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.

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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

the8472 · 2025-10-21T17:17:33Z

@rfcbot merge

rust-rfcbot · 2025-10-21T19:29:49Z

Team member @the8472 has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

rust-rfcbot · 2025-10-27T16:15:33Z

🔔 This is now entering its final comment period, as per the review above. 🔔

SUPERCILEX · 2025-10-30T23:47:51Z

Can we get rid of my transpose function in favor of the from impl? Seems a bit weird to have both.

clarfonthey · 2025-10-31T02:41:18Z

I think that dedicated methods are nice because they make things a little clearer than just into(). We're allowed to have both.

SUPERCILEX · 2025-10-31T03:34:01Z

Fair enough

rust-rfcbot · 2025-11-06T16:15:47Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

tgross35

As mentioned above, these could be #[inline] and not #inline(always)]. That and a squash then r=me

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rustbot assigned Mark-Simulacrum Aug 16, 2025

Jules-Bertholet mentioned this pull request Aug 16, 2025

Tracking Issue for MaybeUninit methods for arrays #96097

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Jules-Bertholet force-pushed the more_conversion_trait_impls branch from 7ef29d9 to 3a96604 Compare August 16, 2025 17:22

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Jules-Bertholet force-pushed the more_conversion_trait_impls branch 2 times, most recently from 676ff1f to bd960c9 Compare August 16, 2025 18:13

rustbot assigned m-ou-se and unassigned Mark-Simulacrum Aug 17, 2025

clarfonthey reviewed Aug 17, 2025

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rustbot added the T-libs Relevant to the library team, which will review and decide on the PR/issue. label Sep 5, 2025

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rust-bors bot added a commit that referenced this pull request Sep 5, 2025

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

0498c15

…r=<try> Add some conversion trait impls

rustbot unassigned m-ou-se Sep 5, 2025

rustbot added the I-libs-api-nominated Nominated for discussion during a libs-api team meeting. label Sep 5, 2025

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rust-rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Oct 21, 2025

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rustbot mentioned this pull request Nov 6, 2025

Tracking issue for release notes of #145504: Add some conversion trait impls #148584

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tgross35 requested changes Nov 6, 2025

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rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Nov 6, 2025

Add some conversion trait impls #145504

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Jules-Bertholet commented Aug 16, 2025 •

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