7f787e397c
Add `Iterator::map_windows` Tracking issue: #87155. This is inherited from the old PR #82413. Unlike #82413, this PR implements the `MapWindows` to be lazy: only when pulling from the outer iterator, `.next()` of the inner iterator will be called. ## Implementaion Steps - [x] Implement `MapWindows` to keep the iterators' [*Laziness*](https://doc.rust-lang.org/std/iter/index.html#laziness) contract. - [x] Fix the known bug of memory access error. - [ ] Full specialization of iterator-related traits for `MapWindows`. - [x] `Iterator::size_hint`, - [x] ~`Iterator::count`~, - [x] `ExactSizeIterator` (when `I: ExactSizeIterator`), - [x] ~`TrustedLen` (when `I: TrustedLen`)~, - [x] `FusedIterator`, - [x] ~`Iterator::advance_by`~, - [x] ~`Iterator::nth`~, - [ ] ... - [ ] More tests and docs. ## Unresolved Questions: - [ ] Is there any more iterator-related traits should be specialized? - [ ] Is the double-space buffer worth? - [ ] Should there be `rmap_windows` or something else? - [ ] Taking GAT for consideration, should the mapper function be `FnMut(&[I::Item; N]) -> R` or something like `FnMut(ArrayView<'_, I::Item, N>) -> R`? Where `ArrayView` is mentioned in https://github.com/rust-lang/generic-associated-types-initiative/issues/2. - It can save memory, only the same size as the array window is needed, - It is more efficient, which requires less data copies, - It is possibly compatible with the GATified version of `LendingIterator::windows`. - But it prevents the array pattern matching like `iter.map_windows(|_arr: [_; N]| ())`, unless we extend the array pattern to allow matching the `ArrayView`. |
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