Algorithm:

• Push items onto the stack.
• Pop items off. Last one in is the first one out. Like a stack of dishes.

Rust implementation:

use std::mem;

struct Stack {
    head: Link
}

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

enum Link {
    Empty,
    Some(Box<Node>),
}

impl Stack {
    fn new() -> Self {
        Stack { head: Link::Empty }
    }

    fn push(&mut self, value: i32) {
        let node = Node {value, next: mem::replace(&mut self.head, Link::Empty)};
        self.head = Link::Some(Box::new(node));
    }

    fn pop(&mut self) -> Option<i32> {
        match mem::replace(&mut self.head, Link::Empty) {
            Link::Empty => None,
            Link::Some(boxed_node) => {
                self.head = boxed_node.next;
                Some(boxed_node.value)
            }
        }
    }
}