Tracking Issue for `Iterator::exactly_one` and `Iterator::collect_array`

Feature gate: #![feature(exact_length_collection)]

This is a tracking issue for exact length collection, concerning originally one but after discussion two new APIs on iterators:

• exactly_one() to collect the one and only element from an iterator
• collect_array() to collect an iterator into an array of an exact predetermined length.

Public API

// trait Iterator

// note: unlike itertools, returns an Option, not a result as per ACP
fn exactly_one(self) -> Option<Self::Item>
where
    Self: Sized;
fn collect_array<const N: usize>(self) -> Option<[Self::Item; N]>
where
    Self: Sized;

Steps / History

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

• ACP: rust-lang/libs-team#676
• Implementation: https://github.com/rust-lang/rust/pull/149270
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• None yet.

Start with the public API shown in the issue and read the linked implementation PR (rust-lang/rust#149270) to understand the current state of both iterator methods. Done means completing the remaining Final Comment Period and stabilization PR steps, with the feature gate and tracking checklist updated accordingly.