Add a-bad-stack

linkedlist/a-bad-stack/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "a-bad-stack"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

linkedlist/a-bad-stack/src/main.rs

@@ -0,0 +1,91 @@
+#![allow(unused)]
+
+use std::mem;
+
+#[derive(Debug)]
+pub struct List {
+    head: Link,
+}
+
+#[derive(Debug)]
+enum Link {
+    Empty,
+    More(Box<Node>),
+}
+
+#[derive(Debug)]
+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,
+            next: mem::replace(&mut self.head, Link::Empty),
+        });
+
+        self.head = Link::More(new_node);
+    }
+
+    pub fn pop(&mut self) -> Option<i32> {
+        match mem::replace(&mut self.head, Link::Empty) {
+            Link::Empty => None,
+            Link::More(node) => {
+                self.head = node.next;
+                Some(node.elem)
+            }
+        }
+    }
+}
+
+impl Drop for List {
+    fn drop(&mut self) {
+        let mut cur_link = mem::replace(&mut self.head, Link::Empty);
+
+        while let Link::More(mut boxed_node) = cur_link {
+            cur_link = mem::replace(&mut boxed_node.next, Link::Empty);
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::List;
+
+    #[test]
+    fn basics() {
+        let mut list = List::new();
+
+        // Check empty list behaves right
+        assert_eq!(list.pop(), None);
+
+        // Populate list
+        list.push(1);
+        list.push(2);
+        list.push(3);
+
+        // Check normal removal
+        assert_eq!(list.pop(), Some(3));
+        assert_eq!(list.pop(), Some(2));
+
+        // Push some more just to make sure nothing's corrupted
+        list.push(4);
+        list.push(5);
+
+        // Check normal removal
+        assert_eq!(list.pop(), Some(5));
+        assert_eq!(list.pop(), Some(4));
+
+        // Check exhaustion
+        assert_eq!(list.pop(), Some(1));
+        assert_eq!(list.pop(), None);
+    }
+}
+
+fn main() {}