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Rollup merge of #102023 - SUPERCILEX:maybeuninit-transpose, r=scottmcm

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Add MaybeUninit array transpose From impls

See discussion in https://github.com/rust-lang/rust/pull/101179 and https://github.com/rust-lang/rust/issues/96097. I believe this solution offers the simplest implementation with minimal future API regret.

`@RalfJung` mind doing a correctness review?
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Yuki Okushi 2022-10-16 11:41:12 +09:00 committed by GitHub
parent cbc0a73c95 393434c29e
commit 166f664037
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37
library/core/src/mem/maybe_uninit.rs
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@ -1284,3 +1284,40 @@ pub fn slice_as_bytes_mut(this: &mut [MaybeUninit<T>]) -> &mut [MaybeUninit<u8>]
}
}
}
impl<T, const N: usize> MaybeUninit<[T; N]> {
/// Transposes a `MaybeUninit<[T; N]>` into a `[MaybeUninit<T>; N]`.
///
/// # Examples
///
/// ```
/// #![feature(maybe_uninit_uninit_array_transpose)]
/// # use std::mem::MaybeUninit;
///
/// let data: [MaybeUninit<u8>; 1000] = MaybeUninit::uninit().transpose();
/// ```
#[unstable(feature = "maybe_uninit_uninit_array_transpose", issue = "96097")]
pub fn transpose(self) -> [MaybeUninit<T>; N] {
// SAFETY: T and MaybeUninit<T> have the same layout
unsafe { super::transmute_copy(&ManuallyDrop::new(self)) }
}
}
impl<T, const N: usize> [MaybeUninit<T>; N] {
/// Transposes a `[MaybeUninit<T>; N]` into a `MaybeUninit<[T; N]>`.
///
/// # Examples
///
/// ```
/// #![feature(maybe_uninit_uninit_array_transpose)]
/// # use std::mem::MaybeUninit;
///
/// let data = [MaybeUninit::<u8>::uninit(); 1000];
/// let data: MaybeUninit<[u8; 1000]> = data.transpose();
/// ```
#[unstable(feature = "maybe_uninit_uninit_array_transpose", issue = "96097")]
pub fn transpose(self) -> MaybeUninit<[T; N]> {
// SAFETY: T and MaybeUninit<T> have the same layout
unsafe { super::transmute_copy(&ManuallyDrop::new(self)) }
}
}