#![allow(unused_variables)]
fn main() {
    use std::rc::Rc;
    let x = Rc::new(3);
    assert_eq!(Rc::into_inner(x), Some(3));
    let x = Rc::new(4);
    let y = Rc::clone(&x);
    assert_eq!(Rc::into_inner(y), None);
    assert_eq!(Rc::into_inner(x), Some(4));
}