Tracking Issue for `Vec::push_mut`

[balt-dev]

Feature gate: #![feature(push_mut)]

This is a tracking issue for Vec::push_mut, as discussed in the comments of this ACP. This adds a way to get a reference to the just-pushed value, which can eliminate having to .unwrap() or access the back of the list twice.

Public API

#[must_use = "if you don't need a reference to the value, use Vec::push")]
pub fn push_mut(&mut self, value: T) -> &mut T { /* ... */ }

Steps / History

• Implementation: Implement push_mut #135975
• Final comment period (FCP)
• Stabilization PR

Unresolved Questions

None

[balt-dev]

Here's an example from the documentation:

#![feature(push_mut)]

let mut vec = vec![];
// Polonius moment.
let last = if let Some(v) = vec.last_mut() { v } else { vec.push_mut(0) };
*last += 6;
assert_eq!(vec, [6]);

[balt-dev]

(Note: I did go back and change the // Polonius moment. comment to something more descriptive.)

[balt-dev]

Thoughts on an unsafe push_raw that returns a *mut T?
Actually, wait, that's unnecessary since you can just downgrade the reference to a pointer in all cases.