fn main() {
    enum TrayState { Available(u32), Empty }
    let states = [TrayState::Available(8), TrayState::Empty];
    let total: u32 = states.iter().map(|state| match state { TrayState::Available(n) => *n, TrayState::Empty => 0 }).sum();
    assert_eq!(total, 8);
    println!("Available packets across states: {total}");
}