O(1) count,nth,last for slice::{Windows,Chunks,ChunksMut} #27652
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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @aturon (or someone else) soon. If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes. Please see the contribution instructions for more information. |
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| #[inline] | ||
| fn nth(&mut self, n: usize) -> Option<Self::Item> { | ||
| let end = self.size + n; |
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This addition may overflow. The methods for add with overflow might be appropriate, take the None case on overflow.
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I noticed that that said module is flagged as unstable - does that present an obstacle for using in in an impl which is stable?
Alternatively I could handle this manually.
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Not an obstacle! There are several ways to do this, you can use .checked_add for example, but i thought overflowing_add would be the correct one for this particular line.
(saturating_add produces usize::MAX instead of overflowing, but that's not correct for the comparison end > self.len() — usize::MAX is not guaranteed to be larger).
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Addressed the well-raised concerns regarding overflow in the I opted to use both checked and overflowing methods as I found convenient - is this seen as bad style? |
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Great! Handling overflow cases is of course an issue of correctness, not safety. @bors r+ |
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📌 Commit b223abb has been approved by |
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@bors r- Actually, can you squash this together into just one commit? Since the commits partly change and change things back. |
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r=me with squash |
Implemented count, nth, and last in constant time for Windows, Chunks, and ChunksMut created from a slice. Included checks for overflow in the implementation of nth(). Also added a test for each implemented method to libcoretest. Addresses rust-lang#24214
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Thank you! (No notifications go out from commit changes, need a message on the PR thread for that) @bors r+ |
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📌 Commit e09f83e has been approved by |
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Cool - I'll remember to post after commits in the future. |
bluss
added
the
relnotes
Provides a custom implementation of Iterator methods
count,nth, andlastfor the structuresslice::{Windows,Chunks,ChunksMut}in the core module.These implementations run in constant time as opposed to the default implementations which run in linear time.
Addresses Issue #24214
r? @aturon