tree/src/lib.rs

@@ -3,21 +3,25 @@
 //!
 //! This surely already exists. I am created it to test my own ability to do things in Rust.
 
-use std::{cell::RefCell, collections::VecDeque, rc::Rc};
+use std::{
+    cell::{Ref, RefCell},
+    collections::VecDeque,
+    rc::Rc,
+};
 
 #[derive(Debug)]
-pub enum Tree<T: Clone> {
+pub enum Tree<T> {
     Empty,
     Root(Node<T>),
 }
 
-impl<T: Clone> Default for Tree<T> {
+impl<T> Default for Tree<T> {
     fn default() -> Self {
         Tree::Empty
     }
 }
 
-impl<T: Clone> Tree<T> {
+impl<T> Tree<T> {
     pub fn set_value(&mut self, value: T) {
         *self = Tree::Root(Node::new(value));
     }
@@ -41,7 +45,7 @@ impl<T: Clone> Tree<T> {
                 return Some(node.clone());
             }
 
-            for child in node.children() {
+            for child in node.children().iter() {
                 queue.push_back(child.clone())
             }
         }
@@ -54,16 +58,25 @@ impl<T: Clone> Tree<T> {
 // make the visible objects mutable.
 //
 // This feels like cheating the type system.
-#[derive(Clone, Debug)]
-pub struct Node<T: Clone>(Rc<RefCell<Node_<T>>>);
+//
+// However, since I've moved the RefCell inside of the node, I can borrow the node multiple times
+// in a traversal function and I can make changes to nodes that I find.
+#[derive(Debug)]
+pub struct Node<T>(Rc<RefCell<Node_<T>>>);
+
+impl<T> Clone for Node<T> {
+    fn clone(&self) -> Self {
+        Node(Rc::clone(&self.0))
+    }
+}
 
 #[derive(Debug)]
-struct Node_<T: Clone> {
+struct Node_<T> {
     value: T,
     children: Vec<Node<T>>,
 }
 
-impl<T: Clone> Node<T> {
+impl<T> Node<T> {
     pub fn new(value: T) -> Self {
         Self(Rc::new(RefCell::new(Node_ {
             value,
@@ -71,12 +84,15 @@ impl<T: Clone> Node<T> {
         })))
     }
 
-    pub fn value<'a>(&'a self) -> T {
-        self.0.borrow().value.clone()
+    // I am copying the value because I don't have a mechanism for keeping the borrow ref active.
+    // My next step is to figure out how to keep the borrow ref active so that I don't have to
+    // clone the item. Then I could drop the Clone constraint.
+    pub fn value<'a>(&'a self) -> Ref<T> {
+        Ref::map(self.0.borrow(), |v| &v.value)
     }
 
-    pub fn children<'a>(&'a self) -> Vec<Node<T>> {
-        self.0.borrow().children.clone()
+    pub fn children<'a>(&'a self) -> Ref<Vec<Node<T>>> {
+        Ref::map(self.0.borrow(), |v| &v.children)
     }
 
     pub fn add_child_node(&self, child: Node<T>) {
@@ -110,7 +126,7 @@ mod tests {
         let n = Node::new(15);
         n.add_child_value(20);
 
-        assert_eq!(n.value(), 15);
+        assert_eq!(*n.value(), 15);
         // assert_eq!(n.children(), vec![Rc::new(RefCell::new(Node::new(20)))]);
     }
 }