This repository was archived by the owner on May 3, 2026. It is now read-only.
Improve performance characteristics of Vector iterators to better match Vec iterators - #104
Open
jessegrosjean wants to merge 2 commits into
Open
Improve performance characteristics of Vector iterators to better match Vec iterators#104jessegrosjean wants to merge 2 commits into
jessegrosjean wants to merge 2 commits into
Conversation
timotree3
suggested changes
Oct 23, 2019
timotree3
left a comment
timotree3
left a comment
There was a problem hiding this comment.
Just passing by and I noticed what I believe to be multiple bugs in this implementation. All my comments apply to both the Iterator and DoubleEndedIterator implementations for all the mutability variants.
| if n >= self.len() { | ||
| None | ||
| } else { | ||
| self.front_index += n; |
|
|
||
| fn nth(&mut self, n: usize) -> Option<Self::Item> { | ||
| if n >= self.len() { | ||
| None |
There was a problem hiding this comment.
I don't believe this shortcut is correct. It introduces a bug.
Before this change, this works:
let vec = vector![1, 2, 3];
let mut iter = vec.iter();
assert_eq!(iter.nth(3), None);
assert_eq!(iter.next(), None);Afterwards, it panics because the call to next() returns Some(1).
Since the implementation of next() already has a check for exhaustion, I would remove this if altogether and replace it with its else case.
| impl<'a, A: Clone> ExactSizeIterator for Iter<'a, A> {} | ||
| impl<'a, A: Clone> ExactSizeIterator for Iter<'a, A> { | ||
| fn len(&self) -> usize { | ||
| self.back_index - self.front_index |
There was a problem hiding this comment.
What if this underflows?
Suggested change
| self.back_index - self.front_index | |
| self.back_index.saturating_sub(self.front_index) |
| impl<'a, A: Clone> ExactSizeIterator for IterMut<'a, A> {} | ||
| impl<'a, A: Clone> ExactSizeIterator for IterMut<'a, A> { | ||
| fn len(&self) -> usize { | ||
| self.back_index - self.front_index |
There was a problem hiding this comment.
Suggested change
| self.back_index - self.front_index | |
| self.back_index.saturing_sub(self.front_index) |
|
|
||
| impl<'a, A: Clone> ExactSizeIterator for Chunks<'a, A> { | ||
| fn len(&self) -> usize { | ||
| self.back_index - self.front_index |
There was a problem hiding this comment.
Suggested change
| self.back_index - self.front_index | |
| self.back_index.saturing_sub(self.front_index) |
|
|
||
| impl<'a, A: Clone> ExactSizeIterator for ChunksMut<'a, A> { | ||
| fn len(&self) -> usize { | ||
| self.back_index - self.front_index |
There was a problem hiding this comment.
Suggested change
| self.back_index - self.front_index | |
| self.back_index.saturing_sub(self.front_index) |
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to subscribe to this conversation on GitHub.
Already have an account?
Sign in.
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
In particular provided implementations of
len,count,nth, andnth_backforIter,IterMut,Chunks,ChunksMutthat make use offront_indexandback_indexto improve performance.Similar work might also be useful for
ConsumingIter, but I couldn't easily trace that code to see where/if such improvements would make sense.