+
+Intense! In effect, this error message means that Rust doesn’t understand how
+to add an `i8` and an `Option`, because they’re different types. When we
+have a value of a type like `i8` in Rust, the compiler will ensure that we
+always have a valid value. We can proceed confidently without having to check
+for null before using that value. Only when we have an `Option` (or
+whatever type of value we’re working with) do we have to worry about possibly
+not having a value, and the compiler will make sure we handle that case before
+using the value.
+
+In other words, you have to convert an `Option` to a `T` before you can
+perform `T` operations with it. Generally, this helps catch one of the most
+common issues with null: assuming that something isn’t null when it actually is.
+
+Eliminating the risk of incorrectly assuming a not-null value helps you be more
+confident in your code. In order to have a value that can possibly be null, you
+must explicitly opt in by making the type of that value `Option`. Then, when
+you use that value, you are required to explicitly handle the case when the
+value is null. Everywhere that a value has a type that isn’t an `Option`,
+you _can_ safely assume that the value isn’t null. This was a deliberate design
+decision for Rust to limit null’s pervasiveness and increase the safety of Rust
+code.
+
+So how do you get the `T` value out of a `Some` variant when you have a value
+of type `Option` so that you can use that value? The `Option` enum has a
+large number of methods that are useful in a variety of situations; you can
+check them out in [its documentation][docs]. Becoming familiar
+with the methods on `Option` will be extremely useful in your journey with
+Rust.
+
+In general, in order to use an `Option` value, you want to have code that
+will handle each variant. You want some code that will run only when you have a
+`Some(T)` value, and this code is allowed to use the inner `T`. You want some
+other code to run only if you have a `None` value, and that code doesn’t have a
+`T` value available. The `match` expression is a control flow construct that
+does just this when used with enums: It will run different code depending on
+which variant of the enum it has, and that code can use the data inside the
+matching value.
+
+[IpAddr]: ../std/net/enum.IpAddr.html
+[option]: ../std/option/enum.Option.html
+[docs]: ../std/option/enum.Option.html
diff --git a/documents/markdown/rust-book/ch06-02-match.md b/documents/markdown/rust-book/ch06-02-match.md
new file mode 100644
index 0000000..e96ec79
--- /dev/null
+++ b/documents/markdown/rust-book/ch06-02-match.md
@@ -0,0 +1,265 @@
+
+
+
+
+## The `match` Control Flow Construct
+
+Rust has an extremely powerful control flow construct called `match` that
+allows you to compare a value against a series of patterns and then execute
+code based on which pattern matches. Patterns can be made up of literal values,
+variable names, wildcards, and many other things; [Chapter
+19][ch19-00-patterns] covers all the different kinds of patterns
+and what they do. The power of `match` comes from the expressiveness of the
+patterns and the fact that the compiler confirms that all possible cases are
+handled.
+
+Think of a `match` expression as being like a coin-sorting machine: Coins slide
+down a track with variously sized holes along it, and each coin falls through
+the first hole it encounters that it fits into. In the same way, values go
+through each pattern in a `match`, and at the first pattern the value “fits,”
+the value falls into the associated code block to be used during execution.
+
+Speaking of coins, let’s use them as an example using `match`! We can write a
+function that takes an unknown US coin and, in a similar way as the counting
+machine, determines which coin it is and returns its value in cents, as shown
+in Listing 6-3.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-03/src/main.rs:here}}
+```
+
+
+
+Let’s break down the `match` in the `value_in_cents` function. First, we list
+the `match` keyword followed by an expression, which in this case is the value
+`coin`. This seems very similar to a conditional expression used with `if`, but
+there’s a big difference: With `if`, the condition needs to evaluate to a
+Boolean value, but here it can be any type. The type of `coin` in this example
+is the `Coin` enum that we defined on the first line.
+
+Next are the `match` arms. An arm has two parts: a pattern and some code. The
+first arm here has a pattern that is the value `Coin::Penny` and then the `=>`
+operator that separates the pattern and the code to run. The code in this case
+is just the value `1`. Each arm is separated from the next with a comma.
+
+When the `match` expression executes, it compares the resultant value against
+the pattern of each arm, in order. If a pattern matches the value, the code
+associated with that pattern is executed. If that pattern doesn’t match the
+value, execution continues to the next arm, much as in a coin-sorting machine.
+We can have as many arms as we need: In Listing 6-3, our `match` has four arms.
+
+The code associated with each arm is an expression, and the resultant value of
+the expression in the matching arm is the value that gets returned for the
+entire `match` expression.
+
+We don’t typically use curly brackets if the match arm code is short, as it is
+in Listing 6-3 where each arm just returns a value. If you want to run multiple
+lines of code in a match arm, you must use curly brackets, and the comma
+following the arm is then optional. For example, the following code prints
+“Lucky penny!” every time the method is called with a `Coin::Penny`, but it
+still returns the last value of the block, `1`:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-08-match-arm-multiple-lines/src/main.rs:here}}
+```
+
+### Patterns That Bind to Values
+
+Another useful feature of match arms is that they can bind to the parts of the
+values that match the pattern. This is how we can extract values out of enum
+variants.
+
+As an example, let’s change one of our enum variants to hold data inside it.
+From 1999 through 2008, the United States minted quarters with different
+designs for each of the 50 states on one side. No other coins got state
+designs, so only quarters have this extra value. We can add this information to
+our `enum` by changing the `Quarter` variant to include a `UsState` value
+stored inside it, which we’ve done in Listing 6-4.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-04/src/main.rs:here}}
+```
+
+
+
+Let’s imagine that a friend is trying to collect all 50 state quarters. While
+we sort our loose change by coin type, we’ll also call out the name of the
+state associated with each quarter so that if it’s one our friend doesn’t have,
+they can add it to their collection.
+
+In the match expression for this code, we add a variable called `state` to the
+pattern that matches values of the variant `Coin::Quarter`. When a
+`Coin::Quarter` matches, the `state` variable will bind to the value of that
+quarter’s state. Then, we can use `state` in the code for that arm, like so:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-09-variable-in-pattern/src/main.rs:here}}
+```
+
+If we were to call `value_in_cents(Coin::Quarter(UsState::Alaska))`, `coin`
+would be `Coin::Quarter(UsState::Alaska)`. When we compare that value with each
+of the match arms, none of them match until we reach `Coin::Quarter(state)`. At
+that point, the binding for `state` will be the value `UsState::Alaska`. We can
+then use that binding in the `println!` expression, thus getting the inner
+state value out of the `Coin` enum variant for `Quarter`.
+
+
+
+
+
+### The `Option` `match` Pattern
+
+
+In the previous section, we wanted to get the inner `T` value out of the `Some`
+case when using `Option`; we can also handle `Option` using `match`, as
+we did with the `Coin` enum! Instead of comparing coins, we’ll compare the
+variants of `Option`, but the way the `match` expression works remains the
+same.
+
+Let’s say we want to write a function that takes an `Option` and, if
+there’s a value inside, adds 1 to that value. If there isn’t a value inside,
+the function should return the `None` value and not attempt to perform any
+operations.
+
+This function is very easy to write, thanks to `match`, and will look like
+Listing 6-5.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-05/src/main.rs:here}}
+```
+
+
+
+Let’s examine the first execution of `plus_one` in more detail. When we call
+`plus_one(five)`, the variable `x` in the body of `plus_one` will have the
+value `Some(5)`. We then compare that against each match arm:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-05/src/main.rs:first_arm}}
+```
+
+The `Some(5)` value doesn’t match the pattern `None`, so we continue to the
+next arm:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-05/src/main.rs:second_arm}}
+```
+
+Does `Some(5)` match `Some(i)`? It does! We have the same variant. The `i`
+binds to the value contained in `Some`, so `i` takes the value `5`. The code in
+the match arm is then executed, so we add 1 to the value of `i` and create a
+new `Some` value with our total `6` inside.
+
+Now let’s consider the second call of `plus_one` in Listing 6-5, where `x` is
+`None`. We enter the `match` and compare to the first arm:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-05/src/main.rs:first_arm}}
+```
+
+It matches! There’s no value to add to, so the program stops and returns the
+`None` value on the right side of `=>`. Because the first arm matched, no other
+arms are compared.
+
+Combining `match` and enums is useful in many situations. You’ll see this
+pattern a lot in Rust code: `match` against an enum, bind a variable to the
+data inside, and then execute code based on it. It’s a bit tricky at first, but
+once you get used to it, you’ll wish you had it in all languages. It’s
+consistently a user favorite.
+
+### Matches Are Exhaustive
+
+There’s one other aspect of `match` we need to discuss: The arms’ patterns must
+cover all possibilities. Consider this version of our `plus_one` function,
+which has a bug and won’t compile:
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/src/main.rs:here}}
+```
+
+We didn’t handle the `None` case, so this code will cause a bug. Luckily, it’s
+a bug Rust knows how to catch. If we try to compile this code, we’ll get this
+error:
+
+```console
+{{#include ../listings/ch06-enums-and-pattern-matching/no-listing-10-non-exhaustive-match/output.txt}}
+```
+
+Rust knows that we didn’t cover every possible case and even knows which
+pattern we forgot! Matches in Rust are _exhaustive_: We must exhaust every last
+possibility in order for the code to be valid. Especially in the case of
+`Option`, when Rust prevents us from forgetting to explicitly handle the
+`None` case, it protects us from assuming that we have a value when we might
+have null, thus making the billion-dollar mistake discussed earlier impossible.
+
+### Catch-All Patterns and the `_` Placeholder
+
+Using enums, we can also take special actions for a few particular values, but
+for all other values take one default action. Imagine we’re implementing a game
+where, if you roll a 3 on a dice roll, your player doesn’t move but instead
+gets a fancy new hat. If you roll a 7, your player loses a fancy hat. For all
+other values, your player moves that number of spaces on the game board. Here’s
+a `match` that implements that logic, with the result of the dice roll
+hardcoded rather than a random value, and all other logic represented by
+functions without bodies because actually implementing them is out of scope for
+this example:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-15-binding-catchall/src/main.rs:here}}
+```
+
+For the first two arms, the patterns are the literal values `3` and `7`. For
+the last arm that covers every other possible value, the pattern is the
+variable we’ve chosen to name `other`. The code that runs for the `other` arm
+uses the variable by passing it to the `move_player` function.
+
+This code compiles, even though we haven’t listed all the possible values a
+`u8` can have, because the last pattern will match all values not specifically
+listed. This catch-all pattern meets the requirement that `match` must be
+exhaustive. Note that we have to put the catch-all arm last because the
+patterns are evaluated in order. If we had put the catch-all arm earlier, the
+other arms would never run, so Rust will warn us if we add arms after a
+catch-all!
+
+Rust also has a pattern we can use when we want a catch-all but don’t want to
+_use_ the value in the catch-all pattern: `_` is a special pattern that matches
+any value and does not bind to that value. This tells Rust we aren’t going to
+use the value, so Rust won’t warn us about an unused variable.
+
+Let’s change the rules of the game: Now, if you roll anything other than a 3 or
+a 7, you must roll again. We no longer need to use the catch-all value, so we
+can change our code to use `_` instead of the variable named `other`:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-16-underscore-catchall/src/main.rs:here}}
+```
+
+This example also meets the exhaustiveness requirement because we’re explicitly
+ignoring all other values in the last arm; we haven’t forgotten anything.
+
+Finally, we’ll change the rules of the game one more time so that nothing else
+happens on your turn if you roll anything other than a 3 or a 7. We can express
+that by using the unit value (the empty tuple type we mentioned in [“The Tuple
+Type”][tuples] section) as the code that goes with the `_` arm:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-17-underscore-unit/src/main.rs:here}}
+```
+
+Here, we’re telling Rust explicitly that we aren’t going to use any other value
+that doesn’t match a pattern in an earlier arm, and we don’t want to run any
+code in this case.
+
+There’s more about patterns and matching that we’ll cover in [Chapter
+19][ch19-00-patterns]. For now, we’re going to move on to the
+`if let` syntax, which can be useful in situations where the `match` expression
+is a bit wordy.
+
+[tuples]: ch03-02-data-types.html#the-tuple-type
+[ch19-00-patterns]: ch19-00-patterns.html
diff --git a/documents/markdown/rust-book/ch06-03-if-let.md b/documents/markdown/rust-book/ch06-03-if-let.md
new file mode 100644
index 0000000..06b517e
--- /dev/null
+++ b/documents/markdown/rust-book/ch06-03-if-let.md
@@ -0,0 +1,147 @@
+## Concise Control Flow with `if let` and `let...else`
+
+The `if let` syntax lets you combine `if` and `let` into a less verbose way to
+handle values that match one pattern while ignoring the rest. Consider the
+program in Listing 6-6 that matches on an `Option` value in the
+`config_max` variable but only wants to execute code if the value is the `Some`
+variant.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-06/src/main.rs:here}}
+```
+
+
+
+If the value is `Some`, we print out the value in the `Some` variant by binding
+the value to the variable `max` in the pattern. We don’t want to do anything
+with the `None` value. To satisfy the `match` expression, we have to add `_ =>
+()` after processing just one variant, which is annoying boilerplate code to
+add.
+
+Instead, we could write this in a shorter way using `if let`. The following
+code behaves the same as the `match` in Listing 6-6:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-12-if-let/src/main.rs:here}}
+```
+
+The syntax `if let` takes a pattern and an expression separated by an equal
+sign. It works the same way as a `match`, where the expression is given to the
+`match` and the pattern is its first arm. In this case, the pattern is
+`Some(max)`, and the `max` binds to the value inside the `Some`. We can then
+use `max` in the body of the `if let` block in the same way we used `max` in
+the corresponding `match` arm. The code in the `if let` block only runs if the
+value matches the pattern.
+
+Using `if let` means less typing, less indentation, and less boilerplate code.
+However, you lose the exhaustive checking `match` enforces that ensures that
+you aren’t forgetting to handle any cases. Choosing between `match` and `if
+let` depends on what you’re doing in your particular situation and whether
+gaining conciseness is an appropriate trade-off for losing exhaustive checking.
+
+In other words, you can think of `if let` as syntax sugar for a `match` that
+runs code when the value matches one pattern and then ignores all other values.
+
+We can include an `else` with an `if let`. The block of code that goes with the
+`else` is the same as the block of code that would go with the `_` case in the
+`match` expression that is equivalent to the `if let` and `else`. Recall the
+`Coin` enum definition in Listing 6-4, where the `Quarter` variant also held a
+`UsState` value. If we wanted to count all non-quarter coins we see while also
+announcing the state of the quarters, we could do that with a `match`
+expression, like this:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-13-count-and-announce-match/src/main.rs:here}}
+```
+
+Or we could use an `if let` and `else` expression, like this:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/no-listing-14-count-and-announce-if-let-else/src/main.rs:here}}
+```
+
+## Staying on the “Happy Path” with `let...else`
+
+The common pattern is to perform some computation when a value is present and
+return a default value otherwise. Continuing with our example of coins with a
+`UsState` value, if we wanted to say something funny depending on how old the
+state on the quarter was, we might introduce a method on `UsState` to check the
+age of a state, like so:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-07/src/main.rs:state}}
+```
+
+Then, we might use `if let` to match on the type of coin, introducing a `state`
+variable within the body of the condition, as in Listing 6-7.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-07/src/main.rs:describe}}
+```
+
+
+
+That gets the job done, but it has pushed the work into the body of the `if
+let` statement, and if the work to be done is more complicated, it might be
+hard to follow exactly how the top-level branches relate. We could also take
+advantage of the fact that expressions produce a value either to produce the
+`state` from the `if let` or to return early, as in Listing 6-8. (You could do
+something similar with a `match`, too.)
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-08/src/main.rs:describe}}
+```
+
+
+
+This is a bit annoying to follow in its own way, though! One branch of the `if
+let` produces a value, and the other one returns from the function entirely.
+
+To make this common pattern nicer to express, Rust has `let...else`. The
+`let...else` syntax takes a pattern on the left side and an expression on the
+right, very similar to `if let`, but it does not have an `if` branch, only an
+`else` branch. If the pattern matches, it will bind the value from the pattern
+in the outer scope. If the pattern does _not_ match, the program will flow into
+the `else` arm, which must return from the function.
+
+In Listing 6-9, you can see how Listing 6-8 looks when using `let...else` in
+place of `if let`.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-09/src/main.rs:describe}}
+```
+
+
+
+Notice that it stays on the “happy path” in the main body of the function this
+way, without having significantly different control flow for two branches the
+way the `if let` did.
+
+If you have a situation in which your program has logic that is too verbose to
+express using a `match`, remember that `if let` and `let...else` are in your
+Rust toolbox as well.
+
+## Summary
+
+We’ve now covered how to use enums to create custom types that can be one of a
+set of enumerated values. We’ve shown how the standard library’s `Option`
+type helps you use the type system to prevent errors. When enum values have
+data inside them, you can use `match` or `if let` to extract and use those
+values, depending on how many cases you need to handle.
+
+Your Rust programs can now express concepts in your domain using structs and
+enums. Creating custom types to use in your API ensures type safety: The
+compiler will make certain your functions only get values of the type each
+function expects.
+
+In order to provide a well-organized API to your users that is straightforward
+to use and only exposes exactly what your users will need, let’s now turn to
+Rust’s modules.
diff --git a/documents/markdown/rust-book/ch07-00-managing-growing-projects-with-packages-crates-and-modules.md b/documents/markdown/rust-book/ch07-00-managing-growing-projects-with-packages-crates-and-modules.md
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@@ -0,0 +1,52 @@
+
+
+
+
+# Packages, Crates, and Modules
+
+As you write large programs, organizing your code will become increasingly
+important. By grouping related functionality and separating code with distinct
+features, you’ll clarify where to find code that implements a particular
+feature and where to go to change how a feature works.
+
+The programs we’ve written so far have been in one module in one file. As a
+project grows, you should organize code by splitting it into multiple modules
+and then multiple files. A package can contain multiple binary crates and
+optionally one library crate. As a package grows, you can extract parts into
+separate crates that become external dependencies. This chapter covers all
+these techniques. For very large projects comprising a set of interrelated
+packages that evolve together, Cargo provides workspaces, which we’ll cover in
+[“Cargo Workspaces”][workspaces] in Chapter 14.
+
+We’ll also discuss encapsulating implementation details, which lets you reuse
+code at a higher level: Once you’ve implemented an operation, other code can
+call your code via its public interface without having to know how the
+implementation works. The way you write code defines which parts are public for
+other code to use and which parts are private implementation details that you
+reserve the right to change. This is another way to limit the amount of detail
+you have to keep in your head.
+
+A related concept is scope: The nested context in which code is written has a
+set of names that are defined as “in scope.” When reading, writing, and
+compiling code, programmers and compilers need to know whether a particular
+name at a particular spot refers to a variable, function, struct, enum, module,
+constant, or other item and what that item means. You can create scopes and
+change which names are in or out of scope. You can’t have two items with the
+same name in the same scope; tools are available to resolve name conflicts.
+
+Rust has a number of features that allow you to manage your code’s
+organization, including which details are exposed, which details are private,
+and what names are in each scope in your programs. These features, sometimes
+collectively referred to as the _module system_, include:
+
+* **Packages**: A Cargo feature that lets you build, test, and share crates
+* **Crates**: A tree of modules that produces a library or executable
+* **Modules and use**: Let you control the organization, scope, and privacy of
+paths
+* **Paths**: A way of naming an item, such as a struct, function, or module
+
+In this chapter, we’ll cover all these features, discuss how they interact, and
+explain how to use them to manage scope. By the end, you should have a solid
+understanding of the module system and be able to work with scopes like a pro!
+
+[workspaces]: ch14-03-cargo-workspaces.html
diff --git a/documents/markdown/rust-book/ch07-01-packages-and-crates.md b/documents/markdown/rust-book/ch07-01-packages-and-crates.md
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@@ -0,0 +1,72 @@
+## Packages and Crates
+
+The first parts of the module system we’ll cover are packages and crates.
+
+A _crate_ is the smallest amount of code that the Rust compiler considers at a
+time. Even if you run `rustc` rather than `cargo` and pass a single source code
+file (as we did all the way back in [“Rust Program Basics”][basics] in Chapter 1), the compiler considers that file to be a crate. Crates can
+contain modules, and the modules may be defined in other files that get
+compiled with the crate, as we’ll see in the coming sections.
+
+A crate can come in one of two forms: a binary crate or a library crate.
+_Binary crates_ are programs you can compile to an executable that you can run,
+such as a command line program or a server. Each must have a function called
+`main` that defines what happens when the executable runs. All the crates we’ve
+created so far have been binary crates.
+
+_Library crates_ don’t have a `main` function, and they don’t compile to an
+executable. Instead, they define functionality intended to be shared with
+multiple projects. For example, the `rand` crate we used in [Chapter
+2][rand] provides functionality that generates random numbers.
+Most of the time when Rustaceans say “crate,” they mean library crate, and they
+use “crate” interchangeably with the general programming concept of a “library.”
+
+The _crate root_ is a source file that the Rust compiler starts from and makes
+up the root module of your crate (we’ll explain modules in depth in [“Control
+Scope and Privacy with Modules”][modules]).
+
+A _package_ is a bundle of one or more crates that provides a set of
+functionality. A package contains a _Cargo.toml_ file that describes how to
+build those crates. Cargo is actually a package that contains the binary crate
+for the command line tool you’ve been using to build your code. The Cargo
+package also contains a library crate that the binary crate depends on. Other
+projects can depend on the Cargo library crate to use the same logic the Cargo
+command line tool uses.
+
+A package can contain as many binary crates as you like, but at most only one
+library crate. A package must contain at least one crate, whether that’s a
+library or binary crate.
+
+Let’s walk through what happens when we create a package. First, we enter the
+command `cargo new my-project`:
+
+```console
+$ cargo new my-project
+ Created binary (application) `my-project` package
+$ ls my-project
+Cargo.toml
+src
+$ ls my-project/src
+main.rs
+```
+
+After we run `cargo new my-project`, we use `ls` to see what Cargo creates. In
+the _my-project_ directory, there’s a _Cargo.toml_ file, giving us a package.
+There’s also a _src_ directory that contains _main.rs_. Open _Cargo.toml_ in
+your text editor and note that there’s no mention of _src/main.rs_. Cargo
+follows a convention that _src/main.rs_ is the crate root of a binary crate
+with the same name as the package. Likewise, Cargo knows that if the package
+directory contains _src/lib.rs_, the package contains a library crate with the
+same name as the package, and _src/lib.rs_ is its crate root. Cargo passes the
+crate root files to `rustc` to build the library or binary.
+
+Here, we have a package that only contains _src/main.rs_, meaning it only
+contains a binary crate named `my-project`. If a package contains _src/main.rs_
+and _src/lib.rs_, it has two crates: a binary and a library, both with the same
+name as the package. A package can have multiple binary crates by placing files
+in the _src/bin_ directory: Each file will be a separate binary crate.
+
+[basics]: ch01-02-hello-world.html#rust-program-basics
+[modules]: ch07-02-defining-modules-to-control-scope-and-privacy.html
+[rand]: ch02-00-guessing-game-tutorial.html#generating-a-random-number
diff --git a/documents/markdown/rust-book/ch07-02-defining-modules-to-control-scope-and-privacy.md b/documents/markdown/rust-book/ch07-02-defining-modules-to-control-scope-and-privacy.md
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@@ -0,0 +1,180 @@
+
+
+
+
+## Control Scope and Privacy with Modules
+
+In this section, we’ll talk about modules and other parts of the module system,
+namely _paths_, which allow you to name items; the `use` keyword that brings a
+path into scope; and the `pub` keyword to make items public. We’ll also discuss
+the `as` keyword, external packages, and the glob operator.
+
+### Modules Cheat Sheet
+
+Before we get to the details of modules and paths, here we provide a quick
+reference on how modules, paths, the `use` keyword, and the `pub` keyword work
+in the compiler, and how most developers organize their code. We’ll be going
+through examples of each of these rules throughout this chapter, but this is a
+great place to refer to as a reminder of how modules work.
+
+- **Start from the crate root**: When compiling a crate, the compiler first
+ looks in the crate root file (usually _src/lib.rs_ for a library crate and
+ _src/main.rs_ for a binary crate) for code to compile.
+- **Declaring modules**: In the crate root file, you can declare new modules;
+ say you declare a “garden” module with `mod garden;`. The compiler will look
+ for the module’s code in these places:
+ - Inline, within curly brackets that replace the semicolon following `mod
+ garden`
+ - In the file _src/garden.rs_
+ - In the file _src/garden/mod.rs_
+- **Declaring submodules**: In any file other than the crate root, you can
+ declare submodules. For example, you might declare `mod vegetables;` in
+ _src/garden.rs_. The compiler will look for the submodule’s code within the
+ directory named for the parent module in these places:
+ - Inline, directly following `mod vegetables`, within curly brackets instead
+ of the semicolon
+ - In the file _src/garden/vegetables.rs_
+ - In the file _src/garden/vegetables/mod.rs_
+- **Paths to code in modules**: Once a module is part of your crate, you can
+ refer to code in that module from anywhere else in that same crate, as long
+ as the privacy rules allow, using the path to the code. For example, an
+ `Asparagus` type in the garden vegetables module would be found at
+ `crate::garden::vegetables::Asparagus`.
+- **Private vs. public**: Code within a module is private from its parent
+ modules by default. To make a module public, declare it with `pub mod`
+ instead of `mod`. To make items within a public module public as well, use
+ `pub` before their declarations.
+- **The `use` keyword**: Within a scope, the `use` keyword creates shortcuts to
+ items to reduce repetition of long paths. In any scope that can refer to
+ `crate::garden::vegetables::Asparagus`, you can create a shortcut with `use
+ crate::garden::vegetables::Asparagus;`, and from then on you only need to
+ write `Asparagus` to make use of that type in the scope.
+
+Here, we create a binary crate named `backyard` that illustrates these rules.
+The crate’s directory, also named _backyard_, contains these files and
+directories:
+
+```text
+backyard
+├── Cargo.lock
+├── Cargo.toml
+└── src
+ ├── garden
+ │ └── vegetables.rs
+ ├── garden.rs
+ └── main.rs
+```
+
+The crate root file in this case is _src/main.rs_, and it contains:
+
+
+
+```rust,noplayground,ignore
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/quick-reference-example/src/main.rs}}
+```
+
+
+
+The `pub mod garden;` line tells the compiler to include the code it finds in
+_src/garden.rs_, which is:
+
+
+
+```rust,noplayground,ignore
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/quick-reference-example/src/garden.rs}}
+```
+
+
+
+Here, `pub mod vegetables;` means the code in _src/garden/vegetables.rs_ is
+included too. That code is:
+
+```rust,noplayground,ignore
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/quick-reference-example/src/garden/vegetables.rs}}
+```
+
+Now let’s get into the details of these rules and demonstrate them in action!
+
+### Grouping Related Code in Modules
+
+_Modules_ let us organize code within a crate for readability and easy reuse.
+Modules also allow us to control the _privacy_ of items because code within a
+module is private by default. Private items are internal implementation details
+not available for outside use. We can choose to make modules and the items
+within them public, which exposes them to allow external code to use and depend
+on them.
+
+As an example, let’s write a library crate that provides the functionality of a
+restaurant. We’ll define the signatures of functions but leave their bodies
+empty to concentrate on the organization of the code rather than the
+implementation of a restaurant.
+
+In the restaurant industry, some parts of a restaurant are referred to as front
+of house and others as back of house. _Front of house_ is where customers are;
+this encompasses where the hosts seat customers, servers take orders and
+payment, and bartenders make drinks. _Back of house_ is where the chefs and
+cooks work in the kitchen, dishwashers clean up, and managers do administrative
+work.
+
+To structure our crate in this way, we can organize its functions into nested
+modules. Create a new library named `restaurant` by running `cargo new
+restaurant --lib`. Then, enter the code in Listing 7-1 into _src/lib.rs_ to
+define some modules and function signatures; this code is the front of house
+section.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-01/src/lib.rs}}
+```
+
+
+
+We define a module with the `mod` keyword followed by the name of the module
+(in this case, `front_of_house`). The body of the module then goes inside curly
+brackets. Inside modules, we can place other modules, as in this case with the
+modules `hosting` and `serving`. Modules can also hold definitions for other
+items, such as structs, enums, constants, traits, and as in Listing 7-1,
+functions.
+
+By using modules, we can group related definitions together and name why
+they’re related. Programmers using this code can navigate the code based on the
+groups rather than having to read through all the definitions, making it easier
+to find the definitions relevant to them. Programmers adding new functionality
+to this code would know where to place the code to keep the program organized.
+
+Earlier, we mentioned that _src/main.rs_ and _src/lib.rs_ are called _crate
+roots_. The reason for their name is that the contents of either of these two
+files form a module named `crate` at the root of the crate’s module structure,
+known as the _module tree_.
+
+Listing 7-2 shows the module tree for the structure in Listing 7-1.
+
+
+
+```text
+crate
+ └── front_of_house
+ ├── hosting
+ │ ├── add_to_waitlist
+ │ └── seat_at_table
+ └── serving
+ ├── take_order
+ ├── serve_order
+ └── take_payment
+```
+
+
+
+This tree shows how some of the modules nest inside other modules; for example,
+`hosting` nests inside `front_of_house`. The tree also shows that some modules
+are _siblings_, meaning they’re defined in the same module; `hosting` and
+`serving` are siblings defined within `front_of_house`. If module A is
+contained inside module B, we say that module A is the _child_ of module B and
+that module B is the _parent_ of module A. Notice that the entire module tree
+is rooted under the implicit module named `crate`.
+
+The module tree might remind you of the filesystem’s directory tree on your
+computer; this is a very apt comparison! Just like directories in a filesystem,
+you use modules to organize your code. And just like files in a directory, we
+need a way to find our modules.
diff --git a/documents/markdown/rust-book/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.md b/documents/markdown/rust-book/ch07-03-paths-for-referring-to-an-item-in-the-module-tree.md
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+## Paths for Referring to an Item in the Module Tree
+
+To show Rust where to find an item in a module tree, we use a path in the same
+way we use a path when navigating a filesystem. To call a function, we need to
+know its path.
+
+A path can take two forms:
+
+- An _absolute path_ is the full path starting from a crate root; for code
+ from an external crate, the absolute path begins with the crate name, and for
+ code from the current crate, it starts with the literal `crate`.
+- A _relative path_ starts from the current module and uses `self`, `super`, or
+ an identifier in the current module.
+
+Both absolute and relative paths are followed by one or more identifiers
+separated by double colons (`::`).
+
+Returning to Listing 7-1, say we want to call the `add_to_waitlist` function.
+This is the same as asking: What’s the path of the `add_to_waitlist` function?
+Listing 7-3 contains Listing 7-1 with some of the modules and functions removed.
+
+We’ll show two ways to call the `add_to_waitlist` function from a new function,
+`eat_at_restaurant`, defined in the crate root. These paths are correct, but
+there’s another problem remaining that will prevent this example from compiling
+as is. We’ll explain why in a bit.
+
+The `eat_at_restaurant` function is part of our library crate’s public API, so
+we mark it with the `pub` keyword. In the [“Exposing Paths with the `pub`
+Keyword”][pub] section, we’ll go into more detail about `pub`.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-03/src/lib.rs}}
+```
+
+
+
+The first time we call the `add_to_waitlist` function in `eat_at_restaurant`,
+we use an absolute path. The `add_to_waitlist` function is defined in the same
+crate as `eat_at_restaurant`, which means we can use the `crate` keyword to
+start an absolute path. We then include each of the successive modules until we
+make our way to `add_to_waitlist`. You can imagine a filesystem with the same
+structure: We’d specify the path `/front_of_house/hosting/add_to_waitlist` to
+run the `add_to_waitlist` program; using the `crate` name to start from the
+crate root is like using `/` to start from the filesystem root in your shell.
+
+The second time we call `add_to_waitlist` in `eat_at_restaurant`, we use a
+relative path. The path starts with `front_of_house`, the name of the module
+defined at the same level of the module tree as `eat_at_restaurant`. Here the
+filesystem equivalent would be using the path
+`front_of_house/hosting/add_to_waitlist`. Starting with a module name means
+that the path is relative.
+
+Choosing whether to use a relative or absolute path is a decision you’ll make
+based on your project, and it depends on whether you’re more likely to move
+item definition code separately from or together with the code that uses the
+item. For example, if we moved the `front_of_house` module and the
+`eat_at_restaurant` function into a module named `customer_experience`, we’d
+need to update the absolute path to `add_to_waitlist`, but the relative path
+would still be valid. However, if we moved the `eat_at_restaurant` function
+separately into a module named `dining`, the absolute path to the
+`add_to_waitlist` call would stay the same, but the relative path would need to
+be updated. Our preference in general is to specify absolute paths because it’s
+more likely we’ll want to move code definitions and item calls independently of
+each other.
+
+Let’s try to compile Listing 7-3 and find out why it won’t compile yet! The
+errors we get are shown in Listing 7-4.
+
+
+
+```console
+{{#include ../listings/ch07-managing-growing-projects/listing-07-03/output.txt}}
+```
+
+
+
+The error messages say that module `hosting` is private. In other words, we
+have the correct paths for the `hosting` module and the `add_to_waitlist`
+function, but Rust won’t let us use them because it doesn’t have access to the
+private sections. In Rust, all items (functions, methods, structs, enums,
+modules, and constants) are private to parent modules by default. If you want
+to make an item like a function or struct private, you put it in a module.
+
+Items in a parent module can’t use the private items inside child modules, but
+items in child modules can use the items in their ancestor modules. This is
+because child modules wrap and hide their implementation details, but the child
+modules can see the context in which they’re defined. To continue with our
+metaphor, think of the privacy rules as being like the back office of a
+restaurant: What goes on in there is private to restaurant customers, but
+office managers can see and do everything in the restaurant they operate.
+
+Rust chose to have the module system function this way so that hiding inner
+implementation details is the default. That way, you know which parts of the
+inner code you can change without breaking the outer code. However, Rust does
+give you the option to expose inner parts of child modules’ code to outer
+ancestor modules by using the `pub` keyword to make an item public.
+
+### Exposing Paths with the `pub` Keyword
+
+Let’s return to the error in Listing 7-4 that told us the `hosting` module is
+private. We want the `eat_at_restaurant` function in the parent module to have
+access to the `add_to_waitlist` function in the child module, so we mark the
+`hosting` module with the `pub` keyword, as shown in Listing 7-5.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-05/src/lib.rs:here}}
+```
+
+
+
+Unfortunately, the code in Listing 7-5 still results in compiler errors, as
+shown in Listing 7-6.
+
+
+
+```console
+{{#include ../listings/ch07-managing-growing-projects/listing-07-05/output.txt}}
+```
+
+
+
+What happened? Adding the `pub` keyword in front of `mod hosting` makes the
+module public. With this change, if we can access `front_of_house`, we can
+access `hosting`. But the _contents_ of `hosting` are still private; making the
+module public doesn’t make its contents public. The `pub` keyword on a module
+only lets code in its ancestor modules refer to it, not access its inner code.
+Because modules are containers, there’s not much we can do by only making the
+module public; we need to go further and choose to make one or more of the
+items within the module public as well.
+
+The errors in Listing 7-6 say that the `add_to_waitlist` function is private.
+The privacy rules apply to structs, enums, functions, and methods as well as
+modules.
+
+Let’s also make the `add_to_waitlist` function public by adding the `pub`
+keyword before its definition, as in Listing 7-7.
+
+
+
+```rust,noplayground,test_harness
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-07/src/lib.rs:here}}
+```
+
+
+
+Now the code will compile! To see why adding the `pub` keyword lets us use
+these paths in `eat_at_restaurant` with respect to the privacy rules, let’s
+look at the absolute and the relative paths.
+
+In the absolute path, we start with `crate`, the root of our crate’s module
+tree. The `front_of_house` module is defined in the crate root. While
+`front_of_house` isn’t public, because the `eat_at_restaurant` function is
+defined in the same module as `front_of_house` (that is, `eat_at_restaurant`
+and `front_of_house` are siblings), we can refer to `front_of_house` from
+`eat_at_restaurant`. Next is the `hosting` module marked with `pub`. We can
+access the parent module of `hosting`, so we can access `hosting`. Finally, the
+`add_to_waitlist` function is marked with `pub`, and we can access its parent
+module, so this function call works!
+
+In the relative path, the logic is the same as the absolute path except for the
+first step: Rather than starting from the crate root, the path starts from
+`front_of_house`. The `front_of_house` module is defined within the same module
+as `eat_at_restaurant`, so the relative path starting from the module in which
+`eat_at_restaurant` is defined works. Then, because `hosting` and
+`add_to_waitlist` are marked with `pub`, the rest of the path works, and this
+function call is valid!
+
+If you plan to share your library crate so that other projects can use your
+code, your public API is your contract with users of your crate that determines
+how they can interact with your code. There are many considerations around
+managing changes to your public API to make it easier for people to depend on
+your crate. These considerations are beyond the scope of this book; if you’re
+interested in this topic, see [the Rust API Guidelines][api-guidelines].
+
+> #### Best Practices for Packages with a Binary and a Library
+>
+> We mentioned that a package can contain both a _src/main.rs_ binary crate
+> root as well as a _src/lib.rs_ library crate root, and both crates will have
+> the package name by default. Typically, packages with this pattern of
+> containing both a library and a binary crate will have just enough code in the
+> binary crate to start an executable that calls code defined in the library
+> crate. This lets other projects benefit from the most functionality that the
+> package provides because the library crate’s code can be shared.
+>
+> The module tree should be defined in _src/lib.rs_. Then, any public items can
+> be used in the binary crate by starting paths with the name of the package.
+> The binary crate becomes a user of the library crate just like a completely
+> external crate would use the library crate: It can only use the public API.
+> This helps you design a good API; not only are you the author, but you’re
+> also a client!
+>
+> In [Chapter 12][ch12], we’ll demonstrate this organizational
+> practice with a command line program that will contain both a binary crate
+> and a library crate.
+
+### Starting Relative Paths with `super`
+
+We can construct relative paths that begin in the parent module, rather than
+the current module or the crate root, by using `super` at the start of the
+path. This is like starting a filesystem path with the `..` syntax that means
+to go to the parent directory. Using `super` allows us to reference an item
+that we know is in the parent module, which can make rearranging the module
+tree easier when the module is closely related to the parent but the parent
+might be moved elsewhere in the module tree someday.
+
+Consider the code in Listing 7-8 that models the situation in which a chef
+fixes an incorrect order and personally brings it out to the customer. The
+function `fix_incorrect_order` defined in the `back_of_house` module calls the
+function `deliver_order` defined in the parent module by specifying the path to
+`deliver_order`, starting with `super`.
+
+
+
+```rust,noplayground,test_harness
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-08/src/lib.rs}}
+```
+
+
+
+The `fix_incorrect_order` function is in the `back_of_house` module, so we can
+use `super` to go to the parent module of `back_of_house`, which in this case
+is `crate`, the root. From there, we look for `deliver_order` and find it.
+Success! We think the `back_of_house` module and the `deliver_order` function
+are likely to stay in the same relationship to each other and get moved
+together should we decide to reorganize the crate’s module tree. Therefore, we
+used `super` so that we’ll have fewer places to update code in the future if
+this code gets moved to a different module.
+
+### Making Structs and Enums Public
+
+We can also use `pub` to designate structs and enums as public, but there are a
+few extra details to the usage of `pub` with structs and enums. If we use `pub`
+before a struct definition, we make the struct public, but the struct’s fields
+will still be private. We can make each field public or not on a case-by-case
+basis. In Listing 7-9, we’ve defined a public `back_of_house::Breakfast` struct
+with a public `toast` field but a private `seasonal_fruit` field. This models
+the case in a restaurant where the customer can pick the type of bread that
+comes with a meal, but the chef decides which fruit accompanies the meal based
+on what’s in season and in stock. The available fruit changes quickly, so
+customers can’t choose the fruit or even see which fruit they’ll get.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-09/src/lib.rs}}
+```
+
+
+
+Because the `toast` field in the `back_of_house::Breakfast` struct is public,
+in `eat_at_restaurant` we can write and read to the `toast` field using dot
+notation. Notice that we can’t use the `seasonal_fruit` field in
+`eat_at_restaurant`, because `seasonal_fruit` is private. Try uncommenting the
+line modifying the `seasonal_fruit` field value to see what error you get!
+
+Also, note that because `back_of_house::Breakfast` has a private field, the
+struct needs to provide a public associated function that constructs an
+instance of `Breakfast` (we’ve named it `summer` here). If `Breakfast` didn’t
+have such a function, we couldn’t create an instance of `Breakfast` in
+`eat_at_restaurant`, because we couldn’t set the value of the private
+`seasonal_fruit` field in `eat_at_restaurant`.
+
+In contrast, if we make an enum public, all of its variants are then public. We
+only need the `pub` before the `enum` keyword, as shown in Listing 7-10.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-10/src/lib.rs}}
+```
+
+
+
+Because we made the `Appetizer` enum public, we can use the `Soup` and `Salad`
+variants in `eat_at_restaurant`.
+
+Enums aren’t very useful unless their variants are public; it would be annoying
+to have to annotate all enum variants with `pub` in every case, so the default
+for enum variants is to be public. Structs are often useful without their
+fields being public, so struct fields follow the general rule of everything
+being private by default unless annotated with `pub`.
+
+There’s one more situation involving `pub` that we haven’t covered, and that is
+our last module system feature: the `use` keyword. We’ll cover `use` by itself
+first, and then we’ll show how to combine `pub` and `use`.
+
+[pub]: ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html#exposing-paths-with-the-pub-keyword
+[api-guidelines]: https://rust-lang.github.io/api-guidelines/
+[ch12]: ch12-00-an-io-project.html
diff --git a/documents/markdown/rust-book/ch07-04-bringing-paths-into-scope-with-the-use-keyword.md b/documents/markdown/rust-book/ch07-04-bringing-paths-into-scope-with-the-use-keyword.md
new file mode 100644
index 0000000..8397114
--- /dev/null
+++ b/documents/markdown/rust-book/ch07-04-bringing-paths-into-scope-with-the-use-keyword.md
@@ -0,0 +1,314 @@
+## Bringing Paths into Scope with the `use` Keyword
+
+Having to write out the paths to call functions can feel inconvenient and
+repetitive. In Listing 7-7, whether we chose the absolute or relative path to
+the `add_to_waitlist` function, every time we wanted to call `add_to_waitlist`
+we had to specify `front_of_house` and `hosting` too. Fortunately, there’s a
+way to simplify this process: We can create a shortcut to a path with the `use`
+keyword once and then use the shorter name everywhere else in the scope.
+
+In Listing 7-11, we bring the `crate::front_of_house::hosting` module into the
+scope of the `eat_at_restaurant` function so that we only have to specify
+`hosting::add_to_waitlist` to call the `add_to_waitlist` function in
+`eat_at_restaurant`.
+
+
+
+```rust,noplayground,test_harness
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-11/src/lib.rs}}
+```
+
+
+
+Adding `use` and a path in a scope is similar to creating a symbolic link in
+the filesystem. By adding `use crate::front_of_house::hosting` in the crate
+root, `hosting` is now a valid name in that scope, just as though the `hosting`
+module had been defined in the crate root. Paths brought into scope with `use`
+also check privacy, like any other paths.
+
+Note that `use` only creates the shortcut for the particular scope in which the
+`use` occurs. Listing 7-12 moves the `eat_at_restaurant` function into a new
+child module named `customer`, which is then a different scope than the `use`
+statement, so the function body won’t compile.
+
+
+
+```rust,noplayground,test_harness,does_not_compile,ignore
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-12/src/lib.rs}}
+```
+
+
+
+The compiler error shows that the shortcut no longer applies within the
+`customer` module:
+
+```console
+{{#include ../listings/ch07-managing-growing-projects/listing-07-12/output.txt}}
+```
+
+Notice there’s also a warning that the `use` is no longer used in its scope! To
+fix this problem, move the `use` within the `customer` module too, or reference
+the shortcut in the parent module with `super::hosting` within the child
+`customer` module.
+
+### Creating Idiomatic `use` Paths
+
+In Listing 7-11, you might have wondered why we specified `use
+crate::front_of_house::hosting` and then called `hosting::add_to_waitlist` in
+`eat_at_restaurant`, rather than specifying the `use` path all the way out to
+the `add_to_waitlist` function to achieve the same result, as in Listing 7-13.
+
+
+
+```rust,noplayground,test_harness
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-13/src/lib.rs}}
+```
+
+
+
+Although both Listing 7-11 and Listing 7-13 accomplish the same task, Listing
+7-11 is the idiomatic way to bring a function into scope with `use`. Bringing
+the function’s parent module into scope with `use` means we have to specify the
+parent module when calling the function. Specifying the parent module when
+calling the function makes it clear that the function isn’t locally defined
+while still minimizing repetition of the full path. The code in Listing 7-13 is
+unclear as to where `add_to_waitlist` is defined.
+
+On the other hand, when bringing in structs, enums, and other items with `use`,
+it’s idiomatic to specify the full path. Listing 7-14 shows the idiomatic way
+to bring the standard library’s `HashMap` struct into the scope of a binary
+crate.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-14/src/main.rs}}
+```
+
+
+
+There’s no strong reason behind this idiom: It’s just the convention that has
+emerged, and folks have gotten used to reading and writing Rust code this way.
+
+The exception to this idiom is if we’re bringing two items with the same name
+into scope with `use` statements, because Rust doesn’t allow that. Listing 7-15
+shows how to bring two `Result` types into scope that have the same name but
+different parent modules, and how to refer to them.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-15/src/lib.rs:here}}
+```
+
+
+
+As you can see, using the parent modules distinguishes the two `Result` types.
+If instead we specified `use std::fmt::Result` and `use std::io::Result`, we’d
+have two `Result` types in the same scope, and Rust wouldn’t know which one we
+meant when we used `Result`.
+
+### Providing New Names with the `as` Keyword
+
+There’s another solution to the problem of bringing two types of the same name
+into the same scope with `use`: After the path, we can specify `as` and a new
+local name, or _alias_, for the type. Listing 7-16 shows another way to write
+the code in Listing 7-15 by renaming one of the two `Result` types using `as`.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-16/src/lib.rs:here}}
+```
+
+
+
+In the second `use` statement, we chose the new name `IoResult` for the
+`std::io::Result` type, which won’t conflict with the `Result` from `std::fmt`
+that we’ve also brought into scope. Listing 7-15 and Listing 7-16 are
+considered idiomatic, so the choice is up to you!
+
+### Re-exporting Names with `pub use`
+
+When we bring a name into scope with the `use` keyword, the name is private to
+the scope into which we imported it. To enable code outside that scope to refer
+to that name as if it had been defined in that scope, we can combine `pub` and
+`use`. This technique is called _re-exporting_ because we’re bringing an item
+into scope but also making that item available for others to bring into their
+scope.
+
+Listing 7-17 shows the code in Listing 7-11 with `use` in the root module
+changed to `pub use`.
+
+
+
+```rust,noplayground,test_harness
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-17/src/lib.rs}}
+```
+
+
+
+Before this change, external code would have to call the `add_to_waitlist`
+function by using the path
+`restaurant::front_of_house::hosting::add_to_waitlist()`, which also would have
+required the `front_of_house` module to be marked as `pub`. Now that this `pub
+use` has re-exported the `hosting` module from the root module, external code
+can use the path `restaurant::hosting::add_to_waitlist()` instead.
+
+Re-exporting is useful when the internal structure of your code is different
+from how programmers calling your code would think about the domain. For
+example, in this restaurant metaphor, the people running the restaurant think
+about “front of house” and “back of house.” But customers visiting a restaurant
+probably won’t think about the parts of the restaurant in those terms. With `pub
+use`, we can write our code with one structure but expose a different structure.
+Doing so makes our library well organized for programmers working on the library
+and programmers calling the library. We’ll look at another example of `pub use`
+and how it affects your crate’s documentation in [“Exporting a Convenient Public
+API”][ch14-pub-use] in Chapter 14.
+
+### Using External Packages
+
+In Chapter 2, we programmed a guessing game project that used an external
+package called `rand` to get random numbers. To use `rand` in our project, we
+added this line to _Cargo.toml_:
+
+
+
+
+
+```toml
+{{#include ../listings/ch02-guessing-game-tutorial/listing-02-02/Cargo.toml:9:}}
+```
+
+
+
+Adding `rand` as a dependency in _Cargo.toml_ tells Cargo to download the
+`rand` package and any dependencies from [crates.io](https://crates.io/) and
+make `rand` available to our project.
+
+Then, to bring `rand` definitions into the scope of our package, we added a
+`use` line starting with the name of the crate, `rand`, and listed the items we
+wanted to bring into scope. Recall that in [“Generating a Random
+Number”][rand] in Chapter 2, we brought the `Rng` trait into
+scope and called the `rand::thread_rng` function:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch02-guessing-game-tutorial/listing-02-03/src/main.rs:ch07-04}}
+```
+
+Members of the Rust community have made many packages available at
+[crates.io](https://crates.io/), and pulling any of them into your package
+involves these same steps: listing them in your package’s _Cargo.toml_ file and
+using `use` to bring items from their crates into scope.
+
+Note that the standard `std` library is also a crate that’s external to our
+package. Because the standard library is shipped with the Rust language, we
+don’t need to change _Cargo.toml_ to include `std`. But we do need to refer to
+it with `use` to bring items from there into our package’s scope. For example,
+with `HashMap` we would use this line:
+
+```rust
+use std::collections::HashMap;
+```
+
+This is an absolute path starting with `std`, the name of the standard library
+crate.
+
+
+
+
+
+### Using Nested Paths to Clean Up `use` Lists
+
+If we’re using multiple items defined in the same crate or same module, listing
+each item on its own line can take up a lot of vertical space in our files. For
+example, these two `use` statements we had in the guessing game in Listing 2-4
+bring items from `std` into scope:
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/no-listing-01-use-std-unnested/src/main.rs:here}}
+```
+
+
+
+Instead, we can use nested paths to bring the same items into scope in one
+line. We do this by specifying the common part of the path, followed by two
+colons, and then curly brackets around a list of the parts of the paths that
+differ, as shown in Listing 7-18.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-18/src/main.rs:here}}
+```
+
+
+
+In bigger programs, bringing many items into scope from the same crate or
+module using nested paths can reduce the number of separate `use` statements
+needed by a lot!
+
+We can use a nested path at any level in a path, which is useful when combining
+two `use` statements that share a subpath. For example, Listing 7-19 shows two
+`use` statements: one that brings `std::io` into scope and one that brings
+`std::io::Write` into scope.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-19/src/lib.rs}}
+```
+
+
+
+The common part of these two paths is `std::io`, and that’s the complete first
+path. To merge these two paths into one `use` statement, we can use `self` in
+the nested path, as shown in Listing 7-20.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-20/src/lib.rs}}
+```
+
+
+
+This line brings `std::io` and `std::io::Write` into scope.
+
+
+
+
+
+### Importing Items with the Glob Operator
+
+If we want to bring _all_ public items defined in a path into scope, we can
+specify that path followed by the `*` glob operator:
+
+```rust
+use std::collections::*;
+```
+
+This `use` statement brings all public items defined in `std::collections` into
+the current scope. Be careful when using the glob operator! Glob can make it
+harder to tell what names are in scope and where a name used in your program
+was defined. Additionally, if the dependency changes its definitions, what
+you’ve imported changes as well, which may lead to compiler errors when you
+upgrade the dependency if the dependency adds a definition with the same name
+as a definition of yours in the same scope, for example.
+
+The glob operator is often used when testing to bring everything under test into
+the `tests` module; we’ll talk about that in [“How to Write
+Tests”][writing-tests] in Chapter 11. The glob operator is also
+sometimes used as part of the prelude pattern: See [the standard library
+documentation](../std/prelude/index.html#other-preludes) for more
+information on that pattern.
+
+[ch14-pub-use]: ch14-02-publishing-to-crates-io.html#exporting-a-convenient-public-api
+[rand]: ch02-00-guessing-game-tutorial.html#generating-a-random-number
+[writing-tests]: ch11-01-writing-tests.html#how-to-write-tests
diff --git a/documents/markdown/rust-book/ch07-05-separating-modules-into-different-files.md b/documents/markdown/rust-book/ch07-05-separating-modules-into-different-files.md
new file mode 100644
index 0000000..ed3f49f
--- /dev/null
+++ b/documents/markdown/rust-book/ch07-05-separating-modules-into-different-files.md
@@ -0,0 +1,129 @@
+## Separating Modules into Different Files
+
+So far, all the examples in this chapter defined multiple modules in one file.
+When modules get large, you might want to move their definitions to a separate
+file to make the code easier to navigate.
+
+For example, let’s start from the code in Listing 7-17 that had multiple
+restaurant modules. We’ll extract modules into files instead of having all the
+modules defined in the crate root file. In this case, the crate root file is
+_src/lib.rs_, but this procedure also works with binary crates whose crate root
+file is _src/main.rs_.
+
+First, we’ll extract the `front_of_house` module to its own file. Remove the
+code inside the curly brackets for the `front_of_house` module, leaving only
+the `mod front_of_house;` declaration, so that _src/lib.rs_ contains the code
+shown in Listing 7-21. Note that this won’t compile until we create the
+_src/front_of_house.rs_ file in Listing 7-22.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-21-and-22/src/lib.rs}}
+```
+
+
+
+Next, place the code that was in the curly brackets into a new file named
+_src/front_of_house.rs_, as shown in Listing 7-22. The compiler knows to look
+in this file because it came across the module declaration in the crate root
+with the name `front_of_house`.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/listing-07-21-and-22/src/front_of_house.rs}}
+```
+
+
+
+Note that you only need to load a file using a `mod` declaration _once_ in your
+module tree. Once the compiler knows the file is part of the project (and knows
+where in the module tree the code resides because of where you’ve put the `mod`
+statement), other files in your project should refer to the loaded file’s code
+using a path to where it was declared, as covered in the [“Paths for Referring
+to an Item in the Module Tree”][paths] section. In other words,
+`mod` is _not_ an “include” operation that you may have seen in other
+programming languages.
+
+Next, we’ll extract the `hosting` module to its own file. The process is a bit
+different because `hosting` is a child module of `front_of_house`, not of the
+root module. We’ll place the file for `hosting` in a new directory that will be
+named for its ancestors in the module tree, in this case _src/front_of_house_.
+
+To start moving `hosting`, we change _src/front_of_house.rs_ to contain only
+the declaration of the `hosting` module:
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/no-listing-02-extracting-hosting/src/front_of_house.rs}}
+```
+
+
+
+Then, we create a _src/front_of_house_ directory and a _hosting.rs_ file to
+contain the definitions made in the `hosting` module:
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch07-managing-growing-projects/no-listing-02-extracting-hosting/src/front_of_house/hosting.rs}}
+```
+
+
+
+If we instead put _hosting.rs_ in the _src_ directory, the compiler would
+expect the _hosting.rs_ code to be in a `hosting` module declared in the crate
+root and not declared as a child of the `front_of_house` module. The
+compiler’s rules for which files to check for which modules’ code mean the
+directories and files more closely match the module tree.
+
+> ### Alternate File Paths
+>
+> So far we’ve covered the most idiomatic file paths the Rust compiler uses,
+> but Rust also supports an older style of file path. For a module named
+> `front_of_house` declared in the crate root, the compiler will look for the
+> module’s code in:
+>
+> - _src/front_of_house.rs_ (what we covered)
+> - _src/front_of_house/mod.rs_ (older style, still supported path)
+>
+> For a module named `hosting` that is a submodule of `front_of_house`, the
+> compiler will look for the module’s code in:
+>
+> - _src/front_of_house/hosting.rs_ (what we covered)
+> - _src/front_of_house/hosting/mod.rs_ (older style, still supported path)
+>
+> If you use both styles for the same module, you’ll get a compiler error.
+> Using a mix of both styles for different modules in the same project is
+> allowed but might be confusing for people navigating your project.
+>
+> The main downside to the style that uses files named _mod.rs_ is that your
+> project can end up with many files named _mod.rs_, which can get confusing
+> when you have them open in your editor at the same time.
+
+We’ve moved each module’s code to a separate file, and the module tree remains
+the same. The function calls in `eat_at_restaurant` will work without any
+modification, even though the definitions live in different files. This
+technique lets you move modules to new files as they grow in size.
+
+Note that the `pub use crate::front_of_house::hosting` statement in
+_src/lib.rs_ also hasn’t changed, nor does `use` have any impact on what files
+are compiled as part of the crate. The `mod` keyword declares modules, and Rust
+looks in a file with the same name as the module for the code that goes into
+that module.
+
+## Summary
+
+Rust lets you split a package into multiple crates and a crate into modules so
+that you can refer to items defined in one module from another module. You can
+do this by specifying absolute or relative paths. These paths can be brought
+into scope with a `use` statement so that you can use a shorter path for
+multiple uses of the item in that scope. Module code is private by default, but
+you can make definitions public by adding the `pub` keyword.
+
+In the next chapter, we’ll look at some collection data structures in the
+standard library that you can use in your neatly organized code.
+
+[paths]: ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html
diff --git a/documents/markdown/rust-book/ch08-00-common-collections.md b/documents/markdown/rust-book/ch08-00-common-collections.md
new file mode 100644
index 0000000..550ee2c
--- /dev/null
+++ b/documents/markdown/rust-book/ch08-00-common-collections.md
@@ -0,0 +1,25 @@
+# Common Collections
+
+Rust’s standard library includes a number of very useful data structures called
+_collections_. Most other data types represent one specific value, but
+collections can contain multiple values. Unlike the built-in array and tuple
+types, the data that these collections point to is stored on the heap, which
+means the amount of data does not need to be known at compile time and can grow
+or shrink as the program runs. Each kind of collection has different
+capabilities and costs, and choosing an appropriate one for your current
+situation is a skill you’ll develop over time. In this chapter, we’ll discuss
+three collections that are used very often in Rust programs:
+
+- A _vector_ allows you to store a variable number of values next to each other.
+- A _string_ is a collection of characters. We’ve mentioned the `String` type
+ previously, but in this chapter, we’ll talk about it in depth.
+- A _hash map_ allows you to associate a value with a specific key. It’s a
+ particular implementation of the more general data structure called a _map_.
+
+To learn about the other kinds of collections provided by the standard library,
+see [the documentation][collections].
+
+We’ll discuss how to create and update vectors, strings, and hash maps, as well
+as what makes each special.
+
+[collections]: ../std/collections/index.html
diff --git a/documents/markdown/rust-book/ch08-01-vectors.md b/documents/markdown/rust-book/ch08-01-vectors.md
new file mode 100644
index 0000000..25b8f67
--- /dev/null
+++ b/documents/markdown/rust-book/ch08-01-vectors.md
@@ -0,0 +1,260 @@
+## Storing Lists of Values with Vectors
+
+The first collection type we’ll look at is `Vec`, also known as a vector.
+Vectors allow you to store more than one value in a single data structure that
+puts all the values next to each other in memory. Vectors can only store values
+of the same type. They are useful when you have a list of items, such as the
+lines of text in a file or the prices of items in a shopping cart.
+
+### Creating a New Vector
+
+To create a new, empty vector, we call the `Vec::new` function, as shown in
+Listing 8-1.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-01/src/main.rs:here}}
+```
+
+
+
+Note that we added a type annotation here. Because we aren’t inserting any
+values into this vector, Rust doesn’t know what kind of elements we intend to
+store. This is an important point. Vectors are implemented using generics;
+we’ll cover how to use generics with your own types in Chapter 10. For now,
+know that the `Vec` type provided by the standard library can hold any type.
+When we create a vector to hold a specific type, we can specify the type within
+angle brackets. In Listing 8-1, we’ve told Rust that the `Vec` in `v` will
+hold elements of the `i32` type.
+
+More often, you’ll create a `Vec` with initial values, and Rust will infer
+the type of value you want to store, so you rarely need to do this type
+annotation. Rust conveniently provides the `vec!` macro, which will create a
+new vector that holds the values you give it. Listing 8-2 creates a new
+`Vec` that holds the values `1`, `2`, and `3`. The integer type is `i32`
+because that’s the default integer type, as we discussed in the [“Data
+Types”][data-types] section of Chapter 3.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-02/src/main.rs:here}}
+```
+
+
+
+Because we’ve given initial `i32` values, Rust can infer that the type of `v`
+is `Vec`, and the type annotation isn’t necessary. Next, we’ll look at how
+to modify a vector.
+
+### Updating a Vector
+
+To create a vector and then add elements to it, we can use the `push` method,
+as shown in Listing 8-3.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-03/src/main.rs:here}}
+```
+
+
+
+As with any variable, if we want to be able to change its value, we need to
+make it mutable using the `mut` keyword, as discussed in Chapter 3. The numbers
+we place inside are all of type `i32`, and Rust infers this from the data, so
+we don’t need the `Vec` annotation.
+
+### Reading Elements of Vectors
+
+There are two ways to reference a value stored in a vector: via indexing or by
+using the `get` method. In the following examples, we’ve annotated the types of
+the values that are returned from these functions for extra clarity.
+
+Listing 8-4 shows both methods of accessing a value in a vector, with indexing
+syntax and the `get` method.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-04/src/main.rs:here}}
+```
+
+
+
+Note a few details here. We use the index value of `2` to get the third element
+because vectors are indexed by number, starting at zero. Using `&` and `[]`
+gives us a reference to the element at the index value. When we use the `get`
+method with the index passed as an argument, we get an `Option<&T>` that we can
+use with `match`.
+
+Rust provides these two ways to reference an element so that you can choose how
+the program behaves when you try to use an index value outside the range of
+existing elements. As an example, let’s see what happens when we have a vector
+of five elements and then we try to access an element at index 100 with each
+technique, as shown in Listing 8-5.
+
+
+
+```rust,should_panic,panics
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-05/src/main.rs:here}}
+```
+
+
+
+When we run this code, the first `[]` method will cause the program to panic
+because it references a nonexistent element. This method is best used when you
+want your program to crash if there’s an attempt to access an element past the
+end of the vector.
+
+When the `get` method is passed an index that is outside the vector, it returns
+`None` without panicking. You would use this method if accessing an element
+beyond the range of the vector may happen occasionally under normal
+circumstances. Your code will then have logic to handle having either
+`Some(&element)` or `None`, as discussed in Chapter 6. For example, the index
+could be coming from a person entering a number. If they accidentally enter a
+number that’s too large and the program gets a `None` value, you could tell the
+user how many items are in the current vector and give them another chance to
+enter a valid value. That would be more user-friendly than crashing the program
+due to a typo!
+
+When the program has a valid reference, the borrow checker enforces the
+ownership and borrowing rules (covered in Chapter 4) to ensure that this
+reference and any other references to the contents of the vector remain valid.
+Recall the rule that states you can’t have mutable and immutable references in
+the same scope. That rule applies in Listing 8-6, where we hold an immutable
+reference to the first element in a vector and try to add an element to the
+end. This program won’t work if we also try to refer to that element later in
+the function.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-06/src/main.rs:here}}
+```
+
+
+
+Compiling this code will result in this error:
+
+```console
+{{#include ../listings/ch08-common-collections/listing-08-06/output.txt}}
+```
+
+The code in Listing 8-6 might look like it should work: Why should a reference
+to the first element care about changes at the end of the vector? This error is
+due to the way vectors work: Because vectors put the values next to each other
+in memory, adding a new element onto the end of the vector might require
+allocating new memory and copying the old elements to the new space, if there
+isn’t enough room to put all the elements next to each other where the vector
+is currently stored. In that case, the reference to the first element would be
+pointing to deallocated memory. The borrowing rules prevent programs from
+ending up in that situation.
+
+> Note: For more on the implementation details of the `Vec` type, see [“The
+> Rustonomicon”][nomicon].
+
+### Iterating Over the Values in a Vector
+
+To access each element in a vector in turn, we would iterate through all of the
+elements rather than use indices to access one at a time. Listing 8-7 shows how
+to use a `for` loop to get immutable references to each element in a vector of
+`i32` values and print them.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-07/src/main.rs:here}}
+```
+
+
+
+We can also iterate over mutable references to each element in a mutable vector
+in order to make changes to all the elements. The `for` loop in Listing 8-8
+will add `50` to each element.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-08/src/main.rs:here}}
+```
+
+
+
+To change the value that the mutable reference refers to, we have to use the
+`*` dereference operator to get to the value in `i` before we can use the `+=`
+operator. We’ll talk more about the dereference operator in the [“Following the
+Reference to the Value”][deref] section of Chapter 15.
+
+Iterating over a vector, whether immutably or mutably, is safe because of the
+borrow checker’s rules. If we attempted to insert or remove items in the `for`
+loop bodies in Listing 8-7 and Listing 8-8, we would get a compiler error
+similar to the one we got with the code in Listing 8-6. The reference to the
+vector that the `for` loop holds prevents simultaneous modification of the
+whole vector.
+
+### Using an Enum to Store Multiple Types
+
+Vectors can only store values that are of the same type. This can be
+inconvenient; there are definitely use cases for needing to store a list of
+items of different types. Fortunately, the variants of an enum are defined
+under the same enum type, so when we need one type to represent elements of
+different types, we can define and use an enum!
+
+For example, say we want to get values from a row in a spreadsheet in which
+some of the columns in the row contain integers, some floating-point numbers,
+and some strings. We can define an enum whose variants will hold the different
+value types, and all the enum variants will be considered the same type: that
+of the enum. Then, we can create a vector to hold that enum and so, ultimately,
+hold different types. We’ve demonstrated this in Listing 8-9.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-09/src/main.rs:here}}
+```
+
+
+
+Rust needs to know what types will be in the vector at compile time so that it
+knows exactly how much memory on the heap will be needed to store each element.
+We must also be explicit about what types are allowed in this vector. If Rust
+allowed a vector to hold any type, there would be a chance that one or more of
+the types would cause errors with the operations performed on the elements of
+the vector. Using an enum plus a `match` expression means that Rust will ensure
+at compile time that every possible case is handled, as discussed in Chapter 6.
+
+If you don’t know the exhaustive set of types a program will get at runtime to
+store in a vector, the enum technique won’t work. Instead, you can use a trait
+object, which we’ll cover in Chapter 18.
+
+Now that we’ve discussed some of the most common ways to use vectors, be sure
+to review [the API documentation][vec-api] for all of the many
+useful methods defined on `Vec` by the standard library. For example, in
+addition to `push`, a `pop` method removes and returns the last element.
+
+### Dropping a Vector Drops Its Elements
+
+Like any other `struct`, a vector is freed when it goes out of scope, as
+annotated in Listing 8-10.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-10/src/main.rs:here}}
+```
+
+
+
+When the vector gets dropped, all of its contents are also dropped, meaning the
+integers it holds will be cleaned up. The borrow checker ensures that any
+references to contents of a vector are only used while the vector itself is
+valid.
+
+Let’s move on to the next collection type: `String`!
+
+[data-types]: ch03-02-data-types.html#data-types
+[nomicon]: ../nomicon/vec/vec.html
+[vec-api]: ../std/vec/struct.Vec.html
+[deref]: ch15-02-deref.html#following-the-pointer-to-the-value-with-the-dereference-operator
diff --git a/documents/markdown/rust-book/ch08-02-strings.md b/documents/markdown/rust-book/ch08-02-strings.md
new file mode 100644
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--- /dev/null
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@@ -0,0 +1,447 @@
+## Storing UTF-8 Encoded Text with Strings
+
+We talked about strings in Chapter 4, but we’ll look at them in more depth now.
+New Rustaceans commonly get stuck on strings for a combination of three
+reasons: Rust’s propensity for exposing possible errors, strings being a more
+complicated data structure than many programmers give them credit for, and
+UTF-8. These factors combine in a way that can seem difficult when you’re
+coming from other programming languages.
+
+We discuss strings in the context of collections because strings are
+implemented as a collection of bytes, plus some methods to provide useful
+functionality when those bytes are interpreted as text. In this section, we’ll
+talk about the operations on `String` that every collection type has, such as
+creating, updating, and reading. We’ll also discuss the ways in which `String`
+is different from the other collections, namely, how indexing into a `String` is
+complicated by the differences between how people and computers interpret
+`String` data.
+
+
+
+
+
+### Defining Strings
+
+We’ll first define what we mean by the term _string_. Rust has only one string
+type in the core language, which is the string slice `str` that is usually seen
+in its borrowed form, `&str`. In Chapter 4, we talked about string slices,
+which are references to some UTF-8 encoded string data stored elsewhere. String
+literals, for example, are stored in the program’s binary and are therefore
+string slices.
+
+The `String` type, which is provided by Rust’s standard library rather than
+coded into the core language, is a growable, mutable, owned, UTF-8 encoded
+string type. When Rustaceans refer to “strings” in Rust, they might be
+referring to either the `String` or the string slice `&str` types, not just one
+of those types. Although this section is largely about `String`, both types are
+used heavily in Rust’s standard library, and both `String` and string slices
+are UTF-8 encoded.
+
+### Creating a New String
+
+Many of the same operations available with `Vec` are available with `String`
+as well because `String` is actually implemented as a wrapper around a vector
+of bytes with some extra guarantees, restrictions, and capabilities. An example
+of a function that works the same way with `Vec` and `String` is the `new`
+function to create an instance, shown in Listing 8-11.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-11/src/main.rs:here}}
+```
+
+
+
+This line creates a new, empty string called `s`, into which we can then load
+data. Often, we’ll have some initial data with which we want to start the
+string. For that, we use the `to_string` method, which is available on any type
+that implements the `Display` trait, as string literals do. Listing 8-12 shows
+two examples.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-12/src/main.rs:here}}
+```
+
+
+
+This code creates a string containing `initial contents`.
+
+We can also use the function `String::from` to create a `String` from a string
+literal. The code in Listing 8-13 is equivalent to the code in Listing 8-12
+that uses `to_string`.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-13/src/main.rs:here}}
+```
+
+
+
+Because strings are used for so many things, we can use many different generic
+APIs for strings, providing us with a lot of options. Some of them can seem
+redundant, but they all have their place! In this case, `String::from` and
+`to_string` do the same thing, so which one you choose is a matter of style and
+readability.
+
+Remember that strings are UTF-8 encoded, so we can include any properly encoded
+data in them, as shown in Listing 8-14.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-14/src/main.rs:here}}
+```
+
+
+
+All of these are valid `String` values.
+
+### Updating a String
+
+A `String` can grow in size and its contents can change, just like the contents
+of a `Vec`, if you push more data into it. In addition, you can conveniently
+use the `+` operator or the `format!` macro to concatenate `String` values.
+
+
+
+
+
+#### Appending with `push_str` or `push`
+
+We can grow a `String` by using the `push_str` method to append a string slice,
+as shown in Listing 8-15.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-15/src/main.rs:here}}
+```
+
+
+
+After these two lines, `s` will contain `foobar`. The `push_str` method takes a
+string slice because we don’t necessarily want to take ownership of the
+parameter. For example, in the code in Listing 8-16, we want to be able to use
+`s2` after appending its contents to `s1`.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-16/src/main.rs:here}}
+```
+
+
+
+If the `push_str` method took ownership of `s2`, we wouldn’t be able to print
+its value on the last line. However, this code works as we’d expect!
+
+The `push` method takes a single character as a parameter and adds it to the
+`String`. Listing 8-17 adds the letter _l_ to a `String` using the `push`
+method.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-17/src/main.rs:here}}
+```
+
+
+
+As a result, `s` will contain `lol`.
+
+
+
+
+
+#### Concatenating with `+` or `format!`
+
+Often, you’ll want to combine two existing strings. One way to do so is to use
+the `+` operator, as shown in Listing 8-18.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-18/src/main.rs:here}}
+```
+
+
+
+The string `s3` will contain `Hello, world!`. The reason `s1` is no longer
+valid after the addition, and the reason we used a reference to `s2`, has to do
+with the signature of the method that’s called when we use the `+` operator.
+The `+` operator uses the `add` method, whose signature looks something like
+this:
+
+```rust,ignore
+fn add(self, s: &str) -> String {
+```
+
+In the standard library, you’ll see `add` defined using generics and associated
+types. Here, we’ve substituted in concrete types, which is what happens when we
+call this method with `String` values. We’ll discuss generics in Chapter 10.
+This signature gives us the clues we need in order to understand the tricky
+bits of the `+` operator.
+
+First, `s2` has an `&`, meaning that we’re adding a reference of the second
+string to the first string. This is because of the `s` parameter in the `add`
+function: We can only add a string slice to a `String`; we can’t add two
+`String` values together. But wait—the type of `&s2` is `&String`, not `&str`,
+as specified in the second parameter to `add`. So, why does Listing 8-18
+compile?
+
+The reason we’re able to use `&s2` in the call to `add` is that the compiler
+can coerce the `&String` argument into a `&str`. When we call the `add` method,
+Rust uses a deref coercion, which here turns `&s2` into `&s2[..]`. We’ll
+discuss deref coercion in more depth in Chapter 15. Because `add` does not take
+ownership of the `s` parameter, `s2` will still be a valid `String` after this
+operation.
+
+Second, we can see in the signature that `add` takes ownership of `self`
+because `self` does _not_ have an `&`. This means `s1` in Listing 8-18 will be
+moved into the `add` call and will no longer be valid after that. So, although
+`let s3 = s1 + &s2;` looks like it will copy both strings and create a new one,
+this statement actually takes ownership of `s1`, appends a copy of the contents
+of `s2`, and then returns ownership of the result. In other words, it looks
+like it’s making a lot of copies, but it isn’t; the implementation is more
+efficient than copying.
+
+If we need to concatenate multiple strings, the behavior of the `+` operator
+gets unwieldy:
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/no-listing-01-concat-multiple-strings/src/main.rs:here}}
+```
+
+At this point, `s` will be `tic-tac-toe`. With all of the `+` and `"`
+characters, it’s difficult to see what’s going on. For combining strings in
+more complicated ways, we can instead use the `format!` macro:
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/no-listing-02-format/src/main.rs:here}}
+```
+
+This code also sets `s` to `tic-tac-toe`. The `format!` macro works like
+`println!`, but instead of printing the output to the screen, it returns a
+`String` with the contents. The version of the code using `format!` is much
+easier to read, and the code generated by the `format!` macro uses references
+so that this call doesn’t take ownership of any of its parameters.
+
+### Indexing into Strings
+
+In many other programming languages, accessing individual characters in a
+string by referencing them by index is a valid and common operation. However,
+if you try to access parts of a `String` using indexing syntax in Rust, you’ll
+get an error. Consider the invalid code in Listing 8-19.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-19/src/main.rs:here}}
+```
+
+
+
+This code will result in the following error:
+
+```console
+{{#include ../listings/ch08-common-collections/listing-08-19/output.txt}}
+```
+
+The error tells the story: Rust strings don’t support indexing. But why not? To
+answer that question, we need to discuss how Rust stores strings in memory.
+
+#### Internal Representation
+
+A `String` is a wrapper over a `Vec`. Let’s look at some of our properly
+encoded UTF-8 example strings from Listing 8-14. First, this one:
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-14/src/main.rs:spanish}}
+```
+
+In this case, `len` will be `4`, which means the vector storing the string
+`"Hola"` is 4 bytes long. Each of these letters takes 1 byte when encoded in
+UTF-8. The following line, however, may surprise you (note that this string
+begins with the capital Cyrillic letter _Ze_, not the number 3):
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-14/src/main.rs:russian}}
+```
+
+If you were asked how long the string is, you might say 12. In fact, Rust’s
+answer is 24: That’s the number of bytes it takes to encode “Здравствуйте” in
+UTF-8, because each Unicode scalar value in that string takes 2 bytes of
+storage. Therefore, an index into the string’s bytes will not always correlate
+to a valid Unicode scalar value. To demonstrate, consider this invalid Rust
+code:
+
+```rust,ignore,does_not_compile
+let hello = "Здравствуйте";
+let answer = &hello[0];
+```
+
+You already know that `answer` will not be `З`, the first letter. When encoded
+in UTF-8, the first byte of `З` is `208` and the second is `151`, so it would
+seem that `answer` should in fact be `208`, but `208` is not a valid character
+on its own. Returning `208` is likely not what a user would want if they asked
+for the first letter of this string; however, that’s the only data that Rust
+has at byte index 0. Users generally don’t want the byte value returned, even
+if the string contains only Latin letters: If `&"hi"[0]` were valid code that
+returned the byte value, it would return `104`, not `h`.
+
+The answer, then, is that to avoid returning an unexpected value and causing
+bugs that might not be discovered immediately, Rust doesn’t compile this code
+at all and prevents misunderstandings early in the development process.
+
+
+
+
+
+#### Bytes, Scalar Values, and Grapheme Clusters
+
+Another point about UTF-8 is that there are actually three relevant ways to
+look at strings from Rust’s perspective: as bytes, scalar values, and grapheme
+clusters (the closest thing to what we would call _letters_).
+
+If we look at the Hindi word “नमस्ते” written in the Devanagari script, it is
+stored as a vector of `u8` values that looks like this:
+
+```text
+[224, 164, 168, 224, 164, 174, 224, 164, 184, 224, 165, 141, 224, 164, 164,
+224, 165, 135]
+```
+
+That’s 18 bytes and is how computers ultimately store this data. If we look at
+them as Unicode scalar values, which are what Rust’s `char` type is, those
+bytes look like this:
+
+```text
+['न', 'म', 'स', '्', 'त', 'े']
+```
+
+There are six `char` values here, but the fourth and sixth are not letters:
+They’re diacritics that don’t make sense on their own. Finally, if we look at
+them as grapheme clusters, we’d get what a person would call the four letters
+that make up the Hindi word:
+
+```text
+["न", "म", "स्", "ते"]
+```
+
+Rust provides different ways of interpreting the raw string data that computers
+store so that each program can choose the interpretation it needs, no matter
+what human language the data is in.
+
+A final reason Rust doesn’t allow us to index into a `String` to get a
+character is that indexing operations are expected to always take constant time
+(O(1)). But it isn’t possible to guarantee that performance with a `String`,
+because Rust would have to walk through the contents from the beginning to the
+index to determine how many valid characters there were.
+
+### Slicing Strings
+
+Indexing into a string is often a bad idea because it’s not clear what the
+return type of the string-indexing operation should be: a byte value, a
+character, a grapheme cluster, or a string slice. If you really need to use
+indices to create string slices, therefore, Rust asks you to be more specific.
+
+Rather than indexing using `[]` with a single number, you can use `[]` with a
+range to create a string slice containing particular bytes:
+
+```rust
+let hello = "Здравствуйте";
+
+let s = &hello[0..4];
+```
+
+Here, `s` will be a `&str` that contains the first 4 bytes of the string.
+Earlier, we mentioned that each of these characters was 2 bytes, which means
+`s` will be `Зд`.
+
+If we were to try to slice only part of a character’s bytes with something like
+`&hello[0..1]`, Rust would panic at runtime in the same way as if an invalid
+index were accessed in a vector:
+
+```console
+{{#include ../listings/ch08-common-collections/output-only-01-not-char-boundary/output.txt}}
+```
+
+You should use caution when creating string slices with ranges, because doing
+so can crash your program.
+
+
+
+
+
+### Iterating Over Strings
+
+The best way to operate on pieces of strings is to be explicit about whether
+you want characters or bytes. For individual Unicode scalar values, use the
+`chars` method. Calling `chars` on “Зд” separates out and returns two values of
+type `char`, and you can iterate over the result to access each element:
+
+```rust
+for c in "Зд".chars() {
+ println!("{c}");
+}
+```
+
+This code will print the following:
+
+```text
+З
+д
+```
+
+Alternatively, the `bytes` method returns each raw byte, which might be
+appropriate for your domain:
+
+```rust
+for b in "Зд".bytes() {
+ println!("{b}");
+}
+```
+
+This code will print the 4 bytes that make up this string:
+
+```text
+208
+151
+208
+180
+```
+
+But be sure to remember that valid Unicode scalar values may be made up of more
+than 1 byte.
+
+Getting grapheme clusters from strings, as with the Devanagari script, is
+complex, so this functionality is not provided by the standard library. Crates
+are available on [crates.io](https://crates.io/) if this is the
+functionality you need.
+
+
+
+
+
+### Handling the Complexities of Strings
+
+To summarize, strings are complicated. Different programming languages make
+different choices about how to present this complexity to the programmer. Rust
+has chosen to make the correct handling of `String` data the default behavior
+for all Rust programs, which means programmers have to put more thought into
+handling UTF-8 data up front. This trade-off exposes more of the complexity of
+strings than is apparent in other programming languages, but it prevents you
+from having to handle errors involving non-ASCII characters later in your
+development life cycle.
+
+The good news is that the standard library offers a lot of functionality built
+off the `String` and `&str` types to help handle these complex situations
+correctly. Be sure to check out the documentation for useful methods like
+`contains` for searching in a string and `replace` for substituting parts of a
+string with another string.
+
+Let’s switch to something a bit less complex: hash maps!
diff --git a/documents/markdown/rust-book/ch08-03-hash-maps.md b/documents/markdown/rust-book/ch08-03-hash-maps.md
new file mode 100644
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--- /dev/null
+++ b/documents/markdown/rust-book/ch08-03-hash-maps.md
@@ -0,0 +1,252 @@
+## Storing Keys with Associated Values in Hash Maps
+
+The last of our common collections is the hash map. The type `HashMap`
+stores a mapping of keys of type `K` to values of type `V` using a _hashing
+function_, which determines how it places these keys and values into memory.
+Many programming languages support this kind of data structure, but they often
+use a different name, such as _hash_, _map_, _object_, _hash table_,
+_dictionary_, or _associative array_, just to name a few.
+
+Hash maps are useful when you want to look up data not by using an index, as
+you can with vectors, but by using a key that can be of any type. For example,
+in a game, you could keep track of each team’s score in a hash map in which
+each key is a team’s name and the values are each team’s score. Given a team
+name, you can retrieve its score.
+
+We’ll go over the basic API of hash maps in this section, but many more goodies
+are hiding in the functions defined on `HashMap` by the standard library.
+As always, check the standard library documentation for more information.
+
+### Creating a New Hash Map
+
+One way to create an empty hash map is to use `new` and to add elements with
+`insert`. In Listing 8-20, we’re keeping track of the scores of two teams whose
+names are _Blue_ and _Yellow_. The Blue team starts with 10 points, and the
+Yellow team starts with 50.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-20/src/main.rs:here}}
+```
+
+
+
+Note that we need to first `use` the `HashMap` from the collections portion of
+the standard library. Of our three common collections, this one is the least
+often used, so it’s not included in the features brought into scope
+automatically in the prelude. Hash maps also have less support from the
+standard library; there’s no built-in macro to construct them, for example.
+
+Just like vectors, hash maps store their data on the heap. This `HashMap` has
+keys of type `String` and values of type `i32`. Like vectors, hash maps are
+homogeneous: All of the keys must have the same type, and all of the values
+must have the same type.
+
+### Accessing Values in a Hash Map
+
+We can get a value out of the hash map by providing its key to the `get`
+method, as shown in Listing 8-21.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-21/src/main.rs:here}}
+```
+
+
+
+Here, `score` will have the value that’s associated with the Blue team, and the
+result will be `10`. The `get` method returns an `Option<&V>`; if there’s no
+value for that key in the hash map, `get` will return `None`. This program
+handles the `Option` by calling `copied` to get an `Option` rather than an
+`Option<&i32>`, then `unwrap_or` to set `score` to zero if `scores` doesn’t
+have an entry for the key.
+
+We can iterate over each key-value pair in a hash map in a similar manner as we
+do with vectors, using a `for` loop:
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/no-listing-03-iterate-over-hashmap/src/main.rs:here}}
+```
+
+This code will print each pair in an arbitrary order:
+
+```text
+Yellow: 50
+Blue: 10
+```
+
+
+
+
+
+### Managing Ownership in Hash Maps
+
+For types that implement the `Copy` trait, like `i32`, the values are copied
+into the hash map. For owned values like `String`, the values will be moved and
+the hash map will be the owner of those values, as demonstrated in Listing 8-22.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-22/src/main.rs:here}}
+```
+
+
+
+We aren’t able to use the variables `field_name` and `field_value` after
+they’ve been moved into the hash map with the call to `insert`.
+
+If we insert references to values into the hash map, the values won’t be moved
+into the hash map. The values that the references point to must be valid for at
+least as long as the hash map is valid. We’ll talk more about these issues in
+[“Validating References with
+Lifetimes”][validating-references-with-lifetimes] in Chapter 10.
+
+### Updating a Hash Map
+
+Although the number of key and value pairs is growable, each unique key can
+only have one value associated with it at a time (but not vice versa: For
+example, both the Blue team and the Yellow team could have the value `10`
+stored in the `scores` hash map).
+
+When you want to change the data in a hash map, you have to decide how to
+handle the case when a key already has a value assigned. You could replace the
+old value with the new value, completely disregarding the old value. You could
+keep the old value and ignore the new value, only adding the new value if the
+key _doesn’t_ already have a value. Or you could combine the old value and the
+new value. Let’s look at how to do each of these!
+
+#### Overwriting a Value
+
+If we insert a key and a value into a hash map and then insert that same key
+with a different value, the value associated with that key will be replaced.
+Even though the code in Listing 8-23 calls `insert` twice, the hash map will
+only contain one key-value pair because we’re inserting the value for the Blue
+team’s key both times.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-23/src/main.rs:here}}
+```
+
+
+
+This code will print `{"Blue": 25}`. The original value of `10` has been
+overwritten.
+
+
+
+
+
+#### Adding a Key and Value Only If a Key Isn’t Present
+
+It’s common to check whether a particular key already exists in the hash map
+with a value and then to take the following actions: If the key does exist in
+the hash map, the existing value should remain the way it is; if the key
+doesn’t exist, insert it and a value for it.
+
+Hash maps have a special API for this called `entry` that takes the key you
+want to check as a parameter. The return value of the `entry` method is an enum
+called `Entry` that represents a value that might or might not exist. Let’s say
+we want to check whether the key for the Yellow team has a value associated
+with it. If it doesn’t, we want to insert the value `50`, and the same for the
+Blue team. Using the `entry` API, the code looks like Listing 8-24.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-24/src/main.rs:here}}
+```
+
+
+
+The `or_insert` method on `Entry` is defined to return a mutable reference to
+the value for the corresponding `Entry` key if that key exists, and if not, it
+inserts the parameter as the new value for this key and returns a mutable
+reference to the new value. This technique is much cleaner than writing the
+logic ourselves and, in addition, plays more nicely with the borrow checker.
+
+Running the code in Listing 8-24 will print `{"Yellow": 50, "Blue": 10}`. The
+first call to `entry` will insert the key for the Yellow team with the value
+`50` because the Yellow team doesn’t have a value already. The second call to
+`entry` will not change the hash map, because the Blue team already has the
+value `10`.
+
+#### Updating a Value Based on the Old Value
+
+Another common use case for hash maps is to look up a key’s value and then
+update it based on the old value. For instance, Listing 8-25 shows code that
+counts how many times each word appears in some text. We use a hash map with
+the words as keys and increment the value to keep track of how many times we’ve
+seen that word. If it’s the first time we’ve seen a word, we’ll first insert
+the value `0`.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch08-common-collections/listing-08-25/src/main.rs:here}}
+```
+
+
+
+This code will print `{"world": 2, "hello": 1, "wonderful": 1}`. You might see
+the same key-value pairs printed in a different order: Recall from [“Accessing
+Values in a Hash Map”][access] that iterating over a hash map
+happens in an arbitrary order.
+
+The `split_whitespace` method returns an iterator over subslices, separated by
+whitespace, of the value in `text`. The `or_insert` method returns a mutable
+reference (`&mut V`) to the value for the specified key. Here, we store that
+mutable reference in the `count` variable, so in order to assign to that value,
+we must first dereference `count` using the asterisk (`*`). The mutable
+reference goes out of scope at the end of the `for` loop, so all of these
+changes are safe and allowed by the borrowing rules.
+
+### Hashing Functions
+
+By default, `HashMap` uses a hashing function called _SipHash_ that can provide
+resistance to denial-of-service (DoS) attacks involving hash
+tables[^siphash]. This is not the fastest hashing algorithm
+available, but the trade-off for better security that comes with the drop in
+performance is worth it. If you profile your code and find that the default
+hash function is too slow for your purposes, you can switch to another function
+by specifying a different hasher. A _hasher_ is a type that implements the
+`BuildHasher` trait. We’ll talk about traits and how to implement them in
+[Chapter 10][traits]. You don’t necessarily have to implement
+your own hasher from scratch; [crates.io](https://crates.io/)
+has libraries shared by other Rust users that provide hashers implementing many
+common hashing algorithms.
+
+[^siphash]: [https://en.wikipedia.org/wiki/SipHash](https://en.wikipedia.org/wiki/SipHash)
+
+## Summary
+
+Vectors, strings, and hash maps will provide a large amount of functionality
+necessary in programs when you need to store, access, and modify data. Here are
+some exercises you should now be equipped to solve:
+
+1. Given a list of integers, use a vector and return the median (when sorted,
+ the value in the middle position) and mode (the value that occurs most
+ often; a hash map will be helpful here) of the list.
+1. Convert strings to Pig Latin. The first consonant of each word is moved to
+ the end of the word and _ay_ is added, so _first_ becomes _irst-fay_. Words
+ that start with a vowel have _hay_ added to the end instead (_apple_ becomes
+ _apple-hay_). Keep in mind the details about UTF-8 encoding!
+1. Using a hash map and vectors, create a text interface to allow a user to add
+ employee names to a department in a company; for example, “Add Sally to
+ Engineering” or “Add Amir to Sales.” Then, let the user retrieve a list of
+ all people in a department or all people in the company by department, sorted
+ alphabetically.
+
+The standard library API documentation describes methods that vectors, strings,
+and hash maps have that will be helpful for these exercises!
+
+We’re getting into more complex programs in which operations can fail, so it’s
+a perfect time to discuss error handling. We’ll do that next!
+
+[validating-references-with-lifetimes]: ch10-03-lifetime-syntax.html#validating-references-with-lifetimes
+[access]: #accessing-values-in-a-hash-map
+[traits]: ch10-02-traits.html
diff --git a/documents/markdown/rust-book/ch09-00-error-handling.md b/documents/markdown/rust-book/ch09-00-error-handling.md
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+# Error Handling
+
+Errors are a fact of life in software, so Rust has a number of features for
+handling situations in which something goes wrong. In many cases, Rust requires
+you to acknowledge the possibility of an error and take some action before your
+code will compile. This requirement makes your program more robust by ensuring
+that you’ll discover errors and handle them appropriately before deploying your
+code to production!
+
+Rust groups errors into two major categories: recoverable and unrecoverable
+errors. For a _recoverable error_, such as a _file not found_ error, we most
+likely just want to report the problem to the user and retry the operation.
+_Unrecoverable errors_ are always symptoms of bugs, such as trying to access a
+location beyond the end of an array, and so we want to immediately stop the
+program.
+
+Most languages don’t distinguish between these two kinds of errors and handle
+both in the same way, using mechanisms such as exceptions. Rust doesn’t have
+exceptions. Instead, it has the type `Result` for recoverable errors and
+the `panic!` macro that stops execution when the program encounters an
+unrecoverable error. This chapter covers calling `panic!` first and then talks
+about returning `Result` values. Additionally, we’ll explore
+considerations when deciding whether to try to recover from an error or to stop
+execution.
diff --git a/documents/markdown/rust-book/ch09-01-unrecoverable-errors-with-panic.md b/documents/markdown/rust-book/ch09-01-unrecoverable-errors-with-panic.md
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@@ -0,0 +1,170 @@
+## Unrecoverable Errors with `panic!`
+
+Sometimes bad things happen in your code, and there’s nothing you can do about
+it. In these cases, Rust has the `panic!` macro. There are two ways to cause a
+panic in practice: by taking an action that causes our code to panic (such as
+accessing an array past the end) or by explicitly calling the `panic!` macro.
+In both cases, we cause a panic in our program. By default, these panics will
+print a failure message, unwind, clean up the stack, and quit. Via an
+environment variable, you can also have Rust display the call stack when a
+panic occurs to make it easier to track down the source of the panic.
+
+> ### Unwinding the Stack or Aborting in Response to a Panic
+>
+> By default, when a panic occurs, the program starts _unwinding_, which means
+> Rust walks back up the stack and cleans up the data from each function it
+> encounters. However, walking back and cleaning up is a lot of work. Rust
+> therefore allows you to choose the alternative of immediately _aborting_,
+> which ends the program without cleaning up.
+>
+> Memory that the program was using will then need to be cleaned up by the
+> operating system. If in your project you need to make the resultant binary as
+> small as possible, you can switch from unwinding to aborting upon a panic by
+> adding `panic = 'abort'` to the appropriate `[profile]` sections in your
+> _Cargo.toml_ file. For example, if you want to abort on panic in release mode,
+> add this:
+>
+> ```toml
+> [profile.release]
+> panic = 'abort'
+> ```
+
+Let’s try calling `panic!` in a simple program:
+
+
+
+```rust,should_panic,panics
+{{#rustdoc_include ../listings/ch09-error-handling/no-listing-01-panic/src/main.rs}}
+```
+
+
+
+When you run the program, you’ll see something like this:
+
+```console
+{{#include ../listings/ch09-error-handling/no-listing-01-panic/output.txt}}
+```
+
+The call to `panic!` causes the error message contained in the last two lines.
+The first line shows our panic message and the place in our source code where
+the panic occurred: _src/main.rs:2:5_ indicates that it’s the second line,
+fifth character of our _src/main.rs_ file.
+
+In this case, the line indicated is part of our code, and if we go to that
+line, we see the `panic!` macro call. In other cases, the `panic!` call might
+be in code that our code calls, and the filename and line number reported by
+the error message will be someone else’s code where the `panic!` macro is
+called, not the line of our code that eventually led to the `panic!` call.
+
+
+
+
+
+We can use the backtrace of the functions the `panic!` call came from to figure
+out the part of our code that is causing the problem. To understand how to use
+a `panic!` backtrace, let’s look at another example and see what it’s like when
+a `panic!` call comes from a library because of a bug in our code instead of
+from our code calling the macro directly. Listing 9-1 has some code that
+attempts to access an index in a vector beyond the range of valid indexes.
+
+
+
+```rust,should_panic,panics
+{{#rustdoc_include ../listings/ch09-error-handling/listing-09-01/src/main.rs}}
+```
+
+
+
+Here, we’re attempting to access the 100th element of our vector (which is at
+index 99 because indexing starts at zero), but the vector has only three
+elements. In this situation, Rust will panic. Using `[]` is supposed to return
+an element, but if you pass an invalid index, there’s no element that Rust
+could return here that would be correct.
+
+In C, attempting to read beyond the end of a data structure is undefined
+behavior. You might get whatever is at the location in memory that would
+correspond to that element in the data structure, even though the memory
+doesn’t belong to that structure. This is called a _buffer overread_ and can
+lead to security vulnerabilities if an attacker is able to manipulate the index
+in such a way as to read data they shouldn’t be allowed to that is stored after
+the data structure.
+
+To protect your program from this sort of vulnerability, if you try to read an
+element at an index that doesn’t exist, Rust will stop execution and refuse to
+continue. Let’s try it and see:
+
+```console
+{{#include ../listings/ch09-error-handling/listing-09-01/output.txt}}
+```
+
+This error points at line 4 of our _main.rs_ where we attempt to access index
+99 of the vector in `v`.
+
+The `note:` line tells us that we can set the `RUST_BACKTRACE` environment
+variable to get a backtrace of exactly what happened to cause the error. A
+_backtrace_ is a list of all the functions that have been called to get to this
+point. Backtraces in Rust work as they do in other languages: The key to
+reading the backtrace is to start from the top and read until you see files you
+wrote. That’s the spot where the problem originated. The lines above that spot
+are code that your code has called; the lines below are code that called your
+code. These before-and-after lines might include core Rust code, standard
+library code, or crates that you’re using. Let’s try to get a backtrace by
+setting the `RUST_BACKTRACE` environment variable to any value except `0`.
+Listing 9-2 shows output similar to what you’ll see.
+
+
+
+
+
+```console
+$ RUST_BACKTRACE=1 cargo run
+thread 'main' panicked at src/main.rs:4:6:
+index out of bounds: the len is 3 but the index is 99
+stack backtrace:
+ 0: rust_begin_unwind
+ at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/std/src/panicking.rs:692:5
+ 1: core::panicking::panic_fmt
+ at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/panicking.rs:75:14
+ 2: core::panicking::panic_bounds_check
+ at /rustc/4d91de4e48198da2e33413efdcd9cd2cc0c46688/library/core/src/panicking.rs:273:5
+ 3: >::index
+ at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/core/src/slice/index.rs:274:10
+ 4: core::slice::index:: for [T]>::index
+ at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/core/src/slice/index.rs:16:9
+ 5: as core::ops::index::Index>::index
+ at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/alloc/src/vec/mod.rs:3361:9
+ 6: panic::main
+ at ./src/main.rs:4:6
+ 7: core::ops::function::FnOnce::call_once
+ at file:///home/.rustup/toolchains/1.85/lib/rustlib/src/rust/library/core/src/ops/function.rs:250:5
+note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
+```
+
+
+
+That’s a lot of output! The exact output you see might be different depending
+on your operating system and Rust version. In order to get backtraces with this
+information, debug symbols must be enabled. Debug symbols are enabled by
+default when using `cargo build` or `cargo run` without the `--release` flag,
+as we have here.
+
+In the output in Listing 9-2, line 6 of the backtrace points to the line in our
+project that’s causing the problem: line 4 of _src/main.rs_. If we don’t want
+our program to panic, we should start our investigation at the location pointed
+to by the first line mentioning a file we wrote. In Listing 9-1, where we
+deliberately wrote code that would panic, the way to fix the panic is to not
+request an element beyond the range of the vector indexes. When your code
+panics in the future, you’ll need to figure out what action the code is taking
+with what values to cause the panic and what the code should do instead.
+
+We’ll come back to `panic!` and when we should and should not use `panic!` to
+handle error conditions in the [“To `panic!` or Not to
+`panic!`”][to-panic-or-not-to-panic] section later in this
+chapter. Next, we’ll look at how to recover from an error using `Result`.
+
+[to-panic-or-not-to-panic]: ch09-03-to-panic-or-not-to-panic.html#to-panic-or-not-to-panic
diff --git a/documents/markdown/rust-book/ch09-02-recoverable-errors-with-result.md b/documents/markdown/rust-book/ch09-02-recoverable-errors-with-result.md
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+## Recoverable Errors with `Result`
+
+Most errors aren’t serious enough to require the program to stop entirely.
+Sometimes when a function fails, it’s for a reason that you can easily interpret
+and respond to. For example, if you try to open a file and that operation fails
+because the file doesn’t exist, you might want to create the file instead of
+terminating the process.
+
+Recall from [“Handling Potential Failure with `Result`”][handle_failure] in Chapter 2 that the `Result` enum is defined as having two
+variants, `Ok` and `Err`, as follows:
+
+```rust
+enum Result {
+ Ok(T),
+ Err(E),
+}
+```
+
+The `T` and `E` are generic type parameters: We’ll discuss generics in more
+detail in Chapter 10. What you need to know right now is that `T` represents
+the type of the value that will be returned in a success case within the `Ok`
+variant, and `E` represents the type of the error that will be returned in a
+failure case within the `Err` variant. Because `Result` has these generic type
+parameters, we can use the `Result` type and the functions defined on it in
+many different situations where the success value and error value we want to
+return may differ.
+
+Let’s call a function that returns a `Result` value because the function could
+fail. In Listing 9-3, we try to open a file.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch09-error-handling/listing-09-03/src/main.rs}}
+```
+
+
+
+The return type of `File::open` is a `Result`. The generic parameter `T`
+has been filled in by the implementation of `File::open` with the type of the
+success value, `std::fs::File`, which is a file handle. The type of `E` used in
+the error value is `std::io::Error`. This return type means the call to
+`File::open` might succeed and return a file handle that we can read from or
+write to. The function call also might fail: For example, the file might not
+exist, or we might not have permission to access the file. The `File::open`
+function needs to have a way to tell us whether it succeeded or failed and at
+the same time give us either the file handle or error information. This
+information is exactly what the `Result` enum conveys.
+
+In the case where `File::open` succeeds, the value in the variable
+`greeting_file_result` will be an instance of `Ok` that contains a file handle.
+In the case where it fails, the value in `greeting_file_result` will be an
+instance of `Err` that contains more information about the kind of error that
+occurred.
+
+We need to add to the code in Listing 9-3 to take different actions depending
+on the value `File::open` returns. Listing 9-4 shows one way to handle the
+`Result` using a basic tool, the `match` expression that we discussed in
+Chapter 6.
+
+
+
+```rust,should_panic
+{{#rustdoc_include ../listings/ch09-error-handling/listing-09-04/src/main.rs}}
+```
+
+
+
+Note that, like the `Option` enum, the `Result` enum and its variants have been
+brought into scope by the prelude, so we don’t need to specify `Result::`
+before the `Ok` and `Err` variants in the `match` arms.
+
+When the result is `Ok`, this code will return the inner `file` value out of
+the `Ok` variant, and we then assign that file handle value to the variable
+`greeting_file`. After the `match`, we can use the file handle for reading or
+writing.
+
+The other arm of the `match` handles the case where we get an `Err` value from
+`File::open`. In this example, we’ve chosen to call the `panic!` macro. If
+there’s no file named _hello.txt_ in our current directory and we run this
+code, we’ll see the following output from the `panic!` macro:
+
+```console
+{{#include ../listings/ch09-error-handling/listing-09-04/output.txt}}
+```
+
+As usual, this output tells us exactly what has gone wrong.
+
+### Matching on Different Errors
+
+The code in Listing 9-4 will `panic!` no matter why `File::open` failed.
+However, we want to take different actions for different failure reasons. If
+`File::open` failed because the file doesn’t exist, we want to create the file
+and return the handle to the new file. If `File::open` failed for any other
+reason—for example, because we didn’t have permission to open the file—we still
+want the code to `panic!` in the same way it did in Listing 9-4. For this, we
+add an inner `match` expression, shown in Listing 9-5.
+
+
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch09-error-handling/listing-09-05/src/main.rs}}
+```
+
+
+
+The type of the value that `File::open` returns inside the `Err` variant is
+`io::Error`, which is a struct provided by the standard library. This struct
+has a method, `kind`, that we can call to get an `io::ErrorKind` value. The
+enum `io::ErrorKind` is provided by the standard library and has variants
+representing the different kinds of errors that might result from an `io`
+operation. The variant we want to use is `ErrorKind::NotFound`, which indicates
+the file we’re trying to open doesn’t exist yet. So, we match on
+`greeting_file_result`, but we also have an inner match on `error.kind()`.
+
+The condition we want to check in the inner match is whether the value returned
+by `error.kind()` is the `NotFound` variant of the `ErrorKind` enum. If it is,
+we try to create the file with `File::create`. However, because `File::create`
+could also fail, we need a second arm in the inner `match` expression. When the
+file can’t be created, a different error message is printed. The second arm of
+the outer `match` stays the same, so the program panics on any error besides
+the missing file error.
+
+> #### Alternatives to Using `match` with `Result`
+>
+> That’s a lot of `match`! The `match` expression is very useful but also very
+> much a primitive. In Chapter 13, you’ll learn about closures, which are used
+> with many of the methods defined on `Result`. These methods can be more
+> concise than using `match` when handling `Result` values in your code.
+>
+> For example, here’s another way to write the same logic as shown in Listing
+> 9-5, this time using closures and the `unwrap_or_else` method:
+>
+>
+>
+> ```rust,ignore
+> use std::fs::File;
+> use std::io::ErrorKind;
+>
+> fn main() {
+> let greeting_file = File::open("hello.txt").unwrap_or_else(|error| {
+> if error.kind() == ErrorKind::NotFound {
+> File::create("hello.txt").unwrap_or_else(|error| {
+> panic!("Problem creating the file: {error:?}");
+> })
+> } else {
+> panic!("Problem opening the file: {error:?}");
+> }
+> });
+> }
+> ```
+>
+> Although this code has the same behavior as Listing 9-5, it doesn’t contain
+> any `match` expressions and is cleaner to read. Come back to this example
+> after you’ve read Chapter 13 and look up the `unwrap_or_else` method in the
+> standard library documentation. Many more of these methods can clean up huge,
+> nested `match` expressions when you’re dealing with errors.
+
+
+
+
+
+#### Shortcuts for Panic on Error
+
+Using `match` works well enough, but it can be a bit verbose and doesn’t always
+communicate intent well. The `Result` type has many helper methods
+defined on it to do various, more specific tasks. The `unwrap` method is a
+shortcut method implemented just like the `match` expression we wrote in
+Listing 9-4. If the `Result` value is the `Ok` variant, `unwrap` will return
+the value inside the `Ok`. If the `Result` is the `Err` variant, `unwrap` will
+call the `panic!` macro for us. Here is an example of `unwrap` in action:
+
+
+
+```rust,should_panic
+{{#rustdoc_include ../listings/ch09-error-handling/no-listing-04-unwrap/src/main.rs}}
+```
+
+
+
+If we run this code without a _hello.txt_ file, we’ll see an error message from
+the `panic!` call that the `unwrap` method makes:
+
+
+
+```text
+thread 'main' panicked at src/main.rs:4:49:
+called `Result::unwrap()` on an `Err` value: Os { code: 2, kind: NotFound, message: "No such file or directory" }
+```
+
+Similarly, the `expect` method lets us also choose the `panic!` error message.
+Using `expect` instead of `unwrap` and providing good error messages can convey
+your intent and make tracking down the source of a panic easier. The syntax of
+`expect` looks like this:
+
+
+
+```rust,should_panic
+{{#rustdoc_include ../listings/ch09-error-handling/no-listing-05-expect/src/main.rs}}
+```
+
+
+
+We use `expect` in the same way as `unwrap`: to return the file handle or call
+the `panic!` macro. The error message used by `expect` in its call to `panic!`
+will be the parameter that we pass to `expect`, rather than the default
+`panic!` message that `unwrap` uses. Here’s what it looks like:
+
+
+
+```text
+thread 'main' panicked at src/main.rs:5:10:
+hello.txt should be included in this project: Os { code: 2, kind: NotFound, message: "No such file or directory" }
+```
+
+In production-quality code, most Rustaceans choose `expect` rather than
+`unwrap` and give more context about why the operation is expected to always
+succeed. That way, if your assumptions are ever proven wrong, you have more
+information to use in debugging.
+
+### Propagating Errors
+
+When a function’s implementation calls something that might fail, instead of
+handling the error within the function itself, you can return the error to the
+calling code so that it can decide what to do. This is known as _propagating_
+the error and gives more control to the calling code, where there might be more
+information or logic that dictates how the error should be handled than what
+you have available in the context of your code.
+
+For example, Listing 9-6 shows a function that reads a username from a file. If
+the file doesn’t exist or can’t be read, this function will return those errors
+to the code that called the function.
+
+
+
+
+
+```rust
+{{#include ../listings/ch09-error-handling/listing-09-06/src/main.rs:here}}
+```
+
+
+
+This function can be written in a much shorter way, but we’re going to start by
+doing a lot of it manually in order to explore error handling; at the end,
+we’ll show the shorter way. Let’s look at the return type of the function
+first: `Result`. This means the function is returning a
+value of the type `Result`, where the generic parameter `T` has been
+filled in with the concrete type `String` and the generic type `E` has been
+filled in with the concrete type `io::Error`.
+
+If this function succeeds without any problems, the code that calls this
+function will receive an `Ok` value that holds a `String`—the `username` that
+this function read from the file. If this function encounters any problems, the
+calling code will receive an `Err` value that holds an instance of `io::Error`
+that contains more information about what the problems were. We chose
+`io::Error` as the return type of this function because that happens to be the
+type of the error value returned from both of the operations we’re calling in
+this function’s body that might fail: the `File::open` function and the
+`read_to_string` method.
+
+The body of the function starts by calling the `File::open` function. Then, we
+handle the `Result` value with a `match` similar to the `match` in Listing 9-4.
+If `File::open` succeeds, the file handle in the pattern variable `file`
+becomes the value in the mutable variable `username_file` and the function
+continues. In the `Err` case, instead of calling `panic!`, we use the `return`
+keyword to return early out of the function entirely and pass the error value
+from `File::open`, now in the pattern variable `e`, back to the calling code as
+this function’s error value.
+
+So, if we have a file handle in `username_file`, the function then creates a
+new `String` in variable `username` and calls the `read_to_string` method on
+the file handle in `username_file` to read the contents of the file into
+`username`. The `read_to_string` method also returns a `Result` because it
+might fail, even though `File::open` succeeded. So, we need another `match` to
+handle that `Result`: If `read_to_string` succeeds, then our function has
+succeeded, and we return the username from the file that’s now in `username`
+wrapped in an `Ok`. If `read_to_string` fails, we return the error value in the
+same way that we returned the error value in the `match` that handled the
+return value of `File::open`. However, we don’t need to explicitly say
+`return`, because this is the last expression in the function.
+
+The code that calls this code will then handle getting either an `Ok` value
+that contains a username or an `Err` value that contains an `io::Error`. It’s
+up to the calling code to decide what to do with those values. If the calling
+code gets an `Err` value, it could call `panic!` and crash the program, use a
+default username, or look up the username from somewhere other than a file, for
+example. We don’t have enough information on what the calling code is actually
+trying to do, so we propagate all the success or error information upward for
+it to handle appropriately.
+
+This pattern of propagating errors is so common in Rust that Rust provides the
+question mark operator `?` to make this easier.
+
+
+
+
+
+#### The `?` Operator Shortcut
+
+Listing 9-7 shows an implementation of `read_username_from_file` that has the
+same functionality as in Listing 9-6, but this implementation uses the `?`
+operator.
+
+
+
+
+
+```rust
+{{#include ../listings/ch09-error-handling/listing-09-07/src/main.rs:here}}
+```
+
+
+
+The `?` placed after a `Result` value is defined to work in almost the same way
+as the `match` expressions that we defined to handle the `Result` values in
+Listing 9-6. If the value of the `Result` is an `Ok`, the value inside the `Ok`
+will get returned from this expression, and the program will continue. If the
+value is an `Err`, the `Err` will be returned from the whole function as if we
+had used the `return` keyword so that the error value gets propagated to the
+calling code.
+
+There is a difference between what the `match` expression from Listing 9-6 does
+and what the `?` operator does: Error values that have the `?` operator called
+on them go through the `from` function, defined in the `From` trait in the
+standard library, which is used to convert values from one type into another.
+When the `?` operator calls the `from` function, the error type received is
+converted into the error type defined in the return type of the current
+function. This is useful when a function returns one error type to represent
+all the ways a function might fail, even if parts might fail for many different
+reasons.
+
+For example, we could change the `read_username_from_file` function in Listing
+9-7 to return a custom error type named `OurError` that we define. If we also
+define `impl From for OurError` to construct an instance of
+`OurError` from an `io::Error`, then the `?` operator calls in the body of
+`read_username_from_file` will call `from` and convert the error types without
+needing to add any more code to the function.
+
+In the context of Listing 9-7, the `?` at the end of the `File::open` call will
+return the value inside an `Ok` to the variable `username_file`. If an error
+occurs, the `?` operator will return early out of the whole function and give
+any `Err` value to the calling code. The same thing applies to the `?` at the
+end of the `read_to_string` call.
+
+The `?` operator eliminates a lot of boilerplate and makes this function’s
+implementation simpler. We could even shorten this code further by chaining
+method calls immediately after the `?`, as shown in Listing 9-8.
+
+
+
+
+
+```rust
+{{#include ../listings/ch09-error-handling/listing-09-08/src/main.rs:here}}
+```
+
+
+
+We’ve moved the creation of the new `String` in `username` to the beginning of
+the function; that part hasn’t changed. Instead of creating a variable
+`username_file`, we’ve chained the call to `read_to_string` directly onto the
+result of `File::open("hello.txt")?`. We still have a `?` at the end of the
+`read_to_string` call, and we still return an `Ok` value containing `username`
+when both `File::open` and `read_to_string` succeed rather than returning
+errors. The functionality is again the same as in Listing 9-6 and Listing 9-7;
+this is just a different, more ergonomic way to write it.
+
+Listing 9-9 shows a way to make this even shorter using `fs::read_to_string`.
+
+
+
+
+
+```rust
+{{#include ../listings/ch09-error-handling/listing-09-09/src/main.rs:here}}
+```
+
+
+
+Reading a file into a string is a fairly common operation, so the standard
+library provides the convenient `fs::read_to_string` function that opens the
+file, creates a new `String`, reads the contents of the file, puts the contents
+into that `String`, and returns it. Of course, using `fs::read_to_string`
+doesn’t give us the opportunity to explain all the error handling, so we did it
+the longer way first.
+
+
+
+
+
+#### Where to Use the `?` Operator
+
+The `?` operator can only be used in functions whose return type is compatible
+with the value the `?` is used on. This is because the `?` operator is defined
+to perform an early return of a value out of the function, in the same manner
+as the `match` expression we defined in Listing 9-6. In Listing 9-6, the
+`match` was using a `Result` value, and the early return arm returned an
+`Err(e)` value. The return type of the function has to be a `Result` so that
+it’s compatible with this `return`.
+
+In Listing 9-10, let’s look at the error we’ll get if we use the `?` operator
+in a `main` function with a return type that is incompatible with the type of
+the value we use `?` on.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch09-error-handling/listing-09-10/src/main.rs}}
+```
+
+
+
+This code opens a file, which might fail. The `?` operator follows the `Result`
+value returned by `File::open`, but this `main` function has the return type of
+`()`, not `Result`. When we compile this code, we get the following error
+message:
+
+```console
+{{#include ../listings/ch09-error-handling/listing-09-10/output.txt}}
+```
+
+This error points out that we’re only allowed to use the `?` operator in a
+function that returns `Result`, `Option`, or another type that implements
+`FromResidual`.
+
+To fix the error, you have two choices. One choice is to change the return type
+of your function to be compatible with the value you’re using the `?` operator
+on as long as you have no restrictions preventing that. The other choice is to
+use a `match` or one of the `Result` methods to handle the `Result`
+in whatever way is appropriate.
+
+The error message also mentioned that `?` can be used with `Option` values
+as well. As with using `?` on `Result`, you can only use `?` on `Option` in a
+function that returns an `Option`. The behavior of the `?` operator when called
+on an `Option` is similar to its behavior when called on a `Result`:
+If the value is `None`, the `None` will be returned early from the function at
+that point. If the value is `Some`, the value inside the `Some` is the
+resultant value of the expression, and the function continues. Listing 9-11 has
+an example of a function that finds the last character of the first line in the
+given text.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch09-error-handling/listing-09-11/src/main.rs:here}}
+```
+
+
+
+This function returns `Option` because it’s possible that there is a
+character there, but it’s also possible that there isn’t. This code takes the
+`text` string slice argument and calls the `lines` method on it, which returns
+an iterator over the lines in the string. Because this function wants to
+examine the first line, it calls `next` on the iterator to get the first value
+from the iterator. If `text` is the empty string, this call to `next` will
+return `None`, in which case we use `?` to stop and return `None` from
+`last_char_of_first_line`. If `text` is not the empty string, `next` will
+return a `Some` value containing a string slice of the first line in `text`.
+
+The `?` extracts the string slice, and we can call `chars` on that string slice
+to get an iterator of its characters. We’re interested in the last character in
+this first line, so we call `last` to return the last item in the iterator.
+This is an `Option` because it’s possible that the first line is the empty
+string; for example, if `text` starts with a blank line but has characters on
+other lines, as in `"\nhi"`. However, if there is a last character on the first
+line, it will be returned in the `Some` variant. The `?` operator in the middle
+gives us a concise way to express this logic, allowing us to implement the
+function in one line. If we couldn’t use the `?` operator on `Option`, we’d
+have to implement this logic using more method calls or a `match` expression.
+
+Note that you can use the `?` operator on a `Result` in a function that returns
+`Result`, and you can use the `?` operator on an `Option` in a function that
+returns `Option`, but you can’t mix and match. The `?` operator won’t
+automatically convert a `Result` to an `Option` or vice versa; in those cases,
+you can use methods like the `ok` method on `Result` or the `ok_or` method on
+`Option` to do the conversion explicitly.
+
+So far, all the `main` functions we’ve used return `()`. The `main` function is
+special because it’s the entry point and exit point of an executable program,
+and there are restrictions on what its return type can be for the program to
+behave as expected.
+
+Luckily, `main` can also return a `Result<(), E>`. Listing 9-12 has the code
+from Listing 9-10, but we’ve changed the return type of `main` to be
+`Result<(), Box>` and added a return value `Ok(())` to the end. This
+code will now compile.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch09-error-handling/listing-09-12/src/main.rs}}
+```
+
+
+
+The `Box` type is a trait object, which we’ll talk about in [“Using
+Trait Objects to Abstract over Shared Behavior”][trait-objects]
+in Chapter 18. For now, you can read `Box` to mean “any kind of
+error.” Using `?` on a `Result` value in a `main` function with the error type
+`Box` is allowed because it allows any `Err` value to be returned
+early. Even though the body of this `main` function will only ever return
+errors of type `std::io::Error`, by specifying `Box`, this signature
+will continue to be correct even if more code that returns other errors is
+added to the body of `main`.
+
+When a `main` function returns a `Result<(), E>`, the executable will exit with
+a value of `0` if `main` returns `Ok(())` and will exit with a nonzero value if
+`main` returns an `Err` value. Executables written in C return integers when
+they exit: Programs that exit successfully return the integer `0`, and programs
+that error return some integer other than `0`. Rust also returns integers from
+executables to be compatible with this convention.
+
+The `main` function may return any types that implement [the
+`std::process::Termination` trait][termination], which contains
+a function `report` that returns an `ExitCode`. Consult the standard library
+documentation for more information on implementing the `Termination` trait for
+your own types.
+
+Now that we’ve discussed the details of calling `panic!` or returning `Result`,
+let’s return to the topic of how to decide which is appropriate to use in which
+cases.
+
+[handle_failure]: ch02-00-guessing-game-tutorial.html#handling-potential-failure-with-result
+[trait-objects]: ch18-02-trait-objects.html#using-trait-objects-to-abstract-over-shared-behavior
+[termination]: ../std/process/trait.Termination.html
diff --git a/documents/markdown/rust-book/ch09-03-to-panic-or-not-to-panic.md b/documents/markdown/rust-book/ch09-03-to-panic-or-not-to-panic.md
new file mode 100644
index 0000000..256c367
--- /dev/null
+++ b/documents/markdown/rust-book/ch09-03-to-panic-or-not-to-panic.md
@@ -0,0 +1,236 @@
+## To `panic!` or Not to `panic!`
+
+So, how do you decide when you should call `panic!` and when you should return
+`Result`? When code panics, there’s no way to recover. You could call `panic!`
+for any error situation, whether there’s a possible way to recover or not, but
+then you’re making the decision that a situation is unrecoverable on behalf of
+the calling code. When you choose to return a `Result` value, you give the
+calling code options. The calling code could choose to attempt to recover in a
+way that’s appropriate for its situation, or it could decide that an `Err`
+value in this case is unrecoverable, so it can call `panic!` and turn your
+recoverable error into an unrecoverable one. Therefore, returning `Result` is a
+good default choice when you’re defining a function that might fail.
+
+In situations such as examples, prototype code, and tests, it’s more
+appropriate to write code that panics instead of returning a `Result`. Let’s
+explore why, then discuss situations in which the compiler can’t tell that
+failure is impossible, but you as a human can. The chapter will conclude with
+some general guidelines on how to decide whether to panic in library code.
+
+### Examples, Prototype Code, and Tests
+
+When you’re writing an example to illustrate some concept, also including
+robust error-handling code can make the example less clear. In examples, it’s
+understood that a call to a method like `unwrap` that could panic is meant as a
+placeholder for the way you’d want your application to handle errors, which can
+differ based on what the rest of your code is doing.
+
+Similarly, the `unwrap` and `expect` methods are very handy when you’re
+prototyping and you’re not yet ready to decide how to handle errors. They leave
+clear markers in your code for when you’re ready to make your program more
+robust.
+
+If a method call fails in a test, you’d want the whole test to fail, even if
+that method isn’t the functionality under test. Because `panic!` is how a test
+is marked as a failure, calling `unwrap` or `expect` is exactly what should
+happen.
+
+
+
+
+
+### When You Have More Information Than the Compiler
+
+It would also be appropriate to call `expect` when you have some other logic
+that ensures that the `Result` will have an `Ok` value, but the logic isn’t
+something the compiler understands. You’ll still have a `Result` value that you
+need to handle: Whatever operation you’re calling still has the possibility of
+failing in general, even though it’s logically impossible in your particular
+situation. If you can ensure by manually inspecting the code that you’ll never
+have an `Err` variant, it’s perfectly acceptable to call `expect` and document
+the reason you think you’ll never have an `Err` variant in the argument text.
+Here’s an example:
+
+```rust
+{{#rustdoc_include ../listings/ch09-error-handling/no-listing-08-unwrap-that-cant-fail/src/main.rs:here}}
+```
+
+We’re creating an `IpAddr` instance by parsing a hardcoded string. We can see
+that `127.0.0.1` is a valid IP address, so it’s acceptable to use `expect`
+here. However, having a hardcoded, valid string doesn’t change the return type
+of the `parse` method: We still get a `Result` value, and the compiler will
+still make us handle the `Result` as if the `Err` variant is a possibility
+because the compiler isn’t smart enough to see that this string is always a
+valid IP address. If the IP address string came from a user rather than being
+hardcoded into the program and therefore _did_ have a possibility of failure,
+we’d definitely want to handle the `Result` in a more robust way instead.
+Mentioning the assumption that this IP address is hardcoded will prompt us to
+change `expect` to better error-handling code if, in the future, we need to get
+the IP address from some other source instead.
+
+### Guidelines for Error Handling
+
+It’s advisable to have your code panic when it’s possible that your code could
+end up in a bad state. In this context, a _bad state_ is when some assumption,
+guarantee, contract, or invariant has been broken, such as when invalid values,
+contradictory values, or missing values are passed to your code—plus one or
+more of the following:
+
+- The bad state is something that is unexpected, as opposed to something that
+ will likely happen occasionally, like a user entering data in the wrong
+ format.
+- Your code after this point needs to rely on not being in this bad state,
+ rather than checking for the problem at every step.
+- There’s not a good way to encode this information in the types you use. We’ll
+ work through an example of what we mean in [“Encoding States and Behavior as
+ Types”][encoding] in Chapter 18.
+
+If someone calls your code and passes in values that don’t make sense, it’s
+best to return an error if you can so that the user of the library can decide
+what they want to do in that case. However, in cases where continuing could be
+insecure or harmful, the best choice might be to call `panic!` and alert the
+person using your library to the bug in their code so that they can fix it
+during development. Similarly, `panic!` is often appropriate if you’re calling
+external code that is out of your control and returns an invalid state that you
+have no way of fixing.
+
+However, when failure is expected, it’s more appropriate to return a `Result`
+than to make a `panic!` call. Examples include a parser being given malformed
+data or an HTTP request returning a status that indicates you have hit a rate
+limit. In these cases, returning a `Result` indicates that failure is an
+expected possibility that the calling code must decide how to handle.
+
+When your code performs an operation that could put a user at risk if it’s
+called using invalid values, your code should verify the values are valid first
+and panic if the values aren’t valid. This is mostly for safety reasons:
+Attempting to operate on invalid data can expose your code to vulnerabilities.
+This is the main reason the standard library will call `panic!` if you attempt
+an out-of-bounds memory access: Trying to access memory that doesn’t belong to
+the current data structure is a common security problem. Functions often have
+_contracts_: Their behavior is only guaranteed if the inputs meet particular
+requirements. Panicking when the contract is violated makes sense because a
+contract violation always indicates a caller-side bug, and it’s not a kind of
+error you want the calling code to have to explicitly handle. In fact, there’s
+no reasonable way for calling code to recover; the calling _programmers_ need
+to fix the code. Contracts for a function, especially when a violation will
+cause a panic, should be explained in the API documentation for the function.
+
+However, having lots of error checks in all of your functions would be verbose
+and annoying. Fortunately, you can use Rust’s type system (and thus the type
+checking done by the compiler) to do many of the checks for you. If your
+function has a particular type as a parameter, you can proceed with your code’s
+logic knowing that the compiler has already ensured that you have a valid
+value. For example, if you have a type rather than an `Option`, your program
+expects to have _something_ rather than _nothing_. Your code then doesn’t have
+to handle two cases for the `Some` and `None` variants: It will only have one
+case for definitely having a value. Code trying to pass nothing to your
+function won’t even compile, so your function doesn’t have to check for that
+case at runtime. Another example is using an unsigned integer type such as
+`u32`, which ensures that the parameter is never negative.
+
+
+
+
+
+### Custom Types for Validation
+
+Let’s take the idea of using Rust’s type system to ensure that we have a valid
+value one step further and look at creating a custom type for validation.
+Recall the guessing game in Chapter 2 in which our code asked the user to guess
+a number between 1 and 100. We never validated that the user’s guess was
+between those numbers before checking it against our secret number; we only
+validated that the guess was positive. In this case, the consequences were not
+very dire: Our output of “Too high” or “Too low” would still be correct. But it
+would be a useful enhancement to guide the user toward valid guesses and have
+different behavior when the user guesses a number that’s out of range versus
+when the user types, for example, letters instead.
+
+One way to do this would be to parse the guess as an `i32` instead of only a
+`u32` to allow potentially negative numbers, and then add a check for the
+number being in range, like so:
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch09-error-handling/no-listing-09-guess-out-of-range/src/main.rs:here}}
+```
+
+
+
+The `if` expression checks whether our value is out of range, tells the user
+about the problem, and calls `continue` to start the next iteration of the loop
+and ask for another guess. After the `if` expression, we can proceed with the
+comparisons between `guess` and the secret number knowing that `guess` is
+between 1 and 100.
+
+However, this is not an ideal solution: If it were absolutely critical that the
+program only operated on values between 1 and 100, and it had many functions
+with this requirement, having a check like this in every function would be
+tedious (and might impact performance).
+
+Instead, we can make a new type in a dedicated module and put the validations
+in a function to create an instance of the type rather than repeating the
+validations everywhere. That way, it’s safe for functions to use the new type
+in their signatures and confidently use the values they receive. Listing 9-13
+shows one way to define a `Guess` type that will only create an instance of
+`Guess` if the `new` function receives a value between 1 and 100.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch09-error-handling/listing-09-13/src/guessing_game.rs}}
+```
+
+
+
+Note that this code in *src/guessing_game.rs* depends on adding a module
+declaration `mod guessing_game;` in *src/lib.rs* that we haven’t shown here.
+Within this new module’s file, we define a struct named `Guess` that has a
+field named `value` that holds an `i32`. This is where the number will be
+stored.
+
+Then, we implement an associated function named `new` on `Guess` that creates
+instances of `Guess` values. The `new` function is defined to have one
+parameter named `value` of type `i32` and to return a `Guess`. The code in the
+body of the `new` function tests `value` to make sure it’s between 1 and 100.
+If `value` doesn’t pass this test, we make a `panic!` call, which will alert
+the programmer who is writing the calling code that they have a bug they need
+to fix, because creating a `Guess` with a `value` outside this range would
+violate the contract that `Guess::new` is relying on. The conditions in which
+`Guess::new` might panic should be discussed in its public-facing API
+documentation; we’ll cover documentation conventions indicating the possibility
+of a `panic!` in the API documentation that you create in Chapter 14. If
+`value` does pass the test, we create a new `Guess` with its `value` field set
+to the `value` parameter and return the `Guess`.
+
+Next, we implement a method named `value` that borrows `self`, doesn’t have any
+other parameters, and returns an `i32`. This kind of method is sometimes called
+a _getter_ because its purpose is to get some data from its fields and return
+it. This public method is necessary because the `value` field of the `Guess`
+struct is private. It’s important that the `value` field be private so that
+code using the `Guess` struct is not allowed to set `value` directly: Code
+outside the `guessing_game` module _must_ use the `Guess::new` function to
+create an instance of `Guess`, thereby ensuring that there’s no way for a
+`Guess` to have a `value` that hasn’t been checked by the conditions in the
+`Guess::new` function.
+
+A function that has a parameter or returns only numbers between 1 and 100 could
+then declare in its signature that it takes or returns a `Guess` rather than an
+`i32` and wouldn’t need to do any additional checks in its body.
+
+## Summary
+
+Rust’s error-handling features are designed to help you write more robust code.
+The `panic!` macro signals that your program is in a state it can’t handle and
+lets you tell the process to stop instead of trying to proceed with invalid or
+incorrect values. The `Result` enum uses Rust’s type system to indicate that
+operations might fail in a way that your code could recover from. You can use
+`Result` to tell code that calls your code that it needs to handle potential
+success or failure as well. Using `panic!` and `Result` in the appropriate
+situations will make your code more reliable in the face of inevitable problems.
+
+Now that you’ve seen useful ways that the standard library uses generics with
+the `Option` and `Result` enums, we’ll talk about how generics work and how you
+can use them in your code.
+
+[encoding]: ch18-03-oo-design-patterns.html#encoding-states-and-behavior-as-types
diff --git a/documents/markdown/rust-book/ch10-00-generics.md b/documents/markdown/rust-book/ch10-00-generics.md
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+# Generic Types, Traits, and Lifetimes
+
+Every programming language has tools for effectively handling the duplication
+of concepts. In Rust, one such tool is _generics_: abstract stand-ins for
+concrete types or other properties. We can express the behavior of generics or
+how they relate to other generics without knowing what will be in their place
+when compiling and running the code.
+
+Functions can take parameters of some generic type, instead of a concrete type
+like `i32` or `String`, in the same way they take parameters with unknown
+values to run the same code on multiple concrete values. In fact, we already
+used generics in Chapter 6 with `Option`, in Chapter 8 with `Vec` and
+`HashMap`, and in Chapter 9 with `Result`. In this chapter, you’ll
+explore how to define your own types, functions, and methods with generics!
+
+First, we’ll review how to extract a function to reduce code duplication. We’ll
+then use the same technique to make a generic function from two functions that
+differ only in the types of their parameters. We’ll also explain how to use
+generic types in struct and enum definitions.
+
+Then, you’ll learn how to use traits to define behavior in a generic way. You
+can combine traits with generic types to constrain a generic type to accept
+only those types that have a particular behavior, as opposed to just any type.
+
+Finally, we’ll discuss _lifetimes_: a variety of generics that give the
+compiler information about how references relate to each other. Lifetimes allow
+us to give the compiler enough information about borrowed values so that it can
+ensure that references will be valid in more situations than it could without
+our help.
+
+## Removing Duplication by Extracting a Function
+
+Generics allow us to replace specific types with a placeholder that represents
+multiple types to remove code duplication. Before diving into generics syntax,
+let’s first look at how to remove duplication in a way that doesn’t involve
+generic types by extracting a function that replaces specific values with a
+placeholder that represents multiple values. Then, we’ll apply the same
+technique to extract a generic function! By looking at how to recognize
+duplicated code you can extract into a function, you’ll start to recognize
+duplicated code that can use generics.
+
+We’ll begin with the short program in Listing 10-1 that finds the largest
+number in a list.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-01/src/main.rs:here}}
+```
+
+
+
+We store a list of integers in the variable `number_list` and place a reference
+to the first number in the list in a variable named `largest`. We then iterate
+through all the numbers in the list, and if the current number is greater than
+the number stored in `largest`, we replace the reference in that variable.
+However, if the current number is less than or equal to the largest number seen
+so far, the variable doesn’t change, and the code moves on to the next number
+in the list. After considering all the numbers in the list, `largest` should
+refer to the largest number, which in this case is 100.
+
+We’ve now been tasked with finding the largest number in two different lists of
+numbers. To do so, we can choose to duplicate the code in Listing 10-1 and use
+the same logic at two different places in the program, as shown in Listing 10-2.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-02/src/main.rs}}
+```
+
+
+
+Although this code works, duplicating code is tedious and error-prone. We also
+have to remember to update the code in multiple places when we want to change
+it.
+
+To eliminate this duplication, we’ll create an abstraction by defining a
+function that operates on any list of integers passed in as a parameter. This
+solution makes our code clearer and lets us express the concept of finding the
+largest number in a list abstractly.
+
+In Listing 10-3, we extract the code that finds the largest number into a
+function named `largest`. Then, we call the function to find the largest number
+in the two lists from Listing 10-2. We could also use the function on any other
+list of `i32` values we might have in the future.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-03/src/main.rs:here}}
+```
+
+
+
+The `largest` function has a parameter called `list`, which represents any
+concrete slice of `i32` values we might pass into the function. As a result,
+when we call the function, the code runs on the specific values that we pass
+in.
+
+In summary, here are the steps we took to change the code from Listing 10-2 to
+Listing 10-3:
+
+1. Identify duplicate code.
+1. Extract the duplicate code into the body of the function, and specify the
+ inputs and return values of that code in the function signature.
+1. Update the two instances of duplicated code to call the function instead.
+
+Next, we’ll use these same steps with generics to reduce code duplication. In
+the same way that the function body can operate on an abstract `list` instead
+of specific values, generics allow code to operate on abstract types.
+
+For example, say we had two functions: one that finds the largest item in a
+slice of `i32` values and one that finds the largest item in a slice of `char`
+values. How would we eliminate that duplication? Let’s find out!
diff --git a/documents/markdown/rust-book/ch10-01-syntax.md b/documents/markdown/rust-book/ch10-01-syntax.md
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+## Generic Data Types
+
+We use generics to create definitions for items like function signatures or
+structs, which we can then use with many different concrete data types. Let’s
+first look at how to define functions, structs, enums, and methods using
+generics. Then, we’ll discuss how generics affect code performance.
+
+### In Function Definitions
+
+When defining a function that uses generics, we place the generics in the
+signature of the function where we would usually specify the data types of the
+parameters and return value. Doing so makes our code more flexible and provides
+more functionality to callers of our function while preventing code duplication.
+
+Continuing with our `largest` function, Listing 10-4 shows two functions that
+both find the largest value in a slice. We’ll then combine these into a single
+function that uses generics.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-04/src/main.rs:here}}
+```
+
+
+
+The `largest_i32` function is the one we extracted in Listing 10-3 that finds
+the largest `i32` in a slice. The `largest_char` function finds the largest
+`char` in a slice. The function bodies have the same code, so let’s eliminate
+the duplication by introducing a generic type parameter in a single function.
+
+To parameterize the types in a new single function, we need to name the type
+parameter, just as we do for the value parameters to a function. You can use
+any identifier as a type parameter name. But we’ll use `T` because, by
+convention, type parameter names in Rust are short, often just one letter, and
+Rust’s type-naming convention is UpperCamelCase. Short for _type_, `T` is the
+default choice of most Rust programmers.
+
+When we use a parameter in the body of the function, we have to declare the
+parameter name in the signature so that the compiler knows what that name
+means. Similarly, when we use a type parameter name in a function signature, we
+have to declare the type parameter name before we use it. To define the generic
+`largest` function, we place type name declarations inside angle brackets,
+`<>`, between the name of the function and the parameter list, like this:
+
+```rust,ignore
+fn largest(list: &[T]) -> &T {
+```
+
+We read this definition as “The function `largest` is generic over some type
+`T`.” This function has one parameter named `list`, which is a slice of values
+of type `T`. The `largest` function will return a reference to a value of the
+same type `T`.
+
+Listing 10-5 shows the combined `largest` function definition using the generic
+data type in its signature. The listing also shows how we can call the function
+with either a slice of `i32` values or `char` values. Note that this code won’t
+compile yet.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/src/main.rs}}
+```
+
+
+
+If we compile this code right now, we’ll get this error:
+
+```console
+{{#include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-05/output.txt}}
+```
+
+The help text mentions `std::cmp::PartialOrd`, which is a trait, and we’re
+going to talk about traits in the next section. For now, know that this error
+states that the body of `largest` won’t work for all possible types that `T`
+could be. Because we want to compare values of type `T` in the body, we can
+only use types whose values can be ordered. To enable comparisons, the standard
+library has the `std::cmp::PartialOrd` trait that you can implement on types
+(see Appendix C for more on this trait). To fix Listing 10-5, we can follow the
+help text’s suggestion and restrict the types valid for `T` to only those that
+implement `PartialOrd`. The listing will then compile, because the standard
+library implements `PartialOrd` on both `i32` and `char`.
+
+### In Struct Definitions
+
+We can also define structs to use a generic type parameter in one or more
+fields using the `<>` syntax. Listing 10-6 defines a `Point` struct to hold
+`x` and `y` coordinate values of any type.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-06/src/main.rs}}
+```
+
+
+
+The syntax for using generics in struct definitions is similar to that used in
+function definitions. First, we declare the name of the type parameter inside
+angle brackets just after the name of the struct. Then, we use the generic type
+in the struct definition where we would otherwise specify concrete data types.
+
+Note that because we’ve used only one generic type to define `Point`, this
+definition says that the `Point` struct is generic over some type `T`, and
+the fields `x` and `y` are _both_ that same type, whatever that type may be. If
+we create an instance of a `Point` that has values of different types, as in
+Listing 10-7, our code won’t compile.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/src/main.rs}}
+```
+
+
+
+In this example, when we assign the integer value `5` to `x`, we let the
+compiler know that the generic type `T` will be an integer for this instance of
+`Point`. Then, when we specify `4.0` for `y`, which we’ve defined to have
+the same type as `x`, we’ll get a type mismatch error like this:
+
+```console
+{{#include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-07/output.txt}}
+```
+
+To define a `Point` struct where `x` and `y` are both generics but could have
+different types, we can use multiple generic type parameters. For example, in
+Listing 10-8, we change the definition of `Point` to be generic over types `T`
+and `U` where `x` is of type `T` and `y` is of type `U`.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-08/src/main.rs}}
+```
+
+
+
+Now all the instances of `Point` shown are allowed! You can use as many generic
+type parameters in a definition as you want, but using more than a few makes
+your code hard to read. If you’re finding you need lots of generic types in
+your code, it could indicate that your code needs restructuring into smaller
+pieces.
+
+### In Enum Definitions
+
+As we did with structs, we can define enums to hold generic data types in their
+variants. Let’s take another look at the `Option` enum that the standard
+library provides, which we used in Chapter 6:
+
+```rust
+enum Option {
+ Some(T),
+ None,
+}
+```
+
+This definition should now make more sense to you. As you can see, the
+`Option` enum is generic over type `T` and has two variants: `Some`, which
+holds one value of type `T`, and a `None` variant that doesn’t hold any value.
+By using the `Option` enum, we can express the abstract concept of an
+optional value, and because `Option` is generic, we can use this abstraction
+no matter what the type of the optional value is.
+
+Enums can use multiple generic types as well. The definition of the `Result`
+enum that we used in Chapter 9 is one example:
+
+```rust
+enum Result {
+ Ok(T),
+ Err(E),
+}
+```
+
+The `Result` enum is generic over two types, `T` and `E`, and has two variants:
+`Ok`, which holds a value of type `T`, and `Err`, which holds a value of type
+`E`. This definition makes it convenient to use the `Result` enum anywhere we
+have an operation that might succeed (return a value of some type `T`) or fail
+(return an error of some type `E`). In fact, this is what we used to open a
+file in Listing 9-3, where `T` was filled in with the type `std::fs::File` when
+the file was opened successfully and `E` was filled in with the type
+`std::io::Error` when there were problems opening the file.
+
+When you recognize situations in your code with multiple struct or enum
+definitions that differ only in the types of the values they hold, you can
+avoid duplication by using generic types instead.
+
+### In Method Definitions
+
+We can implement methods on structs and enums (as we did in Chapter 5) and use
+generic types in their definitions too. Listing 10-9 shows the `Point`
+struct we defined in Listing 10-6 with a method named `x` implemented on it.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-09/src/main.rs}}
+```
+
+
+
+Here, we’ve defined a method named `x` on `Point` that returns a reference
+to the data in the field `x`.
+
+Note that we have to declare `T` just after `impl` so that we can use `T` to
+specify that we’re implementing methods on the type `Point`. By declaring
+`T` as a generic type after `impl`, Rust can identify that the type in the
+angle brackets in `Point` is a generic type rather than a concrete type. We
+could have chosen a different name for this generic parameter than the generic
+parameter declared in the struct definition, but using the same name is
+conventional. If you write a method within an `impl` that declares a generic
+type, that method will be defined on any instance of the type, no matter what
+concrete type ends up substituting for the generic type.
+
+We can also specify constraints on generic types when defining methods on the
+type. We could, for example, implement methods only on `Point` instances
+rather than on `Point` instances with any generic type. In Listing 10-10, we
+use the concrete type `f32`, meaning we don’t declare any types after `impl`.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-10/src/main.rs:here}}
+```
+
+
+
+This code means the type `Point` will have a `distance_from_origin`
+method; other instances of `Point` where `T` is not of type `f32` will not
+have this method defined. The method measures how far our point is from the
+point at coordinates (0.0, 0.0) and uses mathematical operations that are
+available only for floating-point types.
+
+Generic type parameters in a struct definition aren’t always the same as those
+you use in that same struct’s method signatures. Listing 10-11 uses the generic
+types `X1` and `Y1` for the `Point` struct and `X2` and `Y2` for the `mixup`
+method signature to make the example clearer. The method creates a new `Point`
+instance with the `x` value from the `self` `Point` (of type `X1`) and the `y`
+value from the passed-in `Point` (of type `Y2`).
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-11/src/main.rs}}
+```
+
+
+
+In `main`, we’ve defined a `Point` that has an `i32` for `x` (with value `5`)
+and an `f64` for `y` (with value `10.4`). The `p2` variable is a `Point` struct
+that has a string slice for `x` (with value `"Hello"`) and a `char` for `y`
+(with value `c`). Calling `mixup` on `p1` with the argument `p2` gives us `p3`,
+which will have an `i32` for `x` because `x` came from `p1`. The `p3` variable
+will have a `char` for `y` because `y` came from `p2`. The `println!` macro
+call will print `p3.x = 5, p3.y = c`.
+
+The purpose of this example is to demonstrate a situation in which some generic
+parameters are declared with `impl` and some are declared with the method
+definition. Here, the generic parameters `X1` and `Y1` are declared after
+`impl` because they go with the struct definition. The generic parameters `X2`
+and `Y2` are declared after `fn mixup` because they’re only relevant to the
+method.
+
+### Performance of Code Using Generics
+
+You might be wondering whether there is a runtime cost when using generic type
+parameters. The good news is that using generic types won’t make your program
+run any slower than it would with concrete types.
+
+Rust accomplishes this by performing monomorphization of the code using
+generics at compile time. _Monomorphization_ is the process of turning generic
+code into specific code by filling in the concrete types that are used when
+compiled. In this process, the compiler does the opposite of the steps we used
+to create the generic function in Listing 10-5: The compiler looks at all the
+places where generic code is called and generates code for the concrete types
+the generic code is called with.
+
+Let’s look at how this works by using the standard library’s generic
+`Option` enum:
+
+```rust
+let integer = Some(5);
+let float = Some(5.0);
+```
+
+When Rust compiles this code, it performs monomorphization. During that
+process, the compiler reads the values that have been used in `Option`
+instances and identifies two kinds of `Option`: One is `i32` and the other
+is `f64`. As such, it expands the generic definition of `Option` into two
+definitions specialized to `i32` and `f64`, thereby replacing the generic
+definition with the specific ones.
+
+The monomorphized version of the code looks similar to the following (the
+compiler uses different names than what we’re using here for illustration):
+
+
+
+```rust
+enum Option_i32 {
+ Some(i32),
+ None,
+}
+
+enum Option_f64 {
+ Some(f64),
+ None,
+}
+
+fn main() {
+ let integer = Option_i32::Some(5);
+ let float = Option_f64::Some(5.0);
+}
+```
+
+
+
+The generic `Option` is replaced with the specific definitions created by
+the compiler. Because Rust compiles generic code into code that specifies the
+type in each instance, we pay no runtime cost for using generics. When the code
+runs, it performs just as it would if we had duplicated each definition by
+hand. The process of monomorphization makes Rust’s generics extremely efficient
+at runtime.
diff --git a/documents/markdown/rust-book/ch10-02-traits.md b/documents/markdown/rust-book/ch10-02-traits.md
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+
+
+
+
+## Defining Shared Behavior with Traits
+
+A _trait_ defines the functionality a particular type has and can share with
+other types. We can use traits to define shared behavior in an abstract way. We
+can use _trait bounds_ to specify that a generic type can be any type that has
+certain behavior.
+
+> Note: Traits are similar to a feature often called _interfaces_ in other
+> languages, although with some differences.
+
+### Defining a Trait
+
+A type’s behavior consists of the methods we can call on that type. Different
+types share the same behavior if we can call the same methods on all of those
+types. Trait definitions are a way to group method signatures together to
+define a set of behaviors necessary to accomplish some purpose.
+
+For example, let’s say we have multiple structs that hold various kinds and
+amounts of text: a `NewsArticle` struct that holds a news story filed in a
+particular location and a `SocialPost` that can have, at most, 280 characters
+along with metadata that indicates whether it was a new post, a repost, or a
+reply to another post.
+
+We want to make a media aggregator library crate named `aggregator` that can
+display summaries of data that might be stored in a `NewsArticle` or
+`SocialPost` instance. To do this, we need a summary from each type, and we’ll
+request that summary by calling a `summarize` method on an instance. Listing
+10-12 shows the definition of a public `Summary` trait that expresses this
+behavior.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-12/src/lib.rs}}
+```
+
+
+
+Here, we declare a trait using the `trait` keyword and then the trait’s name,
+which is `Summary` in this case. We also declare the trait as `pub` so that
+crates depending on this crate can make use of this trait too, as we’ll see in
+a few examples. Inside the curly brackets, we declare the method signatures
+that describe the behaviors of the types that implement this trait, which in
+this case is `fn summarize(&self) -> String`.
+
+After the method signature, instead of providing an implementation within curly
+brackets, we use a semicolon. Each type implementing this trait must provide
+its own custom behavior for the body of the method. The compiler will enforce
+that any type that has the `Summary` trait will have the method `summarize`
+defined with this signature exactly.
+
+A trait can have multiple methods in its body: The method signatures are listed
+one per line, and each line ends in a semicolon.
+
+### Implementing a Trait on a Type
+
+Now that we’ve defined the desired signatures of the `Summary` trait’s methods,
+we can implement it on the types in our media aggregator. Listing 10-13 shows
+an implementation of the `Summary` trait on the `NewsArticle` struct that uses
+the headline, the author, and the location to create the return value of
+`summarize`. For the `SocialPost` struct, we define `summarize` as the username
+followed by the entire text of the post, assuming that the post content is
+already limited to 280 characters.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-13/src/lib.rs:here}}
+```
+
+
+
+Implementing a trait on a type is similar to implementing regular methods. The
+difference is that after `impl`, we put the trait name we want to implement,
+then use the `for` keyword, and then specify the name of the type we want to
+implement the trait for. Within the `impl` block, we put the method signatures
+that the trait definition has defined. Instead of adding a semicolon after each
+signature, we use curly brackets and fill in the method body with the specific
+behavior that we want the methods of the trait to have for the particular type.
+
+Now that the library has implemented the `Summary` trait on `NewsArticle` and
+`SocialPost`, users of the crate can call the trait methods on instances of
+`NewsArticle` and `SocialPost` in the same way we call regular methods. The only
+difference is that the user must bring the trait into scope as well as the
+types. Here’s an example of how a binary crate could use our `aggregator`
+library crate:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-01-calling-trait-method/src/main.rs}}
+```
+
+This code prints `1 new post: horse_ebooks: of course, as you probably already
+know, people`.
+
+Other crates that depend on the `aggregator` crate can also bring the `Summary`
+trait into scope to implement `Summary` on their own types. One restriction to
+note is that we can implement a trait on a type only if either the trait or the
+type, or both, are local to our crate. For example, we can implement standard
+library traits like `Display` on a custom type like `SocialPost` as part of our
+`aggregator` crate functionality because the type `SocialPost` is local to our
+`aggregator` crate. We can also implement `Summary` on `Vec` in our
+`aggregator` crate because the trait `Summary` is local to our `aggregator`
+crate.
+
+But we can’t implement external traits on external types. For example, we can’t
+implement the `Display` trait on `Vec` within our `aggregator` crate,
+because `Display` and `Vec` are both defined in the standard library and
+aren’t local to our `aggregator` crate. This restriction is part of a property
+called _coherence_, and more specifically the _orphan rule_, so named because
+the parent type is not present. This rule ensures that other people’s code
+can’t break your code and vice versa. Without the rule, two crates could
+implement the same trait for the same type, and Rust wouldn’t know which
+implementation to use.
+
+
+
+
+
+### Using Default Implementations
+
+Sometimes it’s useful to have default behavior for some or all of the methods
+in a trait instead of requiring implementations for all methods on every type.
+Then, as we implement the trait on a particular type, we can keep or override
+each method’s default behavior.
+
+In Listing 10-14, we specify a default string for the `summarize` method of the
+`Summary` trait instead of only defining the method signature, as we did in
+Listing 10-12.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-14/src/lib.rs:here}}
+```
+
+
+
+To use a default implementation to summarize instances of `NewsArticle`, we
+specify an empty `impl` block with `impl Summary for NewsArticle {}`.
+
+Even though we’re no longer defining the `summarize` method on `NewsArticle`
+directly, we’ve provided a default implementation and specified that
+`NewsArticle` implements the `Summary` trait. As a result, we can still call
+the `summarize` method on an instance of `NewsArticle`, like this:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-02-calling-default-impl/src/main.rs:here}}
+```
+
+This code prints `New article available! (Read more...)`.
+
+Creating a default implementation doesn’t require us to change anything about
+the implementation of `Summary` on `SocialPost` in Listing 10-13. The reason is
+that the syntax for overriding a default implementation is the same as the
+syntax for implementing a trait method that doesn’t have a default
+implementation.
+
+Default implementations can call other methods in the same trait, even if those
+other methods don’t have a default implementation. In this way, a trait can
+provide a lot of useful functionality and only require implementors to specify
+a small part of it. For example, we could define the `Summary` trait to have a
+`summarize_author` method whose implementation is required, and then define a
+`summarize` method that has a default implementation that calls the
+`summarize_author` method:
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/lib.rs:here}}
+```
+
+To use this version of `Summary`, we only need to define `summarize_author`
+when we implement the trait on a type:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/lib.rs:impl}}
+```
+
+After we define `summarize_author`, we can call `summarize` on instances of the
+`SocialPost` struct, and the default implementation of `summarize` will call the
+definition of `summarize_author` that we’ve provided. Because we’ve implemented
+`summarize_author`, the `Summary` trait has given us the behavior of the
+`summarize` method without requiring us to write any more code. Here’s what
+that looks like:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-03-default-impl-calls-other-methods/src/main.rs:here}}
+```
+
+This code prints `1 new post: (Read more from @horse_ebooks...)`.
+
+Note that it isn’t possible to call the default implementation from an
+overriding implementation of that same method.
+
+
+
+
+
+### Using Traits as Parameters
+
+Now that you know how to define and implement traits, we can explore how to use
+traits to define functions that accept many different types. We’ll use the
+`Summary` trait we implemented on the `NewsArticle` and `SocialPost` types in
+Listing 10-13 to define a `notify` function that calls the `summarize` method
+on its `item` parameter, which is of some type that implements the `Summary`
+trait. To do this, we use the `impl Trait` syntax, like this:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-04-traits-as-parameters/src/lib.rs:here}}
+```
+
+Instead of a concrete type for the `item` parameter, we specify the `impl`
+keyword and the trait name. This parameter accepts any type that implements the
+specified trait. In the body of `notify`, we can call any methods on `item`
+that come from the `Summary` trait, such as `summarize`. We can call `notify`
+and pass in any instance of `NewsArticle` or `SocialPost`. Code that calls the
+function with any other type, such as a `String` or an `i32`, won’t compile,
+because those types don’t implement `Summary`.
+
+
+
+
+
+#### Trait Bound Syntax
+
+The `impl Trait` syntax works for straightforward cases but is actually syntax
+sugar for a longer form known as a _trait bound_; it looks like this:
+
+```rust,ignore
+pub fn notify(item: &T) {
+ println!("Breaking news! {}", item.summarize());
+}
+```
+
+This longer form is equivalent to the example in the previous section but is
+more verbose. We place trait bounds with the declaration of the generic type
+parameter after a colon and inside angle brackets.
+
+The `impl Trait` syntax is convenient and makes for more concise code in simple
+cases, while the fuller trait bound syntax can express more complexity in other
+cases. For example, we can have two parameters that implement `Summary`. Doing
+so with the `impl Trait` syntax looks like this:
+
+```rust,ignore
+pub fn notify(item1: &impl Summary, item2: &impl Summary) {
+```
+
+Using `impl Trait` is appropriate if we want this function to allow `item1` and
+`item2` to have different types (as long as both types implement `Summary`). If
+we want to force both parameters to have the same type, however, we must use a
+trait bound, like this:
+
+```rust,ignore
+pub fn notify(item1: &T, item2: &T) {
+```
+
+The generic type `T` specified as the type of the `item1` and `item2`
+parameters constrains the function such that the concrete type of the value
+passed as an argument for `item1` and `item2` must be the same.
+
+
+
+
+
+#### Multiple Trait Bounds with the `+` Syntax
+
+We can also specify more than one trait bound. Say we wanted `notify` to use
+display formatting as well as `summarize` on `item`: We specify in the `notify`
+definition that `item` must implement both `Display` and `Summary`. We can do
+so using the `+` syntax:
+
+```rust,ignore
+pub fn notify(item: &(impl Summary + Display)) {
+```
+
+The `+` syntax is also valid with trait bounds on generic types:
+
+```rust,ignore
+pub fn notify(item: &T) {
+```
+
+With the two trait bounds specified, the body of `notify` can call `summarize`
+and use `{}` to format `item`.
+
+#### Clearer Trait Bounds with `where` Clauses
+
+Using too many trait bounds has its downsides. Each generic has its own trait
+bounds, so functions with multiple generic type parameters can contain lots of
+trait bound information between the function’s name and its parameter list,
+making the function signature hard to read. For this reason, Rust has alternate
+syntax for specifying trait bounds inside a `where` clause after the function
+signature. So, instead of writing this:
+
+```rust,ignore
+fn some_function(t: &T, u: &U) -> i32 {
+```
+
+we can use a `where` clause, like this:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-07-where-clause/src/lib.rs:here}}
+```
+
+This function’s signature is less cluttered: The function name, parameter list,
+and return type are close together, similar to a function without lots of trait
+bounds.
+
+### Returning Types That Implement Traits
+
+We can also use the `impl Trait` syntax in the return position to return a
+value of some type that implements a trait, as shown here:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-05-returning-impl-trait/src/lib.rs:here}}
+```
+
+By using `impl Summary` for the return type, we specify that the
+`returns_summarizable` function returns some type that implements the `Summary`
+trait without naming the concrete type. In this case, `returns_summarizable`
+returns a `SocialPost`, but the code calling this function doesn’t need to know
+that.
+
+The ability to specify a return type only by the trait it implements is
+especially useful in the context of closures and iterators, which we cover in
+Chapter 13. Closures and iterators create types that only the compiler knows or
+types that are very long to specify. The `impl Trait` syntax lets you concisely
+specify that a function returns some type that implements the `Iterator` trait
+without needing to write out a very long type.
+
+However, you can only use `impl Trait` if you’re returning a single type. For
+example, this code that returns either a `NewsArticle` or a `SocialPost` with
+the return type specified as `impl Summary` wouldn’t work:
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-06-impl-trait-returns-one-type/src/lib.rs:here}}
+```
+
+Returning either a `NewsArticle` or a `SocialPost` isn’t allowed due to
+restrictions around how the `impl Trait` syntax is implemented in the compiler.
+We’ll cover how to write a function with this behavior in the [“Using Trait
+Objects to Abstract over Shared Behavior”][trait-objects]
+section of Chapter 18.
+
+### Using Trait Bounds to Conditionally Implement Methods
+
+By using a trait bound with an `impl` block that uses generic type parameters,
+we can implement methods conditionally for types that implement the specified
+traits. For example, the type `Pair` in Listing 10-15 always implements the
+`new` function to return a new instance of `Pair` (recall from the [“Method
+Syntax”][methods] section of Chapter 5 that `Self` is a type
+alias for the type of the `impl` block, which in this case is `Pair`). But
+in the next `impl` block, `Pair` only implements the `cmp_display` method if
+its inner type `T` implements the `PartialOrd` trait that enables comparison
+_and_ the `Display` trait that enables printing.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-15/src/lib.rs}}
+```
+
+
+
+We can also conditionally implement a trait for any type that implements
+another trait. Implementations of a trait on any type that satisfies the trait
+bounds are called _blanket implementations_ and are used extensively in the
+Rust standard library. For example, the standard library implements the
+`ToString` trait on any type that implements the `Display` trait. The `impl`
+block in the standard library looks similar to this code:
+
+```rust,ignore
+impl ToString for T {
+ // --snip--
+}
+```
+
+Because the standard library has this blanket implementation, we can call the
+`to_string` method defined by the `ToString` trait on any type that implements
+the `Display` trait. For example, we can turn integers into their corresponding
+`String` values like this because integers implement `Display`:
+
+```rust
+let s = 3.to_string();
+```
+
+Blanket implementations appear in the documentation for the trait in the
+“Implementors” section.
+
+Traits and trait bounds let us write code that uses generic type parameters to
+reduce duplication but also specify to the compiler that we want the generic
+type to have particular behavior. The compiler can then use the trait bound
+information to check that all the concrete types used with our code provide the
+correct behavior. In dynamically typed languages, we would get an error at
+runtime if we called a method on a type that didn’t define the method. But Rust
+moves these errors to compile time so that we’re forced to fix the problems
+before our code is even able to run. Additionally, we don’t have to write code
+that checks for behavior at runtime, because we’ve already checked at compile
+time. Doing so improves performance without having to give up the flexibility
+of generics.
+
+[trait-objects]: ch18-02-trait-objects.html#using-trait-objects-to-abstract-over-shared-behavior
+[methods]: ch05-03-method-syntax.html#method-syntax
diff --git a/documents/markdown/rust-book/ch10-03-lifetime-syntax.md b/documents/markdown/rust-book/ch10-03-lifetime-syntax.md
new file mode 100644
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--- /dev/null
+++ b/documents/markdown/rust-book/ch10-03-lifetime-syntax.md
@@ -0,0 +1,641 @@
+## Validating References with Lifetimes
+
+Lifetimes are another kind of generic that we’ve already been using. Rather
+than ensuring that a type has the behavior we want, lifetimes ensure that
+references are valid as long as we need them to be.
+
+One detail we didn’t discuss in the [“References and
+Borrowing”][references-and-borrowing] section in Chapter 4 is
+that every reference in Rust has a lifetime, which is the scope for which
+that reference is valid. Most of the time, lifetimes are implicit and inferred,
+just like most of the time, types are inferred. We are only required to
+annotate types when multiple types are possible. In a similar way, we must
+annotate lifetimes when the lifetimes of references could be related in a few
+different ways. Rust requires us to annotate the relationships using generic
+lifetime parameters to ensure that the actual references used at runtime will
+definitely be valid.
+
+Annotating lifetimes is not even a concept most other programming languages
+have, so this is going to feel unfamiliar. Although we won’t cover lifetimes in
+their entirety in this chapter, we’ll discuss common ways you might encounter
+lifetime syntax so that you can get comfortable with the concept.
+
+
+
+
+
+### Dangling References
+
+The main aim of lifetimes is to prevent dangling references, which, if they
+were allowed to exist, would cause a program to reference data other than the
+data it’s intended to reference. Consider the program in Listing 10-16, which
+has an outer scope and an inner scope.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/src/main.rs}}
+```
+
+
+
+> Note: The examples in Listings 10-16, 10-17, and 10-23 declare variables
+> without giving them an initial value, so the variable name exists in the outer
+> scope. At first glance, this might appear to be in conflict with Rust having
+> no null values. However, if we try to use a variable before giving it a value,
+> we’ll get a compile-time error, which shows that indeed Rust does not allow
+> null values.
+
+The outer scope declares a variable named `r` with no initial value, and the
+inner scope declares a variable named `x` with the initial value of `5`. Inside
+the inner scope, we attempt to set the value of `r` as a reference to `x`.
+Then, the inner scope ends, and we attempt to print the value in `r`. This code
+won’t compile, because the value that `r` is referring to has gone out of scope
+before we try to use it. Here is the error message:
+
+```console
+{{#include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-16/output.txt}}
+```
+
+The error message says that the variable `x` “does not live long enough.” The
+reason is that `x` will be out of scope when the inner scope ends on line 7.
+But `r` is still valid for the outer scope; because its scope is larger, we say
+that it “lives longer.” If Rust allowed this code to work, `r` would be
+referencing memory that was deallocated when `x` went out of scope, and
+anything we tried to do with `r` wouldn’t work correctly. So, how does Rust
+determine that this code is invalid? It uses a borrow checker.
+
+### The Borrow Checker
+
+The Rust compiler has a _borrow checker_ that compares scopes to determine
+whether all borrows are valid. Listing 10-17 shows the same code as Listing
+10-16 but with annotations showing the lifetimes of the variables.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-17/src/main.rs}}
+```
+
+
+
+Here, we’ve annotated the lifetime of `r` with `'a` and the lifetime of `x`
+with `'b`. As you can see, the inner `'b` block is much smaller than the outer
+`'a` lifetime block. At compile time, Rust compares the size of the two
+lifetimes and sees that `r` has a lifetime of `'a` but that it refers to memory
+with a lifetime of `'b`. The program is rejected because `'b` is shorter than
+`'a`: The subject of the reference doesn’t live as long as the reference.
+
+Listing 10-18 fixes the code so that it doesn’t have a dangling reference and
+it compiles without any errors.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-18/src/main.rs}}
+```
+
+
+
+Here, `x` has the lifetime `'b`, which in this case is larger than `'a`. This
+means `r` can reference `x` because Rust knows that the reference in `r` will
+always be valid while `x` is valid.
+
+Now that you know where the lifetimes of references are and how Rust analyzes
+lifetimes to ensure that references will always be valid, let’s explore generic
+lifetimes in function parameters and return values.
+
+### Generic Lifetimes in Functions
+
+We’ll write a function that returns the longer of two string slices. This
+function will take two string slices and return a single string slice. After
+we’ve implemented the `longest` function, the code in Listing 10-19 should
+print `The longest string is abcd`.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-19/src/main.rs}}
+```
+
+
+
+Note that we want the function to take string slices, which are references,
+rather than strings, because we don’t want the `longest` function to take
+ownership of its parameters. Refer to [“String Slices as
+Parameters”][string-slices-as-parameters] in Chapter 4 for more
+discussion about why the parameters we use in Listing 10-19 are the ones we
+want.
+
+If we try to implement the `longest` function as shown in Listing 10-20, it
+won’t compile.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/src/main.rs:here}}
+```
+
+
+
+Instead, we get the following error that talks about lifetimes:
+
+```console
+{{#include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-20/output.txt}}
+```
+
+The help text reveals that the return type needs a generic lifetime parameter
+on it because Rust can’t tell whether the reference being returned refers to
+`x` or `y`. Actually, we don’t know either, because the `if` block in the body
+of this function returns a reference to `x` and the `else` block returns a
+reference to `y`!
+
+When we’re defining this function, we don’t know the concrete values that will
+be passed into this function, so we don’t know whether the `if` case or the
+`else` case will execute. We also don’t know the concrete lifetimes of the
+references that will be passed in, so we can’t look at the scopes as we did in
+Listings 10-17 and 10-18 to determine whether the reference we return will
+always be valid. The borrow checker can’t determine this either, because it
+doesn’t know how the lifetimes of `x` and `y` relate to the lifetime of the
+return value. To fix this error, we’ll add generic lifetime parameters that
+define the relationship between the references so that the borrow checker can
+perform its analysis.
+
+### Lifetime Annotation Syntax
+
+Lifetime annotations don’t change how long any of the references live. Rather,
+they describe the relationships of the lifetimes of multiple references to each
+other without affecting the lifetimes. Just as functions can accept any type
+when the signature specifies a generic type parameter, functions can accept
+references with any lifetime by specifying a generic lifetime parameter.
+
+Lifetime annotations have a slightly unusual syntax: The names of lifetime
+parameters must start with an apostrophe (`'`) and are usually all lowercase
+and very short, like generic types. Most people use the name `'a` for the first
+lifetime annotation. We place lifetime parameter annotations after the `&` of a
+reference, using a space to separate the annotation from the reference’s type.
+
+Here are some examples—a reference to an `i32` without a lifetime parameter, a
+reference to an `i32` that has a lifetime parameter named `'a`, and a mutable
+reference to an `i32` that also has the lifetime `'a`:
+
+```rust,ignore
+&i32 // a reference
+&'a i32 // a reference with an explicit lifetime
+&'a mut i32 // a mutable reference with an explicit lifetime
+```
+
+One lifetime annotation by itself doesn’t have much meaning, because the
+annotations are meant to tell Rust how generic lifetime parameters of multiple
+references relate to each other. Let’s examine how the lifetime annotations
+relate to each other in the context of the `longest` function.
+
+
+
+
+
+### In Function Signatures
+
+To use lifetime annotations in function signatures, we need to declare the
+generic lifetime parameters inside angle brackets between the function name and
+the parameter list, just as we did with generic type parameters.
+
+We want the signature to express the following constraint: The returned
+reference will be valid as long as both of the parameters are valid. This is
+the relationship between lifetimes of the parameters and the return value.
+We’ll name the lifetime `'a` and then add it to each reference, as shown in
+Listing 10-21.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-21/src/main.rs:here}}
+```
+
+
+
+This code should compile and produce the result we want when we use it with the
+`main` function in Listing 10-19.
+
+The function signature now tells Rust that for some lifetime `'a`, the function
+takes two parameters, both of which are string slices that live at least as
+long as lifetime `'a`. The function signature also tells Rust that the string
+slice returned from the function will live at least as long as lifetime `'a`.
+In practice, it means that the lifetime of the reference returned by the
+`longest` function is the same as the smaller of the lifetimes of the values
+referred to by the function arguments. These relationships are what we want
+Rust to use when analyzing this code.
+
+Remember, when we specify the lifetime parameters in this function signature,
+we’re not changing the lifetimes of any values passed in or returned. Rather,
+we’re specifying that the borrow checker should reject any values that don’t
+adhere to these constraints. Note that the `longest` function doesn’t need to
+know exactly how long `x` and `y` will live, only that some scope can be
+substituted for `'a` that will satisfy this signature.
+
+When annotating lifetimes in functions, the annotations go in the function
+signature, not in the function body. The lifetime annotations become part of
+the contract of the function, much like the types in the signature. Having
+function signatures contain the lifetime contract means the analysis the Rust
+compiler does can be simpler. If there’s a problem with the way a function is
+annotated or the way it is called, the compiler errors can point to the part of
+our code and the constraints more precisely. If, instead, the Rust compiler
+made more inferences about what we intended the relationships of the lifetimes
+to be, the compiler might only be able to point to a use of our code many steps
+away from the cause of the problem.
+
+When we pass concrete references to `longest`, the concrete lifetime that is
+substituted for `'a` is the part of the scope of `x` that overlaps with the
+scope of `y`. In other words, the generic lifetime `'a` will get the concrete
+lifetime that is equal to the smaller of the lifetimes of `x` and `y`. Because
+we’ve annotated the returned reference with the same lifetime parameter `'a`,
+the returned reference will also be valid for the length of the smaller of the
+lifetimes of `x` and `y`.
+
+Let’s look at how the lifetime annotations restrict the `longest` function by
+passing in references that have different concrete lifetimes. Listing 10-22 is
+a straightforward example.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-22/src/main.rs:here}}
+```
+
+
+
+In this example, `string1` is valid until the end of the outer scope, `string2`
+is valid until the end of the inner scope, and `result` references something
+that is valid until the end of the inner scope. Run this code and you’ll see
+that the borrow checker approves; it will compile and print `The longest string
+is long string is long`.
+
+Next, let’s try an example that shows that the lifetime of the reference in
+`result` must be the smaller lifetime of the two arguments. We’ll move the
+declaration of the `result` variable outside the inner scope but leave the
+assignment of the value to the `result` variable inside the scope with
+`string2`. Then, we’ll move the `println!` that uses `result` to outside the
+inner scope, after the inner scope has ended. The code in Listing 10-23 will
+not compile.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/src/main.rs:here}}
+```
+
+
+
+When we try to compile this code, we get this error:
+
+```console
+{{#include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-23/output.txt}}
+```
+
+The error shows that for `result` to be valid for the `println!` statement,
+`string2` would need to be valid until the end of the outer scope. Rust knows
+this because we annotated the lifetimes of the function parameters and return
+values using the same lifetime parameter `'a`.
+
+As humans, we can look at this code and see that `string1` is longer than
+`string2`, and therefore, `result` will contain a reference to `string1`.
+Because `string1` has not gone out of scope yet, a reference to `string1` will
+still be valid for the `println!` statement. However, the compiler can’t see
+that the reference is valid in this case. We’ve told Rust that the lifetime of
+the reference returned by the `longest` function is the same as the smaller of
+the lifetimes of the references passed in. Therefore, the borrow checker
+disallows the code in Listing 10-23 as possibly having an invalid reference.
+
+Try designing more experiments that vary the values and lifetimes of the
+references passed in to the `longest` function and how the returned reference
+is used. Make hypotheses about whether or not your experiments will pass the
+borrow checker before you compile; then, check to see if you’re right!
+
+
+
+
+
+### Relationships
+
+The way in which you need to specify lifetime parameters depends on what your
+function is doing. For example, if we changed the implementation of the
+`longest` function to always return the first parameter rather than the longest
+string slice, we wouldn’t need to specify a lifetime on the `y` parameter. The
+following code will compile:
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-08-only-one-reference-with-lifetime/src/main.rs:here}}
+```
+
+
+
+We’ve specified a lifetime parameter `'a` for the parameter `x` and the return
+type, but not for the parameter `y`, because the lifetime of `y` does not have
+any relationship with the lifetime of `x` or the return value.
+
+When returning a reference from a function, the lifetime parameter for the
+return type needs to match the lifetime parameter for one of the parameters. If
+the reference returned does _not_ refer to one of the parameters, it must refer
+to a value created within this function. However, this would be a dangling
+reference because the value will go out of scope at the end of the function.
+Consider this attempted implementation of the `longest` function that won’t
+compile:
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/src/main.rs:here}}
+```
+
+
+
+Here, even though we’ve specified a lifetime parameter `'a` for the return
+type, this implementation will fail to compile because the return value
+lifetime is not related to the lifetime of the parameters at all. Here is the
+error message we get:
+
+```console
+{{#include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-09-unrelated-lifetime/output.txt}}
+```
+
+The problem is that `result` goes out of scope and gets cleaned up at the end
+of the `longest` function. We’re also trying to return a reference to `result`
+from the function. There is no way we can specify lifetime parameters that
+would change the dangling reference, and Rust won’t let us create a dangling
+reference. In this case, the best fix would be to return an owned data type
+rather than a reference so that the calling function is then responsible for
+cleaning up the value.
+
+Ultimately, lifetime syntax is about connecting the lifetimes of various
+parameters and return values of functions. Once they’re connected, Rust has
+enough information to allow memory-safe operations and disallow operations that
+would create dangling pointers or otherwise violate memory safety.
+
+
+
+
+
+### In Struct Definitions
+
+So far, the structs we’ve defined all hold owned types. We can define structs
+to hold references, but in that case, we would need to add a lifetime
+annotation on every reference in the struct’s definition. Listing 10-24 has a
+struct named `ImportantExcerpt` that holds a string slice.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-24/src/main.rs}}
+```
+
+
+
+This struct has the single field `part` that holds a string slice, which is a
+reference. As with generic data types, we declare the name of the generic
+lifetime parameter inside angle brackets after the name of the struct so that
+we can use the lifetime parameter in the body of the struct definition. This
+annotation means an instance of `ImportantExcerpt` can’t outlive the reference
+it holds in its `part` field.
+
+The `main` function here creates an instance of the `ImportantExcerpt` struct
+that holds a reference to the first sentence of the `String` owned by the
+variable `novel`. The data in `novel` exists before the `ImportantExcerpt`
+instance is created. In addition, `novel` doesn’t go out of scope until after
+the `ImportantExcerpt` goes out of scope, so the reference in the
+`ImportantExcerpt` instance is valid.
+
+### Lifetime Elision
+
+You’ve learned that every reference has a lifetime and that you need to specify
+lifetime parameters for functions or structs that use references. However, we
+had a function in Listing 4-9, shown again in Listing 10-25, that compiled
+without lifetime annotations.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/listing-10-25/src/main.rs:here}}
+```
+
+
+
+The reason this function compiles without lifetime annotations is historical:
+In early versions (pre-1.0) of Rust, this code wouldn’t have compiled, because
+every reference needed an explicit lifetime. At that time, the function
+signature would have been written like this:
+
+```rust,ignore
+fn first_word<'a>(s: &'a str) -> &'a str {
+```
+
+After writing a lot of Rust code, the Rust team found that Rust programmers
+were entering the same lifetime annotations over and over in particular
+situations. These situations were predictable and followed a few deterministic
+patterns. The developers programmed these patterns into the compiler’s code so
+that the borrow checker could infer the lifetimes in these situations and
+wouldn’t need explicit annotations.
+
+This piece of Rust history is relevant because it’s possible that more
+deterministic patterns will emerge and be added to the compiler. In the future,
+even fewer lifetime annotations might be required.
+
+The patterns programmed into Rust’s analysis of references are called the
+_lifetime elision rules_. These aren’t rules for programmers to follow; they’re
+a set of particular cases that the compiler will consider, and if your code
+fits these cases, you don’t need to write the lifetimes explicitly.
+
+The elision rules don’t provide full inference. If there is still ambiguity
+about what lifetimes the references have after Rust applies the rules, the
+compiler won’t guess what the lifetime of the remaining references should be.
+Instead of guessing, the compiler will give you an error that you can resolve
+by adding the lifetime annotations.
+
+Lifetimes on function or method parameters are called _input lifetimes_, and
+lifetimes on return values are called _output lifetimes_.
+
+The compiler uses three rules to figure out the lifetimes of the references
+when there aren’t explicit annotations. The first rule applies to input
+lifetimes, and the second and third rules apply to output lifetimes. If the
+compiler gets to the end of the three rules and there are still references for
+which it can’t figure out lifetimes, the compiler will stop with an error.
+These rules apply to `fn` definitions as well as `impl` blocks.
+
+The first rule is that the compiler assigns a lifetime parameter to each
+parameter that’s a reference. In other words, a function with one parameter
+gets one lifetime parameter: `fn foo<'a>(x: &'a i32)`; a function with two
+parameters gets two separate lifetime parameters: `fn foo<'a, 'b>(x: &'a i32,
+y: &'b i32)`; and so on.
+
+The second rule is that, if there is exactly one input lifetime parameter, that
+lifetime is assigned to all output lifetime parameters: `fn foo<'a>(x: &'a i32)
+-> &'a i32`.
+
+The third rule is that, if there are multiple input lifetime parameters, but
+one of them is `&self` or `&mut self` because this is a method, the lifetime of
+`self` is assigned to all output lifetime parameters. This third rule makes
+methods much nicer to read and write because fewer symbols are necessary.
+
+Let’s pretend we’re the compiler. We’ll apply these rules to figure out the
+lifetimes of the references in the signature of the `first_word` function in
+Listing 10-25. The signature starts without any lifetimes associated with the
+references:
+
+```rust,ignore
+fn first_word(s: &str) -> &str {
+```
+
+Then, the compiler applies the first rule, which specifies that each parameter
+gets its own lifetime. We’ll call it `'a` as usual, so now the signature is
+this:
+
+```rust,ignore
+fn first_word<'a>(s: &'a str) -> &str {
+```
+
+The second rule applies because there is exactly one input lifetime. The second
+rule specifies that the lifetime of the one input parameter gets assigned to
+the output lifetime, so the signature is now this:
+
+```rust,ignore
+fn first_word<'a>(s: &'a str) -> &'a str {
+```
+
+Now all the references in this function signature have lifetimes, and the
+compiler can continue its analysis without needing the programmer to annotate
+the lifetimes in this function signature.
+
+Let’s look at another example, this time using the `longest` function that had
+no lifetime parameters when we started working with it in Listing 10-20:
+
+```rust,ignore
+fn longest(x: &str, y: &str) -> &str {
+```
+
+Let’s apply the first rule: Each parameter gets its own lifetime. This time we
+have two parameters instead of one, so we have two lifetimes:
+
+```rust,ignore
+fn longest<'a, 'b>(x: &'a str, y: &'b str) -> &str {
+```
+
+You can see that the second rule doesn’t apply, because there is more than one
+input lifetime. The third rule doesn’t apply either, because `longest` is a
+function rather than a method, so none of the parameters are `self`. After
+working through all three rules, we still haven’t figured out what the return
+type’s lifetime is. This is why we got an error trying to compile the code in
+Listing 10-20: The compiler worked through the lifetime elision rules but still
+couldn’t figure out all the lifetimes of the references in the signature.
+
+Because the third rule really only applies in method signatures, we’ll look at
+lifetimes in that context next to see why the third rule means we don’t have to
+annotate lifetimes in method signatures very often.
+
+
+
+
+
+### In Method Definitions
+
+When we implement methods on a struct with lifetimes, we use the same syntax as
+that of generic type parameters, as shown in Listing 10-11. Where we declare
+and use the lifetime parameters depends on whether they’re related to the
+struct fields or the method parameters and return values.
+
+Lifetime names for struct fields always need to be declared after the `impl`
+keyword and then used after the struct’s name because those lifetimes are part
+of the struct’s type.
+
+In method signatures inside the `impl` block, references might be tied to the
+lifetime of references in the struct’s fields, or they might be independent. In
+addition, the lifetime elision rules often make it so that lifetime annotations
+aren’t necessary in method signatures. Let’s look at some examples using the
+struct named `ImportantExcerpt` that we defined in Listing 10-24.
+
+First, we’ll use a method named `level` whose only parameter is a reference to
+`self` and whose return value is an `i32`, which is not a reference to anything:
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-10-lifetimes-on-methods/src/main.rs:1st}}
+```
+
+The lifetime parameter declaration after `impl` and its use after the type name
+are required, but because of the first elision rule, we’re not required to
+annotate the lifetime of the reference to `self`.
+
+Here is an example where the third lifetime elision rule applies:
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-10-lifetimes-on-methods/src/main.rs:3rd}}
+```
+
+There are two input lifetimes, so Rust applies the first lifetime elision rule
+and gives both `&self` and `announcement` their own lifetimes. Then, because
+one of the parameters is `&self`, the return type gets the lifetime of `&self`,
+and all lifetimes have been accounted for.
+
+### The Static Lifetime
+
+One special lifetime we need to discuss is `'static`, which denotes that the
+affected reference _can_ live for the entire duration of the program. All
+string literals have the `'static` lifetime, which we can annotate as follows:
+
+```rust
+let s: &'static str = "I have a static lifetime.";
+```
+
+The text of this string is stored directly in the program’s binary, which is
+always available. Therefore, the lifetime of all string literals is `'static`.
+
+You might see suggestions in error messages to use the `'static` lifetime. But
+before specifying `'static` as the lifetime for a reference, think about
+whether or not the reference you have actually lives the entire lifetime of
+your program, and whether you want it to. Most of the time, an error message
+suggesting the `'static` lifetime results from attempting to create a dangling
+reference or a mismatch of the available lifetimes. In such cases, the solution
+is to fix those problems, not to specify the `'static` lifetime.
+
+
+
+
+
+## Generic Type Parameters, Trait Bounds, and Lifetimes
+
+Let’s briefly look at the syntax of specifying generic type parameters, trait
+bounds, and lifetimes all in one function!
+
+```rust
+{{#rustdoc_include ../listings/ch10-generic-types-traits-and-lifetimes/no-listing-11-generics-traits-and-lifetimes/src/main.rs:here}}
+```
+
+This is the `longest` function from Listing 10-21 that returns the longer of
+two string slices. But now it has an extra parameter named `ann` of the generic
+type `T`, which can be filled in by any type that implements the `Display`
+trait as specified by the `where` clause. This extra parameter will be printed
+using `{}`, which is why the `Display` trait bound is necessary. Because
+lifetimes are a type of generic, the declarations of the lifetime parameter
+`'a` and the generic type parameter `T` go in the same list inside the angle
+brackets after the function name.
+
+## Summary
+
+We covered a lot in this chapter! Now that you know about generic type
+parameters, traits and trait bounds, and generic lifetime parameters, you’re
+ready to write code without repetition that works in many different situations.
+Generic type parameters let you apply the code to different types. Traits and
+trait bounds ensure that even though the types are generic, they’ll have the
+behavior the code needs. You learned how to use lifetime annotations to ensure
+that this flexible code won’t have any dangling references. And all of this
+analysis happens at compile time, which doesn’t affect runtime performance!
+
+Believe it or not, there is much more to learn on the topics we discussed in
+this chapter: Chapter 18 discusses trait objects, which are another way to use
+traits. There are also more complex scenarios involving lifetime annotations
+that you will only need in very advanced scenarios; for those, you should read
+the [Rust Reference][reference]. But next, you’ll learn how to write tests in
+Rust so that you can make sure your code is working the way it should.
+
+[references-and-borrowing]: ch04-02-references-and-borrowing.html#references-and-borrowing
+[string-slices-as-parameters]: ch04-03-slices.html#string-slices-as-parameters
+[reference]: ../reference/trait-bounds.html
diff --git a/documents/markdown/rust-book/ch11-00-testing.md b/documents/markdown/rust-book/ch11-00-testing.md
new file mode 100644
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+++ b/documents/markdown/rust-book/ch11-00-testing.md
@@ -0,0 +1,34 @@
+# Writing Automated Tests
+
+In his 1972 essay “The Humble Programmer,” Edsger W. Dijkstra said that “program
+testing can be a very effective way to show the presence of bugs, but it is
+hopelessly inadequate for showing their absence.” That doesn’t mean we shouldn’t
+try to test as much as we can!
+
+_Correctness_ in our programs is the extent to which our code does what we
+intend it to do. Rust is designed with a high degree of concern about the
+correctness of programs, but correctness is complex and not easy to prove.
+Rust’s type system shoulders a huge part of this burden, but the type system
+cannot catch everything. As such, Rust includes support for writing automated
+software tests.
+
+Say we write a function `add_two` that adds 2 to whatever number is passed to
+it. This function’s signature accepts an integer as a parameter and returns an
+integer as a result. When we implement and compile that function, Rust does all
+the type checking and borrow checking that you’ve learned so far to ensure
+that, for instance, we aren’t passing a `String` value or an invalid reference
+to this function. But Rust _can’t_ check that this function will do precisely
+what we intend, which is return the parameter plus 2 rather than, say, the
+parameter plus 10 or the parameter minus 50! That’s where tests come in.
+
+We can write tests that assert, for example, that when we pass `3` to the
+`add_two` function, the returned value is `5`. We can run these tests whenever
+we make changes to our code to make sure any existing correct behavior has not
+changed.
+
+Testing is a complex skill: Although we can’t cover in one chapter every detail
+about how to write good tests, in this chapter we will discuss the mechanics of
+Rust’s testing facilities. We’ll talk about the annotations and macros
+available to you when writing your tests, the default behavior and options
+provided for running your tests, and how to organize tests into unit tests and
+integration tests.
diff --git a/documents/markdown/rust-book/ch11-01-writing-tests.md b/documents/markdown/rust-book/ch11-01-writing-tests.md
new file mode 100644
index 0000000..e071b4c
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+++ b/documents/markdown/rust-book/ch11-01-writing-tests.md
@@ -0,0 +1,557 @@
+## How to Write Tests
+
+_Tests_ are Rust functions that verify that the non-test code is functioning in
+the expected manner. The bodies of test functions typically perform these three
+actions:
+
+- Set up any needed data or state.
+- Run the code you want to test.
+- Assert that the results are what you expect.
+
+Let’s look at the features Rust provides specifically for writing tests that
+take these actions, which include the `test` attribute, a few macros, and the
+`should_panic` attribute.
+
+
+
+
+
+### Structuring Test Functions
+
+At its simplest, a test in Rust is a function that’s annotated with the `test`
+attribute. Attributes are metadata about pieces of Rust code; one example is
+the `derive` attribute we used with structs in Chapter 5. To change a function
+into a test function, add `#[test]` on the line before `fn`. When you run your
+tests with the `cargo test` command, Rust builds a test runner binary that runs
+the annotated functions and reports on whether each test function passes or
+fails.
+
+Whenever we make a new library project with Cargo, a test module with a test
+function in it is automatically generated for us. This module gives you a
+template for writing your tests so that you don’t have to look up the exact
+structure and syntax every time you start a new project. You can add as many
+additional test functions and as many test modules as you want!
+
+We’ll explore some aspects of how tests work by experimenting with the template
+test before we actually test any code. Then, we’ll write some real-world tests
+that call some code that we’ve written and assert that its behavior is correct.
+
+Let’s create a new library project called `adder` that will add two numbers:
+
+```console
+$ cargo new adder --lib
+ Created library `adder` project
+$ cd adder
+```
+
+The contents of the _src/lib.rs_ file in your `adder` library should look like
+Listing 11-1.
+
+
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs}}
+```
+
+
+
+The file starts with an example `add` function so that we have something to
+test.
+
+For now, let’s focus solely on the `it_works` function. Note the `#[test]`
+annotation: This attribute indicates this is a test function, so the test
+runner knows to treat this function as a test. We might also have non-test
+functions in the `tests` module to help set up common scenarios or perform
+common operations, so we always need to indicate which functions are tests.
+
+The example function body uses the `assert_eq!` macro to assert that `result`,
+which contains the result of calling `add` with 2 and 2, equals 4. This
+assertion serves as an example of the format for a typical test. Let’s run it
+to see that this test passes.
+
+The `cargo test` command runs all tests in our project, as shown in Listing
+11-2.
+
+
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/listing-11-01/output.txt}}
+```
+
+
+
+Cargo compiled and ran the test. We see the line `running 1 test`. The next
+line shows the name of the generated test function, called `tests::it_works`,
+and that the result of running that test is `ok`. The overall summary `test
+result: ok.` means that all the tests passed, and the portion that reads `1
+passed; 0 failed` totals the number of tests that passed or failed.
+
+It’s possible to mark a test as ignored so that it doesn’t run in a particular
+instance; we’ll cover that in the [“Ignoring Tests Unless Specifically
+Requested”][ignoring] section later in this chapter. Because we
+haven’t done that here, the summary shows `0 ignored`. We can also pass an
+argument to the `cargo test` command to run only tests whose name matches a
+string; this is called _filtering_, and we’ll cover it in the [“Running a
+Subset of Tests by Name”][subset] section. Here, we haven’t
+filtered the tests being run, so the end of the summary shows `0 filtered out`.
+
+The `0 measured` statistic is for benchmark tests that measure performance.
+Benchmark tests are, as of this writing, only available in nightly Rust. See
+[the documentation about benchmark tests][bench] to learn more.
+
+The next part of the test output starting at `Doc-tests adder` is for the
+results of any documentation tests. We don’t have any documentation tests yet,
+but Rust can compile any code examples that appear in our API documentation.
+This feature helps keep your docs and your code in sync! We’ll discuss how to
+write documentation tests in the [“Documentation Comments as
+Tests”][doc-comments] section of Chapter 14. For now, we’ll
+ignore the `Doc-tests` output.
+
+Let’s start to customize the test to our own needs. First, change the name of
+the `it_works` function to a different name, such as `exploration`, like so:
+
+Filename: src/lib.rs
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/src/lib.rs}}
+```
+
+Then, run `cargo test` again. The output now shows `exploration` instead of
+`it_works`:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/no-listing-01-changing-test-name/output.txt}}
+```
+
+Now we’ll add another test, but this time we’ll make a test that fails! Tests
+fail when something in the test function panics. Each test is run in a new
+thread, and when the main thread sees that a test thread has died, the test is
+marked as failed. In Chapter 9, we talked about how the simplest way to panic
+is to call the `panic!` macro. Enter the new test as a function named
+`another`, so your _src/lib.rs_ file looks like Listing 11-3.
+
+
+
+```rust,panics,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-03/src/lib.rs}}
+```
+
+
+
+Run the tests again using `cargo test`. The output should look like Listing
+11-4, which shows that our `exploration` test passed and `another` failed.
+
+
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/listing-11-03/output.txt}}
+```
+
+
+
+
+
+Instead of `ok`, the line `test tests::another` shows `FAILED`. Two new
+sections appear between the individual results and the summary: The first
+displays the detailed reason for each test failure. In this case, we get the
+details that `tests::another` failed because it panicked with the message `Make
+this test fail` on line 17 in the _src/lib.rs_ file. The next section lists
+just the names of all the failing tests, which is useful when there are lots of
+tests and lots of detailed failing test output. We can use the name of a
+failing test to run just that test to debug it more easily; we’ll talk more
+about ways to run tests in the [“Controlling How Tests Are
+Run”][controlling-how-tests-are-run] section.
+
+The summary line displays at the end: Overall, our test result is `FAILED`. We
+had one test pass and one test fail.
+
+Now that you’ve seen what the test results look like in different scenarios,
+let’s look at some macros other than `panic!` that are useful in tests.
+
+
+
+
+
+### Checking Results with `assert!`
+
+The `assert!` macro, provided by the standard library, is useful when you want
+to ensure that some condition in a test evaluates to `true`. We give the
+`assert!` macro an argument that evaluates to a Boolean. If the value is
+`true`, nothing happens and the test passes. If the value is `false`, the
+`assert!` macro calls `panic!` to cause the test to fail. Using the `assert!`
+macro helps us check that our code is functioning in the way we intend.
+
+In Chapter 5, Listing 5-15, we used a `Rectangle` struct and a `can_hold`
+method, which are repeated here in Listing 11-5. Let’s put this code in the
+_src/lib.rs_ file, then write some tests for it using the `assert!` macro.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-05/src/lib.rs}}
+```
+
+
+
+The `can_hold` method returns a Boolean, which means it’s a perfect use case
+for the `assert!` macro. In Listing 11-6, we write a test that exercises the
+`can_hold` method by creating a `Rectangle` instance that has a width of 8 and
+a height of 7 and asserting that it can hold another `Rectangle` instance that
+has a width of 5 and a height of 1.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-06/src/lib.rs:here}}
+```
+
+
+
+Note the `use super::*;` line inside the `tests` module. The `tests` module is
+a regular module that follows the usual visibility rules we covered in Chapter
+7 in the [“Paths for Referring to an Item in the Module
+Tree”][paths-for-referring-to-an-item-in-the-module-tree]
+section. Because the `tests` module is an inner module, we need to bring the
+code under test in the outer module into the scope of the inner module. We use
+a glob here, so anything we define in the outer module is available to this
+`tests` module.
+
+We’ve named our test `larger_can_hold_smaller`, and we’ve created the two
+`Rectangle` instances that we need. Then, we called the `assert!` macro and
+passed it the result of calling `larger.can_hold(&smaller)`. This expression is
+supposed to return `true`, so our test should pass. Let’s find out!
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/listing-11-06/output.txt}}
+```
+
+It does pass! Let’s add another test, this time asserting that a smaller
+rectangle cannot hold a larger rectangle:
+
+Filename: src/lib.rs
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-02-adding-another-rectangle-test/src/lib.rs:here}}
+```
+
+Because the correct result of the `can_hold` function in this case is `false`,
+we need to negate that result before we pass it to the `assert!` macro. As a
+result, our test will pass if `can_hold` returns `false`:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/no-listing-02-adding-another-rectangle-test/output.txt}}
+```
+
+Two tests that pass! Now let’s see what happens to our test results when we
+introduce a bug in our code. We’ll change the implementation of the `can_hold`
+method by replacing the greater-than sign (`>`) with a less-than sign (`<`)
+when it compares the widths:
+
+```rust,not_desired_behavior,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/src/lib.rs:here}}
+```
+
+Running the tests now produces the following:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/no-listing-03-introducing-a-bug/output.txt}}
+```
+
+Our tests caught the bug! Because `larger.width` is `8` and `smaller.width` is
+`5`, the comparison of the widths in `can_hold` now returns `false`: 8 is not
+less than 5.
+
+
+
+
+
+### Testing Equality with `assert_eq!` and `assert_ne!`
+
+A common way to verify functionality is to test for equality between the result
+of the code under test and the value you expect the code to return. You could
+do this by using the `assert!` macro and passing it an expression using the
+`==` operator. However, this is such a common test that the standard library
+provides a pair of macros—`assert_eq!` and `assert_ne!`—to perform this test
+more conveniently. These macros compare two arguments for equality or
+inequality, respectively. They’ll also print the two values if the assertion
+fails, which makes it easier to see _why_ the test failed; conversely, the
+`assert!` macro only indicates that it got a `false` value for the `==`
+expression, without printing the values that led to the `false` value.
+
+In Listing 11-7, we write a function named `add_two` that adds `2` to its
+parameter, and then we test this function using the `assert_eq!` macro.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-07/src/lib.rs}}
+```
+
+
+
+Let’s check that it passes!
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/listing-11-07/output.txt}}
+```
+
+We create a variable named `result` that holds the result of calling
+`add_two(2)`. Then, we pass `result` and `4` as the arguments to the
+`assert_eq!` macro. The output line for this test is `test tests::it_adds_two
+... ok`, and the `ok` text indicates that our test passed!
+
+Let’s introduce a bug into our code to see what `assert_eq!` looks like when it
+fails. Change the implementation of the `add_two` function to instead add `3`:
+
+```rust,not_desired_behavior,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/src/lib.rs:here}}
+```
+
+Run the tests again:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/output.txt}}
+```
+
+Our test caught the bug! The `tests::it_adds_two` test failed, and the message
+tells us that the assertion that failed was `left == right` and what the `left`
+and `right` values are. This message helps us start debugging: The `left`
+argument, where we had the result of calling `add_two(2)`, was `5`, but the
+`right` argument was `4`. You can imagine that this would be especially helpful
+when we have a lot of tests going on.
+
+Note that in some languages and test frameworks, the parameters to equality
+assertion functions are called `expected` and `actual`, and the order in which
+we specify the arguments matters. However, in Rust, they’re called `left` and
+`right`, and the order in which we specify the value we expect and the value
+the code produces doesn’t matter. We could write the assertion in this test as
+`assert_eq!(4, result)`, which would result in the same failure message that
+displays `` assertion `left == right` failed ``.
+
+The `assert_ne!` macro will pass if the two values we give it are not equal and
+will fail if they are equal. This macro is most useful for cases when we’re not
+sure what a value _will_ be, but we know what the value definitely _shouldn’t_
+be. For example, if we’re testing a function that is guaranteed to change its
+input in some way, but the way in which the input is changed depends on the day
+of the week that we run our tests, the best thing to assert might be that the
+output of the function is not equal to the input.
+
+Under the surface, the `assert_eq!` and `assert_ne!` macros use the operators
+`==` and `!=`, respectively. When the assertions fail, these macros print their
+arguments using debug formatting, which means the values being compared must
+implement the `PartialEq` and `Debug` traits. All primitive types and most of
+the standard library types implement these traits. For structs and enums that
+you define yourself, you’ll need to implement `PartialEq` to assert equality of
+those types. You’ll also need to implement `Debug` to print the values when the
+assertion fails. Because both traits are derivable traits, as mentioned in
+Listing 5-12 in Chapter 5, this is usually as straightforward as adding the
+`#[derive(PartialEq, Debug)]` annotation to your struct or enum definition. See
+Appendix C, [“Derivable Traits,”][derivable-traits] for more
+details about these and other derivable traits.
+
+### Adding Custom Failure Messages
+
+You can also add a custom message to be printed with the failure message as
+optional arguments to the `assert!`, `assert_eq!`, and `assert_ne!` macros. Any
+arguments specified after the required arguments are passed along to the
+`format!` macro (discussed in [“Concatenating with `+` or
+`format!`”][concatenating] in Chapter 8), so you can pass a format string that contains `{}`
+placeholders and values to go in those placeholders. Custom messages are useful
+for documenting what an assertion means; when a test fails, you’ll have a better
+idea of what the problem is with the code.
+
+For example, let’s say we have a function that greets people by name and we
+want to test that the name we pass into the function appears in the output:
+
+Filename: src/lib.rs
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-05-greeter/src/lib.rs}}
+```
+
+The requirements for this program haven’t been agreed upon yet, and we’re
+pretty sure the `Hello` text at the beginning of the greeting will change. We
+decided we don’t want to have to update the test when the requirements change,
+so instead of checking for exact equality to the value returned from the
+`greeting` function, we’ll just assert that the output contains the text of the
+input parameter.
+
+Now let’s introduce a bug into this code by changing `greeting` to exclude
+`name` to see what the default test failure looks like:
+
+```rust,not_desired_behavior,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-06-greeter-with-bug/src/lib.rs:here}}
+```
+
+Running this test produces the following:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/no-listing-06-greeter-with-bug/output.txt}}
+```
+
+This result just indicates that the assertion failed and which line the
+assertion is on. A more useful failure message would print the value from the
+`greeting` function. Let’s add a custom failure message composed of a format
+string with a placeholder filled in with the actual value we got from the
+`greeting` function:
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/src/lib.rs:here}}
+```
+
+Now when we run the test, we’ll get a more informative error message:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/no-listing-07-custom-failure-message/output.txt}}
+```
+
+We can see the value we actually got in the test output, which would help us
+debug what happened instead of what we were expecting to happen.
+
+### Checking for Panics with `should_panic`
+
+In addition to checking return values, it’s important to check that our code
+handles error conditions as we expect. For example, consider the `Guess` type
+that we created in Chapter 9, Listing 9-13. Other code that uses `Guess`
+depends on the guarantee that `Guess` instances will contain only values
+between 1 and 100. We can write a test that ensures that attempting to create a
+`Guess` instance with a value outside that range panics.
+
+We do this by adding the attribute `should_panic` to our test function. The
+test passes if the code inside the function panics; the test fails if the code
+inside the function doesn’t panic.
+
+Listing 11-8 shows a test that checks that the error conditions of `Guess::new`
+happen when we expect them to.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-08/src/lib.rs}}
+```
+
+
+
+We place the `#[should_panic]` attribute after the `#[test]` attribute and
+before the test function it applies to. Let’s look at the result when this test
+passes:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/listing-11-08/output.txt}}
+```
+
+Looks good! Now let’s introduce a bug in our code by removing the condition
+that the `new` function will panic if the value is greater than 100:
+
+```rust,not_desired_behavior,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/src/lib.rs:here}}
+```
+
+When we run the test in Listing 11-8, it will fail:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/no-listing-08-guess-with-bug/output.txt}}
+```
+
+We don’t get a very helpful message in this case, but when we look at the test
+function, we see that it’s annotated with `#[should_panic]`. The failure we got
+means that the code in the test function did not cause a panic.
+
+Tests that use `should_panic` can be imprecise. A `should_panic` test would
+pass even if the test panics for a different reason from the one we were
+expecting. To make `should_panic` tests more precise, we can add an optional
+`expected` parameter to the `should_panic` attribute. The test harness will
+make sure that the failure message contains the provided text. For example,
+consider the modified code for `Guess` in Listing 11-9 where the `new` function
+panics with different messages depending on whether the value is too small or
+too large.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-09/src/lib.rs:here}}
+```
+
+
+
+This test will pass because the value we put in the `should_panic` attribute’s
+`expected` parameter is a substring of the message that the `Guess::new`
+function panics with. We could have specified the entire panic message that we
+expect, which in this case would be `Guess value must be less than or equal to
+100, got 200`. What you choose to specify depends on how much of the panic
+message is unique or dynamic and how precise you want your test to be. In this
+case, a substring of the panic message is enough to ensure that the code in the
+test function executes the `else if value > 100` case.
+
+To see what happens when a `should_panic` test with an `expected` message
+fails, let’s again introduce a bug into our code by swapping the bodies of the
+`if value < 1` and the `else if value > 100` blocks:
+
+```rust,ignore,not_desired_behavior
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/src/lib.rs:here}}
+```
+
+This time when we run the `should_panic` test, it will fail:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/no-listing-09-guess-with-panic-msg-bug/output.txt}}
+```
+
+The failure message indicates that this test did indeed panic as we expected,
+but the panic message did not include the expected string `less than or equal
+to 100`. The panic message that we did get in this case was `Guess value must
+be greater than or equal to 1, got 200`. Now we can start figuring out where
+our bug is!
+
+### Using `Result` in Tests
+
+All of our tests so far panic when they fail. We can also write tests that use
+`Result`! Here’s the test from Listing 11-1, rewritten to use `Result` and return an `Err` instead of panicking:
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-10-result-in-tests/src/lib.rs:here}}
+```
+
+The `it_works` function now has the `Result<(), String>` return type. In the
+body of the function, rather than calling the `assert_eq!` macro, we return
+`Ok(())` when the test passes and an `Err` with a `String` inside when the test
+fails.
+
+Writing tests so that they return a `Result` enables you to use the
+question mark operator in the body of tests, which can be a convenient way to
+write tests that should fail if any operation within them returns an `Err`
+variant.
+
+You can’t use the `#[should_panic]` annotation on tests that use `Result`. To assert that an operation returns an `Err` variant, _don’t_ use the
+question mark operator on the `Result` value. Instead, use
+`assert!(value.is_err())`.
+
+Now that you know several ways to write tests, let’s look at what is happening
+when we run our tests and explore the different options we can use with `cargo
+test`.
+
+[concatenating]: ch08-02-strings.html#concatenating-with--or-format
+[bench]: ../unstable-book/library-features/test.html
+[ignoring]: ch11-02-running-tests.html#ignoring-tests-unless-specifically-requested
+[subset]: ch11-02-running-tests.html#running-a-subset-of-tests-by-name
+[controlling-how-tests-are-run]: ch11-02-running-tests.html#controlling-how-tests-are-run
+[derivable-traits]: appendix-03-derivable-traits.html
+[doc-comments]: ch14-02-publishing-to-crates-io.html#documentation-comments-as-tests
+[paths-for-referring-to-an-item-in-the-module-tree]: ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html
diff --git a/documents/markdown/rust-book/ch11-02-running-tests.md b/documents/markdown/rust-book/ch11-02-running-tests.md
new file mode 100644
index 0000000..788ff64
--- /dev/null
+++ b/documents/markdown/rust-book/ch11-02-running-tests.md
@@ -0,0 +1,188 @@
+## Controlling How Tests Are Run
+
+Just as `cargo run` compiles your code and then runs the resultant binary,
+`cargo test` compiles your code in test mode and runs the resultant test
+binary. The default behavior of the binary produced by `cargo test` is to run
+all the tests in parallel and capture output generated during test runs,
+preventing the output from being displayed and making it easier to read the
+output related to the test results. You can, however, specify command line
+options to change this default behavior.
+
+Some command line options go to `cargo test`, and some go to the resultant test
+binary. To separate these two types of arguments, you list the arguments that
+go to `cargo test` followed by the separator `--` and then the ones that go to
+the test binary. Running `cargo test --help` displays the options you can use
+with `cargo test`, and running `cargo test -- --help` displays the options you
+can use after the separator. These options are also documented in [the “Tests”
+section of _The `rustc` Book_][tests].
+
+[tests]: https://doc.rust-lang.org/rustc/tests/index.html
+
+### Running Tests in Parallel or Consecutively
+
+When you run multiple tests, by default they run in parallel using threads,
+meaning they finish running more quickly and you get feedback sooner. Because
+the tests are running at the same time, you must make sure your tests don’t
+depend on each other or on any shared state, including a shared environment,
+such as the current working directory or environment variables.
+
+For example, say each of your tests runs some code that creates a file on disk
+named _test-output.txt_ and writes some data to that file. Then, each test
+reads the data in that file and asserts that the file contains a particular
+value, which is different in each test. Because the tests run at the same time,
+one test might overwrite the file in the time between when another test is
+writing and reading the file. The second test will then fail, not because the
+code is incorrect but because the tests have interfered with each other while
+running in parallel. One solution is to make sure each test writes to a
+different file; another solution is to run the tests one at a time.
+
+If you don’t want to run the tests in parallel or if you want more fine-grained
+control over the number of threads used, you can send the `--test-threads` flag
+and the number of threads you want to use to the test binary. Take a look at
+the following example:
+
+```console
+$ cargo test -- --test-threads=1
+```
+
+We set the number of test threads to `1`, telling the program not to use any
+parallelism. Running the tests using one thread will take longer than running
+them in parallel, but the tests won’t interfere with each other if they share
+state.
+
+### Showing Function Output
+
+By default, if a test passes, Rust’s test library captures anything printed to
+standard output. For example, if we call `println!` in a test and the test
+passes, we won’t see the `println!` output in the terminal; we’ll see only the
+line that indicates the test passed. If a test fails, we’ll see whatever was
+printed to standard output with the rest of the failure message.
+
+As an example, Listing 11-10 has a silly function that prints the value of its
+parameter and returns 10, as well as a test that passes and a test that fails.
+
+
+
+```rust,panics,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-10/src/lib.rs}}
+```
+
+
+
+When we run these tests with `cargo test`, we’ll see the following output:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/listing-11-10/output.txt}}
+```
+
+Note that nowhere in this output do we see `I got the value 4`, which is
+printed when the test that passes runs. That output has been captured. The
+output from the test that failed, `I got the value 8`, appears in the section
+of the test summary output, which also shows the cause of the test failure.
+
+If we want to see printed values for passing tests as well, we can tell Rust to
+also show the output of successful tests with `--show-output`:
+
+```console
+$ cargo test -- --show-output
+```
+
+When we run the tests in Listing 11-10 again with the `--show-output` flag, we
+see the following output:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/output-only-01-show-output/output.txt}}
+```
+
+### Running a Subset of Tests by Name
+
+Running a full test suite can sometimes take a long time. If you’re working on
+code in a particular area, you might want to run only the tests pertaining to
+that code. You can choose which tests to run by passing `cargo test` the name
+or names of the test(s) you want to run as an argument.
+
+To demonstrate how to run a subset of tests, we’ll first create three tests for
+our `add_two` function, as shown in Listing 11-11, and choose which ones to run.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-11/src/lib.rs}}
+```
+
+
+
+If we run the tests without passing any arguments, as we saw earlier, all the
+tests will run in parallel:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/listing-11-11/output.txt}}
+```
+
+#### Running Single Tests
+
+We can pass the name of any test function to `cargo test` to run only that test:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/output-only-02-single-test/output.txt}}
+```
+
+Only the test with the name `one_hundred` ran; the other two tests didn’t match
+that name. The test output lets us know we had more tests that didn’t run by
+displaying `2 filtered out` at the end.
+
+We can’t specify the names of multiple tests in this way; only the first value
+given to `cargo test` will be used. But there is a way to run multiple tests.
+
+#### Filtering to Run Multiple Tests
+
+We can specify part of a test name, and any test whose name matches that value
+will be run. For example, because two of our tests’ names contain `add`, we can
+run those two by running `cargo test add`:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/output-only-03-multiple-tests/output.txt}}
+```
+
+This command ran all tests with `add` in the name and filtered out the test
+named `one_hundred`. Also note that the module in which a test appears becomes
+part of the test’s name, so we can run all the tests in a module by filtering
+on the module’s name.
+
+
+
+
+
+### Ignoring Tests Unless Specifically Requested
+
+Sometimes a few specific tests can be very time-consuming to execute, so you
+might want to exclude them during most runs of `cargo test`. Rather than
+listing as arguments all tests you do want to run, you can instead annotate the
+time-consuming tests using the `ignore` attribute to exclude them, as shown
+here:
+
+Filename: src/lib.rs
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/src/lib.rs:here}}
+```
+
+After `#[test]`, we add the `#[ignore]` line to the test we want to exclude.
+Now when we run our tests, `it_works` runs, but `expensive_test` doesn’t:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/no-listing-11-ignore-a-test/output.txt}}
+```
+
+The `expensive_test` function is listed as `ignored`. If we want to run only
+the ignored tests, we can use `cargo test -- --ignored`:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/output-only-04-running-ignored/output.txt}}
+```
+
+By controlling which tests run, you can make sure your `cargo test` results
+will be returned quickly. When you’re at a point where it makes sense to check
+the results of the `ignored` tests and you have time to wait for the results,
+you can run `cargo test -- --ignored` instead. If you want to run all tests
+whether they’re ignored or not, you can run `cargo test -- --include-ignored`.
diff --git a/documents/markdown/rust-book/ch11-03-test-organization.md b/documents/markdown/rust-book/ch11-03-test-organization.md
new file mode 100644
index 0000000..dad604f
--- /dev/null
+++ b/documents/markdown/rust-book/ch11-03-test-organization.md
@@ -0,0 +1,266 @@
+## Test Organization
+
+As mentioned at the start of the chapter, testing is a complex discipline, and
+different people use different terminology and organization. The Rust community
+thinks about tests in terms of two main categories: unit tests and integration
+tests. _Unit tests_ are small and more focused, testing one module in isolation
+at a time, and can test private interfaces. _Integration tests_ are entirely
+external to your library and use your code in the same way any other external
+code would, using only the public interface and potentially exercising multiple
+modules per test.
+
+Writing both kinds of tests is important to ensure that the pieces of your
+library are doing what you expect them to, separately and together.
+
+### Unit Tests
+
+The purpose of unit tests is to test each unit of code in isolation from the
+rest of the code to quickly pinpoint where code is and isn’t working as
+expected. You’ll put unit tests in the _src_ directory in each file with the
+code that they’re testing. The convention is to create a module named `tests`
+in each file to contain the test functions and to annotate the module with
+`cfg(test)`.
+
+#### The `tests` Module and `#[cfg(test)]`
+
+The `#[cfg(test)]` annotation on the `tests` module tells Rust to compile and
+run the test code only when you run `cargo test`, not when you run `cargo
+build`. This saves compile time when you only want to build the library and
+saves space in the resultant compiled artifact because the tests are not
+included. You’ll see that because integration tests go in a different
+directory, they don’t need the `#[cfg(test)]` annotation. However, because unit
+tests go in the same files as the code, you’ll use `#[cfg(test)]` to specify
+that they shouldn’t be included in the compiled result.
+
+Recall that when we generated the new `adder` project in the first section of
+this chapter, Cargo generated this code for us:
+
+Filename: src/lib.rs
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-01/src/lib.rs}}
+```
+
+On the automatically generated `tests` module, the attribute `cfg` stands for
+_configuration_ and tells Rust that the following item should only be included
+given a certain configuration option. In this case, the configuration option is
+`test`, which is provided by Rust for compiling and running tests. By using the
+`cfg` attribute, Cargo compiles our test code only if we actively run the tests
+with `cargo test`. This includes any helper functions that might be within this
+module, in addition to the functions annotated with `#[test]`.
+
+
+
+
+
+#### Private Function Tests
+
+There’s debate within the testing community about whether or not private
+functions should be tested directly, and other languages make it difficult or
+impossible to test private functions. Regardless of which testing ideology you
+adhere to, Rust’s privacy rules do allow you to test private functions.
+Consider the code in Listing 11-12 with the private function `internal_adder`.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-12/src/lib.rs}}
+```
+
+
+
+Note that the `internal_adder` function is not marked as `pub`. Tests are just
+Rust code, and the `tests` module is just another module. As we discussed in
+[“Paths for Referring to an Item in the Module Tree”][paths],
+items in child modules can use the items in their ancestor modules. In this
+test, we bring all of the items belonging to the `tests` module’s parent into
+scope with `use super::*`, and then the test can call `internal_adder`. If you
+don’t think private functions should be tested, there’s nothing in Rust that
+will compel you to do so.
+
+### Integration Tests
+
+In Rust, integration tests are entirely external to your library. They use your
+library in the same way any other code would, which means they can only call
+functions that are part of your library’s public API. Their purpose is to test
+whether many parts of your library work together correctly. Units of code that
+work correctly on their own could have problems when integrated, so test
+coverage of the integrated code is important as well. To create integration
+tests, you first need a _tests_ directory.
+
+#### The _tests_ Directory
+
+We create a _tests_ directory at the top level of our project directory, next
+to _src_. Cargo knows to look for integration test files in this directory. We
+can then make as many test files as we want, and Cargo will compile each of the
+files as an individual crate.
+
+Let’s create an integration test. With the code in Listing 11-12 still in the
+_src/lib.rs_ file, make a _tests_ directory, and create a new file named
+_tests/integration_test.rs_. Your directory structure should look like this:
+
+```text
+adder
+├── Cargo.lock
+├── Cargo.toml
+├── src
+│ └── lib.rs
+└── tests
+ └── integration_test.rs
+```
+
+Enter the code in Listing 11-13 into the _tests/integration_test.rs_ file.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/listing-11-13/tests/integration_test.rs}}
+```
+
+
+
+Each file in the _tests_ directory is a separate crate, so we need to bring our
+library into each test crate’s scope. For that reason, we add `use
+adder::add_two;` at the top of the code, which we didn’t need in the unit tests.
+
+We don’t need to annotate any code in _tests/integration_test.rs_ with
+`#[cfg(test)]`. Cargo treats the _tests_ directory specially and compiles files
+in this directory only when we run `cargo test`. Run `cargo test` now:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/listing-11-13/output.txt}}
+```
+
+The three sections of output include the unit tests, the integration test, and
+the doc tests. Note that if any test in a section fails, the following sections
+will not be run. For example, if a unit test fails, there won’t be any output
+for integration and doc tests, because those tests will only be run if all unit
+tests are passing.
+
+The first section for the unit tests is the same as we’ve been seeing: one line
+for each unit test (one named `internal` that we added in Listing 11-12) and
+then a summary line for the unit tests.
+
+The integration tests section starts with the line `Running
+tests/integration_test.rs`. Next, there is a line for each test function in
+that integration test and a summary line for the results of the integration
+test just before the `Doc-tests adder` section starts.
+
+Each integration test file has its own section, so if we add more files in the
+_tests_ directory, there will be more integration test sections.
+
+We can still run a particular integration test function by specifying the test
+function’s name as an argument to `cargo test`. To run all the tests in a
+particular integration test file, use the `--test` argument of `cargo test`
+followed by the name of the file:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/output-only-05-single-integration/output.txt}}
+```
+
+This command runs only the tests in the _tests/integration_test.rs_ file.
+
+#### Submodules in Integration Tests
+
+As you add more integration tests, you might want to make more files in the
+_tests_ directory to help organize them; for example, you can group the test
+functions by the functionality they’re testing. As mentioned earlier, each file
+in the _tests_ directory is compiled as its own separate crate, which is useful
+for creating separate scopes to more closely imitate the way end users will be
+using your crate. However, this means files in the _tests_ directory don’t
+share the same behavior as files in _src_ do, as you learned in Chapter 7
+regarding how to separate code into modules and files.
+
+The different behavior of _tests_ directory files is most noticeable when you
+have a set of helper functions to use in multiple integration test files, and
+you try to follow the steps in the [“Separating Modules into Different
+Files”][separating-modules-into-files] section of Chapter 7 to
+extract them into a common module. For example, if we create _tests/common.rs_
+and place a function named `setup` in it, we can add some code to `setup` that
+we want to call from multiple test functions in multiple test files:
+
+Filename: tests/common.rs
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/tests/common.rs}}
+```
+
+When we run the tests again, we’ll see a new section in the test output for the
+_common.rs_ file, even though this file doesn’t contain any test functions nor
+did we call the `setup` function from anywhere:
+
+```console
+{{#include ../listings/ch11-writing-automated-tests/no-listing-12-shared-test-code-problem/output.txt}}
+```
+
+Having `common` appear in the test results with `running 0 tests` displayed for
+it is not what we wanted. We just wanted to share some code with the other
+integration test files. To avoid having `common` appear in the test output,
+instead of creating _tests/common.rs_, we’ll create _tests/common/mod.rs_. The
+project directory now looks like this:
+
+```text
+├── Cargo.lock
+├── Cargo.toml
+├── src
+│ └── lib.rs
+└── tests
+ ├── common
+ │ └── mod.rs
+ └── integration_test.rs
+```
+
+This is the older naming convention that Rust also understands that we mentioned
+in [“Alternate File Paths”][alt-paths] in Chapter 7. Naming the
+file this way tells Rust not to treat the `common` module as an integration test
+file. When we move the `setup` function code into _tests/common/mod.rs_ and
+delete the _tests/common.rs_ file, the section in the test output will no longer
+appear. Files in subdirectories of the _tests_ directory don’t get compiled as
+separate crates or have sections in the test output.
+
+After we’ve created _tests/common/mod.rs_, we can use it from any of the
+integration test files as a module. Here’s an example of calling the `setup`
+function from the `it_adds_two` test in _tests/integration_test.rs_:
+
+Filename: tests/integration_test.rs
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch11-writing-automated-tests/no-listing-13-fix-shared-test-code-problem/tests/integration_test.rs}}
+```
+
+Note that the `mod common;` declaration is the same as the module declaration
+we demonstrated in Listing 7-21. Then, in the test function, we can call the
+`common::setup()` function.
+
+#### Integration Tests for Binary Crates
+
+If our project is a binary crate that only contains a _src/main.rs_ file and
+doesn’t have a _src/lib.rs_ file, we can’t create integration tests in the
+_tests_ directory and bring functions defined in the _src/main.rs_ file into
+scope with a `use` statement. Only library crates expose functions that other
+crates can use; binary crates are meant to be run on their own.
+
+This is one of the reasons Rust projects that provide a binary have a
+straightforward _src/main.rs_ file that calls logic that lives in the
+_src/lib.rs_ file. Using that structure, integration tests _can_ test the
+library crate with `use` to make the important functionality available. If the
+important functionality works, the small amount of code in the _src/main.rs_
+file will work as well, and that small amount of code doesn’t need to be tested.
+
+## Summary
+
+Rust’s testing features provide a way to specify how code should function to
+ensure that it continues to work as you expect, even as you make changes. Unit
+tests exercise different parts of a library separately and can test private
+implementation details. Integration tests check that many parts of the library
+work together correctly, and they use the library’s public API to test the code
+in the same way external code will use it. Even though Rust’s type system and
+ownership rules help prevent some kinds of bugs, tests are still important to
+reduce logic bugs having to do with how your code is expected to behave.
+
+Let’s combine the knowledge you learned in this chapter and in previous
+chapters to work on a project!
+
+[paths]: ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html
+[separating-modules-into-files]: ch07-05-separating-modules-into-different-files.html
+[alt-paths]: ch07-05-separating-modules-into-different-files.html#alternate-file-paths
diff --git a/documents/markdown/rust-book/ch12-00-an-io-project.md b/documents/markdown/rust-book/ch12-00-an-io-project.md
new file mode 100644
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--- /dev/null
+++ b/documents/markdown/rust-book/ch12-00-an-io-project.md
@@ -0,0 +1,48 @@
+# An I/O Project: Building a Command Line Program
+
+This chapter is a recap of the many skills you’ve learned so far and an
+exploration of a few more standard library features. We’ll build a command line
+tool that interacts with file and command line input/output to practice some of
+the Rust concepts you now have under your belt.
+
+Rust’s speed, safety, single binary output, and cross-platform support make it
+an ideal language for creating command line tools, so for our project, we’ll
+make our own version of the classic command line search tool `grep`
+(**g**lobally search a **r**egular **e**xpression and **p**rint). In the
+simplest use case, `grep` searches a specified file for a specified string. To
+do so, `grep` takes as its arguments a file path and a string. Then, it reads
+the file, finds lines in that file that contain the string argument, and prints
+those lines.
+
+Along the way, we’ll show how to make our command line tool use the terminal
+features that many other command line tools use. We’ll read the value of an
+environment variable to allow the user to configure the behavior of our tool.
+We’ll also print error messages to the standard error console stream (`stderr`)
+instead of standard output (`stdout`) so that, for example, the user can
+redirect successful output to a file while still seeing error messages onscreen.
+
+One Rust community member, Andrew Gallant, has already created a fully
+featured, very fast version of `grep`, called `ripgrep`. By comparison, our
+version will be fairly simple, but this chapter will give you some of the
+background knowledge you need to understand a real-world project such as
+`ripgrep`.
+
+Our `grep` project will combine a number of concepts you’ve learned so far:
+
+- Organizing code ([Chapter 7][ch7])
+- Using vectors and strings ([Chapter 8][ch8])
+- Handling errors ([Chapter 9][ch9])
+- Using traits and lifetimes where appropriate ([Chapter 10][ch10])
+- Writing tests ([Chapter 11][ch11])
+
+We’ll also briefly introduce closures, iterators, and trait objects, which
+[Chapter 13][ch13] and [Chapter 18][ch18] will
+cover in detail.
+
+[ch7]: ch07-00-managing-growing-projects-with-packages-crates-and-modules.html
+[ch8]: ch08-00-common-collections.html
+[ch9]: ch09-00-error-handling.html
+[ch10]: ch10-00-generics.html
+[ch11]: ch11-00-testing.html
+[ch13]: ch13-00-functional-features.html
+[ch18]: ch18-00-oop.html
diff --git a/documents/markdown/rust-book/ch12-01-accepting-command-line-arguments.md b/documents/markdown/rust-book/ch12-01-accepting-command-line-arguments.md
new file mode 100644
index 0000000..46f2f37
--- /dev/null
+++ b/documents/markdown/rust-book/ch12-01-accepting-command-line-arguments.md
@@ -0,0 +1,133 @@
+## Accepting Command Line Arguments
+
+Let’s create a new project with, as always, `cargo new`. We’ll call our project
+`minigrep` to distinguish it from the `grep` tool that you might already have
+on your system:
+
+```console
+$ cargo new minigrep
+ Created binary (application) `minigrep` project
+$ cd minigrep
+```
+
+The first task is to make `minigrep` accept its two command line arguments: the
+file path and a string to search for. That is, we want to be able to run our
+program with `cargo run`, two hyphens to indicate the following arguments are
+for our program rather than for `cargo`, a string to search for, and a path to
+a file to search in, like so:
+
+```console
+$ cargo run -- searchstring example-filename.txt
+```
+
+Right now, the program generated by `cargo new` cannot process arguments we
+give it. Some existing libraries on [crates.io](https://crates.io/) can help
+with writing a program that accepts command line arguments, but because you’re
+just learning this concept, let’s implement this capability ourselves.
+
+### Reading the Argument Values
+
+To enable `minigrep` to read the values of command line arguments we pass to
+it, we’ll need the `std::env::args` function provided in Rust’s standard
+library. This function returns an iterator of the command line arguments passed
+to `minigrep`. We’ll cover iterators fully in [Chapter 13][ch13]. For now, you only need to know two details about iterators: Iterators
+produce a series of values, and we can call the `collect` method on an iterator
+to turn it into a collection, such as a vector, which contains all the elements
+the iterator produces.
+
+The code in Listing 12-1 allows your `minigrep` program to read any command
+line arguments passed to it and then collect the values into a vector.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-01/src/main.rs}}
+```
+
+
+
+First, we bring the `std::env` module into scope with a `use` statement so that
+we can use its `args` function. Notice that the `std::env::args` function is
+nested in two levels of modules. As we discussed in [Chapter
+7][ch7-idiomatic-use], in cases where the desired function is
+nested in more than one module, we’ve chosen to bring the parent module into
+scope rather than the function. By doing so, we can easily use other functions
+from `std::env`. It’s also less ambiguous than adding `use std::env::args` and
+then calling the function with just `args`, because `args` might easily be
+mistaken for a function that’s defined in the current module.
+
+> ### The `args` Function and Invalid Unicode
+>
+> Note that `std::env::args` will panic if any argument contains invalid
+> Unicode. If your program needs to accept arguments containing invalid
+> Unicode, use `std::env::args_os` instead. That function returns an iterator
+> that produces `OsString` values instead of `String` values. We’ve chosen to
+> use `std::env::args` here for simplicity because `OsString` values differ per
+> platform and are more complex to work with than `String` values.
+
+On the first line of `main`, we call `env::args`, and we immediately use
+`collect` to turn the iterator into a vector containing all the values produced
+by the iterator. We can use the `collect` function to create many kinds of
+collections, so we explicitly annotate the type of `args` to specify that we
+want a vector of strings. Although you very rarely need to annotate types in
+Rust, `collect` is one function you do often need to annotate because Rust
+isn’t able to infer the kind of collection you want.
+
+Finally, we print the vector using the debug macro. Let’s try running the code
+first with no arguments and then with two arguments:
+
+```console
+{{#include ../listings/ch12-an-io-project/listing-12-01/output.txt}}
+```
+
+```console
+{{#include ../listings/ch12-an-io-project/output-only-01-with-args/output.txt}}
+```
+
+Notice that the first value in the vector is `"target/debug/minigrep"`, which
+is the name of our binary. This matches the behavior of the arguments list in
+C, letting programs use the name by which they were invoked in their execution.
+It’s often convenient to have access to the program name in case you want to
+print it in messages or change the behavior of the program based on what
+command line alias was used to invoke the program. But for the purposes of this
+chapter, we’ll ignore it and save only the two arguments we need.
+
+### Saving the Argument Values in Variables
+
+The program is currently able to access the values specified as command line
+arguments. Now we need to save the values of the two arguments in variables so
+that we can use the values throughout the rest of the program. We do that in
+Listing 12-2.
+
+
+
+```rust,should_panic,noplayground
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-02/src/main.rs}}
+```
+
+
+
+As we saw when we printed the vector, the program’s name takes up the first
+value in the vector at `args[0]`, so we’re starting arguments at index 1. The
+first argument `minigrep` takes is the string we’re searching for, so we put a
+reference to the first argument in the variable `query`. The second argument
+will be the file path, so we put a reference to the second argument in the
+variable `file_path`.
+
+We temporarily print the values of these variables to prove that the code is
+working as we intend. Let’s run this program again with the arguments `test`
+and `sample.txt`:
+
+```console
+{{#include ../listings/ch12-an-io-project/listing-12-02/output.txt}}
+```
+
+Great, the program is working! The values of the arguments we need are being
+saved into the right variables. Later we’ll add some error handling to deal
+with certain potential erroneous situations, such as when the user provides no
+arguments; for now, we’ll ignore that situation and work on adding file-reading
+capabilities instead.
+
+[ch13]: ch13-00-functional-features.html
+[ch7-idiomatic-use]: ch07-04-bringing-paths-into-scope-with-the-use-keyword.html#creating-idiomatic-use-paths
diff --git a/documents/markdown/rust-book/ch12-02-reading-a-file.md b/documents/markdown/rust-book/ch12-02-reading-a-file.md
new file mode 100644
index 0000000..ce2eae5
--- /dev/null
+++ b/documents/markdown/rust-book/ch12-02-reading-a-file.md
@@ -0,0 +1,56 @@
+## Reading a File
+
+Now we’ll add functionality to read the file specified in the `file_path`
+argument. First, we need a sample file to test it with: We’ll use a file with a
+small amount of text over multiple lines with some repeated words. Listing 12-3
+has an Emily Dickinson poem that will work well! Create a file called
+_poem.txt_ at the root level of your project, and enter the poem “I’m Nobody!
+Who are you?”
+
+
+
+```text
+{{#include ../listings/ch12-an-io-project/listing-12-03/poem.txt}}
+```
+
+
+
+With the text in place, edit _src/main.rs_ and add code to read the file, as
+shown in Listing 12-4.
+
+
+
+```rust,should_panic,noplayground
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-04/src/main.rs:here}}
+```
+
+
+
+First, we bring in a relevant part of the standard library with a `use`
+statement: We need `std::fs` to handle files.
+
+In `main`, the new statement `fs::read_to_string` takes the `file_path`, opens
+that file, and returns a value of type `std::io::Result` that contains
+the file’s contents.
+
+After that, we again add a temporary `println!` statement that prints the value
+of `contents` after the file is read so that we can check that the program is
+working so far.
+
+Let’s run this code with any string as the first command line argument (because
+we haven’t implemented the searching part yet) and the _poem.txt_ file as the
+second argument:
+
+```console
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-04/output.txt}}
+```
+
+Great! The code read and then printed the contents of the file. But the code
+has a few flaws. At the moment, the `main` function has multiple
+responsibilities: Generally, functions are clearer and easier to maintain if
+each function is responsible for only one idea. The other problem is that we’re
+not handling errors as well as we could. The program is still small, so these
+flaws aren’t a big problem, but as the program grows, it will be harder to fix
+them cleanly. It’s a good practice to begin refactoring early on when
+developing a program because it’s much easier to refactor smaller amounts of
+code. We’ll do that next.
diff --git a/documents/markdown/rust-book/ch12-03-improving-error-handling-and-modularity.md b/documents/markdown/rust-book/ch12-03-improving-error-handling-and-modularity.md
new file mode 100644
index 0000000..5d3db28
--- /dev/null
+++ b/documents/markdown/rust-book/ch12-03-improving-error-handling-and-modularity.md
@@ -0,0 +1,513 @@
+## Refactoring to Improve Modularity and Error Handling
+
+To improve our program, we’ll fix four problems that have to do with the
+program’s structure and how it’s handling potential errors. First, our `main`
+function now performs two tasks: It parses arguments and reads files. As our
+program grows, the number of separate tasks the `main` function handles will
+increase. As a function gains responsibilities, it becomes more difficult to
+reason about, harder to test, and harder to change without breaking one of its
+parts. It’s best to separate functionality so that each function is responsible
+for one task.
+
+This issue also ties into the second problem: Although `query` and `file_path`
+are configuration variables to our program, variables like `contents` are used
+to perform the program’s logic. The longer `main` becomes, the more variables
+we’ll need to bring into scope; the more variables we have in scope, the harder
+it will be to keep track of the purpose of each. It’s best to group the
+configuration variables into one structure to make their purpose clear.
+
+The third problem is that we’ve used `expect` to print an error message when
+reading the file fails, but the error message just prints `Should have been
+able to read the file`. Reading a file can fail in a number of ways: For
+example, the file could be missing, or we might not have permission to open it.
+Right now, regardless of the situation, we’d print the same error message for
+everything, which wouldn’t give the user any information!
+
+Fourth, we use `expect` to handle an error, and if the user runs our program
+without specifying enough arguments, they’ll get an `index out of bounds` error
+from Rust that doesn’t clearly explain the problem. It would be best if all the
+error-handling code were in one place so that future maintainers had only one
+place to consult the code if the error-handling logic needed to change. Having
+all the error-handling code in one place will also ensure that we’re printing
+messages that will be meaningful to our end users.
+
+Let’s address these four problems by refactoring our project.
+
+
+
+
+
+### Separating Concerns in Binary Projects
+
+The organizational problem of allocating responsibility for multiple tasks to
+the `main` function is common to many binary projects. As a result, many Rust
+programmers find it useful to split up the separate concerns of a binary
+program when the `main` function starts getting large. This process has the
+following steps:
+
+- Split your program into a _main.rs_ file and a _lib.rs_ file and move your
+ program’s logic to _lib.rs_.
+- As long as your command line parsing logic is small, it can remain in
+ the `main` function.
+- When the command line parsing logic starts getting complicated, extract it
+ from the `main` function into other functions or types.
+
+The responsibilities that remain in the `main` function after this process
+should be limited to the following:
+
+- Calling the command line parsing logic with the argument values
+- Setting up any other configuration
+- Calling a `run` function in _lib.rs_
+- Handling the error if `run` returns an error
+
+This pattern is about separating concerns: _main.rs_ handles running the
+program and _lib.rs_ handles all the logic of the task at hand. Because you
+can’t test the `main` function directly, this structure lets you test all of
+your program’s logic by moving it out of the `main` function. The code that
+remains in the `main` function will be small enough to verify its correctness
+by reading it. Let’s rework our program by following this process.
+
+#### Extracting the Argument Parser
+
+We’ll extract the functionality for parsing arguments into a function that
+`main` will call. Listing 12-5 shows the new start of the `main` function that
+calls a new function `parse_config`, which we’ll define in _src/main.rs_.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-05/src/main.rs:here}}
+```
+
+
+
+We’re still collecting the command line arguments into a vector, but instead of
+assigning the argument value at index 1 to the variable `query` and the
+argument value at index 2 to the variable `file_path` within the `main`
+function, we pass the whole vector to the `parse_config` function. The
+`parse_config` function then holds the logic that determines which argument
+goes in which variable and passes the values back to `main`. We still create
+the `query` and `file_path` variables in `main`, but `main` no longer has the
+responsibility of determining how the command line arguments and variables
+correspond.
+
+This rework may seem like overkill for our small program, but we’re refactoring
+in small, incremental steps. After making this change, run the program again to
+verify that the argument parsing still works. It’s good to check your progress
+often, to help identify the cause of problems when they occur.
+
+#### Grouping Configuration Values
+
+We can take another small step to improve the `parse_config` function further.
+At the moment, we’re returning a tuple, but then we immediately break that
+tuple into individual parts again. This is a sign that perhaps we don’t have
+the right abstraction yet.
+
+Another indicator that shows there’s room for improvement is the `config` part
+of `parse_config`, which implies that the two values we return are related and
+are both part of one configuration value. We’re not currently conveying this
+meaning in the structure of the data other than by grouping the two values into
+a tuple; we’ll instead put the two values into one struct and give each of the
+struct fields a meaningful name. Doing so will make it easier for future
+maintainers of this code to understand how the different values relate to each
+other and what their purpose is.
+
+Listing 12-6 shows the improvements to the `parse_config` function.
+
+
+
+```rust,should_panic,noplayground
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-06/src/main.rs:here}}
+```
+
+
+
+We’ve added a struct named `Config` defined to have fields named `query` and
+`file_path`. The signature of `parse_config` now indicates that it returns a
+`Config` value. In the body of `parse_config`, where we used to return
+string slices that reference `String` values in `args`, we now define `Config`
+to contain owned `String` values. The `args` variable in `main` is the owner of
+the argument values and is only letting the `parse_config` function borrow
+them, which means we’d violate Rust’s borrowing rules if `Config` tried to take
+ownership of the values in `args`.
+
+There are a number of ways we could manage the `String` data; the easiest,
+though somewhat inefficient, route is to call the `clone` method on the values.
+This will make a full copy of the data for the `Config` instance to own, which
+takes more time and memory than storing a reference to the string data.
+However, cloning the data also makes our code very straightforward because we
+don’t have to manage the lifetimes of the references; in this circumstance,
+giving up a little performance to gain simplicity is a worthwhile trade-off.
+
+> ### The Trade-Offs of Using `clone`
+>
+> There’s a tendency among many Rustaceans to avoid using `clone` to fix
+> ownership problems because of its runtime cost. In
+> [Chapter 13][ch13], you’ll learn how to use more efficient
+> methods in this type of situation. But for now, it’s okay to copy a few
+> strings to continue making progress because you’ll make these copies only
+> once and your file path and query string are very small. It’s better to have
+> a working program that’s a bit inefficient than to try to hyperoptimize code
+> on your first pass. As you become more experienced with Rust, it’ll be
+> easier to start with the most efficient solution, but for now, it’s
+> perfectly acceptable to call `clone`.
+
+We’ve updated `main` so that it places the instance of `Config` returned by
+`parse_config` into a variable named `config`, and we updated the code that
+previously used the separate `query` and `file_path` variables so that it now
+uses the fields on the `Config` struct instead.
+
+Now our code more clearly conveys that `query` and `file_path` are related and
+that their purpose is to configure how the program will work. Any code that
+uses these values knows to find them in the `config` instance in the fields
+named for their purpose.
+
+#### Creating a Constructor for `Config`
+
+So far, we’ve extracted the logic responsible for parsing the command line
+arguments from `main` and placed it in the `parse_config` function. Doing so
+helped us see that the `query` and `file_path` values were related, and that
+relationship should be conveyed in our code. We then added a `Config` struct to
+name the related purpose of `query` and `file_path` and to be able to return the
+values’ names as struct field names from the `parse_config` function.
+
+So, now that the purpose of the `parse_config` function is to create a `Config`
+instance, we can change `parse_config` from a plain function to a function
+named `new` that is associated with the `Config` struct. Making this change
+will make the code more idiomatic. We can create instances of types in the
+standard library, such as `String`, by calling `String::new`. Similarly, by
+changing `parse_config` into a `new` function associated with `Config`, we’ll
+be able to create instances of `Config` by calling `Config::new`. Listing 12-7
+shows the changes we need to make.
+
+
+
+```rust,should_panic,noplayground
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-07/src/main.rs:here}}
+```
+
+
+
+We’ve updated `main` where we were calling `parse_config` to instead call
+`Config::new`. We’ve changed the name of `parse_config` to `new` and moved it
+within an `impl` block, which associates the `new` function with `Config`. Try
+compiling this code again to make sure it works.
+
+### Fixing the Error Handling
+
+Now we’ll work on fixing our error handling. Recall that attempting to access
+the values in the `args` vector at index 1 or index 2 will cause the program to
+panic if the vector contains fewer than three items. Try running the program
+without any arguments; it will look like this:
+
+```console
+{{#include ../listings/ch12-an-io-project/listing-12-07/output.txt}}
+```
+
+The line `index out of bounds: the len is 1 but the index is 1` is an error
+message intended for programmers. It won’t help our end users understand what
+they should do instead. Let’s fix that now.
+
+#### Improving the Error Message
+
+In Listing 12-8, we add a check in the `new` function that will verify that the
+slice is long enough before accessing index 1 and index 2. If the slice isn’t
+long enough, the program panics and displays a better error message.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-08/src/main.rs:here}}
+```
+
+
+
+This code is similar to [the `Guess::new` function we wrote in Listing
+9-13][ch9-custom-types], where we called `panic!` when the
+`value` argument was out of the range of valid values. Instead of checking for
+a range of values here, we’re checking that the length of `args` is at least
+`3` and the rest of the function can operate under the assumption that this
+condition has been met. If `args` has fewer than three items, this condition
+will be `true`, and we call the `panic!` macro to end the program immediately.
+
+With these extra few lines of code in `new`, let’s run the program without any
+arguments again to see what the error looks like now:
+
+```console
+{{#include ../listings/ch12-an-io-project/listing-12-08/output.txt}}
+```
+
+This output is better: We now have a reasonable error message. However, we also
+have extraneous information we don’t want to give to our users. Perhaps the
+technique we used in Listing 9-13 isn’t the best one to use here: A call to
+`panic!` is more appropriate for a programming problem than a usage problem,
+[as discussed in Chapter 9][ch9-error-guidelines]. Instead,
+we’ll use the other technique you learned about in Chapter 9—[returning a
+`Result`][ch9-result] that indicates either success or an error.
+
+
+
+
+
+#### Returning a `Result` Instead of Calling `panic!`
+
+We can instead return a `Result` value that will contain a `Config` instance in
+the successful case and will describe the problem in the error case. We’re also
+going to change the function name from `new` to `build` because many
+programmers expect `new` functions to never fail. When `Config::build` is
+communicating to `main`, we can use the `Result` type to signal there was a
+problem. Then, we can change `main` to convert an `Err` variant into a more
+practical error for our users without the surrounding text about `thread
+'main'` and `RUST_BACKTRACE` that a call to `panic!` causes.
+
+Listing 12-9 shows the changes we need to make to the return value of the
+function we’re now calling `Config::build` and the body of the function needed
+to return a `Result`. Note that this won’t compile until we update `main` as
+well, which we’ll do in the next listing.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-09/src/main.rs:here}}
+```
+
+
+
+Our `build` function returns a `Result` with a `Config` instance in the success
+case and a string literal in the error case. Our error values will always be
+string literals that have the `'static` lifetime.
+
+We’ve made two changes in the body of the function: Instead of calling `panic!`
+when the user doesn’t pass enough arguments, we now return an `Err` value, and
+we’ve wrapped the `Config` return value in an `Ok`. These changes make the
+function conform to its new type signature.
+
+Returning an `Err` value from `Config::build` allows the `main` function to
+handle the `Result` value returned from the `build` function and exit the
+process more cleanly in the error case.
+
+
+
+
+
+#### Calling `Config::build` and Handling Errors
+
+To handle the error case and print a user-friendly message, we need to update
+`main` to handle the `Result` being returned by `Config::build`, as shown in
+Listing 12-10. We’ll also take the responsibility of exiting the command line
+tool with a nonzero error code away from `panic!` and instead implement it by
+hand. A nonzero exit status is a convention to signal to the process that
+called our program that the program exited with an error state.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-10/src/main.rs:here}}
+```
+
+
+
+In this listing, we’ve used a method we haven’t covered in detail yet:
+`unwrap_or_else`, which is defined on `Result` by the standard library.
+Using `unwrap_or_else` allows us to define some custom, non-`panic!` error
+handling. If the `Result` is an `Ok` value, this method’s behavior is similar
+to `unwrap`: It returns the inner value that `Ok` is wrapping. However, if the
+value is an `Err` value, this method calls the code in the closure, which is
+an anonymous function we define and pass as an argument to `unwrap_or_else`.
+We’ll cover closures in more detail in [Chapter 13][ch13]. For
+now, you just need to know that `unwrap_or_else` will pass the inner value of
+the `Err`, which in this case is the static string `"not enough arguments"`
+that we added in Listing 12-9, to our closure in the argument `err` that
+appears between the vertical pipes. The code in the closure can then use the
+`err` value when it runs.
+
+We’ve added a new `use` line to bring `process` from the standard library into
+scope. The code in the closure that will be run in the error case is only two
+lines: We print the `err` value and then call `process::exit`. The
+`process::exit` function will stop the program immediately and return the
+number that was passed as the exit status code. This is similar to the
+`panic!`-based handling we used in Listing 12-8, but we no longer get all the
+extra output. Let’s try it:
+
+```console
+{{#include ../listings/ch12-an-io-project/listing-12-10/output.txt}}
+```
+
+Great! This output is much friendlier for our users.
+
+
+
+
+
+### Extracting Logic from `main`
+
+Now that we’ve finished refactoring the configuration parsing, let’s turn to
+the program’s logic. As we stated in [“Separating Concerns in Binary
+Projects”](#separation-of-concerns-for-binary-projects), we’ll
+extract a function named `run` that will hold all the logic currently in the
+`main` function that isn’t involved with setting up configuration or handling
+errors. When we’re done, the `main` function will be concise and easy to verify
+by inspection, and we’ll be able to write tests for all the other logic.
+
+Listing 12-11 shows the small, incremental improvement of extracting a `run`
+function.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-11/src/main.rs:here}}
+```
+
+
+
+The `run` function now contains all the remaining logic from `main`, starting
+from reading the file. The `run` function takes the `Config` instance as an
+argument.
+
+
+
+
+
+#### Returning Errors from `run`
+
+With the remaining program logic separated into the `run` function, we can
+improve the error handling, as we did with `Config::build` in Listing 12-9.
+Instead of allowing the program to panic by calling `expect`, the `run`
+function will return a `Result` when something goes wrong. This will let
+us further consolidate the logic around handling errors into `main` in a
+user-friendly way. Listing 12-12 shows the changes we need to make to the
+signature and body of `run`.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-12/src/main.rs:here}}
+```
+
+
+
+We’ve made three significant changes here. First, we changed the return type of
+the `run` function to `Result<(), Box>`. This function previously
+returned the unit type, `()`, and we keep that as the value returned in the
+`Ok` case.
+
+For the error type, we used the trait object `Box` (and we brought
+`std::error::Error` into scope with a `use` statement at the top). We’ll cover
+trait objects in [Chapter 18][ch18]. For now, just know that
+`Box` means the function will return a type that implements the
+`Error` trait, but we don’t have to specify what particular type the return
+value will be. This gives us flexibility to return error values that may be of
+different types in different error cases. The `dyn` keyword is short for
+_dynamic_.
+
+Second, we’ve removed the call to `expect` in favor of the `?` operator, as we
+talked about in [Chapter 9][ch9-question-mark]. Rather than
+`panic!` on an error, `?` will return the error value from the current function
+for the caller to handle.
+
+Third, the `run` function now returns an `Ok` value in the success case.
+We’ve declared the `run` function’s success type as `()` in the signature,
+which means we need to wrap the unit type value in the `Ok` value. This
+`Ok(())` syntax might look a bit strange at first. But using `()` like this is
+the idiomatic way to indicate that we’re calling `run` for its side effects
+only; it doesn’t return a value we need.
+
+When you run this code, it will compile but will display a warning:
+
+```console
+{{#include ../listings/ch12-an-io-project/listing-12-12/output.txt}}
+```
+
+Rust tells us that our code ignored the `Result` value and the `Result` value
+might indicate that an error occurred. But we’re not checking to see whether or
+not there was an error, and the compiler reminds us that we probably meant to
+have some error-handling code here! Let’s rectify that problem now.
+
+#### Handling Errors Returned from `run` in `main`
+
+We’ll check for errors and handle them using a technique similar to one we used
+with `Config::build` in Listing 12-10, but with a slight difference:
+
+Filename: src/main.rs
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch12-an-io-project/no-listing-01-handling-errors-in-main/src/main.rs:here}}
+```
+
+We use `if let` rather than `unwrap_or_else` to check whether `run` returns an
+`Err` value and to call `process::exit(1)` if it does. The `run` function
+doesn’t return a value that we want to `unwrap` in the same way that
+`Config::build` returns the `Config` instance. Because `run` returns `()` in
+the success case, we only care about detecting an error, so we don’t need
+`unwrap_or_else` to return the unwrapped value, which would only be `()`.
+
+The bodies of the `if let` and the `unwrap_or_else` functions are the same in
+both cases: We print the error and exit.
+
+### Splitting Code into a Library Crate
+
+Our `minigrep` project is looking good so far! Now we’ll split the
+_src/main.rs_ file and put some code into the _src/lib.rs_ file. That way, we
+can test the code and have a _src/main.rs_ file with fewer responsibilities.
+
+Let’s define the code responsible for searching text in _src/lib.rs_ rather
+than in _src/main.rs_, which will let us (or anyone else using our
+`minigrep` library) call the searching function from more contexts than our
+`minigrep` binary.
+
+First, let’s define the `search` function signature in _src/lib.rs_ as shown in
+Listing 12-13, with a body that calls the `unimplemented!` macro. We’ll explain
+the signature in more detail when we fill in the implementation.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-13/src/lib.rs}}
+```
+
+
+
+We’ve used the `pub` keyword on the function definition to designate `search`
+as part of our library crate’s public API. We now have a library crate that we
+can use from our binary crate and that we can test!
+
+Now we need to bring the code defined in _src/lib.rs_ into the scope of the
+binary crate in _src/main.rs_ and call it, as shown in Listing 12-14.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-14/src/main.rs:here}}
+```
+
+
+
+We add a `use minigrep::search` line to bring the `search` function from
+the library crate into the binary crate’s scope. Then, in the `run` function,
+rather than printing out the contents of the file, we call the `search`
+function and pass the `config.query` value and `contents` as arguments. Then,
+`run` will use a `for` loop to print each line returned from `search` that
+matched the query. This is also a good time to remove the `println!` calls in
+the `main` function that displayed the query and the file path so that our
+program only prints the search results (if no errors occur).
+
+Note that the search function will be collecting all the results into a vector
+it returns before any printing happens. This implementation could be slow to
+display results when searching large files, because results aren’t printed as
+they’re found; we’ll discuss a possible way to fix this using iterators in
+Chapter 13.
+
+Whew! That was a lot of work, but we’ve set ourselves up for success in the
+future. Now it’s much easier to handle errors, and we’ve made the code more
+modular. Almost all of our work will be done in _src/lib.rs_ from here on out.
+
+Let’s take advantage of this newfound modularity by doing something that would
+have been difficult with the old code but is easy with the new code: We’ll
+write some tests!
+
+[ch13]: ch13-00-functional-features.html
+[ch9-custom-types]: ch09-03-to-panic-or-not-to-panic.html#creating-custom-types-for-validation
+[ch9-error-guidelines]: ch09-03-to-panic-or-not-to-panic.html#guidelines-for-error-handling
+[ch9-result]: ch09-02-recoverable-errors-with-result.html
+[ch18]: ch18-00-oop.html
+[ch9-question-mark]: ch09-02-recoverable-errors-with-result.html#a-shortcut-for-propagating-errors-the--operator
diff --git a/documents/markdown/rust-book/ch12-04-testing-the-librarys-functionality.md b/documents/markdown/rust-book/ch12-04-testing-the-librarys-functionality.md
new file mode 100644
index 0000000..b5b5e4d
--- /dev/null
+++ b/documents/markdown/rust-book/ch12-04-testing-the-librarys-functionality.md
@@ -0,0 +1,218 @@
+
+
+
+## Adding Functionality with Test-Driven Development
+
+Now that we have the search logic in _src/lib.rs_ separate from the `main`
+function, it’s much easier to write tests for the core functionality of our
+code. We can call functions directly with various arguments and check return
+values without having to call our binary from the command line.
+
+In this section, we’ll add the searching logic to the `minigrep` program using
+the test-driven development (TDD) process with the following steps:
+
+1. Write a test that fails and run it to make sure it fails for the reason you
+ expect.
+2. Write or modify just enough code to make the new test pass.
+3. Refactor the code you just added or changed and make sure the tests continue
+ to pass.
+4. Repeat from step 1!
+
+Though it’s just one of many ways to write software, TDD can help drive code
+design. Writing the test before you write the code that makes the test pass
+helps maintain high test coverage throughout the process.
+
+We’ll test-drive the implementation of the functionality that will actually do
+the searching for the query string in the file contents and produce a list of
+lines that match the query. We’ll add this functionality in a function called
+`search`.
+
+### Writing a Failing Test
+
+In _src/lib.rs_, we’ll add a `tests` module with a test function, as we did in
+[Chapter 11][ch11-anatomy]. The test function specifies the
+behavior we want the `search` function to have: It will take a query and the
+text to search, and it will return only the lines from the text that contain
+the query. Listing 12-15 shows this test.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-15/src/lib.rs:here}}
+```
+
+
+
+This test searches for the string `"duct"`. The text we’re searching is three
+lines, only one of which contains `"duct"` (note that the backslash after the
+opening double quote tells Rust not to put a newline character at the beginning
+of the contents of this string literal). We assert that the value returned from
+the `search` function contains only the line we expect.
+
+If we run this test, it will currently fail because the `unimplemented!` macro
+panics with the message “not implemented”. In accordance with TDD principles,
+we’ll take a small step of adding just enough code to get the test to not panic
+when calling the function by defining the `search` function to always return an
+empty vector, as shown in Listing 12-16. Then, the test should compile and fail
+because an empty vector doesn’t match a vector containing the line `"safe,
+fast, productive."`.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-16/src/lib.rs:here}}
+```
+
+
+
+Now let’s discuss why we need to define an explicit lifetime `'a` in the
+signature of `search` and use that lifetime with the `contents` argument and
+the return value. Recall in [Chapter 10][ch10-lifetimes] that
+the lifetime parameters specify which argument lifetime is connected to the
+lifetime of the return value. In this case, we indicate that the returned
+vector should contain string slices that reference slices of the argument
+`contents` (rather than the argument `query`).
+
+In other words, we tell Rust that the data returned by the `search` function
+will live as long as the data passed into the `search` function in the
+`contents` argument. This is important! The data referenced _by_ a slice needs
+to be valid for the reference to be valid; if the compiler assumes we’re making
+string slices of `query` rather than `contents`, it will do its safety checking
+incorrectly.
+
+If we forget the lifetime annotations and try to compile this function, we’ll
+get this error:
+
+```console
+{{#include ../listings/ch12-an-io-project/output-only-02-missing-lifetimes/output.txt}}
+```
+
+Rust can’t know which of the two parameters we need for the output, so we need
+to tell it explicitly. Note that the help text suggests specifying the same
+lifetime parameter for all the parameters and the output type, which is
+incorrect! Because `contents` is the parameter that contains all of our text
+and we want to return the parts of that text that match, we know `contents` is
+the only parameter that should be connected to the return value using the
+lifetime syntax.
+
+Other programming languages don’t require you to connect arguments to return
+values in the signature, but this practice will get easier over time. You might
+want to compare this example with the examples in the [“Validating References
+with Lifetimes”][validating-references-with-lifetimes] section
+in Chapter 10.
+
+### Writing Code to Pass the Test
+
+Currently, our test is failing because we always return an empty vector. To fix
+that and implement `search`, our program needs to follow these steps:
+
+1. Iterate through each line of the contents.
+2. Check whether the line contains our query string.
+3. If it does, add it to the list of values we’re returning.
+4. If it doesn’t, do nothing.
+5. Return the list of results that match.
+
+Let’s work through each step, starting with iterating through lines.
+
+#### Iterating Through Lines with the `lines` Method
+
+Rust has a helpful method to handle line-by-line iteration of strings,
+conveniently named `lines`, that works as shown in Listing 12-17. Note that
+this won’t compile yet.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-17/src/lib.rs:here}}
+```
+
+
+
+The `lines` method returns an iterator. We’ll talk about iterators in depth in
+[Chapter 13][ch13-iterators]. But recall that you saw this way
+of using an iterator in [Listing 3-5][ch3-iter], where we used a
+`for` loop with an iterator to run some code on each item in a collection.
+
+#### Searching Each Line for the Query
+
+Next, we’ll check whether the current line contains our query string.
+Fortunately, strings have a helpful method named `contains` that does this for
+us! Add a call to the `contains` method in the `search` function, as shown in
+Listing 12-18. Note that this still won’t compile yet.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-18/src/lib.rs:here}}
+```
+
+
+
+At the moment, we’re building up functionality. To get the code to compile, we
+need to return a value from the body as we indicated we would in the function
+signature.
+
+#### Storing Matching Lines
+
+To finish this function, we need a way to store the matching lines that we want
+to return. For that, we can make a mutable vector before the `for` loop and
+call the `push` method to store a `line` in the vector. After the `for` loop,
+we return the vector, as shown in Listing 12-19.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-19/src/lib.rs:here}}
+```
+
+
+
+Now the `search` function should return only the lines that contain `query`,
+and our test should pass. Let’s run the test:
+
+```console
+{{#include ../listings/ch12-an-io-project/listing-12-19/output.txt}}
+```
+
+Our test passed, so we know it works!
+
+At this point, we could consider opportunities for refactoring the
+implementation of the search function while keeping the tests passing to
+maintain the same functionality. The code in the search function isn’t too bad,
+but it doesn’t take advantage of some useful features of iterators. We’ll
+return to this example in [Chapter 13][ch13-iterators], where
+we’ll explore iterators in detail, and look at how to improve it.
+
+Now the entire program should work! Let’s try it out, first with a word that
+should return exactly one line from the Emily Dickinson poem: _frog_.
+
+```console
+{{#include ../listings/ch12-an-io-project/no-listing-02-using-search-in-run/output.txt}}
+```
+
+Cool! Now let’s try a word that will match multiple lines, like _body_:
+
+```console
+{{#include ../listings/ch12-an-io-project/output-only-03-multiple-matches/output.txt}}
+```
+
+And finally, let’s make sure that we don’t get any lines when we search for a
+word that isn’t anywhere in the poem, such as _monomorphization_:
+
+```console
+{{#include ../listings/ch12-an-io-project/output-only-04-no-matches/output.txt}}
+```
+
+Excellent! We’ve built our own mini version of a classic tool and learned a lot
+about how to structure applications. We’ve also learned a bit about file input
+and output, lifetimes, testing, and command line parsing.
+
+To round out this project, we’ll briefly demonstrate how to work with
+environment variables and how to print to standard error, both of which are
+useful when you’re writing command line programs.
+
+[validating-references-with-lifetimes]: ch10-03-lifetime-syntax.html#validating-references-with-lifetimes
+[ch11-anatomy]: ch11-01-writing-tests.html#the-anatomy-of-a-test-function
+[ch10-lifetimes]: ch10-03-lifetime-syntax.html
+[ch3-iter]: ch03-05-control-flow.html#looping-through-a-collection-with-for
+[ch13-iterators]: ch13-02-iterators.html
diff --git a/documents/markdown/rust-book/ch12-05-working-with-environment-variables.md b/documents/markdown/rust-book/ch12-05-working-with-environment-variables.md
new file mode 100644
index 0000000..39c3dad
--- /dev/null
+++ b/documents/markdown/rust-book/ch12-05-working-with-environment-variables.md
@@ -0,0 +1,204 @@
+## Working with Environment Variables
+
+We’ll improve the `minigrep` binary by adding an extra feature: an option for
+case-insensitive searching that the user can turn on via an environment
+variable. We could make this feature a command line option and require that
+users enter it each time they want it to apply, but by instead making it an
+environment variable, we allow our users to set the environment variable once
+and have all their searches be case insensitive in that terminal session.
+
+
+
+
+### Writing a Failing Test for Case-Insensitive Search
+
+We first add a new `search_case_insensitive` function to the `minigrep` library
+that will be called when the environment variable has a value. We’ll continue
+to follow the TDD process, so the first step is again to write a failing test.
+We’ll add a new test for the new `search_case_insensitive` function and rename
+our old test from `one_result` to `case_sensitive` to clarify the differences
+between the two tests, as shown in Listing 12-20.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-20/src/lib.rs:here}}
+```
+
+
+
+Note that we’ve edited the old test’s `contents` too. We’ve added a new line
+with the text `"Duct tape."` using a capital _D_ that shouldn’t match the query
+`"duct"` when we’re searching in a case-sensitive manner. Changing the old test
+in this way helps ensure that we don’t accidentally break the case-sensitive
+search functionality that we’ve already implemented. This test should pass now
+and should continue to pass as we work on the case-insensitive search.
+
+The new test for the case-_insensitive_ search uses `"rUsT"` as its query. In
+the `search_case_insensitive` function we’re about to add, the query `"rUsT"`
+should match the line containing `"Rust:"` with a capital _R_ and match the
+line `"Trust me."` even though both have different casing from the query. This
+is our failing test, and it will fail to compile because we haven’t yet defined
+the `search_case_insensitive` function. Feel free to add a skeleton
+implementation that always returns an empty vector, similar to the way we did
+for the `search` function in Listing 12-16 to see the test compile and fail.
+
+### Implementing the `search_case_insensitive` Function
+
+The `search_case_insensitive` function, shown in Listing 12-21, will be almost
+the same as the `search` function. The only difference is that we’ll lowercase
+the `query` and each `line` so that whatever the case of the input arguments,
+they’ll be the same case when we check whether the line contains the query.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-21/src/lib.rs:here}}
+```
+
+
+
+First, we lowercase the `query` string and store it in a new variable with the
+same name, shadowing the original `query`. Calling `to_lowercase` on the query
+is necessary so that no matter whether the user’s query is `"rust"`, `"RUST"`,
+`"Rust"`, or `"rUsT"`, we’ll treat the query as if it were `"rust"` and be
+insensitive to the case. While `to_lowercase` will handle basic Unicode, it
+won’t be 100 percent accurate. If we were writing a real application, we’d want
+to do a bit more work here, but this section is about environment variables,
+not Unicode, so we’ll leave it at that here.
+
+Note that `query` is now a `String` rather than a string slice because calling
+`to_lowercase` creates new data rather than referencing existing data. Say the
+query is `"rUsT"`, as an example: That string slice doesn’t contain a lowercase
+`u` or `t` for us to use, so we have to allocate a new `String` containing
+`"rust"`. When we pass `query` as an argument to the `contains` method now, we
+need to add an ampersand because the signature of `contains` is defined to take
+a string slice.
+
+Next, we add a call to `to_lowercase` on each `line` to lowercase all
+characters. Now that we’ve converted `line` and `query` to lowercase, we’ll
+find matches no matter what the case of the query is.
+
+Let’s see if this implementation passes the tests:
+
+```console
+{{#include ../listings/ch12-an-io-project/listing-12-21/output.txt}}
+```
+
+Great! They passed. Now let’s call the new `search_case_insensitive` function
+from the `run` function. First, we’ll add a configuration option to the `Config`
+struct to switch between case-sensitive and case-insensitive search. Adding
+this field will cause compiler errors because we aren’t initializing this field
+anywhere yet:
+
+Filename: src/main.rs
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-22/src/main.rs:here}}
+```
+
+We added the `ignore_case` field that holds a Boolean. Next, we need the `run`
+function to check the `ignore_case` field’s value and use that to decide
+whether to call the `search` function or the `search_case_insensitive`
+function, as shown in Listing 12-22. This still won’t compile yet.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-22/src/main.rs:there}}
+```
+
+
+
+Finally, we need to check for the environment variable. The functions for
+working with environment variables are in the `env` module in the standard
+library, which is already in scope at the top of _src/main.rs_. We’ll use the
+`var` function from the `env` module to check to see if any value has been set
+for an environment variable named `IGNORE_CASE`, as shown in Listing 12-23.
+
+
+
+```rust,ignore,noplayground
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-23/src/main.rs:here}}
+```
+
+
+
+Here, we create a new variable, `ignore_case`. To set its value, we call the
+`env::var` function and pass it the name of the `IGNORE_CASE` environment
+variable. The `env::var` function returns a `Result` that will be the
+successful `Ok` variant that contains the value of the environment variable if
+the environment variable is set to any value. It will return the `Err` variant
+if the environment variable is not set.
+
+We’re using the `is_ok` method on the `Result` to check whether the environment
+variable is set, which means the program should do a case-insensitive search.
+If the `IGNORE_CASE` environment variable isn’t set to anything, `is_ok` will
+return `false` and the program will perform a case-sensitive search. We don’t
+care about the _value_ of the environment variable, just whether it’s set or
+unset, so we’re checking `is_ok` rather than using `unwrap`, `expect`, or any
+of the other methods we’ve seen on `Result`.
+
+We pass the value in the `ignore_case` variable to the `Config` instance so
+that the `run` function can read that value and decide whether to call
+`search_case_insensitive` or `search`, as we implemented in Listing 12-22.
+
+Let’s give it a try! First, we’ll run our program without the environment
+variable set and with the query `to`, which should match any line that contains
+the word _to_ in all lowercase:
+
+```console
+{{#include ../listings/ch12-an-io-project/listing-12-23/output.txt}}
+```
+
+Looks like that still works! Now let’s run the program with `IGNORE_CASE` set
+to `1` but with the same query `to`:
+
+```console
+$ IGNORE_CASE=1 cargo run -- to poem.txt
+```
+
+If you’re using PowerShell, you will need to set the environment variable and
+run the program as separate commands:
+
+```console
+PS> $Env:IGNORE_CASE=1; cargo run -- to poem.txt
+```
+
+This will make `IGNORE_CASE` persist for the remainder of your shell session.
+It can be unset with the `Remove-Item` cmdlet:
+
+```console
+PS> Remove-Item Env:IGNORE_CASE
+```
+
+We should get lines that contain _to_ that might have uppercase letters:
+
+
+
+```console
+Are you nobody, too?
+How dreary to be somebody!
+To tell your name the livelong day
+To an admiring bog!
+```
+
+Excellent, we also got lines containing _To_! Our `minigrep` program can now do
+case-insensitive searching controlled by an environment variable. Now you know
+how to manage options set using either command line arguments or environment
+variables.
+
+Some programs allow arguments _and_ environment variables for the same
+configuration. In those cases, the programs decide that one or the other takes
+precedence. For another exercise on your own, try controlling case sensitivity
+through either a command line argument or an environment variable. Decide
+whether the command line argument or the environment variable should take
+precedence if the program is run with one set to case sensitive and one set to
+ignore case.
+
+The `std::env` module contains many more useful features for dealing with
+environment variables: Check out its documentation to see what is available.
diff --git a/documents/markdown/rust-book/ch12-06-writing-to-stderr-instead-of-stdout.md b/documents/markdown/rust-book/ch12-06-writing-to-stderr-instead-of-stdout.md
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+++ b/documents/markdown/rust-book/ch12-06-writing-to-stderr-instead-of-stdout.md
@@ -0,0 +1,112 @@
+
+
+
+
+## Redirecting Errors to Standard Error
+
+At the moment, we’re writing all of our output to the terminal using the
+`println!` macro. In most terminals, there are two kinds of output: _standard
+output_ (`stdout`) for general information and _standard error_ (`stderr`) for
+error messages. This distinction enables users to choose to direct the
+successful output of a program to a file but still print error messages to the
+screen.
+
+The `println!` macro is only capable of printing to standard output, so we have
+to use something else to print to standard error.
+
+### Checking Where Errors Are Written
+
+First, let’s observe how the content printed by `minigrep` is currently being
+written to standard output, including any error messages we want to write to
+standard error instead. We’ll do that by redirecting the standard output stream
+to a file while intentionally causing an error. We won’t redirect the standard
+error stream, so any content sent to standard error will continue to display on
+the screen.
+
+Command line programs are expected to send error messages to the standard error
+stream so that we can still see error messages on the screen even if we
+redirect the standard output stream to a file. Our program is not currently
+well behaved: We’re about to see that it saves the error message output to a
+file instead!
+
+To demonstrate this behavior, we’ll run the program with `>` and the file path,
+_output.txt_, that we want to redirect the standard output stream to. We won’t
+pass any arguments, which should cause an error:
+
+```console
+$ cargo run > output.txt
+```
+
+The `>` syntax tells the shell to write the contents of standard output to
+_output.txt_ instead of the screen. We didn’t see the error message we were
+expecting printed to the screen, so that means it must have ended up in the
+file. This is what _output.txt_ contains:
+
+```text
+Problem parsing arguments: not enough arguments
+```
+
+Yup, our error message is being printed to standard output. It’s much more
+useful for error messages like this to be printed to standard error so that
+only data from a successful run ends up in the file. We’ll change that.
+
+### Printing Errors to Standard Error
+
+We’ll use the code in Listing 12-24 to change how error messages are printed.
+Because of the refactoring we did earlier in this chapter, all the code that
+prints error messages is in one function, `main`. The standard library provides
+the `eprintln!` macro that prints to the standard error stream, so let’s change
+the two places we were calling `println!` to print errors to use `eprintln!`
+instead.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-24/src/main.rs:here}}
+```
+
+
+
+Let’s now run the program again in the same way, without any arguments and
+redirecting standard output with `>`:
+
+```console
+$ cargo run > output.txt
+Problem parsing arguments: not enough arguments
+```
+
+Now we see the error onscreen and _output.txt_ contains nothing, which is the
+behavior we expect of command line programs.
+
+Let’s run the program again with arguments that don’t cause an error but still
+redirect standard output to a file, like so:
+
+```console
+$ cargo run -- to poem.txt > output.txt
+```
+
+We won’t see any output to the terminal, and _output.txt_ will contain our
+results:
+
+Filename: output.txt
+
+```text
+Are you nobody, too?
+How dreary to be somebody!
+```
+
+This demonstrates that we’re now using standard output for successful output
+and standard error for error output as appropriate.
+
+## Summary
+
+This chapter recapped some of the major concepts you’ve learned so far and
+covered how to perform common I/O operations in Rust. By using command line
+arguments, files, environment variables, and the `eprintln!` macro for printing
+errors, you’re now prepared to write command line applications. Combined with
+the concepts in previous chapters, your code will be well organized, store data
+effectively in the appropriate data structures, handle errors nicely, and be
+well tested.
+
+Next, we’ll explore some Rust features that were influenced by functional
+languages: closures and iterators.
diff --git a/documents/markdown/rust-book/ch13-00-functional-features.md b/documents/markdown/rust-book/ch13-00-functional-features.md
new file mode 100644
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--- /dev/null
+++ b/documents/markdown/rust-book/ch13-00-functional-features.md
@@ -0,0 +1,24 @@
+# Functional Language Features: Iterators and Closures
+
+Rust’s design has taken inspiration from many existing languages and
+techniques, and one significant influence is _functional programming_.
+Programming in a functional style often includes using functions as values by
+passing them in arguments, returning them from other functions, assigning them
+to variables for later execution, and so forth.
+
+In this chapter, we won’t debate the issue of what functional programming is or
+isn’t but will instead discuss some features of Rust that are similar to
+features in many languages often referred to as functional.
+
+More specifically, we’ll cover:
+
+- _Closures_, a function-like construct you can store in a variable
+- _Iterators_, a way of processing a series of elements
+- How to use closures and iterators to improve the I/O project in Chapter 12
+- The performance of closures and iterators (spoiler alert: They’re faster than
+ you might think!)
+
+We’ve already covered some other Rust features, such as pattern matching and
+enums, that are also influenced by the functional style. Because mastering
+closures and iterators is an important part of writing fast, idiomatic, Rust
+code, we’ll devote this entire chapter to them.
diff --git a/documents/markdown/rust-book/ch13-01-closures.md b/documents/markdown/rust-book/ch13-01-closures.md
new file mode 100644
index 0000000..ecda1ac
--- /dev/null
+++ b/documents/markdown/rust-book/ch13-01-closures.md
@@ -0,0 +1,426 @@
+
+
+
+
+
+## Closures
+
+Rust’s closures are anonymous functions you can save in a variable or pass as
+arguments to other functions. You can create the closure in one place and then
+call the closure elsewhere to evaluate it in a different context. Unlike
+functions, closures can capture values from the scope in which they’re defined.
+We’ll demonstrate how these closure features allow for code reuse and behavior
+customization.
+
+
+
+
+
+
+
+
+### Capturing the Environment
+
+We’ll first examine how we can use closures to capture values from the
+environment they’re defined in for later use. Here’s the scenario: Every so
+often, our T-shirt company gives away an exclusive, limited-edition shirt to
+someone on our mailing list as a promotion. People on the mailing list can
+optionally add their favorite color to their profile. If the person chosen for
+a free shirt has their favorite color set, they get that color shirt. If the
+person hasn’t specified a favorite color, they get whatever color the company
+currently has the most of.
+
+There are many ways to implement this. For this example, we’re going to use an
+enum called `ShirtColor` that has the variants `Red` and `Blue` (limiting the
+number of colors available for simplicity). We represent the company’s
+inventory with an `Inventory` struct that has a field named `shirts` that
+contains a `Vec` representing the shirt colors currently in stock.
+The method `giveaway` defined on `Inventory` gets the optional shirt color
+preference of the free-shirt winner, and it returns the shirt color the
+person will get. This setup is shown in Listing 13-1.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-01/src/main.rs}}
+```
+
+
+
+The `store` defined in `main` has two blue shirts and one red shirt remaining
+to distribute for this limited-edition promotion. We call the `giveaway` method
+for a user with a preference for a red shirt and a user without any preference.
+
+Again, this code could be implemented in many ways, and here, to focus on
+closures, we’ve stuck to concepts you’ve already learned, except for the body of
+the `giveaway` method that uses a closure. In the `giveaway` method, we get the
+user preference as a parameter of type `Option` and call the
+`unwrap_or_else` method on `user_preference`. The [`unwrap_or_else` method on
+`Option`][unwrap-or-else] is defined by the standard library.
+It takes one argument: a closure without any arguments that returns a value `T`
+(the same type stored in the `Some` variant of the `Option`, in this case
+`ShirtColor`). If the `Option` is the `Some` variant, `unwrap_or_else`
+returns the value from within the `Some`. If the `Option` is the `None`
+variant, `unwrap_or_else` calls the closure and returns the value returned by
+the closure.
+
+We specify the closure expression `|| self.most_stocked()` as the argument to
+`unwrap_or_else`. This is a closure that takes no parameters itself (if the
+closure had parameters, they would appear between the two vertical pipes). The
+body of the closure calls `self.most_stocked()`. We’re defining the closure
+here, and the implementation of `unwrap_or_else` will evaluate the closure
+later if the result is needed.
+
+Running this code prints the following:
+
+```console
+{{#include ../listings/ch13-functional-features/listing-13-01/output.txt}}
+```
+
+One interesting aspect here is that we’ve passed a closure that calls
+`self.most_stocked()` on the current `Inventory` instance. The standard library
+didn’t need to know anything about the `Inventory` or `ShirtColor` types we
+defined, or the logic we want to use in this scenario. The closure captures an
+immutable reference to the `self` `Inventory` instance and passes it with the
+code we specify to the `unwrap_or_else` method. Functions, on the other hand,
+are not able to capture their environment in this way.
+
+
+
+
+
+### Inferring and Annotating Closure Types
+
+There are more differences between functions and closures. Closures don’t
+usually require you to annotate the types of the parameters or the return value
+like `fn` functions do. Type annotations are required on functions because the
+types are part of an explicit interface exposed to your users. Defining this
+interface rigidly is important for ensuring that everyone agrees on what types
+of values a function uses and returns. Closures, on the other hand, aren’t used
+in an exposed interface like this: They’re stored in variables, and they’re
+used without naming them and exposing them to users of our library.
+
+Closures are typically short and relevant only within a narrow context rather
+than in any arbitrary scenario. Within these limited contexts, the compiler can
+infer the types of the parameters and the return type, similar to how it’s able
+to infer the types of most variables (there are rare cases where the compiler
+needs closure type annotations too).
+
+As with variables, we can add type annotations if we want to increase
+explicitness and clarity at the cost of being more verbose than is strictly
+necessary. Annotating the types for a closure would look like the definition
+shown in Listing 13-2. In this example, we’re defining a closure and storing it
+in a variable rather than defining the closure in the spot we pass it as an
+argument, as we did in Listing 13-1.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-02/src/main.rs:here}}
+```
+
+
+
+With type annotations added, the syntax of closures looks more similar to the
+syntax of functions. Here, we define a function that adds 1 to its parameter and
+a closure that has the same behavior, for comparison. We’ve added some spaces
+to line up the relevant parts. This illustrates how closure syntax is similar
+to function syntax except for the use of pipes and the amount of syntax that is
+optional:
+
+```rust,ignore
+fn add_one_v1 (x: u32) -> u32 { x + 1 }
+let add_one_v2 = |x: u32| -> u32 { x + 1 };
+let add_one_v3 = |x| { x + 1 };
+let add_one_v4 = |x| x + 1 ;
+```
+
+The first line shows a function definition and the second line shows a fully
+annotated closure definition. In the third line, we remove the type annotations
+from the closure definition. In the fourth line, we remove the brackets, which
+are optional because the closure body has only one expression. These are all
+valid definitions that will produce the same behavior when they’re called. The
+`add_one_v3` and `add_one_v4` lines require the closures to be evaluated to be
+able to compile because the types will be inferred from their usage. This is
+similar to `let v = Vec::new();` needing either type annotations or values of
+some type to be inserted into the `Vec` for Rust to be able to infer the type.
+
+For closure definitions, the compiler will infer one concrete type for each of
+their parameters and for their return value. For instance, Listing 13-3 shows
+the definition of a short closure that just returns the value it receives as a
+parameter. This closure isn’t very useful except for the purposes of this
+example. Note that we haven’t added any type annotations to the definition.
+Because there are no type annotations, we can call the closure with any type,
+which we’ve done here with `String` the first time. If we then try to call
+`example_closure` with an integer, we’ll get an error.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-03/src/main.rs:here}}
+```
+
+
+
+The compiler gives us this error:
+
+```console
+{{#include ../listings/ch13-functional-features/listing-13-03/output.txt}}
+```
+
+The first time we call `example_closure` with the `String` value, the compiler
+infers the type of `x` and the return type of the closure to be `String`. Those
+types are then locked into the closure in `example_closure`, and we get a type
+error when we next try to use a different type with the same closure.
+
+### Capturing References or Moving Ownership
+
+Closures can capture values from their environment in three ways, which
+directly map to the three ways a function can take a parameter: borrowing
+immutably, borrowing mutably, and taking ownership. The closure will decide
+which of these to use based on what the body of the function does with the
+captured values.
+
+In Listing 13-4, we define a closure that captures an immutable reference to
+the vector named `list` because it only needs an immutable reference to print
+the value.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-04/src/main.rs}}
+```
+
+
+
+This example also illustrates that a variable can bind to a closure definition,
+and we can later call the closure by using the variable name and parentheses as
+if the variable name were a function name.
+
+Because we can have multiple immutable references to `list` at the same time,
+`list` is still accessible from the code before the closure definition, after
+the closure definition but before the closure is called, and after the closure
+is called. This code compiles, runs, and prints:
+
+```console
+{{#include ../listings/ch13-functional-features/listing-13-04/output.txt}}
+```
+
+Next, in Listing 13-5, we change the closure body so that it adds an element to
+the `list` vector. The closure now captures a mutable reference.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-05/src/main.rs}}
+```
+
+
+
+This code compiles, runs, and prints:
+
+```console
+{{#include ../listings/ch13-functional-features/listing-13-05/output.txt}}
+```
+
+Note that there’s no longer a `println!` between the definition and the call of
+the `borrows_mutably` closure: When `borrows_mutably` is defined, it captures a
+mutable reference to `list`. We don’t use the closure again after the closure
+is called, so the mutable borrow ends. Between the closure definition and the
+closure call, an immutable borrow to print isn’t allowed, because no other
+borrows are allowed when there’s a mutable borrow. Try adding a `println!`
+there to see what error message you get!
+
+If you want to force the closure to take ownership of the values it uses in the
+environment even though the body of the closure doesn’t strictly need
+ownership, you can use the `move` keyword before the parameter list.
+
+This technique is mostly useful when passing a closure to a new thread to move
+the data so that it’s owned by the new thread. We’ll discuss threads and why
+you would want to use them in detail in Chapter 16 when we talk about
+concurrency, but for now, let’s briefly explore spawning a new thread using a
+closure that needs the `move` keyword. Listing 13-6 shows Listing 13-4 modified
+to print the vector in a new thread rather than in the main thread.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-06/src/main.rs}}
+```
+
+
+
+We spawn a new thread, giving the thread a closure to run as an argument. The
+closure body prints out the list. In Listing 13-4, the closure only captured
+`list` using an immutable reference because that's the least amount of access
+to `list` needed to print it. In this example, even though the closure body
+still only needs an immutable reference, we need to specify that `list` should
+be moved into the closure by putting the `move` keyword at the beginning of the
+closure definition. If the main thread performed more operations before calling
+`join` on the new thread, the new thread might finish before the rest of the
+main thread finishes, or the main thread might finish first. If the main thread
+maintained ownership of `list` but ended before the new thread and drops
+`list`, the immutable reference in the thread would be invalid. Therefore, the
+compiler requires that `list` be moved into the closure given to the new thread
+so that the reference will be valid. Try removing the `move` keyword or using
+`list` in the main thread after the closure is defined to see what compiler
+errors you get!
+
+
+
+
+
+
+
+
+### Moving Captured Values Out of Closures
+
+Once a closure has captured a reference or captured ownership of a value from
+the environment where the closure is defined (thus affecting what, if anything,
+is moved _into_ the closure), the code in the body of the closure defines what
+happens to the references or values when the closure is evaluated later (thus
+affecting what, if anything, is moved _out of_ the closure).
+
+A closure body can do any of the following: Move a captured value out of the
+closure, mutate the captured value, neither move nor mutate the value, or
+capture nothing from the environment to begin with.
+
+The way a closure captures and handles values from the environment affects
+which traits the closure implements, and traits are how functions and structs
+can specify what kinds of closures they can use. Closures will automatically
+implement one, two, or all three of these `Fn` traits, in an additive fashion,
+depending on how the closure’s body handles the values:
+
+* `FnOnce` applies to closures that can be called once. All closures implement
+ at least this trait because all closures can be called. A closure that moves
+ captured values out of its body will only implement `FnOnce` and none of the
+ other `Fn` traits because it can only be called once.
+* `FnMut` applies to closures that don’t move captured values out of their body
+ but might mutate the captured values. These closures can be called more than
+ once.
+* `Fn` applies to closures that don’t move captured values out of their body
+ and don’t mutate captured values, as well as closures that capture nothing
+ from their environment. These closures can be called more than once without
+ mutating their environment, which is important in cases such as calling a closure multiple times concurrently.
+
+Let’s look at the definition of the `unwrap_or_else` method on `Option` that
+we used in Listing 13-1:
+
+```rust,ignore
+impl Option {
+ pub fn unwrap_or_else(self, f: F) -> T
+ where
+ F: FnOnce() -> T
+ {
+ match self {
+ Some(x) => x,
+ None => f(),
+ }
+ }
+}
+```
+
+Recall that `T` is the generic type representing the type of the value in the
+`Some` variant of an `Option`. That type `T` is also the return type of the
+`unwrap_or_else` function: Code that calls `unwrap_or_else` on an
+`Option`, for example, will get a `String`.
+
+Next, notice that the `unwrap_or_else` function has the additional generic type
+parameter `F`. The `F` type is the type of the parameter named `f`, which is
+the closure we provide when calling `unwrap_or_else`.
+
+The trait bound specified on the generic type `F` is `FnOnce() -> T`, which
+means `F` must be able to be called once, take no arguments, and return a `T`.
+Using `FnOnce` in the trait bound expresses the constraint that
+`unwrap_or_else` will not call `f` more than once. In the body of
+`unwrap_or_else`, we can see that if the `Option` is `Some`, `f` won’t be
+called. If the `Option` is `None`, `f` will be called once. Because all
+closures implement `FnOnce`, `unwrap_or_else` accepts all three kinds of
+closures and is as flexible as it can be.
+
+> Note: If what we want to do doesn’t require capturing a value from the
+> environment, we can use the name of a function rather than a closure where we
+> need something that implements one of the `Fn` traits. For example, on an
+> `Option>` value, we could call `unwrap_or_else(Vec::new)` to get a
+> new, empty vector if the value is `None`. The compiler automatically
+> implements whichever of the `Fn` traits is applicable for a function
+> definition.
+
+Now let’s look at the standard library method `sort_by_key`, defined on slices,
+to see how that differs from `unwrap_or_else` and why `sort_by_key` uses
+`FnMut` instead of `FnOnce` for the trait bound. The closure gets one argument
+in the form of a reference to the current item in the slice being considered,
+and it returns a value of type `K` that can be ordered. This function is useful
+when you want to sort a slice by a particular attribute of each item. In
+Listing 13-7, we have a list of `Rectangle` instances, and we use `sort_by_key`
+to order them by their `width` attribute from low to high.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-07/src/main.rs}}
+```
+
+
+
+This code prints:
+
+```console
+{{#include ../listings/ch13-functional-features/listing-13-07/output.txt}}
+```
+
+The reason `sort_by_key` is defined to take an `FnMut` closure is that it calls
+the closure multiple times: once for each item in the slice. The closure `|r|
+r.width` doesn’t capture, mutate, or move anything out from its environment, so
+it meets the trait bound requirements.
+
+In contrast, Listing 13-8 shows an example of a closure that implements just
+the `FnOnce` trait, because it moves a value out of the environment. The
+compiler won’t let us use this closure with `sort_by_key`.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-08/src/main.rs}}
+```
+
+
+
+This is a contrived, convoluted way (that doesn’t work) to try to count the
+number of times `sort_by_key` calls the closure when sorting `list`. This code
+attempts to do this counting by pushing `value`—a `String` from the closure’s
+environment—into the `sort_operations` vector. The closure captures `value` and
+then moves `value` out of the closure by transferring ownership of `value` to
+the `sort_operations` vector. This closure can be called once; trying to call
+it a second time wouldn’t work, because `value` would no longer be in the
+environment to be pushed into `sort_operations` again! Therefore, this closure
+only implements `FnOnce`. When we try to compile this code, we get this error
+that `value` can’t be moved out of the closure because the closure must
+implement `FnMut`:
+
+```console
+{{#include ../listings/ch13-functional-features/listing-13-08/output.txt}}
+```
+
+The error points to the line in the closure body that moves `value` out of the
+environment. To fix this, we need to change the closure body so that it doesn’t
+move values out of the environment. Keeping a counter in the environment and
+incrementing its value in the closure body is a more straightforward way to
+count the number of times the closure is called. The closure in Listing 13-9
+works with `sort_by_key` because it is only capturing a mutable reference to the
+`num_sort_operations` counter and can therefore be called more than once.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-09/src/main.rs}}
+```
+
+
+
+The `Fn` traits are important when defining or using functions or types that
+make use of closures. In the next section, we’ll discuss iterators. Many
+iterator methods take closure arguments, so keep these closure details in mind
+as we continue!
+
+[unwrap-or-else]: ../std/option/enum.Option.html#method.unwrap_or_else
diff --git a/documents/markdown/rust-book/ch13-02-iterators.md b/documents/markdown/rust-book/ch13-02-iterators.md
new file mode 100644
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--- /dev/null
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@@ -0,0 +1,229 @@
+## Processing a Series of Items with Iterators
+
+The iterator pattern allows you to perform some task on a sequence of items in
+turn. An iterator is responsible for the logic of iterating over each item and
+determining when the sequence has finished. When you use iterators, you don’t
+have to reimplement that logic yourself.
+
+In Rust, iterators are _lazy_, meaning they have no effect until you call
+methods that consume the iterator to use it up. For example, the code in
+Listing 13-10 creates an iterator over the items in the vector `v1` by calling
+the `iter` method defined on `Vec`. This code by itself doesn’t do anything
+useful.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-10/src/main.rs:here}}
+```
+
+
+
+The iterator is stored in the `v1_iter` variable. Once we’ve created an
+iterator, we can use it in a variety of ways. In Listing 3-5, we iterated over
+an array using a `for` loop to execute some code on each of its items. Under
+the hood, this implicitly created and then consumed an iterator, but we glossed
+over how exactly that works until now.
+
+In the example in Listing 13-11, we separate the creation of the iterator from
+the use of the iterator in the `for` loop. When the `for` loop is called using
+the iterator in `v1_iter`, each element in the iterator is used in one
+iteration of the loop, which prints out each value.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-11/src/main.rs:here}}
+```
+
+
+
+In languages that don’t have iterators provided by their standard libraries,
+you would likely write this same functionality by starting a variable at index
+0, using that variable to index into the vector to get a value, and
+incrementing the variable value in a loop until it reached the total number of
+items in the vector.
+
+Iterators handle all of that logic for you, cutting down on repetitive code you
+could potentially mess up. Iterators give you more flexibility to use the same
+logic with many different kinds of sequences, not just data structures you can
+index into, like vectors. Let’s examine how iterators do that.
+
+### The `Iterator` Trait and the `next` Method
+
+All iterators implement a trait named `Iterator` that is defined in the
+standard library. The definition of the trait looks like this:
+
+```rust
+pub trait Iterator {
+ type Item;
+
+ fn next(&mut self) -> Option;
+
+ // methods with default implementations elided
+}
+```
+
+Notice that this definition uses some new syntax: `type Item` and `Self::Item`,
+which are defining an associated type with this trait. We’ll talk about
+associated types in depth in Chapter 20. For now, all you need to know is that
+this code says implementing the `Iterator` trait requires that you also define
+an `Item` type, and this `Item` type is used in the return type of the `next`
+method. In other words, the `Item` type will be the type returned from the
+iterator.
+
+The `Iterator` trait only requires implementors to define one method: the
+`next` method, which returns one item of the iterator at a time, wrapped in
+`Some`, and, when iteration is over, returns `None`.
+
+We can call the `next` method on iterators directly; Listing 13-12 demonstrates
+what values are returned from repeated calls to `next` on the iterator created
+from the vector.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-12/src/lib.rs:here}}
+```
+
+
+
+Note that we needed to make `v1_iter` mutable: Calling the `next` method on an
+iterator changes internal state that the iterator uses to keep track of where
+it is in the sequence. In other words, this code _consumes_, or uses up, the
+iterator. Each call to `next` eats up an item from the iterator. We didn’t need
+to make `v1_iter` mutable when we used a `for` loop, because the loop took
+ownership of `v1_iter` and made it mutable behind the scenes.
+
+Also note that the values we get from the calls to `next` are immutable
+references to the values in the vector. The `iter` method produces an iterator
+over immutable references. If we want to create an iterator that takes
+ownership of `v1` and returns owned values, we can call `into_iter` instead of
+`iter`. Similarly, if we want to iterate over mutable references, we can call
+`iter_mut` instead of `iter`.
+
+### Methods That Consume the Iterator
+
+The `Iterator` trait has a number of different methods with default
+implementations provided by the standard library; you can find out about these
+methods by looking in the standard library API documentation for the `Iterator`
+trait. Some of these methods call the `next` method in their definition, which
+is why you’re required to implement the `next` method when implementing the
+`Iterator` trait.
+
+Methods that call `next` are called _consuming adapters_ because calling them
+uses up the iterator. One example is the `sum` method, which takes ownership of
+the iterator and iterates through the items by repeatedly calling `next`, thus
+consuming the iterator. As it iterates through, it adds each item to a running
+total and returns the total when iteration is complete. Listing 13-13 has a
+test illustrating a use of the `sum` method.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-13/src/lib.rs:here}}
+```
+
+
+
+We aren’t allowed to use `v1_iter` after the call to `sum`, because `sum` takes
+ownership of the iterator we call it on.
+
+### Methods That Produce Other Iterators
+
+_Iterator adapters_ are methods defined on the `Iterator` trait that don’t
+consume the iterator. Instead, they produce different iterators by changing
+some aspect of the original iterator.
+
+Listing 13-14 shows an example of calling the iterator adapter method `map`,
+which takes a closure to call on each item as the items are iterated through.
+The `map` method returns a new iterator that produces the modified items. The
+closure here creates a new iterator in which each item from the vector will be
+incremented by 1.
+
+
+
+```rust,not_desired_behavior
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-14/src/main.rs:here}}
+```
+
+
+
+However, this code produces a warning:
+
+```console
+{{#include ../listings/ch13-functional-features/listing-13-14/output.txt}}
+```
+
+The code in Listing 13-14 doesn’t do anything; the closure we’ve specified
+never gets called. The warning reminds us why: Iterator adapters are lazy, and
+we need to consume the iterator here.
+
+To fix this warning and consume the iterator, we’ll use the `collect` method,
+which we used with `env::args` in Listing 12-1. This method consumes the
+iterator and collects the resultant values into a collection data type.
+
+In Listing 13-15, we collect the results of iterating over the iterator that’s
+returned from the call to `map` into a vector. This vector will end up
+containing each item from the original vector, incremented by 1.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-15/src/main.rs:here}}
+```
+
+
+
+Because `map` takes a closure, we can specify any operation we want to perform
+on each item. This is a great example of how closures let you customize some
+behavior while reusing the iteration behavior that the `Iterator` trait
+provides.
+
+You can chain multiple calls to iterator adapters to perform complex actions in
+a readable way. But because all iterators are lazy, you have to call one of the
+consuming adapter methods to get results from calls to iterator adapters.
+
+
+
+
+
+### Closures That Capture Their Environment
+
+Many iterator adapters take closures as arguments, and commonly the closures
+we’ll specify as arguments to iterator adapters will be closures that capture
+their environment.
+
+For this example, we’ll use the `filter` method that takes a closure. The
+closure gets an item from the iterator and returns a `bool`. If the closure
+returns `true`, the value will be included in the iteration produced by
+`filter`. If the closure returns `false`, the value won’t be included.
+
+In Listing 13-16, we use `filter` with a closure that captures the `shoe_size`
+variable from its environment to iterate over a collection of `Shoe` struct
+instances. It will return only shoes that are the specified size.
+
+
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-16/src/lib.rs}}
+```
+
+
+
+The `shoes_in_size` function takes ownership of a vector of shoes and a shoe
+size as parameters. It returns a vector containing only shoes of the specified
+size.
+
+In the body of `shoes_in_size`, we call `into_iter` to create an iterator that
+takes ownership of the vector. Then, we call `filter` to adapt that iterator
+into a new iterator that only contains elements for which the closure returns
+`true`.
+
+The closure captures the `shoe_size` parameter from the environment and
+compares the value with each shoe’s size, keeping only shoes of the size
+specified. Finally, calling `collect` gathers the values returned by the
+adapted iterator into a vector that’s returned by the function.
+
+The test shows that when we call `shoes_in_size`, we get back only shoes that
+have the same size as the value we specified.
diff --git a/documents/markdown/rust-book/ch13-03-improving-our-io-project.md b/documents/markdown/rust-book/ch13-03-improving-our-io-project.md
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+++ b/documents/markdown/rust-book/ch13-03-improving-our-io-project.md
@@ -0,0 +1,193 @@
+## Improving Our I/O Project
+
+With this new knowledge about iterators, we can improve the I/O project in
+Chapter 12 by using iterators to make places in the code clearer and more
+concise. Let’s look at how iterators can improve our implementation of the
+`Config::build` function and the `search` function.
+
+### Removing a `clone` Using an Iterator
+
+In Listing 12-6, we added code that took a slice of `String` values and created
+an instance of the `Config` struct by indexing into the slice and cloning the
+values, allowing the `Config` struct to own those values. In Listing 13-17,
+we’ve reproduced the implementation of the `Config::build` function as it was
+in Listing 12-23.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch13-functional-features/listing-12-23-reproduced/src/main.rs:ch13}}
+```
+
+
+
+At the time, we said not to worry about the inefficient `clone` calls because
+we would remove them in the future. Well, that time is now!
+
+We needed `clone` here because we have a slice with `String` elements in the
+parameter `args`, but the `build` function doesn’t own `args`. To return
+ownership of a `Config` instance, we had to clone the values from the `query`
+and `file_path` fields of `Config` so that the `Config` instance can own its
+values.
+
+With our new knowledge about iterators, we can change the `build` function to
+take ownership of an iterator as its argument instead of borrowing a slice.
+We’ll use the iterator functionality instead of the code that checks the length
+of the slice and indexes into specific locations. This will clarify what the
+`Config::build` function is doing because the iterator will access the values.
+
+Once `Config::build` takes ownership of the iterator and stops using indexing
+operations that borrow, we can move the `String` values from the iterator into
+`Config` rather than calling `clone` and making a new allocation.
+
+#### Using the Returned Iterator Directly
+
+Open your I/O project’s _src/main.rs_ file, which should look like this:
+
+Filename: src/main.rs
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch13-functional-features/listing-12-24-reproduced/src/main.rs:ch13}}
+```
+
+We’ll first change the start of the `main` function that we had in Listing
+12-24 to the code in Listing 13-18, which this time uses an iterator. This
+won’t compile until we update `Config::build` as well.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-18/src/main.rs:here}}
+```
+
+
+
+The `env::args` function returns an iterator! Rather than collecting the
+iterator values into a vector and then passing a slice to `Config::build`, now
+we’re passing ownership of the iterator returned from `env::args` to
+`Config::build` directly.
+
+Next, we need to update the definition of `Config::build`. Let’s change the
+signature of `Config::build` to look like Listing 13-19. This still won’t
+compile, because we need to update the function body.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-19/src/main.rs:here}}
+```
+
+
+
+The standard library documentation for the `env::args` function shows that the
+type of the iterator it returns is `std::env::Args`, and that type implements
+the `Iterator` trait and returns `String` values.
+
+We’ve updated the signature of the `Config::build` function so that the
+parameter `args` has a generic type with the trait bounds `impl Iterator- ` instead of `&[String]`. This usage of the `impl Trait` syntax we
+discussed in the [“Using Traits as Parameters”][impl-trait]
+section of Chapter 10 means that `args` can be any type that implements the
+`Iterator` trait and returns `String` items.
+
+Because we’re taking ownership of `args` and we’ll be mutating `args` by
+iterating over it, we can add the `mut` keyword into the specification of the
+`args` parameter to make it mutable.
+
+
+
+
+
+#### Using `Iterator` Trait Methods
+
+Next, we’ll fix the body of `Config::build`. Because `args` implements the
+`Iterator` trait, we know we can call the `next` method on it! Listing 13-20
+updates the code from Listing 12-23 to use the `next` method.
+
+
+
+```rust,ignore,noplayground
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-20/src/main.rs:here}}
+```
+
+
+
+Remember that the first value in the return value of `env::args` is the name of
+the program. We want to ignore that and get to the next value, so first we call
+`next` and do nothing with the return value. Then, we call `next` to get the
+value we want to put in the `query` field of `Config`. If `next` returns
+`Some`, we use a `match` to extract the value. If it returns `None`, it means
+not enough arguments were given, and we return early with an `Err` value. We do
+the same thing for the `file_path` value.
+
+
+
+
+
+### Clarifying Code with Iterator Adapters
+
+We can also take advantage of iterators in the `search` function in our I/O
+project, which is reproduced here in Listing 13-21 as it was in Listing 12-19.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch12-an-io-project/listing-12-19/src/lib.rs:ch13}}
+```
+
+
+
+We can write this code in a more concise way using iterator adapter methods.
+Doing so also lets us avoid having a mutable intermediate `results` vector. The
+functional programming style prefers to minimize the amount of mutable state to
+make code clearer. Removing the mutable state might enable a future enhancement
+to make searching happen in parallel because we wouldn’t have to manage
+concurrent access to the `results` vector. Listing 13-22 shows this change.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch13-functional-features/listing-13-22/src/lib.rs:here}}
+```
+
+
+
+Recall that the purpose of the `search` function is to return all lines in
+`contents` that contain the `query`. Similar to the `filter` example in Listing
+13-16, this code uses the `filter` adapter to keep only the lines for which
+`line.contains(query)` returns `true`. We then collect the matching lines into
+another vector with `collect`. Much simpler! Feel free to make the same change
+to use iterator methods in the `search_case_insensitive` function as well.
+
+For a further improvement, return an iterator from the `search` function by
+removing the call to `collect` and changing the return type to `impl
+Iterator
- ` so that the function becomes an iterator adapter.
+Note that you’ll also need to update the tests! Search through a large file
+using your `minigrep` tool before and after making this change to observe the
+difference in behavior. Before this change, the program won’t print any results
+until it has collected all of the results, but after the change, the results
+will be printed as each matching line is found because the `for` loop in the
+`run` function is able to take advantage of the laziness of the iterator.
+
+
+
+
+
+### Choosing Between Loops and Iterators
+
+The next logical question is which style you should choose in your own code and
+why: the original implementation in Listing 13-21 or the version using
+iterators in Listing 13-22 (assuming we’re collecting all the results before
+returning them rather than returning the iterator). Most Rust programmers
+prefer to use the iterator style. It’s a bit tougher to get the hang of at
+first, but once you get a feel for the various iterator adapters and what they
+do, iterators can be easier to understand. Instead of fiddling with the various
+bits of looping and building new vectors, the code focuses on the high-level
+objective of the loop. This abstracts away some of the commonplace code so that
+it’s easier to see the concepts that are unique to this code, such as the
+filtering condition each element in the iterator must pass.
+
+But are the two implementations truly equivalent? The intuitive assumption
+might be that the lower-level loop will be faster. Let’s talk about performance.
+
+[impl-trait]: ch10-02-traits.html#traits-as-parameters
diff --git a/documents/markdown/rust-book/ch13-04-performance.md b/documents/markdown/rust-book/ch13-04-performance.md
new file mode 100644
index 0000000..cdc2f98
--- /dev/null
+++ b/documents/markdown/rust-book/ch13-04-performance.md
@@ -0,0 +1,57 @@
+
+
+
+
+## Performance in Loops vs. Iterators
+
+To determine whether to use loops or iterators, you need to know which
+implementation is faster: the version of the `search` function with an explicit
+`for` loop or the version with iterators.
+
+We ran a benchmark by loading the entire contents of _The Adventures of
+Sherlock Holmes_ by Sir Arthur Conan Doyle into a `String` and looking for the
+word _the_ in the contents. Here are the results of the benchmark on the
+version of `search` using the `for` loop and the version using iterators:
+
+```text
+test bench_search_for ... bench: 19,620,300 ns/iter (+/- 915,700)
+test bench_search_iter ... bench: 19,234,900 ns/iter (+/- 657,200)
+```
+
+The two implementations have similar performance! We won’t explain the
+benchmark code here because the point is not to prove that the two versions
+are equivalent but to get a general sense of how these two implementations
+compare performance-wise.
+
+For a more comprehensive benchmark, you should check using various texts of
+various sizes as the `contents`, different words and words of different lengths
+as the `query`, and all kinds of other variations. The point is this:
+Iterators, although a high-level abstraction, get compiled down to roughly the
+same code as if you’d written the lower-level code yourself. Iterators are one
+of Rust’s _zero-cost abstractions_, by which we mean that using the abstraction
+imposes no additional runtime overhead. This is analogous to how Bjarne
+Stroustrup, the original designer and implementor of C++, defines
+zero-overhead in his 2012 ETAPS keynote presentation “Foundations of C++”:
+
+> In general, C++ implementations obey the zero-overhead principle: What you
+> don’t use, you don’t pay for. And further: What you do use, you couldn’t hand
+> code any better.
+
+In many cases, Rust code using iterators compiles to the same assembly you’d
+write by hand. Optimizations such as loop unrolling and eliminating bounds
+checking on array access apply and make the resultant code extremely efficient.
+Now that you know this, you can use iterators and closures without fear! They
+make code seem like it’s higher level but don’t impose a runtime performance
+penalty for doing so.
+
+## Summary
+
+Closures and iterators are Rust features inspired by functional programming
+language ideas. They contribute to Rust’s capability to clearly express
+high-level ideas at low-level performance. The implementations of closures and
+iterators are such that runtime performance is not affected. This is part of
+Rust’s goal to strive to provide zero-cost abstractions.
+
+Now that we’ve improved the expressiveness of our I/O project, let’s look at
+some more features of `cargo` that will help us share the project with the
+world.
diff --git a/documents/markdown/rust-book/ch14-00-more-about-cargo.md b/documents/markdown/rust-book/ch14-00-more-about-cargo.md
new file mode 100644
index 0000000..59408b8
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+++ b/documents/markdown/rust-book/ch14-00-more-about-cargo.md
@@ -0,0 +1,14 @@
+# More About Cargo and Crates.io
+
+So far, we’ve used only the most basic features of Cargo to build, run, and
+test our code, but it can do a lot more. In this chapter, we’ll discuss some of
+its other, more advanced features to show you how to do the following:
+
+- Customize your build through release profiles.
+- Publish libraries on [crates.io](https://crates.io/).
+- Organize large projects with workspaces.
+- Install binaries from [crates.io](https://crates.io/).
+- Extend Cargo using custom commands.
+
+Cargo can do even more than the functionality we cover in this chapter, so for
+a full explanation of all its features, see [its documentation](https://doc.rust-lang.org/cargo/).
diff --git a/documents/markdown/rust-book/ch14-01-release-profiles.md b/documents/markdown/rust-book/ch14-01-release-profiles.md
new file mode 100644
index 0000000..4bbb2d3
--- /dev/null
+++ b/documents/markdown/rust-book/ch14-01-release-profiles.md
@@ -0,0 +1,75 @@
+## Customizing Builds with Release Profiles
+
+In Rust, _release profiles_ are predefined, customizable profiles with
+different configurations that allow a programmer to have more control over
+various options for compiling code. Each profile is configured independently of
+the others.
+
+Cargo has two main profiles: the `dev` profile Cargo uses when you run `cargo
+build`, and the `release` profile Cargo uses when you run `cargo build
+--release`. The `dev` profile is defined with good defaults for development,
+and the `release` profile has good defaults for release builds.
+
+These profile names might be familiar from the output of your builds:
+
+
+
+```console
+$ cargo build
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s
+$ cargo build --release
+ Finished `release` profile [optimized] target(s) in 0.32s
+```
+
+The `dev` and `release` are these different profiles used by the compiler.
+
+Cargo has default settings for each of the profiles that apply when you haven't
+explicitly added any `[profile.*]` sections in the project’s _Cargo.toml_ file.
+By adding `[profile.*]` sections for any profile you want to customize, you
+override any subset of the default settings. For example, here are the default
+values for the `opt-level` setting for the `dev` and `release` profiles:
+
+Filename: Cargo.toml
+
+```toml
+[profile.dev]
+opt-level = 0
+
+[profile.release]
+opt-level = 3
+```
+
+The `opt-level` setting controls the number of optimizations Rust will apply to
+your code, with a range of 0 to 3. Applying more optimizations extends
+compiling time, so if you’re in development and compiling your code often,
+you’ll want fewer optimizations to compile faster even if the resultant code
+runs slower. The default `opt-level` for `dev` is therefore `0`. When you’re
+ready to release your code, it’s best to spend more time compiling. You’ll only
+compile in release mode once, but you’ll run the compiled program many times,
+so release mode trades longer compile time for code that runs faster. That is
+why the default `opt-level` for the `release` profile is `3`.
+
+You can override a default setting by adding a different value for it in
+_Cargo.toml_. For example, if we want to use optimization level 1 in the
+development profile, we can add these two lines to our project’s _Cargo.toml_
+file:
+
+Filename: Cargo.toml
+
+```toml
+[profile.dev]
+opt-level = 1
+```
+
+This code overrides the default setting of `0`. Now when we run `cargo build`,
+Cargo will use the defaults for the `dev` profile plus our customization to
+`opt-level`. Because we set `opt-level` to `1`, Cargo will apply more
+optimizations than the default, but not as many as in a release build.
+
+For the full list of configuration options and defaults for each profile, see
+[Cargo’s documentation](https://doc.rust-lang.org/cargo/reference/profiles.html).
diff --git a/documents/markdown/rust-book/ch14-02-publishing-to-crates-io.md b/documents/markdown/rust-book/ch14-02-publishing-to-crates-io.md
new file mode 100644
index 0000000..2af90dc
--- /dev/null
+++ b/documents/markdown/rust-book/ch14-02-publishing-to-crates-io.md
@@ -0,0 +1,481 @@
+## Publishing a Crate to Crates.io
+
+We’ve used packages from [crates.io](https://crates.io/) as
+dependencies of our project, but you can also share your code with other people
+by publishing your own packages. The crate registry at
+[crates.io](https://crates.io/) distributes the source code of
+your packages, so it primarily hosts code that is open source.
+
+Rust and Cargo have features that make your published package easier for people
+to find and use. We’ll talk about some of these features next and then explain
+how to publish a package.
+
+### Making Useful Documentation Comments
+
+Accurately documenting your packages will help other users know how and when to
+use them, so it’s worth investing the time to write documentation. In Chapter
+3, we discussed how to comment Rust code using two slashes, `//`. Rust also has
+a particular kind of comment for documentation, known conveniently as a
+_documentation comment_, that will generate HTML documentation. The HTML
+displays the contents of documentation comments for public API items intended
+for programmers interested in knowing how to _use_ your crate as opposed to how
+your crate is _implemented_.
+
+Documentation comments use three slashes, `///`, instead of two and support
+Markdown notation for formatting the text. Place documentation comments just
+before the item they’re documenting. Listing 14-1 shows documentation comments
+for an `add_one` function in a crate named `my_crate`.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-01/src/lib.rs}}
+```
+
+
+
+Here, we give a description of what the `add_one` function does, start a
+section with the heading `Examples`, and then provide code that demonstrates
+how to use the `add_one` function. We can generate the HTML documentation from
+this documentation comment by running `cargo doc`. This command runs the
+`rustdoc` tool distributed with Rust and puts the generated HTML documentation
+in the _target/doc_ directory.
+
+For convenience, running `cargo doc --open` will build the HTML for your
+current crate’s documentation (as well as the documentation for all of your
+crate’s dependencies) and open the result in a web browser. Navigate to the
+`add_one` function and you’ll see how the text in the documentation comments is
+rendered, as shown in Figure 14-1.
+
+
+
+Figure 14-1: The HTML documentation for the `add_one`
+function
+
+#### Commonly Used Sections
+
+We used the `# Examples` Markdown heading in Listing 14-1 to create a section
+in the HTML with the title “Examples.” Here are some other sections that crate
+authors commonly use in their documentation:
+
+- **Panics**: These are the scenarios in which the function being documented
+ could panic. Callers of the function who don’t want their programs to panic
+ should make sure they don’t call the function in these situations.
+- **Errors**: If the function returns a `Result`, describing the kinds of
+ errors that might occur and what conditions might cause those errors to be
+ returned can be helpful to callers so that they can write code to handle the
+ different kinds of errors in different ways.
+- **Safety**: If the function is `unsafe` to call (we discuss unsafety in
+ Chapter 20), there should be a section explaining why the function is unsafe
+ and covering the invariants that the function expects callers to uphold.
+
+Most documentation comments don’t need all of these sections, but this is a
+good checklist to remind you of the aspects of your code users will be
+interested in knowing about.
+
+#### Documentation Comments as Tests
+
+Adding example code blocks in your documentation comments can help demonstrate
+how to use your library and has an additional bonus: Running `cargo test` will
+run the code examples in your documentation as tests! Nothing is better than
+documentation with examples. But nothing is worse than examples that don’t work
+because the code has changed since the documentation was written. If we run
+`cargo test` with the documentation for the `add_one` function from Listing
+14-1, we will see a section in the test results that looks like this:
+
+
+
+```text
+ Doc-tests my_crate
+
+running 1 test
+test src/lib.rs - add_one (line 5) ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.27s
+```
+
+Now, if we change either the function or the example so that the `assert_eq!`
+in the example panics, and run `cargo test` again, we’ll see that the doc tests
+catch that the example and the code are out of sync with each other!
+
+
+
+
+
+#### Contained Item Comments
+
+The style of doc comment `//!` adds documentation to the item that *contains*
+the comments rather than to the items *following* the comments. We typically
+use these doc comments inside the crate root file (_src/lib.rs_ by convention)
+or inside a module to document the crate or the module as a whole.
+
+For example, to add documentation that describes the purpose of the `my_crate`
+crate that contains the `add_one` function, we add documentation comments that
+start with `//!` to the beginning of the _src/lib.rs_ file, as shown in Listing
+14-2.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-02/src/lib.rs:here}}
+```
+
+
+
+Notice there isn’t any code after the last line that begins with `//!`. Because
+we started the comments with `//!` instead of `///`, we’re documenting the item
+that contains this comment rather than an item that follows this comment. In
+this case, that item is the _src/lib.rs_ file, which is the crate root. These
+comments describe the entire crate.
+
+When we run `cargo doc --open`, these comments will display on the front page
+of the documentation for `my_crate` above the list of public items in the
+crate, as shown in Figure 14-2.
+
+Documentation comments within items are useful for describing crates and
+modules especially. Use them to explain the overall purpose of the container to
+help your users understand the crate’s organization.
+
+
+
+Figure 14-2: The rendered documentation for `my_crate`,
+including the comment describing the crate as a whole
+
+
+
+
+
+### Exporting a Convenient Public API
+
+The structure of your public API is a major consideration when publishing a
+crate. People who use your crate are less familiar with the structure than you
+are and might have difficulty finding the pieces they want to use if your crate
+has a large module hierarchy.
+
+In Chapter 7, we covered how to make items public using the `pub` keyword, and
+how to bring items into a scope with the `use` keyword. However, the structure
+that makes sense to you while you’re developing a crate might not be very
+convenient for your users. You might want to organize your structs in a
+hierarchy containing multiple levels, but then people who want to use a type
+you’ve defined deep in the hierarchy might have trouble finding out that type
+exists. They might also be annoyed at having to enter `use
+my_crate::some_module::another_module::UsefulType;` rather than `use
+my_crate::UsefulType;`.
+
+The good news is that if the structure _isn’t_ convenient for others to use
+from another library, you don’t have to rearrange your internal organization:
+Instead, you can re-export items to make a public structure that’s different
+from your private structure by using `pub use`. *Re-exporting* takes a public
+item in one location and makes it public in another location, as if it were
+defined in the other location instead.
+
+For example, say we made a library named `art` for modeling artistic concepts.
+Within this library are two modules: a `kinds` module containing two enums
+named `PrimaryColor` and `SecondaryColor` and a `utils` module containing a
+function named `mix`, as shown in Listing 14-3.
+
+
+
+```rust,noplayground,test_harness
+{{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-03/src/lib.rs:here}}
+```
+
+
+
+Figure 14-3 shows what the front page of the documentation for this crate
+generated by `cargo doc` would look like.
+
+
+
+Figure 14-3: The front page of the documentation for `art`
+that lists the `kinds` and `utils` modules
+
+Note that the `PrimaryColor` and `SecondaryColor` types aren’t listed on the
+front page, nor is the `mix` function. We have to click `kinds` and `utils` to
+see them.
+
+Another crate that depends on this library would need `use` statements that
+bring the items from `art` into scope, specifying the module structure that’s
+currently defined. Listing 14-4 shows an example of a crate that uses the
+`PrimaryColor` and `mix` items from the `art` crate.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-04/src/main.rs}}
+```
+
+
+
+The author of the code in Listing 14-4, which uses the `art` crate, had to
+figure out that `PrimaryColor` is in the `kinds` module and `mix` is in the
+`utils` module. The module structure of the `art` crate is more relevant to
+developers working on the `art` crate than to those using it. The internal
+structure doesn’t contain any useful information for someone trying to
+understand how to use the `art` crate, but rather causes confusion because
+developers who use it have to figure out where to look, and must specify the
+module names in the `use` statements.
+
+To remove the internal organization from the public API, we can modify the
+`art` crate code in Listing 14-3 to add `pub use` statements to re-export the
+items at the top level, as shown in Listing 14-5.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-05/src/lib.rs:here}}
+```
+
+
+
+The API documentation that `cargo doc` generates for this crate will now list
+and link re-exports on the front page, as shown in Figure 14-4, making the
+`PrimaryColor` and `SecondaryColor` types and the `mix` function easier to find.
+
+
+
+Figure 14-4: The front page of the documentation for `art`
+that lists the re-exports
+
+The `art` crate users can still see and use the internal structure from Listing
+14-3 as demonstrated in Listing 14-4, or they can use the more convenient
+structure in Listing 14-5, as shown in Listing 14-6.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-06/src/main.rs:here}}
+```
+
+
+
+In cases where there are many nested modules, re-exporting the types at the top
+level with `pub use` can make a significant difference in the experience of
+people who use the crate. Another common use of `pub use` is to re-export
+definitions of a dependency in the current crate to make that crate's
+definitions part of your crate’s public API.
+
+Creating a useful public API structure is more an art than a science, and you
+can iterate to find the API that works best for your users. Choosing `pub use`
+gives you flexibility in how you structure your crate internally and decouples
+that internal structure from what you present to your users. Look at some of
+the code of crates you’ve installed to see if their internal structure differs
+from their public API.
+
+### Setting Up a Crates.io Account
+
+Before you can publish any crates, you need to create an account on
+[crates.io](https://crates.io/) and get an API token. To do so,
+visit the home page at [crates.io](https://crates.io/) and log
+in via a GitHub account. (The GitHub account is currently a requirement, but
+the site might support other ways of creating an account in the future.) Once
+you’re logged in, visit your account settings at
+[https://crates.io/me/](https://crates.io/me/) and retrieve your
+API key. Then, run the `cargo login` command and paste your API key when prompted, like this:
+
+```console
+$ cargo login
+abcdefghijklmnopqrstuvwxyz012345
+```
+
+This command will inform Cargo of your API token and store it locally in
+_~/.cargo/credentials.toml_. Note that this token is a secret: Do not share
+it with anyone else. If you do share it with anyone for any reason, you should
+revoke it and generate a new token on [crates.io](https://crates.io/).
+
+### Adding Metadata to a New Crate
+
+Let’s say you have a crate you want to publish. Before publishing, you’ll need
+to add some metadata in the `[package]` section of the crate’s _Cargo.toml_
+file.
+
+Your crate will need a unique name. While you’re working on a crate locally,
+you can name a crate whatever you’d like. However, crate names on
+[crates.io](https://crates.io/) are allocated on a first-come,
+first-served basis. Once a crate name is taken, no one else can publish a crate
+with that name. Before attempting to publish a crate, search for the name you
+want to use. If the name has been used, you will need to find another name and
+edit the `name` field in the _Cargo.toml_ file under the `[package]` section to
+use the new name for publishing, like so:
+
+Filename: Cargo.toml
+
+```toml
+[package]
+name = "guessing_game"
+```
+
+Even if you’ve chosen a unique name, when you run `cargo publish` to publish
+the crate at this point, you’ll get a warning and then an error:
+
+
+
+```console
+$ cargo publish
+ Updating crates.io index
+warning: manifest has no description, license, license-file, documentation, homepage or repository.
+See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for more info.
+--snip--
+error: failed to publish to registry at https://crates.io
+
+Caused by:
+ the remote server responded with an error (status 400 Bad Request): missing or empty metadata fields: description, license. Please see https://doc.rust-lang.org/cargo/reference/manifest.html for more information on configuring these fields
+```
+
+This results in an error because you’re missing some crucial information: A
+description and license are required so that people will know what your crate
+does and under what terms they can use it. In _Cargo.toml_, add a description
+that's just a sentence or two, because it will appear with your crate in search
+results. For the `license` field, you need to give a _license identifier
+value_. The [Linux Foundation’s Software Package Data Exchange (SPDX)][spdx]
+lists the identifiers you can use for this value. For example, to specify that
+you’ve licensed your crate using the MIT License, add the `MIT` identifier:
+
+Filename: Cargo.toml
+
+```toml
+[package]
+name = "guessing_game"
+license = "MIT"
+```
+
+If you want to use a license that doesn’t appear in the SPDX, you need to place
+the text of that license in a file, include the file in your project, and then
+use `license-file` to specify the name of that file instead of using the
+`license` key.
+
+Guidance on which license is appropriate for your project is beyond the scope
+of this book. Many people in the Rust community license their projects in the
+same way as Rust by using a dual license of `MIT OR Apache-2.0`. This practice
+demonstrates that you can also specify multiple license identifiers separated
+by `OR` to have multiple licenses for your project.
+
+With a unique name, the version, your description, and a license added, the
+_Cargo.toml_ file for a project that is ready to publish might look like this:
+
+Filename: Cargo.toml
+
+```toml
+[package]
+name = "guessing_game"
+version = "0.1.0"
+edition = "2024"
+description = "A fun game where you guess what number the computer has chosen."
+license = "MIT OR Apache-2.0"
+
+[dependencies]
+```
+
+[Cargo’s documentation](https://doc.rust-lang.org/cargo/) describes other
+metadata you can specify to ensure that others can discover and use your crate
+more easily.
+
+### Publishing to Crates.io
+
+Now that you’ve created an account, saved your API token, chosen a name for
+your crate, and specified the required metadata, you’re ready to publish!
+Publishing a crate uploads a specific version to
+[crates.io](https://crates.io/) for others to use.
+
+Be careful, because a publish is _permanent_. The version can never be
+overwritten, and the code cannot be deleted except in certain circumstances.
+One major goal of Crates.io is to act as a permanent archive of code so that
+builds of all projects that depend on crates from
+[crates.io](https://crates.io/) will continue to work. Allowing
+version deletions would make fulfilling that goal impossible. However, there is
+no limit to the number of crate versions you can publish.
+
+Run the `cargo publish` command again. It should succeed now:
+
+
+
+```console
+$ cargo publish
+ Updating crates.io index
+ Packaging guessing_game v0.1.0 (file:///projects/guessing_game)
+ Packaged 6 files, 1.2KiB (895.0B compressed)
+ Verifying guessing_game v0.1.0 (file:///projects/guessing_game)
+ Compiling guessing_game v0.1.0
+(file:///projects/guessing_game/target/package/guessing_game-0.1.0)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.19s
+ Uploading guessing_game v0.1.0 (file:///projects/guessing_game)
+ Uploaded guessing_game v0.1.0 to registry `crates-io`
+note: waiting for `guessing_game v0.1.0` to be available at registry
+`crates-io`.
+You may press ctrl-c to skip waiting; the crate should be available shortly.
+ Published guessing_game v0.1.0 at registry `crates-io`
+```
+
+Congratulations! You’ve now shared your code with the Rust community, and
+anyone can easily add your crate as a dependency of their project.
+
+### Publishing a New Version of an Existing Crate
+
+When you’ve made changes to your crate and are ready to release a new version,
+you change the `version` value specified in your _Cargo.toml_ file and
+republish. Use the [Semantic Versioning rules][semver] to decide what an
+appropriate next version number is, based on the kinds of changes you’ve made.
+Then, run `cargo publish` to upload the new version.
+
+
+
+
+
+
+### Deprecating Versions from Crates.io
+
+Although you can’t remove previous versions of a crate, you can prevent any
+future projects from adding them as a new dependency. This is useful when a
+crate version is broken for one reason or another. In such situations, Cargo
+supports yanking a crate version.
+
+_Yanking_ a version prevents new projects from depending on that version while
+allowing all existing projects that depend on it to continue. Essentially, a
+yank means that all projects with a _Cargo.lock_ will not break, and any future
+_Cargo.lock_ files generated will not use the yanked version.
+
+To yank a version of a crate, in the directory of the crate that you’ve
+previously published, run `cargo yank` and specify which version you want to
+yank. For example, if we’ve published a crate named `guessing_game` version
+1.0.1 and we want to yank it, then we’d run the following in the project
+directory for `guessing_game`:
+
+
+
+```console
+$ cargo yank --vers 1.0.1
+ Updating crates.io index
+ Yank guessing_game@1.0.1
+```
+
+By adding `--undo` to the command, you can also undo a yank and allow projects
+to start depending on a version again:
+
+```console
+$ cargo yank --vers 1.0.1 --undo
+ Updating crates.io index
+ Unyank guessing_game@1.0.1
+```
+
+A yank _does not_ delete any code. It cannot, for example, delete accidentally
+uploaded secrets. If that happens, you must reset those secrets immediately.
+
+[spdx]: https://spdx.org/licenses/
+[semver]: https://semver.org/
diff --git a/documents/markdown/rust-book/ch14-03-cargo-workspaces.md b/documents/markdown/rust-book/ch14-03-cargo-workspaces.md
new file mode 100644
index 0000000..ad47b8b
--- /dev/null
+++ b/documents/markdown/rust-book/ch14-03-cargo-workspaces.md
@@ -0,0 +1,389 @@
+## Cargo Workspaces
+
+In Chapter 12, we built a package that included a binary crate and a library
+crate. As your project develops, you might find that the library crate
+continues to get bigger and you want to split your package further into
+multiple library crates. Cargo offers a feature called _workspaces_ that can
+help manage multiple related packages that are developed in tandem.
+
+### Creating a Workspace
+
+A _workspace_ is a set of packages that share the same _Cargo.lock_ and output
+directory. Let’s make a project using a workspace—we’ll use trivial code so
+that we can concentrate on the structure of the workspace. There are multiple
+ways to structure a workspace, so we'll just show one common way. We’ll have a
+workspace containing a binary and two libraries. The binary, which will provide
+the main functionality, will depend on the two libraries. One library will
+provide an `add_one` function and the other library an `add_two` function.
+These three crates will be part of the same workspace. We’ll start by creating
+a new directory for the workspace:
+
+```console
+$ mkdir add
+$ cd add
+```
+
+Next, in the _add_ directory, we create the _Cargo.toml_ file that will
+configure the entire workspace. This file won’t have a `[package]` section.
+Instead, it will start with a `[workspace]` section that will allow us to add
+members to the workspace. We also make a point to use the latest and greatest
+version of Cargo’s resolver algorithm in our workspace by setting the
+`resolver` value to `"3"`:
+
+Filename: Cargo.toml
+
+```toml
+{{#include ../listings/ch14-more-about-cargo/no-listing-01-workspace/add/Cargo.toml}}
+```
+
+Next, we’ll create the `adder` binary crate by running `cargo new` within the
+_add_ directory:
+
+
+
+```console
+$ cargo new adder
+ Created binary (application) `adder` package
+ Adding `adder` as member of workspace at `file:///projects/add`
+```
+
+Running `cargo new` inside a workspace also automatically adds the newly created
+package to the `members` key in the `[workspace]` definition in the workspace
+_Cargo.toml_, like this:
+
+```toml
+{{#include ../listings/ch14-more-about-cargo/output-only-01-adder-crate/add/Cargo.toml}}
+```
+
+At this point, we can build the workspace by running `cargo build`. The files
+in your _add_ directory should look like this:
+
+```text
+├── Cargo.lock
+├── Cargo.toml
+├── adder
+│ ├── Cargo.toml
+│ └── src
+│ └── main.rs
+└── target
+```
+
+The workspace has one _target_ directory at the top level that the compiled
+artifacts will be placed into; the `adder` package doesn’t have its own
+_target_ directory. Even if we were to run `cargo build` from inside the
+_adder_ directory, the compiled artifacts would still end up in _add/target_
+rather than _add/adder/target_. Cargo structures the _target_ directory in a
+workspace like this because the crates in a workspace are meant to depend on
+each other. If each crate had its own _target_ directory, each crate would have
+to recompile each of the other crates in the workspace to place the artifacts
+in its own _target_ directory. By sharing one _target_ directory, the crates
+can avoid unnecessary rebuilding.
+
+### Creating the Second Package in the Workspace
+
+Next, let’s create another member package in the workspace and call it
+`add_one`. Generate a new library crate named `add_one`:
+
+
+
+```console
+$ cargo new add_one --lib
+ Created library `add_one` package
+ Adding `add_one` as member of workspace at `file:///projects/add`
+```
+
+The top-level _Cargo.toml_ will now include the _add_one_ path in the `members`
+list:
+
+Filename: Cargo.toml
+
+```toml
+{{#include ../listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/Cargo.toml}}
+```
+
+Your _add_ directory should now have these directories and files:
+
+```text
+├── Cargo.lock
+├── Cargo.toml
+├── add_one
+│ ├── Cargo.toml
+│ └── src
+│ └── lib.rs
+├── adder
+│ ├── Cargo.toml
+│ └── src
+│ └── main.rs
+└── target
+```
+
+In the _add_one/src/lib.rs_ file, let’s add an `add_one` function:
+
+Filename: add_one/src/lib.rs
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/add_one/src/lib.rs}}
+```
+
+Now we can have the `adder` package with our binary depend on the `add_one`
+package that has our library. First, we’ll need to add a path dependency on
+`add_one` to _adder/Cargo.toml_.
+
+Filename: adder/Cargo.toml
+
+```toml
+{{#include ../listings/ch14-more-about-cargo/no-listing-02-workspace-with-two-crates/add/adder/Cargo.toml:6:7}}
+```
+
+Cargo doesn’t assume that crates in a workspace will depend on each other, so
+we need to be explicit about the dependency relationships.
+
+Next, let’s use the `add_one` function (from the `add_one` crate) in the
+`adder` crate. Open the _adder/src/main.rs_ file and change the `main`
+function to call the `add_one` function, as in Listing 14-7.
+
+
+
+```rust,ignore
+{{#rustdoc_include ../listings/ch14-more-about-cargo/listing-14-07/add/adder/src/main.rs}}
+```
+
+
+
+Let’s build the workspace by running `cargo build` in the top-level _add_
+directory!
+
+
+
+```console
+$ cargo build
+ Compiling add_one v0.1.0 (file:///projects/add/add_one)
+ Compiling adder v0.1.0 (file:///projects/add/adder)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.22s
+```
+
+To run the binary crate from the _add_ directory, we can specify which package
+in the workspace we want to run by using the `-p` argument and the package name
+with `cargo run`:
+
+
+
+```console
+$ cargo run -p adder
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.00s
+ Running `target/debug/adder`
+Hello, world! 10 plus one is 11!
+```
+
+This runs the code in _adder/src/main.rs_, which depends on the `add_one` crate.
+
+
+
+
+
+### Depending on an External Package
+
+Notice that the workspace has only one _Cargo.lock_ file at the top level,
+rather than having a _Cargo.lock_ in each crate’s directory. This ensures that
+all crates are using the same version of all dependencies. If we add the `rand`
+package to the _adder/Cargo.toml_ and _add_one/Cargo.toml_ files, Cargo will
+resolve both of those to one version of `rand` and record that in the one
+_Cargo.lock_. Making all crates in the workspace use the same dependencies
+means the crates will always be compatible with each other. Let’s add the
+`rand` crate to the `[dependencies]` section in the _add_one/Cargo.toml_ file
+so that we can use the `rand` crate in the `add_one` crate:
+
+
+
+Filename: add_one/Cargo.toml
+
+```toml
+{{#include ../listings/ch14-more-about-cargo/no-listing-03-workspace-with-external-dependency/add/add_one/Cargo.toml:6:7}}
+```
+
+We can now add `use rand;` to the _add_one/src/lib.rs_ file, and building the
+whole workspace by running `cargo build` in the _add_ directory will bring in
+and compile the `rand` crate. We will get one warning because we aren’t
+referring to the `rand` we brought into scope:
+
+
+
+```console
+$ cargo build
+ Updating crates.io index
+ Downloaded rand v0.8.5
+ --snip--
+ Compiling rand v0.8.5
+ Compiling add_one v0.1.0 (file:///projects/add/add_one)
+warning: unused import: `rand`
+ --> add_one/src/lib.rs:1:5
+ |
+1 | use rand;
+ | ^^^^
+ |
+ = note: `#[warn(unused_imports)]` on by default
+
+warning: `add_one` (lib) generated 1 warning (run `cargo fix --lib -p add_one` to apply 1 suggestion)
+ Compiling adder v0.1.0 (file:///projects/add/adder)
+ Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.95s
+```
+
+The top-level _Cargo.lock_ now contains information about the dependency of
+`add_one` on `rand`. However, even though `rand` is used somewhere in the
+workspace, we can’t use it in other crates in the workspace unless we add
+`rand` to their _Cargo.toml_ files as well. For example, if we add `use rand;`
+to the _adder/src/main.rs_ file for the `adder` package, we’ll get an error:
+
+
+
+```console
+$ cargo build
+ --snip--
+ Compiling adder v0.1.0 (file:///projects/add/adder)
+error[E0432]: unresolved import `rand`
+ --> adder/src/main.rs:2:5
+ |
+2 | use rand;
+ | ^^^^ no external crate `rand`
+```
+
+To fix this, edit the _Cargo.toml_ file for the `adder` package and indicate
+that `rand` is a dependency for it as well. Building the `adder` package will
+add `rand` to the list of dependencies for `adder` in _Cargo.lock_, but no
+additional copies of `rand` will be downloaded. Cargo will ensure that every
+crate in every package in the workspace using the `rand` package will use the
+same version as long as they specify compatible versions of `rand`, saving us
+space and ensuring that the crates in the workspace will be compatible with
+each other.
+
+If crates in the workspace specify incompatible versions of the same
+dependency, Cargo will resolve each of them but will still try to resolve as
+few versions as possible.
+
+### Adding a Test to a Workspace
+
+For another enhancement, let’s add a test of the `add_one::add_one` function
+within the `add_one` crate:
+
+Filename: add_one/src/lib.rs
+
+```rust,noplayground
+{{#rustdoc_include ../listings/ch14-more-about-cargo/no-listing-04-workspace-with-tests/add/add_one/src/lib.rs}}
+```
+
+Now run `cargo test` in the top-level _add_ directory. Running `cargo test` in
+a workspace structured like this one will run the tests for all the crates in
+the workspace:
+
+
+
+```console
+$ cargo test
+ Compiling add_one v0.1.0 (file:///projects/add/add_one)
+ Compiling adder v0.1.0 (file:///projects/add/adder)
+ Finished `test` profile [unoptimized + debuginfo] target(s) in 0.20s
+ Running unittests src/lib.rs (target/debug/deps/add_one-93c49ee75dc46543)
+
+running 1 test
+test tests::it_works ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+
+ Running unittests src/main.rs (target/debug/deps/adder-3a47283c568d2b6a)
+
+running 0 tests
+
+test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+
+ Doc-tests add_one
+
+running 0 tests
+
+test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+```
+
+The first section of the output shows that the `it_works` test in the `add_one`
+crate passed. The next section shows that zero tests were found in the `adder`
+crate, and then the last section shows that zero documentation tests were found
+in the `add_one` crate.
+
+We can also run tests for one particular crate in a workspace from the
+top-level directory by using the `-p` flag and specifying the name of the crate
+we want to test:
+
+
+
+```console
+$ cargo test -p add_one
+ Finished `test` profile [unoptimized + debuginfo] target(s) in 0.00s
+ Running unittests src/lib.rs (target/debug/deps/add_one-93c49ee75dc46543)
+
+running 1 test
+test tests::it_works ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+
+ Doc-tests add_one
+
+running 0 tests
+
+test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+```
+
+This output shows `cargo test` only ran the tests for the `add_one` crate and
+didn’t run the `adder` crate tests.
+
+If you publish the crates in the workspace to
+[crates.io](https://crates.io/), each crate in the workspace
+will need to be published separately. Like `cargo test`, we can publish a
+particular crate in our workspace by using the `-p` flag and specifying the
+name of the crate we want to publish.
+
+For additional practice, add an `add_two` crate to this workspace in a similar
+way as the `add_one` crate!
+
+As your project grows, consider using a workspace: It enables you to work with
+smaller, easier-to-understand components than one big blob of code.
+Furthermore, keeping the crates in a workspace can make coordination between
+crates easier if they are often changed at the same time.
diff --git a/documents/markdown/rust-book/ch14-04-installing-binaries.md b/documents/markdown/rust-book/ch14-04-installing-binaries.md
new file mode 100644
index 0000000..40fc633
--- /dev/null
+++ b/documents/markdown/rust-book/ch14-04-installing-binaries.md
@@ -0,0 +1,48 @@
+
+
+
+
+## Installing Binaries with `cargo install`
+
+The `cargo install` command allows you to install and use binary crates
+locally. This isn’t intended to replace system packages; it’s meant to be a
+convenient way for Rust developers to install tools that others have shared on
+[crates.io](https://crates.io/). Note that you can only install
+packages that have binary targets. A _binary target_ is the runnable program
+that is created if the crate has a _src/main.rs_ file or another file specified
+as a binary, as opposed to a library target that isn’t runnable on its own but
+is suitable for including within other programs. Usually, crates have
+information in the README file about whether a crate is a library, has a
+binary target, or both.
+
+All binaries installed with `cargo install` are stored in the installation
+root’s _bin_ folder. If you installed Rust using _rustup.rs_ and don’t have any
+custom configurations, this directory will be *$HOME/.cargo/bin*. Ensure that
+this directory is in your `$PATH` to be able to run programs you’ve installed
+with `cargo install`.
+
+For example, in Chapter 12 we mentioned that there’s a Rust implementation of
+the `grep` tool called `ripgrep` for searching files. To install `ripgrep`, we
+can run the following:
+
+
+
+```console
+$ cargo install ripgrep
+ Updating crates.io index
+ Downloaded ripgrep v14.1.1
+ Downloaded 1 crate (213.6 KB) in 0.40s
+ Installing ripgrep v14.1.1
+--snip--
+ Compiling grep v0.3.2
+ Finished `release` profile [optimized + debuginfo] target(s) in 6.73s
+ Installing ~/.cargo/bin/rg
+ Installed package `ripgrep v14.1.1` (executable `rg`)
+```
+
+The second-to-last line of the output shows the location and the name of the
+installed binary, which in the case of `ripgrep` is `rg`. As long as the
+installation directory is in your `$PATH`, as mentioned previously, you can
+then run `rg --help` and start using a faster, Rustier tool for searching files!
diff --git a/documents/markdown/rust-book/ch14-05-extending-cargo.md b/documents/markdown/rust-book/ch14-05-extending-cargo.md
new file mode 100644
index 0000000..b351d7f
--- /dev/null
+++ b/documents/markdown/rust-book/ch14-05-extending-cargo.md
@@ -0,0 +1,17 @@
+## Extending Cargo with Custom Commands
+
+Cargo is designed so that you can extend it with new subcommands without having
+to modify it. If a binary in your `$PATH` is named `cargo-something`, you can
+run it as if it were a Cargo subcommand by running `cargo something`. Custom
+commands like this are also listed when you run `cargo --list`. Being able to
+use `cargo install` to install extensions and then run them just like the
+built-in Cargo tools is a super-convenient benefit of Cargo’s design!
+
+## Summary
+
+Sharing code with Cargo and [crates.io](https://crates.io/) is
+part of what makes the Rust ecosystem useful for many different tasks. Rust’s
+standard library is small and stable, but crates are easy to share, use, and
+improve on a timeline different from that of the language. Don’t be shy about
+sharing code that’s useful to you on [crates.io](https://crates.io/); it’s likely that it will be useful to someone else as well!
diff --git a/documents/markdown/rust-book/ch15-00-smart-pointers.md b/documents/markdown/rust-book/ch15-00-smart-pointers.md
new file mode 100644
index 0000000..8e0c0e8
--- /dev/null
+++ b/documents/markdown/rust-book/ch15-00-smart-pointers.md
@@ -0,0 +1,46 @@
+# Smart Pointers
+
+A pointer is a general concept for a variable that contains an address in
+memory. This address refers to, or “points at,” some other data. The most
+common kind of pointer in Rust is a reference, which you learned about in
+Chapter 4. References are indicated by the `&` symbol and borrow the value they
+point to. They don’t have any special capabilities other than referring to
+data, and they have no overhead.
+
+_Smart pointers_, on the other hand, are data structures that act like a
+pointer but also have additional metadata and capabilities. The concept of
+smart pointers isn’t unique to Rust: Smart pointers originated in C++ and exist
+in other languages as well. Rust has a variety of smart pointers defined in the
+standard library that provide functionality beyond that provided by references.
+To explore the general concept, we’ll look at a couple of different examples of
+smart pointers, including a _reference counting_ smart pointer type. This
+pointer enables you to allow data to have multiple owners by keeping track of
+the number of owners and, when no owners remain, cleaning up the data.
+
+In Rust, with its concept of ownership and borrowing, there is an additional
+difference between references and smart pointers: While references only borrow
+data, in many cases smart pointers _own_ the data they point to.
+
+Smart pointers are usually implemented using structs. Unlike an ordinary
+struct, smart pointers implement the `Deref` and `Drop` traits. The `Deref`
+trait allows an instance of the smart pointer struct to behave like a reference
+so that you can write your code to work with either references or smart
+pointers. The `Drop` trait allows you to customize the code that’s run when an
+instance of the smart pointer goes out of scope. In this chapter, we’ll discuss
+both of these traits and demonstrate why they’re important to smart pointers.
+
+Given that the smart pointer pattern is a general design pattern used
+frequently in Rust, this chapter won’t cover every existing smart pointer. Many
+libraries have their own smart pointers, and you can even write your own. We’ll
+cover the most common smart pointers in the standard library:
+
+- `Box`, for allocating values on the heap
+- `Rc`, a reference counting type that enables multiple ownership
+- `Ref` and `RefMut`, accessed through `RefCell`, a type that enforces
+ the borrowing rules at runtime instead of compile time
+
+In addition, we’ll cover the _interior mutability_ pattern where an immutable
+type exposes an API for mutating an interior value. We’ll also discuss
+reference cycles: how they can leak memory and how to prevent them.
+
+Let’s dive in!
diff --git a/documents/markdown/rust-book/ch15-01-box.md b/documents/markdown/rust-book/ch15-01-box.md
new file mode 100644
index 0000000..723d2c9
--- /dev/null
+++ b/documents/markdown/rust-book/ch15-01-box.md
@@ -0,0 +1,263 @@
+## Using `Box` to Point to Data on the Heap
+
+The most straightforward smart pointer is a box, whose type is written
+`Box`. _Boxes_ allow you to store data on the heap rather than the stack.
+What remains on the stack is the pointer to the heap data. Refer to Chapter 4
+to review the difference between the stack and the heap.
+
+Boxes don’t have performance overhead, other than storing their data on the
+heap instead of on the stack. But they don’t have many extra capabilities
+either. You’ll use them most often in these situations:
+
+- When you have a type whose size can’t be known at compile time, and you want
+ to use a value of that type in a context that requires an exact size
+- When you have a large amount of data, and you want to transfer ownership but
+ ensure that the data won’t be copied when you do so
+- When you want to own a value, and you care only that it’s a type that
+ implements a particular trait rather than being of a specific type
+
+We’ll demonstrate the first situation in [“Enabling Recursive Types with
+Boxes”](#enabling-recursive-types-with-boxes). In the second
+case, transferring ownership of a large amount of data can take a long time
+because the data is copied around on the stack. To improve performance in this
+situation, we can store the large amount of data on the heap in a box. Then,
+only the small amount of pointer data is copied around on the stack, while the
+data it references stays in one place on the heap. The third case is known as a
+_trait object_, and [“Using Trait Objects to Abstract over Shared
+Behavior”][trait-objects] in Chapter 18 is devoted to that
+topic. So, what you learn here you’ll apply again in that section!
+
+
+
+
+
+### Storing Data on the Heap
+
+Before we discuss the heap storage use case for `Box`, we’ll cover the
+syntax and how to interact with values stored within a `Box`.
+
+Listing 15-1 shows how to use a box to store an `i32` value on the heap.
+
+
+
+```rust
+{{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-01/src/main.rs}}
+```
+
+
+
+We define the variable `b` to have the value of a `Box` that points to the
+value `5`, which is allocated on the heap. This program will print `b = 5`; in
+this case, we can access the data in the box similarly to how we would if this
+data were on the stack. Just like any owned value, when a box goes out of
+scope, as `b` does at the end of `main`, it will be deallocated. The
+deallocation happens both for the box (stored on the stack) and the data it
+points to (stored on the heap).
+
+Putting a single value on the heap isn’t very useful, so you won’t use boxes by
+themselves in this way very often. Having values like a single `i32` on the
+stack, where they’re stored by default, is more appropriate in the majority of
+situations. Let’s look at a case where boxes allow us to define types that we
+wouldn’t be allowed to define if we didn’t have boxes.
+
+### Enabling Recursive Types with Boxes
+
+A value of a _recursive type_ can have another value of the same type as part of
+itself. Recursive types pose an issue because Rust needs to know at compile time
+how much space a type takes up. However, the nesting of values of recursive
+types could theoretically continue infinitely, so Rust can’t know how much space
+the value needs. Because boxes have a known size, we can enable recursive types
+by inserting a box in the recursive type definition.
+
+As an example of a recursive type, let’s explore the cons list. This is a data
+type commonly found in functional programming languages. The cons list type
+we’ll define is straightforward except for the recursion; therefore, the
+concepts in the example we’ll work with will be useful anytime you get into
+more complex situations involving recursive types.
+
+
+
+
+
+#### Understanding the Cons List
+
+A _cons list_ is a data structure that comes from the Lisp programming language
+and its dialects, is made up of nested pairs, and is the Lisp version of a
+linked list. Its name comes from the `cons` function (short for _construct
+function_) in Lisp that constructs a new pair from its two arguments. By
+calling `cons` on a pair consisting of a value and another pair, we can
+construct cons lists made up of recursive pairs.
+
+For example, here’s a pseudocode representation of a cons list containing the
+list `1, 2, 3` with each pair in parentheses:
+
+```text
+(1, (2, (3, Nil)))
+```
+
+Each item in a cons list contains two elements: the value of the current item
+and of the next item. The last item in the list contains only a value called
+`Nil` without a next item. A cons list is produced by recursively calling the
+`cons` function. The canonical name to denote the base case of the recursion is
+`Nil`. Note that this is not the same as the “null” or “nil” concept discussed
+in Chapter 6, which is an invalid or absent value.
+
+The cons list isn’t a commonly used data structure in Rust. Most of the time
+when you have a list of items in Rust, `Vec` is a better choice to use.
+Other, more complex recursive data types _are_ useful in various situations,
+but by starting with the cons list in this chapter, we can explore how boxes
+let us define a recursive data type without much distraction.
+
+Listing 15-2 contains an enum definition for a cons list. Note that this code
+won’t compile yet, because the `List` type doesn’t have a known size, which
+we’ll demonstrate.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-02/src/main.rs:here}}
+```
+
+
+
+> Note: We’re implementing a cons list that holds only `i32` values for the
+> purposes of this example. We could have implemented it using generics, as we
+> discussed in Chapter 10, to define a cons list type that could store values of
+> any type.
+
+Using the `List` type to store the list `1, 2, 3` would look like the code in
+Listing 15-3.
+
+
+
+```rust,ignore,does_not_compile
+{{#rustdoc_include ../listings/ch15-smart-pointers/listing-15-03/src/main.rs:here}}
+```
+
+
+
+The first `Cons` value holds `1` and another `List` value. This `List` value is
+another `Cons` value that holds `2` and another `List` value. This `List` value
+is one more `Cons` value that holds `3` and a `List` value, which is finally
+`Nil`, the non-recursive variant that signals the end of the list.
+
+If we try to compile the code in Listing 15-3, we get the error shown in
+Listing 15-4.
+
+
+
+```console
+{{#include ../listings/ch15-smart-pointers/listing-15-03/output.txt}}
+```
+
+
+
+The error shows this type “has infinite size.” The reason is that we’ve defined
+`List` with a variant that is recursive: It holds another value of itself
+directly. As a result, Rust can’t figure out how much space it needs to store a
+`List` value. Let’s break down why we get this error. First, we’ll look at how
+Rust decides how much space it needs to store a value of a non-recursive type.
+
+#### Computing the Size of a Non-Recursive Type
+
+Recall the `Message` enum we defined in Listing 6-2 when we discussed enum
+definitions in Chapter 6:
+
+```rust
+{{#rustdoc_include ../listings/ch06-enums-and-pattern-matching/listing-06-02/src/main.rs:here}}
+```
+
+To determine how much space to allocate for a `Message` value, Rust goes
+through each of the variants to see which variant needs the most space. Rust
+sees that `Message::Quit` doesn’t need any space, `Message::Move` needs enough
+space to store two `i32` values, and so forth. Because only one variant will be
+used, the most space a `Message` value will need is the space it would take to
+store the largest of its variants.
+
+Contrast this with what happens when Rust tries to determine how much space a
+recursive type like the `List` enum in Listing 15-2 needs. The compiler starts
+by looking at the `Cons` variant, which holds a value of type `i32` and a value
+of type `List`. Therefore, `Cons` needs an amount of space equal to the size of
+an `i32` plus the size of a `List`. To figure out how much memory the `List`
+type needs, the compiler looks at the variants, starting with the `Cons`
+variant. The `Cons` variant holds a value of type `i32` and a value of type
+`List`, and this process continues infinitely, as shown in Figure 15-1.
+
+
+
+Figure 15-1: An infinite `List` consisting of infinite
+`Cons` variants
+
+
+
+
+
+#### Getting a Recursive Type with a Known Size
+
+Because Rust can’t figure out how much space to allocate for recursively
+defined types, the compiler gives an error with this helpful suggestion:
+
+
+
+```text
+help: insert some indirection (e.g., a `Box`, `Rc`, or `&`) to break the cycle
+ |
+2 | Cons(i32, Box),
+ | ++++ +
+```
+
+In this suggestion, _indirection_ means that instead of storing a value
+directly, we should change the data structure to store the value indirectly by
+storing a pointer to the value instead.
+
+Because a `Box` is a pointer, Rust always knows how much space a `Box`
+needs: A pointer’s size doesn’t change based on the amount of data it’s
+pointing to. This means we can put a `Box` inside the `Cons` variant instead
+of another `List` value directly. The `Box
+ 
+
+
\ No newline at end of file
diff --git a/documents/html/mdn-learning-area/advanced-items-sold-headers.html b/documents/html/mdn-learning-area/advanced-items-sold-headers.html
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--- /dev/null
+++ b/documents/html/mdn-learning-area/advanced-items-sold-headers.html
@@ -0,0 +1,77 @@
+
+
+
+
+
+ 
+
+
+
diff --git a/documents/html/mdn-learning-area/images-images2.html b/documents/html/mdn-learning-area/images-images2.html
new file mode 100644
index 0000000..6743d1e
--- /dev/null
+++ b/documents/html/mdn-learning-area/images-images2.html
@@ -0,0 +1,50 @@
+
+
+
+
+ 
+ The Firefox logo, newly abstracted for 2019!
+
+
+
diff --git a/documents/html/mdn-learning-area/images-images3.html b/documents/html/mdn-learning-area/images-images3.html
new file mode 100644
index 0000000..fe2152f
--- /dev/null
+++ b/documents/html/mdn-learning-area/images-images3.html
@@ -0,0 +1,48 @@
+
+
+
+
+ 
+
+
\ No newline at end of file
diff --git a/documents/html/mdn-learning-area/links-links1-download.html b/documents/html/mdn-learning-area/links-links1-download.html
new file mode 100644
index 0000000..333f3b7
--- /dev/null
+++ b/documents/html/mdn-learning-area/links-links1-download.html
@@ -0,0 +1,43 @@
+
+
+
+
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+
+ 
+
+ 
+
+
+
diff --git a/documents/html/mdn-learning-area/structuring-a-page-of-content-finished-index.html b/documents/html/mdn-learning-area/structuring-a-page-of-content-finished-index.html
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@@ -0,0 +1,57 @@
+
+
+
+
+
+ 
+
+
+ 
.default})
+```
+
+```mdx-code-block
+
`, without any processing or file existence checking.
diff --git a/documents/markdown/docusaurus/markdown-features-code-blocks.md b/documents/markdown/docusaurus/markdown-features-code-blocks.md
new file mode 100644
index 0000000..a5a3fb3
--- /dev/null
+++ b/documents/markdown/docusaurus/markdown-features-code-blocks.md
@@ -0,0 +1,848 @@
+---
+id: code-blocks
+description: Handling code blocks in Docusaurus Markdown
+slug: /markdown-features/code-blocks
+---
+
+# Code blocks
+
+import BrowserWindow from '@site/src/components/BrowserWindow';
+import CodeBlock from '@theme/CodeBlock';
+
+Code blocks within documentation are super-powered 💪.
+
+## Code title {/* #code-title */}
+
+You can add a title to the code block by adding a `title` key after the language (leave a space between them).
+
+````md
+```jsx title="/src/components/HelloCodeTitle.js"
+function HelloCodeTitle(props) {
+ return 
`, as-is. However, _that is not the case_.
+
+The Markdown syntax `` only declaratively tells Docusaurus that an image needs to be inserted here, but we may do other things like transforming a [file path to URL path](./markdown-features-assets.mdx#images), so the generated markup may differ from the output of other Markdown renderers, or a naïve hand-transcription to the equivalent JSX/HTML code.
+
+In general, you should only assume the _semantics_ of the markup (` ``` ` fences become [code blocks](./markdown-features-code-blocks.mdx); `>` becomes [quotes](#quotes), etc.), but not the actual compiled output.
+
+