Loops that return values in Rust

loop is an expression: break carries a value out, and labels pick which loop to leave.

fn main() {
    let mut n = 1;
    let doubled = loop {
        n *= 2;
        if n > 50 {
            break n;
        }
    };
    println!("first over fifty: {doubled}");

    'outer: for a in 1..10 {
        for b in 1..10 {
            if a * b == 12 {
                println!("{a} x {b}");
                break 'outer;
            }
        }
    }
}

How it works

1. break value makes the loop evaluate to that value.
2. A 'label lets an inner loop break the outer one.
3. continue 'outer skips to the next outer iteration.

Keywords and builtins used here

• break
• fn
• for
• if
• in
• let
• loop
• main
• mut

The run, in numbers

Lines

19

Characters to type

227

Tokens

78

Three-star pace

85 tpm

At the three-star pace of 85 tokens a minute, this run takes about 55 seconds.

Type this snippet

Step 4 of 8 in Control flow, step 14 of 39 in Language basics.

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