Tracking Issue for core::iter::chain

Feature gate: #![feature(iter_chain)]

This is a tracking issue for the core::iter::chain function that combines two IntoIterator arguments together into a Chain iterator.

Public API

// core::iter
pub fn chain<A, B>(a: A, b: B) -> Chain<A::IntoIter, B::IntoIter>
where
    A: IntoIterator,
    B: IntoIterator<Item = A::Item>;

Steps / History

Approved ACP Add core::iter::chain method libs-team#154
Implementation: Add function core::iter::chain #106186
Final comment period (FCP)¹
Stabilization PR: Stabilize core::iter::chain #144963

Unresolved Questions

None yet.

https://std-dev-guide.rust-lang.org/feature-lifecycle/stabilization.html ↩

I was reminded of this by it showing up on URLO: https://users.rust-lang.org/t/iterator-extension-allthesame/117972/3?u=scottmcm

Can we just stabilize it? Having both sides be IntoIterator is nice.

Only other choice I could come up with for the signature would be

pub fn chain<A, B>(a: impl IntoIterator<IntoIter = A>, b: impl IntoIterator<IntoIter = B>) -> Chain<A, B>
where
    A: Iterator,
    B: Iterator<Item = A::Item>;

but that really doesn't seem materially better, so as it is seems good.

Hi, any news on this?
I'm unfamiliar with the process, but is there any reason why the FCP has not yet started?

@rust-lang/libs-api can we start an FCP for this?

@Mark-Simulacrum

@Mark-Simulacrum / @workingjubilee / @jhpratt can we start an FCP for this?

Unsure why I'm being pinged; I have nothing to do with FCPs, nor have I ever. Maybe try asking on Zulip?

@rfcbot

@rfcbot merge

@Amanieu

Team member @Amanieu has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

🔔 This is now entering its final comment period, as per the review above. 🔔

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

Rollup merge of rust-lang#144963 - rossmacarthur-forks:stabilize-core…

Unrolled build for #144963

Rollup merge of rust-lang#144963 - rossmacarthur-forks:stabilize-core…

build(toolchain): bump Rust to 1.97.1 (#385)

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Tracking Issue for `core::iter::chain` #125964

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Tracking Issue for core::iter::chain #125964

Description

Public API

Steps / History

Unresolved Questions

Footnotes

Activity

scottmcm commented on Sep 23, 2024

japm48 commented on Dec 23, 2024

rossmacarthur commented on Dec 24, 2024

rossmacarthur commented on Jul 16, 2025

jhpratt commented on Jul 16, 2025

Amanieu commented on Jul 22, 2025

rfcbot commented on Jul 22, 2025

rfcbot commented on Aug 5, 2025

rfcbot commented on Aug 15, 2025

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Tracking Issue for `core::iter::chain` #125964