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Member constraints
#61775 introduced "member constraints" as part of stabilizing async functions. These extend region inference to accommodate impl Trait return types that contain multiple unrelated lifetimes (e.g., impl Trait<'a, 'b> where neither 'a: 'b nor 'b: 'a). We decided to introduce a feature gate for other cases until we have time to gain more experience.
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The working of these constraints is described in the rustc-guide -- as of this writing, however, the PR has not yet landed.
Current status
- Described in rustc-guide (Region inference member constraints rustc-dev-guide#344)Stabilized
Related issues
- Impl trait (Tracking issue for
impl Trait(RFC 1522, RFC 1951, RFC 2071) #34511) - Uncertain interaction with impl trait in bindings (
impl_trait_in_bindingsand pick-constraint region bounds #61773)
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Area: `impl Trait`. Universally / existentially quantified anonymous types with static dispatch.Area: Type inferenceArea: Lifetimes / regions`#[feature(member_constraints)]`Blocker: Implemented in the nightly compiler and unstable.Category: An issue tracking the progress of sth. like the implementation of an RFCRelevant to the language team
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impl Trait#63066runiq commentedon Jul 29, 2019
Triage: The first two boxes can be checked and the rustc-guide PR has landed, so this:
is inaccurate now, which is a good thing. :)
nikomatsakis commentedon Apr 26, 2021
I am beginning work towards stabilizing this.
@rustbot claim
Rollup merge of rust-lang#84701 - nikomatsakis:stabilize-member-const…
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