"Interior Mutability" should use Mutex, not Cell/RefCell

[djmitche]

Cell and RefCell are pretty advanced for introducing interior mutability -- a mutex is much more familiar territory.

Mention Cell and RefCell in the speaker notes as alternatives to Mutex for more specific situations.

[hurryabit]

I don't think a mutex is a good idea for this course since we don't handle any form of concurrency here.

A good analogy to explain Cell/RefCell could be the mutable keyword from C++. In combination with a better example, maybe something about caching values or lazy initialisation, this should the concept pretty easy to grasp.

[djmitche]

The argument for Mutex is that it's a pretty familiar way to ensure, at runtime, that only one thing is accessing the value inside. Which is really the crux of interior mutability: you can get an exclusive reference from an immutable reference, but somehow you need to guarantee that is the only one.

Cell just has methods that take &self but actually mutate the value (and references concurrency for the safety of this operation), while RefCell is a new concept.

At any rate, I think the slide should focus on the concept, leaving the particular std type used to achieve the interior mutability as an incidental detail.