#![allow(unused_variables)]
fn main() {
    use std::collections::VecDeque;
    let mut buf = VecDeque::new();
    assert_eq!(buf.swap_remove_back(0), None);
    buf.push_back(1);
    buf.push_back(2);
    buf.push_back(3);
    assert_eq!(buf, [1, 2, 3]);
    assert_eq!(buf.swap_remove_back(0), Some(1));
    assert_eq!(buf, [3, 2]);
}