#![allow(dead_code, deprecated, unused_variables, unused_mut)]
use std::iter::successors;
fn main() {
    let powers_of_10 = successors(Some(1_u16), |n| n.checked_mul(10));
    assert_eq!(powers_of_10.collect::< Vec < _ >> (), & [1, 10, 100, 1_000, 10_000]);
}