Deferred execution

defer schedules one statement or block to run when its enclosing scope is left. Deferred work runs in last-in, first-out order.

fun writeStatus(ready: Bool) {
    defer println("status closed");

    if !ready {
        return;
    }

    println("status open");
}

The deferred println runs both after the normal end of writeStatus and when the function returns early. A deferred block is useful when cleanup has more than one step:

fun publish() {
    defer {
        println("flush");
        println("close");
    }

    println("write");
}

Defers belong to the scope where they appear. Leaving a loop body with break or continue also runs that iteration’s deferred work.