#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#![feature(exact_size_is_empty)]
fn main() {
    let mut one_element = std::iter::once(0);
    assert!(! one_element.is_empty());
    assert_eq!(one_element.next(), Some(0));
    assert!(one_element.is_empty());
    assert_eq!(one_element.next(), None);
}