# Keyword break

source ·
Expand description

Exit early from a loop.

When `break` is encountered, execution of the associated loop body is immediately terminated.

    let mut last = 0;

    for x in 1..100 {
        if x > 12 {
            break;
        }
        last = x;
    }

    assert_eq!(last, 12);
    println!("{last}");

Run

A break expression is normally associated with the innermost loop enclosing the `break` but a label can be used to specify which enclosing loop is affected.

    'outer: for i in 1..=5 {
        println!("outer iteration (i): {i}");

        '_inner: for j in 1..=200 {
            println!("    inner iteration (j): {j}");
            if j >= 3 {
                // breaks from inner loop, lets outer loop continue.
                break;
            }
            if i >= 2 {
                // breaks from outer loop, and directly to "Bye".
                break 'outer;
            }
        }
    }
    println!("Bye.");

Run

When associated with `loop`, a break expression may be used to return a value from that loop. This is only valid with `loop` and not with any other type of loop. If no value is specified, `break;` returns `()`. Every `break` within a loop must return the same type.

    let (mut a, mut b) = (1, 1);
    let result = loop {
        if b > 10 {
            break b;
        }
        let c = a + b;
        a = b;
        b = c;
    };
    // first number in Fibonacci sequence over 10:
    assert_eq!(result, 13);
    println!("{result}");

Run

For more details consult the Reference on “break expression” and the Reference on “break and loop values”.