yield.md

Yield

To use a "switch expression" you put the entire switch to the right hand side of an equals sign¹ and, instead of assigning to a variable, you "yield" the value you want to assign.

enum StopLight {
    RED,
    YELLOW,
    GREEN
}

enum Action {
    STOP,
    SLOW_DOWN,
    GO
}

void main() {
    StopLight light = StopLight.GREEN;

    Action action = switch (light) {
        case RED -> {
            yield Action.STOP;
        }
        case YELLOW -> {
            yield Action.SLOW_DOWN;
        }
        case GREEN -> {
            yield Action.GO;
        }
    };

    System.out.println(action);
}

yield is very similar to return. The difference is that return will exit the entire method. yield just decides what the switch evaluates to.

Footnotes

1. Technically we are talking about an "expression context." Meaning a place where you are allowed to put an expression. The right hand side of an equals sign is one, but there are many others. ↩