fn identity(a: &u32) -> &u32 {
    a
}

fn print_foo(f: &fn(&u32) -> &u32, x: &u32) {
    print!("{}", (*f)(x));
}

fn main() {
    let x = &4;
    let f: fn(&u32) -> &u32 = identity;

    // Didn't print 4 on optimized builds
    print_foo(&f, x);
}