LYR-SEM0236

a jump out of a 'defer' body

error · spec 07-statements

A return stands in a defer body, or a break or continue goes to a loop around the defer.

Explanation

A defer body runs while its scope is being left — at the end of the scope, on a return, a break, a continue or an error. A jump out of it would start a second way out in the middle of the first, and the rest of the scope's defers would not know which one they run for.

A loop inside the body keeps its own break and continue, and a lambda in the body its own return. To end a loop or a function early, decide before the defer runs: set a variable the code after the scope reads.

Wrong

fn main(): void {
    for (i in 0..3) {
        defer {
            if (i == 1) {
                break;
            }
        }
    }
}

Right

fn main(): void {
    var stop = false;
    for (i in 0..3) {
        if (stop) {
            break;
        }
        defer {
            if (i == 1) {
                stop = true;
            }
        }
    }
}