介绍

视频地址：www.bilibili.com/video/av78062009/

相关源码：github.com/anonymousGiga/Rust-link...

详细内容

本节我们为链表实现Drop函数。按照我们常规的方式，我们可能的实现方式如下：

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impl Drop for List {
    fn drop(&mut self) {// NOTE: you can't actually explicitly call `drop` in real Rust code;// we're pretending to be the compiler! 
        self.head.drop(); // tail recursive - good!}
}
 
impl Drop for Link {
    fn drop(&mut self) {
        match *self {
            Link::Empty => {} // Done!
            Link::More(ref mut boxed_node) => {
                boxed_node.drop(); // tail recursive - good!}}}
}
 
impl Drop for Box<Node> {
    fn drop(&mut self) {
        self.ptr.drop(); // uh oh, not tail recursive!deallocate(self.ptr);}
}
 
impl Drop for Node {
    fn drop(&mut self) {
        self.next.drop();}
}

但是此种实现方式在编译时候会报错，因为Box中包含Node无法以递归的方式删除，因此，正确的实现方式如下：

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impl Drop for List {
    fn drop(&mut self) {let mut cur_link = mem::replace(&mut self.head, Link::Empty);while let Link::More(mut boxed_node) = cur_link {
            cur_link = mem::replace(&mut boxed_node.next, Link::Empty);}}
}

完整的代码如下：

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use std::mem;
 
#[derive(Debug)]
pub struct List{
    head: Link,
}
 
#[derive(Debug)]
enum Link {
    Empty,More(Box<Node>),
}
 
#[derive(Debug)]
struct Node {
    elem: i32,
    next: Link,
}
 
impl List {
    pub fn new() -> Self {
        List { head: Link::Empty }}
 
    pub fn push(&mut self, elem: i32) {let node = Box::new(Node {
            elem: elem,
            next: mem::replace(&mut self.head, Link::Empty),});
 
        self.head = Link::More(node);}
 
    pub fn pop(&mut self) -> Option<i32> {
        match mem::replace(&mut self.head, Link::Empty) {
            Link::Empty => None,
            Link::More(node) => {
                self.head = node.next;Some(node.elem)    
            }}}
}
 
//impl Drop for List {
//    fn drop(&mut self) {
//        self.head.drop();
//    }
//}
//
//impl Drop for Link {
//    fn drop(&mut self) {
//        match *self {
//            Link::Empty => {} // Done!
//            Link::More(ref mut boxed_node) => {
//                boxed_node.drop(); // tail recursive - good!
//            }
//        }
//    }
//}
//
//impl Drop for Box<Node> {
//    fn drop(&mut self) {
//        self.ptr.drop(); // uh oh, not tail recursive!
//        deallocate(self.ptr);
//    }
//}
//
//impl Drop for Node {
//    fn drop(&mut self) {
//        self.next.drop();
//    }
//}
 
impl Drop for List {
    fn drop(&mut self) {let mut cur_link = mem::replace(&mut self.head, Link::Empty);while let Link::More(mut boxed_node) = cur_link {
            cur_link = mem::replace(&mut boxed_node.next, Link::Empty);}}
}
 
#[cfg(test)]
mod tests {
    use super::List;
 
    #[test] 
    fn basics() {let mut list = List::new();
 
        assert_eq!(list.pop(), None);
 
        list.push(1);
        list.push(2);
        list.push(3);
 
        assert_eq!(list.pop(), Some(3));
        assert_eq!(list.pop(), Some(2));
 
        list.push(4);
        list.push(5);
 
        assert_eq!(list.pop(), Some(5));
        assert_eq!(list.pop(), Some(4));
 
        assert_eq!(list.pop(), Some(1));
        assert_eq!(list.pop(), None);}
}