[Pre-Pre RFC] Ability to specify a trait as marker trait

Apersoma · April 8, 2026, 10:39pm

nevermind, i missed smth

quinedot · April 8, 2026, 11:04pm

RFC'd and accepted over a decade ago.

github.com/rust-lang/rust

Tracking issue for allowing overlapping implementations for marker trait

opened 05:09PM - 16 Nov 15 UTC

nikomatsakis

A-trait-system T-lang B-unstable B-RFC-implemented C-tracking-issue F-marker_trait_attr S-tracking-needs-to-bake T-types S-tracking-blocked

Tracking issue for rust-lang/rfcs#1268. ## Status - [x] Initial implementa…tion: #41309 - [ ] Documentation - [ ] Move to stabilize - [ ] Stabilization PR ## Known bugs - [ ] [cross-crate support lacking?](https://github.com/rust-lang/rust/issues/29864#issuecomment-295907958) - [x] #102360 ## History - initial implementation #41309 - https://github.com/rust-lang/rust/pull/53693 ## Prior to stabilization 1. Is it ok that adding items to a previously empty trait is a breaking change? Should we make declaring something a marker trait more explicit somehow? --> resolved by adding explicit `#[marker]` annotation, see https://github.com/rust-lang/rust/pull/53693 ## Other notes In #96766 we decided NOT to disable the orphan check for marker traits as part of this work (just the overlap check), which was a proposed extension.

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[Pre-Pre RFC] Ability to specify a trait as marker trait

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