I didn't know that I could do that!

So, I'm watching some videos on c++. Call it continuing education.

Now, I've never formally studied c++. It wasn't part of my education, and I learned it "on the job". I have tried to read and learn as I encountered things I didn't understand, and I like to think I know a lot of things about the language. I mean, I even got a gold tag badge for it on Stack Overflow. Surely I'm not completely ignorant. Right?

One of the talks I'm watching is highlighting some parts of the Core Guidelines. The presenter brings up a case that I actually faced recently.

1. You have a class with a const accessor method that returns the result of a computations (i.e. is not accessing a feature of the current implementation but a feature of the model that can be deduced from stored elements of the implementation)
2. That deduction is expensive enough that you want to cache the result.
3. You run into a conflict between the need to update the value of the cache and the desire to have the accessor marked const because it isn't changing any feature of the underlying model.

I'm happy to say that I didn't do the very bad thing (casting away the const), but I did lose the const marking on the accessor because I didn't know about mutable.

Crap.

Learn something every day.