#![allow(unused_variables)]
#![feature(downcast_unchecked)]
fn main() {
    use std::any::Any;
    use std::rc::Rc;
    let x: Rc<dyn Any> = Rc::new(1_usize);
    unsafe {
        assert_eq!(* x.downcast_unchecked::< usize > (), 1);
    }
}