Use strongly typed wrapped indices in VecDeque#152112
Use strongly typed wrapped indices in VecDeque#152112Kobzol wants to merge 3 commits intorust-lang:mainfrom
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| pub(super) struct WrappedIndex(usize); | ||
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| impl WrappedIndex { | ||
| /// Safety invariant: the newly constructed index must be in-bounds for the VecDeque |
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I don't think this safety invariant is particularly useful, as all functions that act on the buffer still need to require that the WrappedIndex is specific to that particular VecDeque with a given capacity.
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Yeah, it's a relatively weak invariant. That being said, I still thought it would be a good idea to provide a "SLOW DOWN" sign when someone wants to conjure the index out of the blue, which is why I marked the function unsafe.
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I'm just not a big fan of redundant unsafe (this can neither cause UB itself nor be used in safety proofs). Isn't the WrappedIndex::new call enough of a stop-sign?
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Okay, fair enough. Maybe we could just name it something like from_arbitrary_number? 😆 Should I also remove unsafe from add and sub?
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| #[inline(always)] | ||
| pub(super) fn abs_diff(self, other: Self) -> Self { |
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The return type should be usize, right? It isn't a buffer index but rather a length.
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Right, the type represents something like "value in-bounds". My thought process was that if we have two in-bounds values, and we do an absolute diff of them, the result also has to be in-bounds (w.r.t. the same VecDeque). But we do treat it as usize everywhere the function is currently used, so.. I'll change it to usize.
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I did name if |
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I do slightly prefer the Wrapped name, I think that the buffer part is implied by the word "index". The main idea is to express that the index was wrapped to not go over bounds, which is how it is created through most means. @rustbot ready |
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This probably needs a rebase atop #152258. Sorry for taking so long, staring at so many lines makes me dizzy, I've not been in the right mind to do it... |
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This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed. Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers. |
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Huh, the rebase went cleanly without any conflict, surprising.. 😆 No problem, I know from experience how draining it can be to review large diffs. Thank you very much for taking a look! |
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This is far from perfect, but it would have prevented #151769.
r? @joboet