最终代码

好吧，在6000词之后，这是我们实际写成的所有代码：

  1. use std::mem;
  3. pub struct List {
  4.     head: Link,
  5. }
  7. enum Link {
  8.     Empty,
  9.     More(Box<Node>),
  10. }
  12. struct Node {
  13.     elem: i32,
  14.     next: Link,
  15. }
  17. impl List {
  18.     pub fn new() -> Self {
  19.         List { head: Link::Empty }
  20.     }
  22.     pub fn push(&mut self, elem: i32) {
  23.         let new_node = Box::new(Node {
  24.             elem: elem,
  25.             next: mem::replace(&mut self.head, Link::Empty),
  26.         });
  28.         self.head = Link::More(new_node);
  29.     }
  31.     pub fn pop(&mut self) -> Option<i32> {
  32.         match mem::replace(&mut self.head, Link::Empty) {
  33.             Link::Empty => None,
  34.             Link::More(node) => {
  35.                 let node = *node;
  36.                 self.head = node.next;
  37.                 Some(node.elem)
  38.             }
  39.         }
  40.     }
  41. }
  43. impl Drop for List {
  44.     fn drop(&mut self) {
  45.         let mut cur_link = mem::replace(&mut self.head, Link::Empty);
  46.         while let Link::More(mut boxed_node) = cur_link {
  47.             cur_link = mem::replace(&mut boxed_node.next, Link::Empty);
  48.         }
  49.     }
  50. }
  52. #[cfg(test)]
  53. mod test {
  54.     use super::List;
  56.     #[test]
  57.     fn basics() {
  58.         let mut list = List::new();
  60.         // Check empty list behaves right
  61.         assert_eq!(list.pop(), None);
  63.         // Populate list
  64.         list.push(1);
  65.         list.push(2);
  66.         list.push(3);
  68.         // Check normal removal
  69.         assert_eq!(list.pop(), Some(3));
  70.         assert_eq!(list.pop(), Some(2));
  72.         // Push some more just to make sure nothing's corrupted
  73.         list.push(4);
  74.         list.push(5);
  76.         // Check normal removal
  77.         assert_eq!(list.pop(), Some(5));
  78.         assert_eq!(list.pop(), Some(4));
  80.         // Check exhaustion
  81.         assert_eq!(list.pop(), Some(1));
  82.         assert_eq!(list.pop(), None);
  83.     }
  84. }

天。80行，而且其中的一半都是测试！嘛，我确实说过这第一个教程会花一些时间的！