#047 Mar 28, 2026

47. Vec::pop_if — Conditionally Pop the Last Element

Need to remove the last element of a Vec only when it meets a condition? Vec::pop_if does exactly that — no index juggling, no separate check-then-pop.

The old way

Before pop_if, you’d write something like this:

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let mut stack = vec![1, 2, 3, 4];

if stack.last().is_some_and(|x| *x > 3) {
    let val = stack.pop().unwrap();
    println!("Popped: {val}");
}

Two separate calls, and a subtle TOCTOU gap if you’re not careful — last() checks one thing, then pop() acts on an assumption.

Enter `pop_if`

Stabilized in Rust 1.86, pop_if combines the check and the removal into one atomic operation:

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let mut stack = vec![1, 2, 3, 4];

// Pop the last element only if it's greater than 3
let popped = stack.pop_if(|x| *x > 3);
assert_eq!(popped, Some(4));
assert_eq!(stack, [1, 2, 3]);

// Now the last element is 3 — doesn't match, so nothing happens
let stayed = stack.pop_if(|x| *x > 3);
assert_eq!(stayed, None);
assert_eq!(stack, [1, 2, 3]);

The closure receives a &mut T reference to the last element. If it returns true, the element is removed and returned as Some(T). If false (or the vec is empty), you get None.

Mutable access inside the predicate

Because the closure gets &mut T, you can even modify the element before deciding whether to pop it:

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let mut tasks = vec![
    String::from("buy milk"),
    String::from("URGENT: deploy fix"),
];

let urgent = tasks.pop_if(|task| {
    if task.starts_with("URGENT:") {
        *task = task.replacen("URGENT: ", "", 1);
        true
    } else {
        false
    }
});

assert_eq!(urgent.as_deref(), Some("deploy fix"));
assert_eq!(tasks, vec!["buy milk"]);

A practical use: draining from the back

pop_if is handy for processing a sorted vec from the tail. Think of a priority queue backed by a sorted vec where you only want to process items above a threshold:

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let mut scores = vec![10, 25, 50, 75, 90];

let mut high_scores = Vec::new();
while let Some(score) = scores.pop_if(|s| *s >= 70) {
    high_scores.push(score);
}

assert_eq!(high_scores, vec![90, 75]);
assert_eq!(scores, vec![10, 25, 50]);

Clean, expressive, and no off-by-one errors. Another small addition to Vec that makes everyday Rust just a bit nicer.

This post is licensed under CC BY 4.0 by the author.

47. Vec::pop_if — Conditionally Pop the Last Element

The old way

Enter pop_if

Mutable access inside the predicate

A practical use: draining from the back

Enter `pop_if`