我试图add
在二叉树中实现一个操作:
use std::cell::RefCell;
use std::cmp::PartialOrd;
type Link<T> = RefCell<Option<Box<Node<T>>>>;
struct Node<T> {
key: T,
left: Link<T>,
right: Link<T>,
}
struct Tree<T> {
root: Link<T>,
}
impl<T> Node<T> {
fn new(val: T) -> Self {
Node {
key: val,
left: RefCell::new(None),
right: RefCell::new(None),
}
}
}
impl<T: PartialOrd> Tree<T> {
fn new() -> Self {
Tree {
root: RefCell::new(None),
}
}
fn add(&self, val: T) {
let mut next = self.root.borrow();
let node = Box::new(Node::new(val));
match next.as_ref() {
None => {
self.root.replace(Some(node));
()
}
Some(root_ref) => {
let mut prev = root_ref;
let mut cur: Option<&Box<Node<T>>> = Some(root_ref);
while let Some(node_ref) = cur {
prev = node_ref;
if node.key < node_ref.key {
next = node_ref.left.borrow();
} else {
next = node_ref.right.borrow();
}
cur = next.as_ref();
}
if node.key < prev.key {
prev.left.replace(Some(node));
} else {
prev.right.replace(Some(node));
}
}
}
}
}
fn main() {}
我不明白为什么next
变量的寿命不够长:
error[E0597]: `next` does not live long enough
--> src/main.rs:36:15
|
36 | match next.as_ref() {
| ^^^^ borrowed value does not live long enough
...
60 | }
| - `next` dropped here while still borrowed
|
= note: values in a scope are dropped in the opposite order they are created
error[E0597]: `next` does not live long enough
--> src/main.rs:51:27
|
51 | cur = next.as_ref();
| ^^^^ borrowed value does not live long enough
...
60 | }
| - `next` dropped here while still borrowed
|
= note: values in a scope are dropped in the opposite order they are created
next
存在于函数的整个范围内,add
并且在我看来,包含对它的引用的其他变量在删除之前next
就被删除了。
编译器这么说"values in a scope are dropped in the opposite order they are created"
,暗示有另一种方法来声明变量并解决这个问题,但我不知道如何。