Tracking Issue for `VecDeque::pop_front_if` & `VecDeque::pop_back_if`

[GrigorenkoPV]

Feature gate: #![feature(vec_deque_pop_if)]

Similar to #122741, but this time with VecDeque instead of Vec.

Public API

impl<T> VecDeque<T> {
    pub fn pop_front_if(&mut self, predicate: impl FnOnce(&mut T) -> bool) -> Option<T>;
    pub fn pop_back_if(&mut self, predicate: impl FnOnce(&mut T) -> bool) -> Option<T>;
}

Steps / History

• ACP: pop_if or Entry/Peek-like API for Vec and VecDeque libs-team#208
• Implementation: Implement VecDeque::pop_front_if & VecDeque::pop_back_if #135890
• Final comment period (FCP)¹
• Stabilization PR: Stabilize vec_deque_pop_if #145992

Unresolved Questions

• Vec::pop_if uses an explicit generic parameter for the predicate. But that might change (Tracking Issue for Vec::pop_if #122741 (comment)). If it does not, probably change these methods instead to be consistent.

Footnotes

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

[sdroege]

It's implemented now in nightly, so the checkbox for that can be checked :)

[Martinplior]

rust/library/alloc/src/collections/vec_deque/mod.rs

Lines 1848 to 1851 in 18491d5

	pub fn pop_front_if(&mut self, predicate: impl FnOnce(&mut T) -> bool) -> Option<T> {
	let first = self.front_mut()?;
	if predicate(first) { self.pop_front() } else { None }
	}

rust/library/alloc/src/collections/vec_deque/mod.rs

Lines 1871 to 1874 in 18491d5

	pub fn pop_back_if(&mut self, predicate: impl FnOnce(&mut T) -> bool) -> Option<T> {
	let first = self.back_mut()?;
	if predicate(first) { self.pop_back() } else { None }
	}

Not a big problem though, in pop_back_if, it seems like someone forgot to change the variable name first to last or something else.

[Amanieu]

@rfcbot merge

[rust-rfcbot]

Team member @Amanieu has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Amanieu
• @BurntSushi
• @dtolnay
• @joshtriplett
• @m-ou-se
• @the8472

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

[donkeyteethUX]

This would be really nice to have stabilized!