Re: Need some design idea input

Carl Barron <>
6 Jan 2007 11:36:30 -0500
In article <>,
Chris <> wrote:

This may seem like a really dumb question, but I am having a design
hiccup that I can't seem to get past. It all resides on currently
existing classes that I am trying to inherit from and create children
to. However, this is the problem I can't seem to get around. Here's
the problem:

class Parent1

    //constructors, etc...

    virtual void DoThis();
    virtual void DoThat();


    Parent2* pBase;

class Parent2

   //constructors, etc...

   virtual void ParseThis();
   virtual void ParseThat();

Although, the classes I have are more complicated than this.

Let's say I want to create a child class from Parent2 that add more
methods and may or may not re-define ParseThis/ParseThat. What I
really need are new methods. I then need to create a type of this
child that has these new methods. However, I can't just store it in
pBase because then I can't access the new methods. The only thing I
can think of that is possible is to create a new Parent1 object that
has a new data member for the parent2 child, but then that leaves a
dangling pBase that I don't want to have to worry about. Not only
that, but if DoThis() and DoThat() call methods from pBase, I need to
redefine EVERY method in Parent1 that accesses this pointer and re-do
all the code using a new variable name. This may seem like a really
elementary problem (even though I can't remember ever having to conquer
something like this before...), and I'm sure there must be some better
way of doing this. I was thinking of templates somehow, but I can't
see how that would fix the problem...

Any help or pointers on some design ideas would be greatly appreciated!


  How about a new base class that has the virtual newer functions and a
classs derived from this base class that provides do nothing or
otherwise safe implementations of the newer functions? The the already
written classes derive from this derived class such as:

  struct A // new Base class
      virtual void newer()=0;
      virtual void foo() = 0;
      virtual ~A(){}

   struct B:A // old Base class
      void newer(){}

   All the older written clases derive from B. the newer from A. and an
A * is used to store a pointer to base class.

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