使用Rc<RefCell<..>>实现二进制搜索树时的生命周期问题

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

enum BinaryTree<T> {
    Node(T, Rc<RefCell<BinaryTree<T>>>, Rc<RefCell<BinaryTree<T>>>),
    Leaf,
}

impl<T: Ord> BinaryTree<T> {
    fn new() -> Self {
        BinaryTree::Leaf
    }

    fn insert(&mut self, value: T) {
        match self {
            BinaryTree::Node(ref v, ref left, ref right) => {
                if value < *v {
                    left.borrow_mut().insert(value);
                } else {
                    right.borrow_mut().insert(value);
                }
            }
            BinaryTree::Leaf => {
                *self = BinaryTree::Node(value, Rc::new(RefCell::new(BinaryTree::Leaf)), Rc::new(RefCell::new(BinaryTree::Leaf)));
            }
        }
    }

    fn contains(&self, value: T) -> bool {
        match *self {
            BinaryTree::Node(ref v, ref left, ref right) => {
                if value == *v {
                    true
                } else if value < *v {
                    left.borrow().contains(value)
                } else {
                    right.borrow().contains(value)
                }
            }
            BinaryTree::Leaf => false,
        }
    }
}