Partial classes

From:

Adrian Hawryluk <adrian.hawryluk-at-gmail.com@nospam.com>

Newsgroups:

comp.lang.c++

Date:

Sun, 11 Mar 2007 14:51:45 GMT

Message-ID:

<5IUIh.32791$lY6.6371@edtnps90>

Can one define a partial class (first part containing constants like
enums) and then define the rest of the class elsewhere?

I ask this because I've had in the past needed to defined two classes
(call them A and B), each dependent upon the other. Class A requires
the enum type defined in Class B. An example follows:

<header file="A.h">
   #if !defined A_H
   # define A_H

   // Stub for forward referencing
   class A;

   # include ?B.h?

   class A
   {
     // Interface functions
     void f(B* b, B::b_e enums);
   ...
   };
   #endif
</header>

<header file="B.h">
   #if !defined B_H
   # define B_H

   // Stub for forward referencing
   class B;

   # include ?A.h?
   class B
   {
   public:
     enum b_e { enum1, enum2 };

     // Interface functions
   ...
   };
   #endif
</header>

The only way I see around this are:
1. Declare a public base class for B that contains the enums. It is not
    dependent on A so no problem occurs. It would be declared with the
    class B stub;
2. Declare the enums outside of class scope, removing the dependency
    lock. It would be declared with the class B stub;
3. Make a faux template class, making the class a stub. Haven't tried
    this.

Problems for each are:
1. Base classes would have a explicit size of 1, adding a small amount
    of overhead.
2. Enum is not scoped to a class.
3. A bit overkill if it does work.

Any thoughts?

Adrian

--
========================================================
          Adrian Hawryluk BSc. Computer Science
--------------------------------------------------------
  Specialising in: OOD Methodologies in UML
                    OOP Methodologies in C, C++ and more
                                 RT Embedded Programming
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