From 5dbb93455c3ca6ea3891cc898941731ca573c6a6 Mon Sep 17 00:00:00 2001
From: YK <yk@qcl.one>
Date: Sun, 8 Dec 2024 00:38:20 +0300
Subject: [PATCH] a bad linked list (chapter 1)

---
 src/bad.rs | 72 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/lib.rs | 15 +-----------
 2 files changed, 73 insertions(+), 14 deletions(-)
 create mode 100644 src/bad.rs

diff --git a/src/bad.rs b/src/bad.rs
new file mode 100644
index 0000000..55fdac3
--- /dev/null
+++ b/src/bad.rs
@@ -0,0 +1,72 @@
+
+pub struct List {
+    head: Link
+}
+
+enum Link {
+    Empty,
+    More (Box<Node>)
+}
+
+struct Node {
+    val: i32,
+    next: List
+}
+
+
+impl List {
+    fn new () -> Self {
+        List { head: Link::Empty }
+    }
+
+    fn push (&mut self, val: i32) {
+        let new_node = Box::new(Node { val, next: List { head: std::mem::replace(&mut self.head, Link::Empty) } });
+        self.head = Link::More(new_node);
+    }
+
+    fn pop (&mut self) -> Option<i32> {
+        match std::mem::replace(&mut self.head, Link::Empty) {
+            Link::Empty => None,
+            Link::More(v) => {
+                self.head = v.next.head;
+                Some(v.val)
+            }
+        }
+    }
+}
+
+
+#[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);
+
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index b93cf3f..1aef305 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,14 +1 @@
-pub fn add(left: u64, right: u64) -> u64 {
-    left + right
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn it_works() {
-        let result = add(2, 2);
-        assert_eq!(result, 4);
-    }
-}
+pub mod bad;