From addc4ab037ed8d0635841e5ca9db3a1768c42a11 Mon Sep 17 00:00:00 2001
From: Jordan Gong <jordan.gong@protonmail.com>
Date: Mon, 21 Sep 2020 15:27:25 +0800
Subject: Mutate immutable data `RefCell`

---
 smart_pointer/src/main.rs | 28 +++++++++++++++++-----------
 1 file changed, 17 insertions(+), 11 deletions(-)

(limited to 'smart_pointer')

diff --git a/smart_pointer/src/main.rs b/smart_pointer/src/main.rs
index 6778671..a812ca0 100644
--- a/smart_pointer/src/main.rs
+++ b/smart_pointer/src/main.rs
@@ -1,7 +1,9 @@
 // Recursive type using boxes
 use std::rc::Rc;
+use std::cell::RefCell;
+#[derive(Debug)]
 enum List {
-    Cons(i32, Rc<List>),
+    Cons(Rc<RefCell<i32>>, Rc<List>),
     Nil,
 }
 
@@ -39,7 +41,10 @@ fn main() {
     println!("b = {}", b);
 
     use crate::List::{Cons, Nil};
-    let list = Cons(1, Rc::new(Cons(2, Rc::new(Cons(3, Rc::new(Nil))))));
+    let list = Cons(Rc::new(RefCell::new(1)),
+       Rc::new(Cons(Rc::new(RefCell::new(2)), 
+       Rc::new(Cons(Rc::new(RefCell::new(3)),
+                    Rc::new(Nil))))));
 
     // Dereferencing
     let x = 5;
@@ -81,13 +86,14 @@ fn main() {
     drop(c);
     println!("CustomSmartPointer dropped before the end of main.");
 
-    let a = Rc::new(Cons(5, Rc::new(Cons(10, Rc::new(Nil)))));
-    println!("count after creating a = {}", Rc::strong_count(&a));
-    let b = Cons(3, Rc::clone(&a));
-    println!("count after creating b = {}", Rc::strong_count(&a));
-    {
-        let c = Cons(4, Rc::clone(&a));
-        println!("count after creating c = {}", Rc::strong_count(&a));
-    }
-    println!("count after c goes out of scope = {}", Rc::strong_count(&a));
+    let value = Rc::new(RefCell::new(5));
+    let a = Rc::new(Cons(Rc::clone(&value), Rc::new(Nil)));
+    let b = Cons(Rc::new(RefCell::new(3)), Rc::clone(&a));
+    let c = Cons(Rc::new(RefCell::new(4)), Rc::clone(&a));
+
+    *value.borrow_mut() += 10;
+
+    println!("a after = {:?}", a);
+    println!("b after = {:?}", b);
+    println!("c after = {:?}", c);
 }
-- 
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