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: rust-lang/libs-team#626
• Implementation: #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 https://github.com/rust-lang/rust/pull/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?

Start with the option_flat_iter feature gate and review implementation PR #148487. Read the unresolved questions about method variants, fusion, and Result, then follow the stabilization process; done requires those questions to be resolved and the remaining FCP and stabilization steps completed.