enum OptionalInt {
    Value(int),
    Missing,
}

fn main() {
    let x = Value(5);
    let y = Missing;

    match x {
        Value(n) => println!("x is {}", n),
        Missing  => println!("x is missing!"),
    }

    match y {
        Value(n) => println!("y is {}", n),
        Missing  => println!("y is missing!"),
    }
}