不能一次多次使用变量作为可变变量

Question

我正在尝试实施一个特里但借用检查器确实让我很难过：

struct Node {
    // a trie node
    value: char,
    children: Vec<Node>,
}

impl Node {
    fn add_child(&mut self, value: char) -> &mut Node {
        // adds a child to given node
        let vec: Vec<Node> = Vec::new();
        let node = Node {
            value,
            children: vec,
        };
        self.children.push(node);
        self.children.last_mut().unwrap()
    }

    fn get_child(&mut self, value: char) -> Option<&mut Node> {
        // checks if given node has a child with given value, returns the child if it exists
        for child in self.children.iter_mut() {
            if child.value == value {
                return Some(child);
            }
        }
        None
    }

    fn has_child(&self, value: char) -> bool {
        for child in self.children.iter() {
            if child.value == value {
                return true;
            }
        }
        false
    }

    fn add_word(&mut self, word: String) {
        let mut cursor = self;
        for c in word.chars() {
            match cursor.get_child(c) {
                Some(node) => cursor = node,
                None => cursor = cursor.add_child(c),
            }
        }
        cursor.add_child('~');
    }
}

add_word方法给出了以下5个错误：

error[E0499]: cannot borrow `*cursor` as mutable more than once at a time
  --> src/main.rs:41:19
   |
41 |             match cursor.get_child(c) {
   |                   ^^^^^^ mutable borrow starts here in previous iteration of loop
...
47 |     }
   |     - mutable borrow ends here

error[E0506]: cannot assign to `cursor` because it is borrowed
  --> src/main.rs:42:31
   |
41 |             match cursor.get_child(c) {
   |                   ------ borrow of `cursor` occurs here
42 |                 Some(node) => cursor = node,
   |                               ^^^^^^^^^^^^^ assignment to borrowed `cursor` occurs here

error[E0506]: cannot assign to `cursor` because it is borrowed
  --> src/main.rs:43:25
   |
41 |             match cursor.get_child(c) {
   |                   ------ borrow of `cursor` occurs here
42 |                 Some(node) => cursor = node,
43 |                 None => cursor = cursor.add_child(c),
   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ assignment to borrowed `cursor` occurs here

error[E0499]: cannot borrow `*cursor` as mutable more than once at a time
  --> src/main.rs:43:34
   |
41 |             match cursor.get_child(c) {
   |                   ------ first mutable borrow occurs here
42 |                 Some(node) => cursor = node,
43 |                 None => cursor = cursor.add_child(c),
   |                                  ^^^^^^ second mutable borrow occurs here
...
47 |     }
   |     - first borrow ends here

error[E0499]: cannot borrow `*cursor` as mutable more than once at a time
  --> src/main.rs:46:9
   |
41 |             match cursor.get_child(c) {
   |                   ------ first mutable borrow occurs here
...
46 |         cursor.add_child('~');
   |         ^^^^^^ second mutable borrow occurs here
47 |     }
   |     - first borrow ends here

这是我试图翻译的Go代码：

func (n *trieNode) AddWord(word string) {
cursor := n
for i := 0; i < len(word); i++ {
    if cursor.HasChild(byte(word[i])) == nil {
        cursor = cursor.AddChild(byte(word[i]))
    } else {
        cursor = cursor.HasChild(byte(word[i]))
    }
}
// tilde indicates the end of the word
cursor.AddChild(byte('~'))
}