This is the tracking issue for RFC 3519: Arbitrary self types v2.

The feature gate for this issue is #![feature(arbitrary_self_types)].

About tracking issues

Tracking issues are used to record the overall progress of implementation. They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions. A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature. Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

Steps

Current plan is:

• Fix the current lifetime elision bugs
• Search for potentially conflicting method candidates
• Block generic arbitrary self types.
• Introduce an arbitrary_self_types_pointers feature gate
• Rename the old Receiver trait -- currently being run through crater
• Land the new Receiver trait without it doing anything.
• Switch over the method resolution to use the Receiver trait, if the arbitrary_self_types feature is enabled. The main event.
• Add diagnostics for the !Sized case and the NonNull etc. cases.
• Update the Rust reference.
  • Arbitrary self types v2: update reference. reference#1699
  • Method call reference: major rewrite reference#1725
• Add documentation to the dev guide. See the instructions.
• Add formatting for new syntax to the style guide. See the nightly style procedure.
• Decide whether Deref and Receiver traits should be decoupled (cc @dingxiangfei2009).
• (In the alternate:) Make Deref a subtrait of Receiver.
  • Arbitrary self types v2: stabilize #135881 (comment)
• Clear out stabilization blockers.
  • Make ptr_cast_add_auto_to_object lint into hard error #136764
  • Forbid freely casting lifetime bounds of dyn-types #136776
• Stabilize!
  • Arbitrary self types v2: stabilize #135881

Unresolved Questions

None.

Notable for Stabilization

• Arbitrary self types v2: no deshadow pre feature. #134524

Related

• Changing the type of self in methods doesn't work #27941

Implementation history

• Fix ambiguous cases of multiple & in elided self lifetimes #117967
• Arbitrary self types v2: pointers feature gate. #129664
• Reject generic self types. #130098
• Rename Receiver -> LegacyReceiver #130225
• Arbitrary self types v2: (unused) Receiver trait #132144
• Arbitrary self types v2: main compiler changes #132961
• Arbitrary self types v2: adjust diagnostic. #134262
• Arbitrary self types v2: Weak & NonNull diagnostics #134264
• Arbitrary self types v2: better feature gate test #134271
• Arbitrary self types v2: niche deshadowing test #134509
• Arbitrary self types v2: roll loop. #134521
• Arbitrary self types v2: no deshadow pre feature. #134524
• Arbitrary self types v2: unstable doc updates. #134525
• Arbitrary self types v2: explain test. #136124

(Below follows content that predated the accepted Arbitrary Self Types v2 RFC.)

impl RandomType {
    fn foo(*const Self) {}
}

trait Foo {
    fn bar(self: *const Self);
}

fn main() {
    // creates a raw pointer with a garbage vtable
    let foo: *const dyn Foo = unsafe { mem::transmute([0usize, 0x1000usize]) };
    // and call it
    foo.bar(); // this is UB
}

trait MyStuff {
    fn do_async_task(self: Rc<Self>);
}

impl MyStuff for () {
    fn do_async_task(self: Rc<Self>) {
        // ...
    }
}

Rc::new(()).do_async_stuff();