Implementing multiple interfaces in c++

Question

I have the interface hierarchy as follows:

class A
{
public:
 void foo() = 0;
};

class B: public A
{
public:
void testB() = 0;
};

class C: public A
{
publi         


        

Answer 1

I think what you are asking is, how do I create a second class hierarchy of implementations that mirrors my "interace" class hierarchy. You want to do this to reduce the coupling between your interface and implementations. Your problem is that you think your implementation classes should extend your interface classes but also the "natural" inheritance hierarchy in the impl classes, as in

   AImpl
  ^    ^
  |    |
BImpl  CImpl

I suggest you look at the GoF (Gang of Four) Bridge pattern that describes this pattern. Actuall, the example in the book is better than that on Wikipedia but can't seem to find it online. Here's a rough (ascii) UML:

Window <>imp----------------------------> WindowImpl
^    ^                                    ^        ^
|    |                                    |        |
|   TransientWindow                       |     PMWindowImp
IconWindow                              XWindowImp

In the example above, you have a Window class whose #imp references the impementation. So, your IconWindow implementation will have #imp referencing, say XWindowIconWindow to perform the real work but clients will only ever reference it through the IconWindow instance. This reduces your recompile overhead.

The salient points to make are:

• Separate class hierarchy for window types (normal window, icon window, dialog) and window implementations (X-windows, PMWindows). They can be extended independently.
• Operations are implemented in terms of abstract operations on WindowImp So, operations are abstracted from platform specifics.
• Reduce prolieferation of classes that occurs if you try to mix the abstractions and multiple implementations.

I'll leave it to you to translate this to your problem but comment if you have any trouble.