any() and all()

The .any() and .all() consumer methods test a boolean predicate FnMut(Self::Item) -> bool across elements of an iterator (&mut self) with short-circuit evaluation.

Signatures and Short-Circuit Behavior

fn any<F>(&mut self, f: F) -> bool
where
    Self: Sized,
    F: FnMut(Self::Item) -> bool;

fn all<F>(&mut self, f: F) -> bool
where
    Self: Sized,
    F: FnMut(Self::Item) -> bool;

Unlike .filter() and .find(), which pass &Self::Item to their closure, .any() and .all() consume each inspected element and pass Self::Item by value to the predicate.

Method	Logical Quantifier	Short-Circuits When...	Result on Empty Iterator
`.any(f)`	Existential ($\exists$, OR)	First item returns `true` (returns `true` immediately)	`false`
`.all(f)`	Universal ($\forall$, AND)	First item returns `false` (returns `false` immediately)	`true` (vacuous truth)

fn main() {
    let scores = [85, 92, 78, 99, 64];
    let empty: [i32; 0] = [];

    println!("Any >= 95?       {}", scores.iter().any(|&s| s >= 95));
    println!("All >= 70?       {}", scores.iter().all(|&s| s >= 70));
    println!("Empty .any():    {}", empty.iter().any(|&s| s > 0));
    println!("Empty .all():    {}", empty.iter().all(|&s| s > 0));
}

Any >= 95?       true
All >= 70?       false
Empty .any():    false
Empty .all():    true

Resuming an Iterator After Short-Circuiting

Because .any() and .all() take &mut self, they only consume elements up to and including the element that triggered the short-circuit. Any remaining elements stay in the iterator:

fn main() {
    let mut stream = [2, 4, 7, 8, 10].into_iter();

    // Stops as soon as it sees `7`:
    let has_odd = stream.any(|n| n % 2 != 0);
    let remaining: Vec<i32> = stream.collect();

    println!("Has odd:   {has_odd}");
    println!("Remaining: {remaining:?}");
}

Has odd:   true
Remaining: [8, 10]