struct Data(u8);

fn f(mut v: Vec<Data>) -> Option<Data> {
    let a = v.iter().position(a);
    let index = match a {
        Some(i) => i,
        None => v.iter().position(b)?
    };
    Some(v.swap_remove(index))
}

fn a(d: &Data) -> bool {
    match d {
        Data(0) => true,
        _ => false
    }
}

fn b(d: &Data) -> bool {
    match d {
        Data(1) => true,
        _ => false
    }
}

fn main() {
    let v = vec![Data(1), Data(2), Data(3), Data(0)];
    f(v);
    println!("done!");
}