Async fns in traits

[nikomatsakis]

Proposal

Summary and problem statement

• Permit async fn and return-position impl trait in traits
• Support static and dynamic dispatch
• Convenient to use, but also supports less common use-cases like no-std

Motivation, use-cases, and solution sketches

See https://rust-lang.github.io/async-fundamentals-initiative/

Links and related work

None

Initial people involved

• Owner, if known: @tmandry
• Liaison:

What happens now?

This issue is part of the lang-team initiative process. Once this issue is filed, a Zulip topic will be opened for discussion, and the lang-team will review open proposals in its weekly triage meetings. You should receive feedback within a week or two.

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

[joshtriplett]

@rustbot second

[nikomatsakis]

Issue: rust-lang/async-fundamentals-initiative#5

[nikomatsakis]

There has been an accepted RFC and implementation work. Tracking issue: rust-lang/rust#91611