pub struct List {
head: Link,
}
#[allow(dead_code)]
enum Link {
Empty,
More(Box<Node>),
}
#[allow(dead_code)]
struct Node {
elem: i32,
next: Link,
}
impl List {
pub fn new() -> Self {
List { head: Link::Empty }
}
pub fn push(&mut self, elem: i32) {
let new_node = Box::new(Node {
elem: elem,
next: std::mem::replace(&mut self.head, Link::Empty)
});
self.head = Link::More(new_node);
}
pub fn pop(&mut self) -> Option<i32> {
match std::mem::replace(&mut self.head, Link::Empty) {
Link::Empty => None,
Link::More(node) => {
self.head = node.next;
Some(node.elem)
}
}
}
pub fn peek(&self) -> Option<i32> {
match &self.head {
Link::Empty => None,
Link::More(node) => {
Some(node.elem)
}
}
}
}
impl Drop for List {
fn drop(&mut self) {
let mut cur_link = std::mem::replace(&mut self.head, Link::Empty);
while let Link::More(mut boxed_node) = cur_link {
cur_link = std::mem::replace(&mut boxed_node.next, Link::Empty);
}
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn basics() {
let mut list = List::new();
assert_eq!(list.pop(), None);
}
#[test]
fn basc_push_pop() {
let mut list = List::new();
list.push(1);
list.push(2);
list.push(3);
assert_eq!(list.peek(), Some(3));
assert_eq!(list.pop(), Some(3));
assert_eq!(list.pop(), Some(2));
list.push(4);
assert_eq!(list.pop(), Some(4));
assert_eq!(list.pop(), Some(1));
assert_eq!(list.pop(), None);
}
}