rustc/tests/ui/unboxed-closures/unboxed-closures-call-sugar-object.rs

//@ run-pass
fn make_adder(x: isize) -> Box<dyn FnMut(isize)->isize + 'static> {
    Box::new(move |y| { x + y })
}

pub fn main() {
    let mut adder = make_adder(3);
    let z = (*adder)(2);
    println!("{}", z);
    assert_eq!(z, 5);
}