impl-trait-goals

An (experimental) RFC repo devoted to Rust's impl Trait.

This repo is an effort to collect and organize the discussion around future impl Trait RFCs.

Current RFCs and overall vision

impl Trait allows functions to leave their return types "abstract." Abstract return types allow a function to hide a concrete return type behind a trait interface similar to trait objects, while still generating the same statically-dispatched code as with concrete types.

The initial conservative proposal for impl Trait was accepted as RFC 1522 - Conservative impl Trait. This proposal was expanded upon in RFC 1951 - Expand impl Trait, which settled the impl Trait syntax design, resolved questions around type and lifetime parameter scopes, and added impl Trait to argument position.

However, there are still more features left to be added before the impl Trait story can be considered complete. This repo aims to track information and discussion of these additional features, and to address them through a followup RFC (possibly multiple).

How the issues are organized

Help-wanted

The help-wanted label indicates issues where a PR would be most welcome.

Priority (the P labels)

• P-essential means that we have to resolve this.
• P-nice-to-have means that it might be nice to include this feature.
• P-wild-and-crazy means that theses are far-out ideas that may or may not make sense.

Resolution (the Z labels)

Once an issue is closed, it ought to have a resolution tag.

• Z-updated-rfc -- text was added to the RFC resolving this question
• Z-open-question -- text was added to the RFC making this an "open question" to be resolved before stabilization
• Z-alternative -- text was added to the RFC describing this as an alternative but not endorsing it
• Z-no-go -- nothing was added to the RFC. This is out of scope or just something we decided against.
• Z-duplicate -- a duplicate of some other issue