#![allow(dead_code, deprecated, unused_variables, unused_mut)]
use std::iter::Fuse;
#[derive(Default)]
struct Fourever;
impl Iterator for Fourever {
    type Item = u32;
    fn next(&mut self) -> Option<u32> {
        Some(4)
    }
}
fn main() {
    let mut iter: Fuse<Fourever> = Default::default();
    assert_eq!(iter.next(), Some(4));
}