LYR-SEM0149

a 'loop' whose breaks give a value only in part

error · spec 07-statements

Some 'break's of one 'loop' carry a value and others carry none.

Explanation

The value of a loop is the value of the break that ends it. If one break gives a value and another gives none, the loop's value would be missing on one path. A loop gives a value through every break or through none.

Give every break a value — a sentinel or an optional (break null; with ?int) for the case without one — or give none and use a variable.

Wrong

fn indexOf(xs: int[], wanted: int): int {
    var i = 0;
    let at = loop {
        if (i == xs.length()) { break; }
        if (xs[i] == wanted) { break i; }
        i += 1;
    };
    return at;
}

fn main(): void {
    let _ = indexOf([1, 2], 2);
}

Right

fn indexOf(xs: int[], wanted: int): int {
    var i = 0;
    let at = loop {
        if (i == xs.length()) { break -1; }
        if (xs[i] == wanted) { break i; }
        i += 1;
    };
    return at;
}

fn main(): void {
    let _ = indexOf([1, 2], 2);
}