Add some conversion trait impls#145504

Jules-Bertholet · 2025-08-16T16:22:58Z

impl<T, const N: usize> From<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]> (cc Tracking Issue for MaybeUninit methods for arrays #96097)
impl<T, const N: usize> AsRef<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]> (cc Tracking Issue for MaybeUninit methods for arrays #96097)
impl<T, const N: usize> AsRef<[MaybeUninit<T>]> for MaybeUninit<[T; N]> (cc Tracking Issue for MaybeUninit methods for arrays #96097)
impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]> (cc Tracking Issue for MaybeUninit methods for arrays #96097)
impl<T, const N: usize> AsMut<[MaybeUninit<T>]> for MaybeUninit<[T; N]> (cc Tracking Issue for MaybeUninit methods for arrays #96097)
impl<T, const N: usize> From<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N] (cc Tracking Issue for MaybeUninit methods for arrays #96097)
impl<T, const N: usize> AsRef<[Cell<T>; N]> for Cell<[T; N]> (equivalent of as_array_of_cells, cc Tracking Issue for Cell::as_array_of_cells #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.

rustbot · 2025-08-16T16:23:03Z

rustbot has assigned @Mark-Simulacrum.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

jieyouxu · 2025-08-17T01:49:17Z

r? libs-api

library/core/src/mem/maybe_uninit.rs

tgross35 · 2025-09-05T01:52:20Z

Preparing for crater

@bors try

@rustbot label +I-libs-api-nominated
r? libs

…r=<try> Add some conversion trait impls

tgross35 · 2025-09-05T02:47:42Z

library/core/src/ascii/ascii_char.rs

+impl AsMut<str> for AsciiChar {
+    #[inline(always)]
+    fn as_mut(&mut self) -> &mut str {
+        let ascii_ptr: *mut [Self] = crate::slice::from_mut(self);
+        let str_ptr = ascii_ptr as *mut str;
+        // SAFETY: Each ASCII codepoint in UTF-8 is encoded as one single-byte
+        // code unit having the same value as the ASCII byte.
+        unsafe { &mut *str_ptr }
+    }
+}


This could probably be implemented in a new as_mut_str method, similar to as_str

Also, could everything here use #[inline] without the always?

rust-bors · 2025-09-05T04:08:35Z

☀️ Try build successful (CI)
Build commit: 0498c15 (0498c157964e0946754e29e57ee9ef4527dc2a42, parent: af00ff2ce62b6617ed19305ae39e135ac71d0b22)

tgross35 · 2025-09-05T04:09:22Z

@craterbot check

library/core/src/mem/maybe_uninit.rs

- `impl<T, const N: usize> From<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` - `impl<T, const N: usize> AsRef<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` - `impl<T, const N: usize> AsRef<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` - `impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` - `impl<T, const N: usize> AsMut<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` - `impl<T, const N: usize> From<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N]` - `impl<T, const N: usize> AsRef<[Cell<T>; N]> for Cell<[T; N]>` - `impl<T, const N: usize> AsRef<[Cell<T>]> for Cell<[T; N]>` - `impl<T> AsRef<[Cell<T>]> for Cell<[T]>`

rustbot · 2026-02-07T22:10:33Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

tgross35

Thanks!

@bors r+ rollup

View changes since this review

rust-bors · 2026-02-09T10:50:18Z

📌 Commit d0b3a0b has been approved by tgross35

It is now in the queue for this repository.

@rustbot

…ait_impls, r=tgross35 Add some conversion trait impls - `impl<T, const N: usize> From<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> From<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N]` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[Cell<T>; N]> for Cell<[T; N]>` (equivalent of `as_array_of_cells`, cc rust-lang#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.

@rustbot

…ait_impls, r=tgross35 Add some conversion trait impls - `impl<T, const N: usize> From<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> From<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N]` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[Cell<T>; N]> for Cell<[T; N]>` (equivalent of `as_array_of_cells`, cc rust-lang#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.

@rustbot

…ait_impls, r=tgross35 Add some conversion trait impls - `impl<T, const N: usize> From<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> From<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N]` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[Cell<T>; N]> for Cell<[T; N]>` (equivalent of `as_array_of_cells`, cc rust-lang#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.

@rustbot

…ait_impls, r=tgross35 Add some conversion trait impls - `impl<T, const N: usize> From<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> From<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N]` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[Cell<T>; N]> for Cell<[T; N]>` (equivalent of `as_array_of_cells`, cc rust-lang#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.

@rustbot

…ait_impls, r=tgross35 Add some conversion trait impls - `impl<T, const N: usize> From<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc rust-lang#96097) - `impl<T, const N: usize> From<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N]` (cc rust-lang#96097) - `impl<T, const N: usize> AsRef<[Cell<T>; N]> for Cell<[T; N]>` (equivalent of `as_array_of_cells`, cc rust-lang#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.

Rollup of 12 pull requests Successful merges: - #152388 (`rust-analyzer` subtree update) - #151613 (Align `ArrayWindows` trait impls with `Windows`) - #152134 (Set crt_static_allow_dylibs to true for Emscripten target) - #152166 (cleanup some more things in `proc_macro::bridge`) - #152236 (compiletest: `-Zunstable-options` for json targets) - #152287 (Fix an ICE in the vtable iteration for a trait reference in const eval when a supertrait not implemented) - #142957 (std: introduce path normalize methods at top of `std::path`) - #145504 (Add some conversion trait impls) - #152131 (Port rustc_no_implicit_bounds attribute to parser.) - #152315 (fix: rhs_span to rhs_span_new) - #152327 (Check stalled coroutine obligations eagerly) - #152377 (Rename the query system's `JobOwner` to `ActiveJobGuard`, and include `key_hash`)

@rustbot

Rollup merge of #145504 - Jules-Bertholet:more_conversion_trait_impls, r=tgross35 Add some conversion trait impls - `impl<T, const N: usize> From<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc #96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc #96097) - `impl<T, const N: usize> AsRef<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc #96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]>` (cc #96097) - `impl<T, const N: usize> AsMut<[MaybeUninit<T>]> for MaybeUninit<[T; N]>` (cc #96097) - `impl<T, const N: usize> From<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N]` (cc #96097) - `impl<T, const N: usize> AsRef<[Cell<T>; N]> for Cell<[T; N]>` (equivalent of `as_array_of_cells`, cc #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.

nazar-pc · 2026-02-12T00:31:30Z

library/core/src/mem/maybe_uninit.rs

+}
+
+#[stable(feature = "more_conversion_trait_impls", since = "CURRENT_RUSTC_VERSION")]
+impl<T, const N: usize> AsMut<[MaybeUninit<T>; N]> for MaybeUninit<[T; N]> {


Is there a strong reason to not have impl<T, const N: usize> AsMut<MaybeUninit<[T; N]>> for [MaybeUninit<T>; N] too?

And I have a few places where bridging APIs could benefit from impl<T, const N: usize> AsMut<MaybeUninit<[T; N]>> for [T; N] too, which today requires transmute().

You could try adding it, but IIRC it would cause ambiguity errors in existing code.

rustbot assigned Mark-Simulacrum Aug 16, 2025

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Tracking Issue for MaybeUninit methods for arrays #96097

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Auto merge of #145504 - Jules-Bertholet:more_conversion_trait_impls, …

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…r=<try> Add some conversion trait impls

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Jules-Bertholet force-pushed the more_conversion_trait_impls branch from 315ecee to d0b3a0b Compare February 7, 2026 22:10

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Update Rust toolchain nazar-pc/abundance#554

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