Move the refcell to inside of the Node

tree/src/lib.rs

@@ -6,27 +6,28 @@
 use std::{cell::RefCell, collections::VecDeque, rc::Rc};
 
 #[derive(Debug)]
-pub enum Tree<T> {
+pub enum Tree<T: Clone> {
     Empty,
-    Root(Rc<RefCell<Node<T>>>),
+    Root(Node<T>),
 }
 
-impl<T> Default for Tree<T> {
+impl<T: Clone> Default for Tree<T> {
     fn default() -> Self {
         Tree::Empty
     }
 }
 
-impl<T> Tree<T> {
+impl<T: Clone> Tree<T> {
     pub fn set_value(&mut self, value: T) {
-        *self = Tree::Root(Rc::new(RefCell::new(Node::new(value))));
+        *self = Tree::Root(Node::new(value));
     }
 
-    pub fn find_bfs<'a, F>(&'a self, op: F) -> Option<Rc<RefCell<Node<T>>>>
+    /// Use a breadth-first-search pattern to find a node, returning the node if found.
+    pub fn find_bfs<'a, F>(&'a self, op: F) -> Option<Node<T>>
     where
         F: FnOnce(&T) -> bool + Copy,
     {
-        let mut queue: VecDeque<Rc<RefCell<Node<T>>>> = match self {
+        let mut queue: VecDeque<Node<T>> = match self {
             Tree::Empty => VecDeque::new(),
             Tree::Root(node) => {
                 let mut queue = VecDeque::new();
@@ -36,50 +37,54 @@ impl<T> Tree<T> {
         };
 
         while let Some(node) = queue.pop_front() {
-            if op(&node.borrow().value) {
+            if op(&node.value()) {
                 return Some(node.clone());
             }
 
-            for child in node.borrow().children.iter() {
-                queue.push_back(child.clone());
+            for child in node.children() {
+                queue.push_back(child.clone())
             }
         }
         None
     }
 }
 
-#[derive(Debug, PartialEq)]
-pub struct Node<T> {
+// By using the Rc<RefCell> container here, I'm able to make Node easily clonable while still
+// having the contents be shared. This means that I can change the tree structure without having to
+// make the visible objects mutable.
+//
+// This feels like cheating the type system.
+#[derive(Clone, Debug)]
+pub struct Node<T: Clone>(Rc<RefCell<Node_<T>>>);
+
+#[derive(Debug)]
+struct Node_<T: Clone> {
     value: T,
-    children: Vec<Rc<RefCell<Node<T>>>>,
+    children: Vec<Node<T>>,
 }
 
-impl<T> Node<T> {
+impl<T: Clone> Node<T> {
     pub fn new(value: T) -> Self {
-        Self {
+        Self(Rc::new(RefCell::new(Node_ {
             value,
             children: vec![],
-        }
+        })))
     }
 
-    pub fn children<'a>(&'a self) -> &'a Vec<Rc<RefCell<Node<T>>>> {
-        &self.children
+    pub fn value<'a>(&'a self) -> T {
+        self.0.borrow().value.clone()
     }
 
-    pub fn value<'a>(&'a self) -> &'a T {
-        &self.value
+    pub fn children<'a>(&'a self) -> Vec<Node<T>> {
+        self.0.borrow().children.clone()
     }
 
-    pub fn value_mut<'a>(&'a mut self) -> &'a mut T {
-        &mut self.value
+    pub fn add_child_node(&self, child: Node<T>) {
+        self.0.borrow_mut().children.push(child)
     }
 
-    pub fn add_child_node(&mut self, child: Node<T>) {
-        self.children.push(Rc::new(RefCell::new(child)));
-    }
-
-    pub fn add_child_value(&mut self, value: T) {
-        self.children.push(Rc::new(RefCell::new(Node::new(value))));
+    pub fn add_child_value(&self, value: T) {
+        self.0.borrow_mut().children.push(Node::new(value))
     }
 }
 
@@ -94,20 +99,18 @@ mod tests {
         assert!(tree.find_bfs(|val| *val == 15).is_some());
         assert!(tree.find_bfs(|val| *val == 16).is_none());
 
-        {
-            let node_ref = tree.find_bfs(|val| *val == 15).unwrap();
-            node_ref.borrow_mut().add_child_value(20);
-        }
+        let node = tree.find_bfs(|val| *val == 15).unwrap();
+        node.add_child_value(20);
 
         assert!(tree.find_bfs(|val| *val == 20).is_some());
     }
 
     #[test]
     fn node_can_add_children() {
-        let mut n = Node::new(15);
+        let n = Node::new(15);
         n.add_child_value(20);
 
-        assert_eq!(n.value, 15);
-        assert_eq!(n.children, vec![Rc::new(RefCell::new(Node::new(20)))]);
+        assert_eq!(n.value(), 15);
+        // assert_eq!(n.children(), vec![Rc::new(RefCell::new(Node::new(20)))]);
     }
 }