Tracking Issue for Option::into_flat_iter

Feature gate: #![feature(option_flat_iter)]

This is a tracking issue for Option::(into_)flat_iter, methods for getting iterators out of Options.

Public API

impl<T> Option<T> where T: IntoIterator {
    pub fn into_flat_iter(self) -> OptionFlatten<<T as IntoIterator>::IntoIter>;
}

Steps / History

(Remember to update the S-tracking-* label when checking boxes.)

ACP: Option::map_iter() to create an iterator from Option libs-team#626
Implementation: add Option::into_flat_iter #148487
Final comment period (FCP)¹
Stabilization PR

Unresolved Questions

Should there be into_flat_iter and flat_iter or just into_flat_iter and as_ref/as_mut?
This is currently done as pub fn into_flat_iter<A>(self) -> OptionFlatten<A> where T: IntoIterator<IntoIter = A>, but do we want the A there or should it be pub fn into_flat_iter(self) -> OptionFlatten<<T as IntoIterator>::IntoIter>? see Simplify Option::into_flat_iter signature #158741
Should this be unconditionally fused (since the iterator is holding an Option anyway), or only fused when the inner iterator is fused?
Should Result have this too, since it's also IntoIterator?

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

@ChayimFriedman2

@ChayimFriedman2 Do you still want to implement this? If not, I'm happy to try. Regardless, rust-lang/libs-team#626 should be closed.

(for the "Unresolved Questions" section):

Should the by-ref version be spelled as opt.as_ref().into_flat_iter() instead of having a dedicated method?

Alternately, should there be a by-mut-ref method (e.g. flat_iter_mut), instead of spelling it as opt.as_mut().into_flat_iter()?

@Qelxiros

@Qelxiros Feel free to take this, but I was waiting an answer to rust-lang/libs-team#626 (comment).

Rollup merge of rust-lang#148487 - Qelxiros:148441-option-into-flat-i…

Unrolled build for #148487

Rollup merge of #148487 - Qelxiros:148441-option-into-flat-iter, r=sc…

Rollup merge of rust-lang#148487 - Qelxiros:148441-option-into-flat-i…

Rollup merge of #148487 - Qelxiros:148441-option-into-flat-iter, r=sc…

Maybe unresolved question: If the performance benefits can be supplanted with specialization on existing methods, does this method(s) still carry its weight?

Rollup merge of rust-lang#158741 - WaffleLapkin:into_flat_iter_noa, r…

Unrolled build for #158741

Rollup merge of #158741 - WaffleLapkin:into_flat_iter_noa, r=hanna-kr…

#158741 already simplified the signature, and there's a discussion in that PR with justification (being able to turbofish the iterator type is normally not very useful, it should be easier to name the iterable if type annotations are necessary). The second unresolved question should probably be marked as resolved now.

Navigation Menu

Repository navigation

Tracking Issue for `Option::into_flat_iter` #148441

Public API

Steps / History

Unresolved Questions

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Tracking Issue for Option::into_flat_iter #148441

Description

Public API

Steps / History

Unresolved Questions

Footnotes

Activity

Qelxiros commented on Nov 3, 2025

zachs18 commented on Nov 3, 2025

ChayimFriedman2 commented on Nov 3, 2025

camsteffen commented on Jul 2, 2026

aqrln commented on Aug 23, 2026

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

Tracking Issue for `Option::into_flat_iter` #148441