trait Foo {
    fn get_int(&self) -> usize;
}

struct Bar {}

impl Foo for Bar {
    fn get_int(&self) -> usize { 0 }
}

fn do_something(_f: Box<dyn Foo>) {
    println!("hello");
}

fn main() {
    let x = Box::new(Bar {});
    do_something(x);
}