#![allow(dead_code, deprecated, unused_variables, unused_mut)]
fn main() {
    let mut iter = (0..5).peekable();
    assert_eq!(iter.next_if(|& x | x == 0), Some(0));
    assert_eq!(iter.next_if(|& x | x == 0), None);
    assert_eq!(iter.next(), Some(1));
}