#![allow(dead_code, deprecated, unused_variables, unused_mut)]
fn main() {
    let mut x = Some(4);
    match x.iter_mut().next() {
        Some(v) => *v = 42,
        None => {}
    }
    assert_eq!(x, Some(42));
    let mut x: Option<u32> = None;
    assert_eq!(x.iter_mut().next(), None);
}