use std::rc::Rc;
use std::cell::RefCell;

type NodePtr<T> = Option<Rc<RefCell<Node<T>>>>;
struct Node<T> {
    val: T,
    next: NodePtr<T>,
}

impl<T> Drop for Node<T> {
    fn drop(&mut self) {
        println!("dropping");
    }
}

fn main() {
    let head = Rc::new(RefCell::new(Node {
        val: 10, next: None,
    }));
    let tail = Rc::new(RefCell::new(Node {
        val: 20, next: None,
    }));
    // mem leak caused by circular reference, same problem as shared_ptr in C++
    head.borrow_mut().next = Some(tail.clone());
    tail.borrow_mut().next = Some(head.clone());
}