struct S {
  v: i32
}

fn main()
{
  let v  = std::cell::RefCell::new(S{v:666});
  let r1 = v.borrow();
  let r2 = v.borrow();

  println!("{} {}", r1.v, r2.v);
  v.borrow_mut().v = 0;
  println!("{} {}", r1.v, r2.v)
}