From 0e92a87719e03ae0b83d0c3beb2475bbbaa4c8a6 Mon Sep 17 00:00:00 2001
From: Timothy Warren <twarren@nabancard.com>
Date: Wed, 13 Mar 2019 11:11:36 -0400
Subject: [PATCH] Add unsafe queue example

---
 src/fifth.rs | 217 +++++++++++++++++++++++++++++++++++++++++++++++++++
 src/lib.rs   |   1 +
 2 files changed, 218 insertions(+)
 create mode 100644 src/fifth.rs

diff --git a/src/fifth.rs b/src/fifth.rs
new file mode 100644
index 0000000..e084672
--- /dev/null
+++ b/src/fifth.rs
@@ -0,0 +1,217 @@
+//! # An Unsafe Queue
+
+use std::ptr;
+
+pub struct List<T> {
+    head: Link<T>,
+    tail: *mut Node<T>, // DANGER DANGER
+}
+
+type Link<T> = Option<Box<Node<T>>>;
+
+struct Node<T> {
+    elem: T,
+    next: Link<T>,
+}
+
+pub struct IntoIter<T>(List<T>);
+
+pub struct Iter<'a, T: 'a> {
+    next: Option<&'a Node<T>>,
+}
+
+pub struct IterMut<'a, T: 'a> {
+    next: Option<&'a mut Node<T>>,
+}
+
+impl<T> List<T> {
+    pub fn new() -> Self {
+        List{
+            head: None,
+            tail: ptr::null_mut(),
+        }
+    }
+
+    pub fn push(&mut self, elem: T) {
+        let mut new_tail = Box::new(Node {
+            elem,
+            // When you push onto the tail, your next is always None
+            next: None,
+        });
+
+        let raw_tail: *mut _ = &mut *new_tail;
+
+        // .is_null checks for null, equivalent to checking for None
+        if !self.tail.is_null() {
+            // If the old tail existed, update it to point to the new tail
+            unsafe {
+                (*self.tail).next = Some(new_tail);
+            }
+        } else {
+            self.head = Some(new_tail);
+        }
+
+        self.tail = raw_tail;
+    }
+
+    pub fn pop(&mut self) -> Option<T> {
+        self.head.take().map(|head| {
+            let head = *head;
+            self.head = head.next;
+
+            if self.head.is_none() {
+                self.tail = ptr::null_mut();
+            }
+
+            head.elem
+        })
+    }
+
+    pub fn peek(&self) -> Option<&T> {
+        self.head.as_ref().map(|node| {
+            &node.elem
+        })
+    }
+
+    pub fn peek_mut(&mut self) -> Option<&mut T> {
+        self.head.as_mut().map(|node| {
+            &mut node.elem
+        })
+    }
+
+    pub fn into_iter(self) -> IntoIter<T> {
+        IntoIter(self)
+    }
+
+    pub fn iter(&self) -> Iter<T> {
+        Iter { next: self.head.as_ref().map(|node| &**node) }
+    }
+
+    pub fn iter_mut(&mut self) -> IterMut<T> {
+        IterMut { next: self.head.as_mut().map(|node| &mut **node) }
+    }
+}
+
+impl<T> Drop for List<T> {
+    fn drop(&mut self) {
+        let mut cur_link = self.head.take();
+        while let Some(mut boxed_node) = cur_link {
+            cur_link = boxed_node.next.take();
+        }
+    }
+}
+
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.pop()
+    }
+}
+
+impl<'a, T> Iterator for Iter<'a, T> {
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.next.map(|node| {
+            self.next = node.next.as_ref().map(|node| &**node);
+            &node.elem
+        })
+    }
+}
+
+impl<'a, T> Iterator for IterMut<'a, T> {
+    type Item = &'a mut T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.next.take().map(|node| {
+            self.next = node.next.as_mut().map(|node| &mut **node);
+            &mut node.elem
+        })
+    }
+}
+
+#[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(1));
+        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(3));
+        assert_eq!(list.pop(), Some(4));
+
+        // Check exhaustion
+        assert_eq!(list.pop(), Some(5));
+        assert_eq!(list.pop(), None);
+
+        // Check the exhaustion case fixed the pointer right
+        list.push(6);
+        list.push(7);
+
+        // Check normal removal
+        assert_eq!(list.pop(), Some(6));
+        assert_eq!(list.pop(), Some(7));
+        assert_eq!(list.pop(), None);
+    }
+
+
+    #[test]
+    fn into_iter() {
+        let mut list = List::new();
+        list.push(1);
+        list.push(2);
+        list.push(3);
+
+        let mut iter = list.into_iter();
+        assert_eq!(iter.next(), Some(1));
+        assert_eq!(iter.next(), Some(2));
+        assert_eq!(iter.next(), Some(3));
+        assert_eq!(iter.next(), None);
+    }
+
+    #[test]
+    fn iter() {
+        let mut list = List::new();
+        list.push(1);
+        list.push(2);
+        list.push(3);
+
+        let mut iter = list.iter();
+        assert_eq!(iter.next(), Some(&1));
+        assert_eq!(iter.next(), Some(&2));
+        assert_eq!(iter.next(), Some(&3));
+        assert_eq!(iter.next(), None);
+    }
+
+    #[test]
+    fn iter_mut() {
+        let mut list = List::new();
+        list.push(1);
+        list.push(2);
+        list.push(3);
+
+        let mut iter = list.iter_mut();
+        assert_eq!(iter.next(), Some(&mut 1));
+        assert_eq!(iter.next(), Some(&mut 2));
+        assert_eq!(iter.next(), Some(&mut 3));
+        assert_eq!(iter.next(), None);
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 3770e8a..4d2d0c6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2,3 +2,4 @@ pub mod first;
 pub mod second;
 pub mod third;
 pub mod fourth;
+pub mod fifth;