89 lines
1.9 KiB
Rust
89 lines
1.9 KiB
Rust
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use std::mem;
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pub struct List {
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head: Link,
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}
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enum Link {
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Empty,
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More(Box<Node>),
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}
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struct Node {
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elem: i32,
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next: Link,
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}
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impl List {
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pub fn new() -> Self {
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List { head: Link::Empty }
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}
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pub fn push(&mut self, elem: i32) {
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let new_node = Box::new(Node {
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elem,
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next: mem::replace(&mut self.head, Link::Empty),
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});
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self.head = Link::More(new_node)
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}
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pub fn pop(&mut self) -> Option<i32> {
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match mem::replace(&mut self.head, Link::Empty) {
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Link::Empty => None,
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Link::More(boxed_node) => {
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let node = *boxed_node;
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self.head = node.next;
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Some(node.elem)
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}
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}
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}
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}
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impl Drop for List {
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fn drop(&mut self) {
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let mut cur_link = mem::replace(&mut self.head, Link::Empty);
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while let Link::More(mut boxed_node) = cur_link {
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cur_link = mem::replace(&mut boxed_node.next, Link::Empty);
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// boxed_node goes out of scope and gets dropped here;
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// but its Node's `next` field has been set to Link::Empty
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// so no unbounded recursion occurs.
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}
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}
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}
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#[cfg(test)]
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mod test {
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use super::List;
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#[test]
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fn basics() {
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let mut list = List::new();
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// Check empty list behaves right
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assert_eq!(list.pop(), None);
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// Populate list
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list.push(1);
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list.push(2);
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list.push(3);
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// Check normal removal
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assert_eq!(list.pop(), Some(3));
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assert_eq!(list.pop(), Some(2));
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// Push some more just to make sure nothing's corrupted
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list.push(4);
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list.push(5);
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// Check normal removal
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assert_eq!(list.pop(), Some(5));
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assert_eq!(list.pop(), Some(4));
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// Check exhaustion
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assert_eq!(list.pop(), Some(1));
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assert_eq!(list.pop(), None);
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}
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}
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