Implement `AsMut<T>` and `AsRef<T>` for `!`. - #161253

kpreid · 2026-08-17T18:00:33Z

This will allow e.g. &[!] to satisfy &[T] where T: AsRef<str>. It follows the recommendation from the never documentation:

When writing your own traits, ! should have an impl whenever there is an obvious impl which doesn’t panic!.

— https://doc.rust-lang.org/1.97.1/std/primitive.never.html#-and-traits

Tracking issue for never: #35121
(This change has no ACP or tracking issue of its own; I assume it is simple enough that T-libs-api can just accept or reject this PR, and the implementation will be stable when ! is stable.)

@rustbot label -T-libs +T-libs-api +F-never_type

This will allow e.g. `&[!]` to satisfy `&[T] where T: AsRef<str>`. It follows the recommendation from the never documentation: > When writing your own traits, `!` should have an `impl` whenever > there is an obvious `impl` which doesn’t `panic!`. -- <https://doc.rust-lang.org/1.97.1/std/primitive.never.html#-and-traits>

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Implement `AsMut<T>` and `AsRef<T>` for `!`. - #161253