let count = Cell::new(0);
// Again, we have to move ownership if 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);
// 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);
}
}
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.