What does the keyword def/undef do?

[ghost]

I can't find anything about them in the document!

Update: undef is there: https://github.com/AdeptLanguage/Adept#undef-keyword, what about def?

[IsaacShelton]

def/undef declares a variable inside of an expression and returns a pointer to it.

The difference is that def zero-initializes the variable, and undef does not.

It has some weird scoping rules as well, so you can capture the result of a function that outputs via a pointer and only have the variable live within the if-scope.

It is usually a bad idea to use it.

import basics

func main {
    if getValue(undef x int) {
        print("Got x = " + x)
    } else {
        print("Failed to get x")
    }
}

func getValue(result *int) successful {
    *result = 123
    return true
}

which is the same as

import basics

func main {
    x int = undef  // Although, this would be scoped to inside of the if statement
    if getValue(&x) {
        print("Got x = " + x)
    } else {
        print("Failed to get x")
    }
}

func getValue(result *int) successful {
    *result = 123
    return true
}