struct Mylist {
  v: i32,
  next: Option<std::rc::Rc<std::cell::RefCell<Mylist>>>,
  prev: std::rc::Weak<std::cell::RefCell<Mylist>>
}

impl Mylist {
  fn new(val: i32) -> std::rc::Rc<std::cell::RefCell<Mylist>>
  {
    std::rc::Rc::new(std::cell::RefCell::new(Mylist{v: val, next: None, prev: std::rc::Weak::new()})) 
  }

  fn append(val: i32, l: &std::rc::Rc<std::cell::RefCell<Mylist>>) -> std::rc::Rc<std::cell::RefCell<Mylist>>
  {
    let res = std::rc::Rc::new(std::cell::RefCell::new(Mylist{v: val, next: Some(l.clone()), prev: std::rc::Weak::new()}));
    l.borrow_mut().prev = std::rc::Rc::downgrade(&res);
    res
  }
}

impl Drop for Mylist {
  fn drop(&mut self)
  {
    println!("Node with value {} is being destroyed!", self.v) 
  }
}

fn main()
{
  let l1 = Mylist::new(5);
  let l2 = Mylist::append(6, &l1);

  {
    let l3 = Mylist::append(7, &l2);

    println!("l3: {}", l3.borrow().v);
  }
  println!("l2: {}", l2.borrow().v);

  if let Some(next) = l2.borrow().next.clone() {
    println!("l2->next: {}", next.borrow().v);
  } else {
    println!("l2->next is empty!");
  };

  if let Some(prev) = std::rc::Weak::upgrade(&l1.borrow().prev) {
    println!("l1->prev: {}", prev.borrow().v);
  } else {
    println!("l1->prev is empty!");
  };

  if let Some(prev) = std::rc::Weak::upgrade(&l2.borrow().prev) {
    println!("l2->prev: {}", prev.borrow().v);
  } else {
    println!("l2->prev is empty!");
  };
}