#![allow(unused_variables)]
fn main() {
    use std::error::Error;
    let a_string_error = "a string error".to_string();
    let a_boxed_error = Box::<dyn Error + Send + Sync>::from(a_string_error);
    assert!(
        size_of::< Box < dyn Error + Send + Sync >> () == size_of_val(& a_boxed_error)
    )
}