too many lists: first

too-many-lists/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "too-many-lists"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

too-many-lists/src/first.rs

@@ -0,0 +1,92 @@
+use std::mem;
+
+// pub enum List {
+//     Empty,
+//     Elem(i32, Box<List>),
+// }
+
+// struct Node {
+//     elem: i32,
+//     next: List,
+// }
+//
+// pub enum List {
+//     Empty,
+//     More(Box<Node>),
+// }
+
+pub struct List {
+    head: Link,
+}
+
+struct Node {
+    elem: i32,
+    next: Link,
+}
+
+enum Link {
+    Empty,
+    More(Box<Node>),
+}
+
+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: 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();
+
+        assert_eq!(list.pop(), None);
+
+        list.push(1);
+        list.push(2);
+        list.push(3);
+
+        assert_eq!(list.pop(), Some(3));
+        assert_eq!(list.pop(), Some(2));
+
+        list.push(4);
+        list.push(5);
+
+        assert_eq!(list.pop(), Some(5));
+        assert_eq!(list.pop(), Some(4));
+
+        assert_eq!(list.pop(), Some(1));
+        assert_eq!(list.pop(), None);
+    }
+}

too-many-lists/src/lib.rs

@@ -0,0 +1 @@
+pub mod first;