Add unstable Share trait by P8L1 · Pull Request #156828 · rust-lang/rust

P8L1 · 2026-05-22T13:19:09Z

Tracking issue: #156756

This adds an initial unstable Share trait for clone-as-alias types, as part of the 2026 ergonomic ref-counting project goal.

pub trait Share: Clone {
    fn share(&self) -> Self {
        Clone::clone(self)
    }
}

This PR adds a separate unstable feature gate:

#![feature(share_trait)]

and places the trait next to Clone in core::clone.

Implemented initial impls:

impl<T: ?Sized> Share for &T
impl<T: ?Sized, A: Allocator + Clone> Share for Rc<T, A>
impl<T: ?Sized, A: Allocator + Clone> Share for Arc<T, A>
impl<T> Share for std::sync::mpsc::Sender<T>
impl<T> Share for std::sync::mpsc::SyncSender<T>

The PR deliberately does not add Share to the prelude.

r? @nikomatsakis
@rustbot label F-ergonomic_clones

rustbot · 2026-05-22T13:19:30Z

nikomatsakis is currently at their maximum review capacity.
They may take a while to respond.

SimonSapin · 2026-05-23T17:54:46Z

@bors r+ rollup

Additions are unstable and match https://rust-lang.github.io/rust-project-goals/2026/ergonomic-rc.html#the-share-trait

rust-bors · 2026-05-23T17:54:48Z

📌 Commit 2f953da has been approved by SimonSapin

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

@nikomatsakis

…=SimonSapin Add unstable Share trait Tracking issue: rust-lang#156756 This adds an initial unstable `Share` trait for clone-as-alias types, as part of the 2026 ergonomic ref-counting project goal. ```rust pub trait Share: Clone { fn share(&self) -> Self { Clone::clone(self) } } ``` This PR adds a separate unstable feature gate: ```rust #![feature(share_trait)] ``` and places the trait next to `Clone` in `core::clone`. Implemented initial impls: - `impl<T: ?Sized> Share for &T` - `impl<T: ?Sized, A: Allocator + Clone> Share for Rc<T, A>` - `impl<T: ?Sized, A: Allocator + Clone> Share for Arc<T, A>` - `impl<T> Share for std::sync::mpsc::Sender<T>` - `impl<T> Share for std::sync::mpsc::SyncSender<T>` The PR deliberately does not add `Share` to the prelude. r? @nikomatsakis @rustbot label F-ergonomic_clones

Rollup of 4 pull requests Successful merges: - #156736 (Fix jump to def link generation on primitive type associated methods) - #156828 (Add unstable Share trait) - #156830 (Add `#[doc(alias = "phi")]` for float `GOLDEN_RATIO` constants) - #156860 (Fix Pieter-Louis Schoeman mailmap entry)

…uwer Rollup of 6 pull requests Successful merges: - #156769 (Use print instead of po in debuginfo path test) - #156784 (Fix reborrow_info early return skipping field validation) - #156827 (float_literal_f32_fallback: Don't suggest invalid code) - #156828 (Add unstable Share trait) - #156830 (Add `#[doc(alias = "phi")]` for float `GOLDEN_RATIO` constants) - #156860 (Fix Pieter-Louis Schoeman mailmap entry)

@nikomatsakis

…omatsakis Make Share::share final and improve docs Tracking issue: rust-lang#156756 This follows up on the initial unstable `Share` trait added in rust-lang#156828. The original API used an ordinary default method: ```rust fn share(&self) -> Self { Clone::clone(self) } ``` Niko pointed out that `share` should be final, since `Share` is meant to communicate the semantics of `Clone::clone` for clone-as-alias types, not provide a second independently-overridable operation. `Share` remains unstable under `#![feature(share_trait)]`. r? @nikomatsakis

@nikomatsakis

…omatsakis Make Share::share final and improve docs Tracking issue: rust-lang#156756 This follows up on the initial unstable `Share` trait added in rust-lang#156828. The original API used an ordinary default method: ```rust fn share(&self) -> Self { Clone::clone(self) } ``` Niko pointed out that `share` should be final, since `Share` is meant to communicate the semantics of `Clone::clone` for clone-as-alias types, not provide a second independently-overridable operation. `Share` remains unstable under `#![feature(share_trait)]`. r? @nikomatsakis

@nikomatsakis

…omatsakis Make Share::share final and improve docs Tracking issue: rust-lang#156756 This follows up on the initial unstable `Share` trait added in rust-lang#156828. The original API used an ordinary default method: ```rust fn share(&self) -> Self { Clone::clone(self) } ``` Niko pointed out that `share` should be final, since `Share` is meant to communicate the semantics of `Clone::clone` for clone-as-alias types, not provide a second independently-overridable operation. `Share` remains unstable under `#![feature(share_trait)]`. r? @nikomatsakis

@nikomatsakis

…omatsakis Make Share::share final and improve docs Tracking issue: rust-lang#156756 This follows up on the initial unstable `Share` trait added in rust-lang#156828. The original API used an ordinary default method: ```rust fn share(&self) -> Self { Clone::clone(self) } ``` Niko pointed out that `share` should be final, since `Share` is meant to communicate the semantics of `Clone::clone` for clone-as-alias types, not provide a second independently-overridable operation. `Share` remains unstable under `#![feature(share_trait)]`. r? @nikomatsakis

@nikomatsakis

Rollup merge of #157655 - P8L1:share-trait-final-docs, r=nikomatsakis Make Share::share final and improve docs Tracking issue: #156756 This follows up on the initial unstable `Share` trait added in #156828. The original API used an ordinary default method: ```rust fn share(&self) -> Self { Clone::clone(self) } ``` Niko pointed out that `share` should be final, since `Share` is meant to communicate the semantics of `Clone::clone` for clone-as-alias types, not provide a second independently-overridable operation. `Share` remains unstable under `#![feature(share_trait)]`. r? @nikomatsakis

P8L1 added 11 commits May 21, 2026 22:15

Add share_trait feature gate

1521455

Add unstable Share trait

e5a6796

Implement Share for shared references

02109ee

Tighten initial Share trait implementation

d082ac9

Add Share impl for Rc

fc33b6d

Add Share impl for Arc

78b0f9d

Add Share impl for mpsc Sender

4b32cb2

Add Share impl for mpsc SyncSender

4a32c28

Update Share non-implementor diagnostics

71bcc49

Remove provisional Share trait FIXME notes

9b3cd57

Document unstable Share trait semantics

c01e320

rustbot assigned nikomatsakis May 22, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels May 22, 2026

P8L1 mentioned this pull request May 22, 2026

Tracking Issue for Share trait #156756

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Clarify Share trait docs

501ab4e

rustbot added the F-ergonomic_clones `#![feature(ergonomic_clones)]` label May 22, 2026

SimonSapin reviewed May 23, 2026

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Comment thread compiler/rustc_feature/src/unstable.rs Outdated

Remove unnecessary Share feature gate plumbing

2f953da

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 23, 2026

jhpratt mentioned this pull request May 23, 2026

Rollup of 4 pull requests #156864

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JonathanBrouwer mentioned this pull request May 24, 2026

Rollup of 6 pull requests #156870

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rust-bors Bot merged commit eb68b36 into rust-lang:main May 24, 2026
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rustbot added this to the 1.98.0 milestone May 24, 2026

P8L1 mentioned this pull request Jun 9, 2026

Make Share::share final and improve docs #157655

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nikomatsakis mentioned this pull request Jun 10, 2026

Ergonomic ref-counting rust-lang/rust-project-goals#107

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Add unstable Share trait#156828

Add unstable Share trait#156828
rust-bors[bot] merged 13 commits into
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P8L1 commented May 22, 2026 •

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P8L1 commented May 22, 2026 •

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