C++ templates that accept only certain types

Question

In Java you can define generic class that accept only types that extends class of your choice, eg:

public class ObservableList {
  ...
         


        

Answer 1

Is there some simple equivalent to this keyword in C++?

No.

Depending on what you're trying to accomplish, there might be adequate (or even better) substitutes.

I've looked through some STL code (on linux, I think it's the one deriving from SGI's implementation). It has "concept assertions"; for instance, if you require a type which understands *x and ++x, the concept assertion would contain that code in a do-nothing function (or something similar). It does require some overhead, so it might be smart to put it in a macro whose definition depends on #ifdef debug.

If the subclass relationship is really what you want to know about, you could assert in the constructor that T instanceof list (except it's "spelled" differently in C++). That way, you can test your way out of the compiler not being able to check it for you.