#![allow(unused_variables)]
fn main() {
    assert_eq!(["hello", "world"].join(" "), "hello world");
    assert_eq!([[1, 2], [3, 4]].join(& 0), [1, 2, 0, 3, 4]);
    assert_eq!([[1, 2], [3, 4]].join(& [0, 0] [..]), [1, 2, 0, 0, 3, 4]);
}