I like the idea of teaching about RefCells, but I feel like this exercise would have to be somewhat more sophisticated... I'd like people to be able to see the difference of behaviour between the normal compile-time borrow check and what RefCell provides, maybe a more engaging exercise format could be converting something that's impossible with normal borrowing rules to using RefCell?

Thanks for taking a look @shadows-withal. I agree the example could be more sophisticated and I will look into updating it. Potentially following the Rust Book more closely is a good direction to take.

@shadows-withal I have updated the example to use thecompile instead oftest mode. I think this make the logic considerably simpler. The example is a straightforward example of using a RefCell to mutate via an immutable reference.

I think since this may be the first introduction to RefCell a user has, it's simplicity is a feature. Happy to adjust as necessary.

The exercise teaches the usage ofRefCell very well, but not reallywhen to use it. It might be just confusing why the user shouldn't use&mut self since aRefCell is not really required in this example at all.

The exercise teaches the usage ofRefCell very well, but not reallywhen to use it. It might be just confusing why the user shouldn't use&mut self since aRefCell is not really required in this example at all.

I see -- that's fair. At the risk of making the example more convoluted I can update the example to provide a scenario where refcell is a necessity.

I am a very new maintainer. Let's wait for the feedback from @shadows-withal first :D

I think exercises on Cell, RefCell, RwLock and Mutex in sequence would be nice. I remember there was a video that explained when these smart pointers become useful quite nicely. It explains why and when interior mutability is required.
The dude took the construction of a graph and updating the value of a node & its neighbors as the running example throughout the vid. If you want, I could link it!

PS: I'm sorry if exercises on these features have already been discussed and decided. I just finished all exercises and was wondering why these weren't included. BTW doing god's work, you guys! Thank you so much for creating this project!