Tracking Issue for `Vec::peek_mut`

Feature gate: #![feature(vec_peek_mut)]

This feature adds Vec::peek_mut, which returns a PeekMut struct. It is analogous to [BinaryHeap::peek_mut] and enables users to conditionally modify and remove the last element of a Vec without having to call unwrap.

Public API

impl<T> Vec<T> {
    pub fn peek_mut(&mut self) -> Option<PeekMut<'_, T>>;
}

pub struct PeekMut<'a, T>;

impl<'a, T> PeekMut<'a, T> {
    pub fn pop(self) -> T;
}

// impl `Deref`/`DerefMut` for `PeekMut`

Steps / History

• ACP: https://github.com/rust-lang/libs-team/issues/208
• Implementation: pending
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• Should this be named peek or peek_mut?

Start with the vec_peek_mut feature gate and compare the proposed Vec::peek_mut and PeekMut API with BinaryHeap::peek_mut. Review the linked ACP and resolve the naming question before implementing the pending API. Done means the implementation, FCP, and stabilization PR steps are completed.