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Add slice::check_range #75207

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Merged
merged 5 commits into from
Sep 4, 2020
Merged

Add slice::check_range #75207

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bb70e52
Add `slice::check_range`
dylni Aug 6, 2020
202b242
Fix links
dylni Aug 6, 2020
ed02b90
Fix links again
dylni Aug 6, 2020
d04e6b8
Replace ad hoc implementations with `slice::check_range`
dylni Aug 17, 2020
d9e877f
Add more information to safety comment
dylni Aug 24, 2020
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Fix links
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@dylni
dylni committed Aug 6, 2020
commit 202b242d87c30c2fe1475342f9b93a8dfc65cd17
4 changes: 2 additions & 2 deletions library/core/src/slice/mod.rs
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Expand Up @@ -356,7 +356,7 @@ impl<T> [T] {
///
/// [`get_unchecked`]: #method.get_unchecked
/// [`get_unchecked_mut`]: #method.get_unchecked_mut
/// [`Range`]: ../ops/struct.Range.html
/// [`Range`]: ops/struct.Range.html
///
/// # Panics
///
Expand Down Expand Up @@ -393,7 +393,7 @@ impl<T> [T] {
/// [10, 40, 30].check_range(1..=usize::MAX);
/// ```
///
/// [`Index::index`]: ../ops/trait.Index.html#tymethod.index
/// [`Index::index`]: ops/trait.Index.html#tymethod.index
#[track_caller]
#[unstable(feature = "slice_check_range", issue = "none")]
pub fn check_range<R: RangeBounds<usize>>(&self, range: R) -> Range<usize> {
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@leonardo-m leonardo-m Aug 6, 2020 •
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We can't unfortunately return a CheckedRange<usize> because there's no association with a specific range, so it's useless.

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Can you explain more? I don't see how this would be useless, since it converts RangeBounds to usizes. It wasn't meant to reduce unsafe code.

It could return a CheckedRange that has a reference to the slice and a safe get method. However, that would require check_range_mut and CheckedRangeMut too, which would make this simple method much more complex.

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Your code is useful. I meant to say that returning a CheckedRange is not so useful. As you say it could be done with the reference to the slice, but it could make it over engineered, so all is OK.

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Oh, that makes sense. Thanks for the clarification.

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Given that we only need the length of the slice, I don't think this method should take a reference to the full slice. References are very strong types, they assert the aliasing rules and they assert that the memory they point to is initialized. As my other messages here show, that is a problem for this method.

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For future readers, this conversation was continued here.

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