Break out of specific loop and return a value

July 3, 2023

I have just started studying Rust and reaching the control flow section I read break can return a value (the loop is an expression) and it can also break out of a specific loop using a label, e.g. break 'counting_up.

So my question is:

Is it possible to combine the two? i.e. break out of a specific loop by naming it and return a value as well?

If so, what is the syntax for assigning + declaring the loop?

What is the syntax of the break?

The following are two possibilities, but neither syntax compiles:

fn main() {
    let mut count = 0;
    // would this do?
    let result = 'counting_up: loop {
        println!("count = {count}");
        let mut remaining = 10;

        loop {
            println!("remaining = {remaining}");
            if remaining == 9 {
                break;
            }
            if count == 2 {
                // break count*10, 'counting_up;
                // or should it be:
                break 'counting_up, count*10;
            }
            remaining -= 1;
        }

        count += 1;
    };
    println!("End count = {count}");
}

>Solution :

Yes it is, and there is no separator, just break 'label value:

fn main() {
    let mut count = 0;
    let result = 'counting_up: loop {
        println!("count = {count}");
        let mut remaining = 10;

        loop {
            println!("remaining = {remaining}");
            if remaining == 9 {
                break;
            }
            if count == 2 {
                break 'counting_up count*10;
            }
            remaining -= 1;
        }

        count += 1;
    };
    println!("End count = {count}");
}