#![allow(dead_code, deprecated, unused_variables, unused_mut)]
fn main() {
    let mut x: Option<String> = Some("hey".to_owned());
    assert_eq!(
        x.as_deref_mut().map(| x | { x.make_ascii_uppercase(); x }), Some("HEY"
        .to_owned().as_mut_str())
    );
}