struct S {
    v: i32
}

fn main()
{
    let t = std::cell::RefCell::new(S{v: 666});
    let s;
    let s1;

    println!("{}", t.borrow().v);
    t.borrow_mut().v = 0;
    println!("{}", t.borrow().v);
    s  = t.borrow();
    s1 = t.borrow_mut();
    println!("{} {}", s.v, s1.v)
}