enum Val {
    Total(i32),
    Missed(i32),
}

struct Unit {
    val: Val,
}

fn add(t: &mut Unit, u: &Unit) {
    match t.val {
        Val::Total(i1) => match u.val {
            Val::Total(i2) => t.val = Val::Total(i1+i2),
            _ => {},
        },
        Val::Missed(i1) => match u.val {
            Val::Missed(i2) => t.val = Val::Missed(i1+i2),
            _ => {},
        },
    }
}

/*
// Compiler error:
//25 |     match (t.val, u.val) {
//   |            ^ cannot move out of borrowed content
fn add2(t: &mut Unit, u: &Unit) {
    match (t.val, u.val) {
        (Val::Total(i1), Val::Total(i2)) => t.val = Val::Total(i1+i2),
        (Val::Missed(i1), Val::Missed(i2)) => t.val = Val::Missed(i1+i2),
        _ => {},
    }
}
*/

fn main() {
    let mut v1 = Unit{val: Val::Total(10),};
    let v2 = Unit{val: Val::Total(3),};
    add(&mut v1, &v2);
    match v1.val {
        Val::Total(i) => println!("Total: {}", i),
        Val::Missed(i) => println!("Missed: {}", i),
    }
}