re-do deepaksirone's fix on the actual source file

[rust-101.git] / workspace / src / part12.rs

diff --git a/workspace/src/part12.rs b/workspace/src/part12.rs
index a3519957ca7dbfcf0d207f6004c3fa3df909ff1e..1593e8ab03ecb0fe55b060f40179c3dcc96a2d81 100644 (file)
--- a/workspace/src/part12.rs
+++ b/workspace/src/part12.rs
@@ -13,7 +13,7 @@ struct Callbacks {
 
 impl Callbacks {
     pub fn new() -> Self {
-        unimplemented!()
+        Callbacks { callbacks: Vec::new() }
     }
 
     // Registration works just like last time, except that we are creating an `Rc` now.
@@ -46,9 +46,9 @@ pub fn main() {
 fn demo_cell(c: &mut Callbacks) {
     {
         let count = Cell::new(0);
-        // Again, we have to move ownership if the `count` into the environment closure.
+        // Again, we have to move ownership of the `count` into the environment closure.
         c.register(move |val| {
-            // In here, all we have is a shared borrow of our environment. But that's good enough for the `get` and `set` of the cell!
+            // In here, all we have is a shared reference of our environment. But that's good enough for the `get` and `set` of the cell!
             let new_count = count.get()+1;
             count.set(new_count);
             println!("Callback 2: {} ({}. time)", val, new_count);
@@ -69,11 +69,10 @@ struct CallbacksMut {
 
 impl CallbacksMut {
     pub fn new() -> Self {
-        unimplemented!()
+        CallbacksMut { callbacks: Vec::new() }
     }
 
     pub fn register<F: FnMut(i32)+'static>(&mut self, callback: F) {
-        let cell = Rc::new(RefCell::new(callback));
         unimplemented!()
     }
 
@@ -82,7 +81,7 @@ impl CallbacksMut {
             // We have to *explicitly* borrow the contents of a `RefCell` by calling `borrow` or `borrow_mut`.
             let mut closure = callback.borrow_mut();
             // Unfortunately, Rust's auto-dereference of pointers is not clever enough here. We thus have to explicitly
-            // dereference the smart pointer and obtain a mutable borrow of the content.
+            // dereference the smart pointer and obtain a mutable reference to the content.
             (&mut *closure)(val);
         }
     }
@@ -104,7 +103,6 @@ fn demo_mut(c: &mut CallbacksMut) {
     c.call(1); c.clone().call(2);
 }
 
-// **Exercise 12.1**: Change the type of `call` to ask only for a shared borrow. Then write some piece of code using only the available, public
-// interface of `CallbacksMut` such that a reentrant call to `call` is happening, and the program aborts because the `RefCell` refuses to hand
-// out a second mutable borrow to its content.
+// **Exercise 12.1**: Write some piece of code using only the available, public interface of `CallbacksMut` such that a reentrant call to a closure
+// is happening, and the program panics because the `RefCell` refuses to hand out a second mutable borrow of the closure's environment.