Implement PointerLike for isize, NonNull, Cell, UnsafeCell, and SyncUnsafeCell.
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`PointerLike` is already implemented for raw pointers and `usize`, so this should be straightforward.
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Dec 22, 2024
| @@ -2364,6 +2370,9 @@ impl<T: CoerceUnsized<U>, U> CoerceUnsized<SyncUnsafeCell<U>> for SyncUnsafeCell | |||
| //#[unstable(feature = "sync_unsafe_cell", issue = "95439")] | |||
| impl<T: DispatchFromDyn<U>, U> DispatchFromDyn<SyncUnsafeCell<U>> for SyncUnsafeCell<T> {} | |||
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| #[unstable(feature = "pointer_like_trait", issue = "none")] | |||
| impl<T: PointerLike> PointerLike for SyncUnsafeCell<T> {} | |||
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Why not put these with the rest of the impls in core::marker?
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I did this because it is consistent with the existing code organization: impls of other marker traits for “primitive” types are in core::marker and defined using marker_impls!, and impls for library-defined types are next to those types. I’m not aware of a reason why PointerLike should be organized differently than other marker trait impls.
In fact, reviewing the existing usage of marker_impls!, I should probably put the impl for NonNull inside core::ptr::non_null instead of in the marker_impls! to be even more consistent.
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Sure, would you like to change that too?
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Implementing
PointerLikeforUnsafeCellenables the possibility of interior mutabledyn*values. Since this means potentially exercising new codegen behavior, I added a test for it intests/ui/dyn-star/cell.rs. Please let me know if there are further sorts of tests that should be written, or other care that should be taken with this change.It is unfortunately not possible without compiler changes to implement
PointerLikeforAtomic*types, since they are notrepr(transparent)(and, in theory if not in practice,AtomicUsize's alignment may be greater than that of an ordinary pointer orusize).Implementing
PointerLikeforNonNullis useful for pointer types which wrapNonNull.Implementing
PointerLikeforisizeis just for completeness; I have no use cases in mind, but I cannot think of any reason not to do this.Tracking issue: Tracking issue for dyn-star #102425
@rustbot label +F-dyn_star
(there is no label or tracking issue for F-pointer_like_trait)