#![allow(unused_variables)]
fn main() {
    use std::error::Error;
    use std::borrow::Cow;
    let a_cow_str_error = Cow::from("a str error");
    let a_boxed_error = Box::<dyn Error>::from(a_cow_str_error);
    assert!(size_of::< Box < dyn Error >> () == size_of_val(& a_boxed_error))
}