A simple stack in Rust using Option and Box.

stack.rs

struct Node<T> {
    val: T,
    next: Option<Box<Node<T>>>,
}

pub struct Stack<T> {
    top: Option<Box<Node<T>>>,
}

impl <T>Stack<T> {
    pub fn new() -> Stack<T> {
        Stack {
            top: None,
        }
    }

    pub fn push(&mut self, val: T) {
        self.top = Some(Box::new(Node {
            val: val,
            next: self.top.take(),
        }))
    }

    pub fn pop(&mut self) {
        match self.top.take() {
            None => return,
            Some(mut node_box) => self.top = (*node_box).next.take(),
        }
    }

    pub fn top(&self) -> &T {
        match &self.top {
            &None => panic!(),
            &Some(ref node_box) => &(*node_box).val,
        }
    }
}