I posted this to comp.std.c++, but I guess I was supposed to mail it
so I'm mailing it now :-)

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I've got a question about forward declaring a class as a sub-class of
another class.  Is it possible under the C++ draft standard to do
something like:

  class S;
  class T : public S;

The reason I need such a thing is because of the restrictions placed on
redefining the return type of a virtual function.

A simplified version of my class layout is:

class S;
class T;  // This should be something to tell the compiler that
          // class T exists and that it's a subclass of S.

class A {
  public:
    virtual S& belong() = 0;
};

class B : public A {
  public:
    virtual T& belong();                 // This doesn't work but it seems
                                         // that it should be possible!
  private:
    T& myT;
};

class S {
  public:
    virtual A& get() = 0;
};

class T : public S {
  public:
    virtual B& get();                   // This works fine
  private:
    B& myB;
};

I guess a possible solution would be for the redefinition test to be done
on the definition instead of on the declaration.

Is there any hope?

Thanks,
Bradford Mott


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