#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#![feature(slice_split_once)]
fn main() {
    let s = [1, 2, 3, 2, 4];
    assert_eq!(s.split_once(|& x | x == 2), Some((& [1] [..], & [3, 2, 4] [..])));
    assert_eq!(s.split_once(|& x | x == 0), None);
}