Tracking Issue for `clone_from_ref`

[zachs18]

Feature gate: #![feature(clone_from_ref)]

This is a tracking issue for Box::clone_from_ref, Arc::clone_from_ref, and Rc::clone_from_ref. try_* and *_in functions are under this tracking issue as well as allocator_api.

Allows creating a Box<T>/Rc<T>/Arc<T> by cloning from a &T where T: CloneToUninit. Notably, these work even when T is unsized (e.g. a slice).

Public API

// alloc::boxed

impl<T: ?Sized + CloneToUninit> Box<T> {
  pub fn clone_from_ref(val: &T) -> Box<T>;

  // also under feature(allocator_api)
  pub fn try_clone_from_ref(val: &T) -> Result<Box<T>, AllocError>;
}

impl<T: ?Sized + CloneToUninit, A: Allocator> Box<T, A> {
  // also under feature(allocator_api)
  pub fn clone_from_ref_in(val: &T, alloc: A) -> Box<T, A>;
  // also under feature(allocator_api)
  pub fn try_clone_from_ref_in(val: &T, alloc: A) -> Result<Box<T, A>, AllocError>;
}

// alloc::rc

impl<T: ?Sized + CloneToUninit> Rc<T> {
  pub fn clone_from_ref(val: &T) -> Rc<T>;

  // also under feature(allocator_api)
  pub fn try_clone_from_ref(val: &T) -> Result<Rc<T>, AllocError>;
}

impl<T: ?Sized + CloneToUninit, A: Allocator> Rc<T, A> {
  // also under feature(allocator_api)
  pub fn clone_from_ref_in(val: &T, alloc: A) -> Rc<T, A>;
  // also under feature(allocator_api)
  pub fn try_clone_from_ref_in(val: &T, alloc: A) -> Result<Rc<T, A>, AllocError>;
}

// alloc::sync

impl<T: ?Sized + CloneToUninit> Arc<T> {
  pub fn clone_from_ref(val: &T) -> Arc<T>;

  // also under feature(allocator_api)
  pub fn try_clone_from_ref(val: &T) -> Result<Arc<T>, AllocError>;
}

impl<T: ?Sized + CloneToUninit, A: Allocator> Arc<T, A> {
  // also under feature(allocator_api)
  pub fn clone_from_ref_in(val: &T, alloc: A) -> Arc<T, A>;
  // also under feature(allocator_api)
  pub fn try_clone_from_ref_in(val: &T, alloc: A) -> Result<Arc<T, A>, AllocError>;
}

Steps / History

(Remember to update the S-tracking-* label when checking boxes.)

• ACP: Box::new_from_ref for making a Box<T> from a &T where T: CloneToUninit + ?Sized (and Rc and Arc) libs-team#483
• Implementation: Add Box::clone_from_ref and similar under feature(clone_from_ref) #149079
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• None yet.

Footnotes

1. https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩