Hiding a C++ class in a header without using the unnamed namespace

Question

I am writing a C++ header in which I define a

class A {
   // ...
};

that I would like to hide from the outside world (because it may chang

Answer 1

If A is an implementation detail of B, don't put its definition in the header at all. Instead:

class B {

   ...
   class A * myA;
};

and then put the definition of A in the B implementation (i.e. .cpp) file.