"out" function arguments?

[Ixrec]

A few discussions on out/uninit references that are arguably still active:

RFC: Direct and Partial Initialization using &uninit T

[Pre-RFC] Partially Initialized Types

there’s been a lot of talk about &uninit references, MaybeUninit, placement-new… I’d like to propose an alternative to all of them: Partially Initialized Types. They’re, arguably, the cleanest approach to all of this. Consider types: struct Foo { a: i32, b: i32 } struct Bar { a: i32, b: Foo } Then, we can have: let x: Bar(b(a)) = Bar { b: Foo { a: 1 } }; However, passing these to functions is mostly pointless: fn foo(x: &mut Bar()) { // can't do anything with x here } foo(x); // but c…

My impression is also that out/uninit references are lacking compelling motivation. In particular, &mut MaybeUninit<T> seems to cover a lot of the same use cases.

The discussion on that RFC I linked above left me with a vague impression that &out/&uninit don't have any advantages over &mut MaybeUninit<T> after all, but I'm not entirely sure I understood it so cc @cramertj and @RustyYato