#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#![feature(downcast_unchecked)]
use std::any::Any;
fn main() {
    let mut x: Box<dyn Any> = Box::new(1_usize);
    unsafe {
        *x.downcast_mut_unchecked::<usize>() += 1;
    }
    assert_eq!(* x.downcast_ref::< usize > ().unwrap(), 2);
}