从Option <T>提取的可变引用摘录在“ while let”作用域结束之后会消失吗？

Question

我正在Rust中编写一个二叉搜索树，当我要从树中删除元素时，遇到了多个可变引用的问题。

代码如下：

use std::cmp;
use std::cmp::Ordering;

type Root<T> = Option<Box<Node<T>>>;

struct Node<T: cmp::Ord> {
    data: T,
    left: Root<T>,
    right: Root<T>,
}

pub struct BinTree<T: cmp::Ord> {
    size: i32,
    root: Root<T>,
}

impl<T: cmp::Ord> BinTree<T> {
    pub fn remove(&mut self, data: T) {
        let mut curr = &mut self.root;

        while let Some(ref mut node) = curr {
            curr = match data.cmp(&node.data) {
                Ordering::Less => &mut node.left,
                Ordering::Greater => &mut node.right,
                Ordering::Equal => break,
            };
        }

        if let Some(_) = curr {

        }
    }
}

我得到了erorr说

error[E0503]: cannot use `*curr` because it was mutably borrowed
  --> src/lib.rs:53:16
   |
45 |         while let Some(ref mut node) = curr {
   |                        ------------ borrow of `curr.0` occurs here
...
53 |         if let Some(_) = curr {
   |                ^^^^^^^
   |                |
   |                use of borrowed `curr.0`
   |                borrow later used here

error: aborting due to previous error

但是ref mut node应该在while let范围内才对吗？为什么在while let块结束之后进行更多可变的引用会成为问题？

我只想做下面的事情，从这个二叉树中删除一个节点

if let Some(node) = curr {
    match (node.left, node.right) {
        (Some(_), Some(_)) => {
            node.data = BinTree::pop_min_from(&mut node.left);
            // get minimum data from left most node
            // and drop that node by taking ownership of it
        },
        (Some(left), None) => {
            curr.replace(left);
        },
        (None, Some(right)) => {
            curr.replace(right);
        },
        (None, None) => {
            curr.take();
        },
    }
    self.size -= 1;
}

但是在这种情况下，我很容易获得所有权。我的大脑无法承受，甚至无法确保我在if let中做正确的事情来处理目标节点。