#![allow(unused_variables)]
#![feature(linked_list_retain)]
fn main() {
    use std::collections::LinkedList;
    let mut d = LinkedList::new();
    d.push_front(1);
    d.push_front(2);
    d.push_front(3);
    d.retain(|&mut x| x % 2 == 0);
    assert_eq!(d.pop_front(), Some(2));
    assert_eq!(d.pop_front(), None);
}