weakrefs

Author: monnetchr

course/src/main.rs

@@ -13,4 +13,5 @@ fn main() {
     //stuff::error_handling();
     //guessgame::guess_game();
     intmut::intmut();
+    intmut::weakrefs();
 }

intmut/src/lib.rs

@@ -1,5 +1,6 @@
-use std::{cell::RefCell, rc::Rc};
 use List::{Cons, Nil};
+use std::cell::RefCell;
+use std::rc::{Rc, Weak};
 
 #[derive(Debug)]
 enum List {
@@ -98,4 +99,60 @@ mod tests {
 
         assert_eq!(mock_messenger.sent_messages.borrow().len(), 1);
     }
-}
+}
+
+// ******************
+
+#[derive(Debug)]
+struct Node {
+    value: i32,
+    parent: RefCell<Weak<Node>>,
+    children: RefCell<Vec<Rc<Node>>>,
+}
+
+pub fn weakrefs() {
+    let leaf = Rc::new(Node {
+        value: 3,
+        parent: RefCell::new(Weak::new()),
+        children: RefCell::new(vec![]),
+    });
+    {
+        let c = leaf.children.borrow();
+        println!("leaf: ({}, {c:?})", leaf.value);
+    }
+
+    println!(
+        "leaf strong = {}, weak = {}",
+        Rc::strong_count(&leaf),
+        Rc::weak_count(&leaf),
+    );
+
+    {
+        let branch = Rc::new(Node {
+            value: 5,
+            parent: RefCell::new(Weak::new()),
+            children: RefCell::new(vec![Rc::clone(&leaf)]),
+        });
+
+        *leaf.parent.borrow_mut() = Rc::downgrade(&branch);
+
+        println!(
+            "branch strong = {}, weak = {}",
+            Rc::strong_count(&branch),
+            Rc::weak_count(&branch),
+        );
+
+        println!(
+            "leaf strong = {}, weak = {}",
+            Rc::strong_count(&leaf),
+            Rc::weak_count(&leaf),
+        );
+    }
+
+    println!("leaf parent = {:?}", leaf.parent.borrow().upgrade());
+    println!(
+        "leaf strong = {}, weak = {}",
+        Rc::strong_count(&leaf),
+        Rc::weak_count(&leaf),
+    );
+}