Description
Proposal
Problem statement
Add a function to convert a &mut xxx to &mut NonZeroXxx.
Motivation, use-cases
My project requires working on a &mut NonZeroU32 (because only NonZeroU32 implements a certain trait I want to use), but the value actually came from a &mut u32 somewhere deep inside my data structures, so it would be inconvenient to create a separate NonZeroU32 and proxy back the result later on.
Solution sketches
For n: &mut i32, if *n != 0 is currently true, and we provide the aforementioned function to map this reference into a &mut NonZeroI32, since the original n cannot be dereferenced without dropping the new &mut NonZeroI32, it is safe to work with the &mut NonZeroI32 directly.
Links and related work
As this change is very simple, I have already implemented it in a libcore patch: rust-lang/rust#103730
What happens now?
This issue is part of the libs-api team API change proposal process. Once this issue is filed the libs-api team will review open proposals in its weekly meeting. You should receive feedback within a week or two.