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: Generalize {Rc,Arc}::make_mut() to unsized types. #116113
• CloneToUninit impls #126877
• Convert Box::clone to be based on CloneToUninit
  • Generalize impl<T> Clone for Box<T> to unsized types #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. Generalize {Rc,Arc}::make_mut() to unsized types. #116113 (comment)