Add Vec::get_uninit_unchecked #70967
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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 @joshtriplett (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. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed.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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src/liballoc/vec.rs
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| /// assert_eq!(&*x, &[0, 1, 2, 3]); | ||
| /// ``` | ||
| #[unstable(feature = "vec_get_uninit_unchecked", issue = "none")] | ||
| pub fn get_uninit_unchecked(&mut self, index: usize) -> &mut MaybeUninit<T> { |
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Suggested change
| pub fn get_uninit_unchecked(&mut self, index: usize) -> &mut MaybeUninit<T> { | |
| pub unsafe fn get_uninit_unchecked(&mut self, index: usize) -> &mut MaybeUninit<T> { |
There are two ways in which you can violate soundness with this method:
- You provide
indexwhereindex >= self.capacity(). - You do
let elem = vec.get_uninit_unchecked(index); *elem = MaybeUninit::uninit(); drop(vec[index]);.
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Also, you can have a memory leak if you forget to use vec.set_len(...) afterwards in some circumstances; also worth noting in docs.
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…g* Improve the explanation in the assertion* UB and memory leak notes
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Rather than conflating unchecked indexing and conversion to impl<T> Vec<T> {
/// Returns the vector's spare capacity as a mutable slice of maybe-uninitialized values.
///
/// The length of the slice will be `self.capacity() - self.len()`.
pub fn spare_capacity_mut(&mut self) -> &mut [MaybeUninit<T>] { ... }
} |
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Ping from Triage: Hi @moshg - any updates? |
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Ping from Triage: Closing due to inactivity. @moshg please reopen with updates. Thanks for the PR. |
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This is intended to reduce misusing
get_unchecked_mutto access out of bounds.In addition, we can detect out-of-allocation with this method unlike
x.as_ptr_mut().add(index).I hope this to help
get_uncheckedto do bound check in debug build in the future. #36976Though immutable
get_uninit_uncheckedis useless, should I nameget_uninit_unchecked_mut?