Design Problem Aggregation

From: Merlin (merlin2769_at_hotmail.com)
Date: 05/10/04 

Date: 9 May 2004 15:54:24 -0700

Hi

Imagine the following classes (A class diagram will help)

BASE, A, B, C, D, E, F, G.

A, B, C, D, G inherit from BASE.

E, F inherit from D.

Class E has a member (aggregation by value) of type A.
Class F has a member (aggregation by value) of type B.

Class G has a member that is container that can accept objects of type
D. As D is the base class of E and F we can add to the container
objects of type E or F. I have made the container type safe in this
way.

I wanted G to be a collection of objects of type A or B but never C so
I introduced an abstract class D and made the container of that type
so it would only accept objects of base type D. However, although this
looks ok, I am not happy with the extra work it has created.
As I need to access the interface to A and B, I need to repeat all
that interface in E and F. A and B have many member functions and I
dont want to rewrite all that interface in E and F and delegate the
calls to the aggregate.

The solution where I provide a member function in classes E and F to
return the aggregate seems wrong as its exposing a private data
member.

How can I change my design to make it better and flexible?

I have intentionally used meaningless letters in order to focus on the
relationships of the classes as oppose to what they model.
I hope this wont confuse anyone.

Many Thanks in advance

Relevant Pages

  • Re: Design Problem Aggregation
    ... > Classes A, D, F, G, J inherit from BASE. ... > Class H has a member of type C. ... As G is the base class of H and I we can add to the container ... this case that it must be a reference or pointer to BASE (note that H and I ...
    (comp.lang.cpp)
  • Re: Design Problem Aggregation
    ... Something else also has to inherit from A or else B is an identity set ... > Class H has a member of type C. ... As G is the base class of H and I we can add to the container ... > that interface in H and I. C and E have many member functions and I ...
    (comp.object)
  • Re: Design Problem Aggregation
    ... Classes A, D, F, G, J inherit from BASE. ... Class H has a member of type C. ... Class J has a member that is container that can accept objects of type ... As I need to access the interface to C and E, ...
    (comp.object)
  • Re: Design Problem Aggregation
    ... > A, B, C, D, G inherit from BASE. ... > Class E has a member (aggregation by value) of type A. ... > Class G has a member that is container that can accept objects of type ...
    (comp.lang.cpp)
  • Design Problem Aggregation
    ... A, B, C, D, G inherit from BASE. ... Class E has a member (aggregation by value) of type A. ... Class G has a member that is container that can accept objects of type ...
    (comp.lang.cpp)