#![allow(dead_code, deprecated, unused_variables, unused_mut)]
fn main() {
    let maybe_some_string = Some(String::from("Hello, World!"));
    let maybe_some_len = maybe_some_string.map(|s| s.len());
    assert_eq!(maybe_some_len, Some(13));
    let x: Option<&str> = None;
    assert_eq!(x.map(| s | s.len()), None);
}