simple list implementation in rust

simple_list.rs

struct List {
    head: Link,
}

type Link = Option<Box<Node>>;

struct Node {
    elem: i32,
    next: Link,
}

impl List {
    fn new() -> Self {
        return List {
            head: None
        };
    }

    fn push(&mut self, elem: i32) {
        let new_node = Box::new(Node {
            elem: elem,
            next: self.head.take(),
        });
        self.head = Some(new_node);
    }

    fn pop(&mut self) -> Option<i32> {
        match self.head.take() {
            None => None,
            Some(node) => {
                let node = *node;
                self.head = node.next;
                Some(node.elem)
            }
        }
    }
}

impl Drop for List {
    fn drop(&mut self) {
        let mut cur_link = self.head.take();
        // 从box中解出node本身，把指针清空，避免递归的清空资源
        while let Some(mut boxed_node) = cur_link {
            cur_link = boxed_node.next.take();
        }
    }
}

fn main() {
    let mut l = List::new();
    l.push(1);
    l.push(2);
    l.push(3);

    let a = l.pop().unwrap();
    println!("elem: {}", a);
}