Tracking Issue for `core::clone::CloneToUninit` trait

Feature gate: #![feature(clone_to_uninit)]

This is a tracking issue for CloneToUninit and its impls. This trait backs the behavior of Rc::make_mut and Arc::make_mut, and likely in the future also Box::clone.

Public API

// core::clone

pub unsafe trait CloneToUninit {
    unsafe fn clone_to_uninit(&self, dst: *mut Self);
}

unsafe impl<T: Clone> CloneToUninit for T;
unsafe impl<T: Clone> CloneToUninit for [T];

// TODO:
// unsafe impl CloneToUninit for str;
// unsafe impl CloneToUninit for CStr;
// unsafe impl CloneToUninit for OsStr;
// unsafe impl CloneToUninit for Path;

Steps / History

• Implementation: https://github.com/rust-lang/rust/pull/116113
• https://github.com/rust-lang/rust/pull/126877
• Convert Box::clone to be based on CloneToUninit
  • https://github.com/rust-lang/rust/pull/146381
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• Consider using *mut () in the signature instead of *mut Self. This makes CloneToUninit dyn-safe. https://github.com/rust-lang/rust/pull/116113#discussion_r1335303908

Start with the core::clone::CloneToUninit public API and review the linked work for converting Box::clone, alongside its use by Rc::make_mut and Arc::make_mut. Done means resolving the *mut Self versus *mut () question, completing the remaining checklist items, and preparing the feature for FCP and stabilization.