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Rollup merge of #145504 - Jules-Bertholet:more_conversion_trait_impls, r=tgross35

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Add some conversion trait impls

- `impl<T, const N: usize> From<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc https://github.com/rust-lang/rust/issues/96097)
- `impl<T, const N: usize> AsRef<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc https://github.com/rust-lang/rust/issues/96097)
- `impl<T, const N: usize> AsRef<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc https://github.com/rust-lang/rust/issues/96097)
- `impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc https://github.com/rust-lang/rust/issues/96097)
- `impl<T, const N: usize> AsMut<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc https://github.com/rust-lang/rust/issues/96097)
- `impl<T, const N: usize> From<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N]` (cc https://github.com/rust-lang/rust/issues/96097)
- `impl<T, const N: usize> AsRef<[Cell<T>; N]> for Cell<[T; N]>` (equivalent of `as_array_of_cells`, cc https://github.com/rust-lang/rust/issues/88248)
- `impl<T, const N: usize> AsRef<[Cell<T>]> for Cell<[T; N]>`
- `impl<T> AsRef<[Cell<T>]> for Cell<[T]>` (equivalent of `as_slice_of_cells`)

@rustbot label T-libs-api needs-fcp -T-libs

I’ve tried to only add impls that are unlikely to cause single-applicable-impl inference breakage.
This commit is contained in:
Matthias Krüger 2026-02-09 18:39:42 +01:00 • committed by GitHub
commit 2ce5f487e0
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3 changed files with 75 additions and 1 deletions
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24
library/core/src/cell.rs
View file

@ -689,6 +689,30 @@ impl<T: CoerceUnsized<U>, U> CoerceUnsized<Cell<U>> for Cell<T> {}
#[unstable(feature = "dispatch_from_dyn", issue = "none")]
impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<Cell<U>> for Cell<T> {}
#[stable(feature = "more_conversion_trait_impls", since = "CURRENT_RUSTC_VERSION")]
impl<T, const N: usize> AsRef<[Cell<T>; N]> for Cell<[T; N]> {
#[inline]
fn as_ref(&self) -> &[Cell<T>; N] {
self.as_array_of_cells()
}
}
#[stable(feature = "more_conversion_trait_impls", since = "CURRENT_RUSTC_VERSION")]
impl<T, const N: usize> AsRef<[Cell<T>]> for Cell<[T; N]> {
#[inline]
fn as_ref(&self) -> &[Cell<T>] {
&*self.as_array_of_cells()
}
}
#[stable(feature = "more_conversion_trait_impls", since = "CURRENT_RUSTC_VERSION")]
impl<T> AsRef<[Cell<T>]> for Cell<[T]> {
#[inline]
fn as_ref(&self) -> &[Cell<T>] {
self.as_slice_of_cells()
}
}
impl<T> Cell<[T]> {
/// Returns a `&[Cell<T>]` from a `&Cell<[T]>`
///

50
library/core/src/mem/maybe_uninit.rs
View file

@ -1532,6 +1532,56 @@ impl<T, const N: usize> MaybeUninit<[T; N]> {
}
}
#[stable(feature = "more_conversion_trait_impls", since = "CURRENT_RUSTC_VERSION")]
impl<T, const N: usize> From<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]> {
#[inline]
fn from(arr: [MaybeUninit<T>; N]) -> Self {
arr.transpose()
}
}
#[stable(feature = "more_conversion_trait_impls", since = "CURRENT_RUSTC_VERSION")]
impl<T, const N: usize> AsRef<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]> {
#[inline]
fn as_ref(&self) -> &[MaybeUninit<T>; N] {
// SAFETY: T and MaybeUninit<T> have the same layout
unsafe { &*ptr::from_ref(self).cast() }
}
}
#[stable(feature = "more_conversion_trait_impls", since = "CURRENT_RUSTC_VERSION")]
impl<T, const N: usize> AsRef<[MaybeUninit<T>]> for MaybeUninit<[T; N]> {
#[inline]
fn as_ref(&self) -> &[MaybeUninit<T>] {
&*AsRef::<[MaybeUninit<T>; N]>::as_ref(self)
}
}
#[stable(feature = "more_conversion_trait_impls", since = "CURRENT_RUSTC_VERSION")]
impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]> {
#[inline]
fn as_mut(&mut self) -> &mut [MaybeUninit<T>; N] {
// SAFETY: T and MaybeUninit<T> have the same layout
unsafe { &mut *ptr::from_mut(self).cast() }
}
}
#[stable(feature = "more_conversion_trait_impls", since = "CURRENT_RUSTC_VERSION")]
impl<T, const N: usize> AsMut<[MaybeUninit<T>]> for MaybeUninit<[T; N]> {
#[inline]
fn as_mut(&mut self) -> &mut [MaybeUninit<T>] {
&mut *AsMut::<[MaybeUninit<T>; N]>::as_mut(self)
}
}
#[stable(feature = "more_conversion_trait_impls", since = "CURRENT_RUSTC_VERSION")]
impl<T, const N: usize> From<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N] {
#[inline]
fn from(arr: MaybeUninit<[T; N]>) -> Self {
arr.transpose()
}
}
impl<T, const N: usize> [MaybeUninit<T>; N] {
/// Transposes a `[MaybeUninit<T>; N]` into a `MaybeUninit<[T; N]>`.
///

2
tests/ui/suggestions/issue-71394-no-from-impl.stderr
View file

@ -13,7 +13,7 @@ LL | let _: &[i8] = data.into();
`[T; 6]` implements `From<(T, T, T, T, T, T)>`
`[T; 7]` implements `From<(T, T, T, T, T, T, T)>`
`[T; 8]` implements `From<(T, T, T, T, T, T, T, T)>`
and 6 others
and 7 others
= note: required for `&[u8]` to implement `Into<&[i8]>`
error: aborting due to 1 previous error