I need to get more information and/or people's experience with the
following OO related questions:


 + DLL/customer intergration: suppose your company writes
          an all OO project in obj-c or c++.  Your product pro-
          vides a fairly general out-of-the-box implementation of
          a certain function, say finding all work-in-progress
          and then prioritizing it.

          scenario: a customer wants to modify your default code
          (presumably in some executable) to better suit himself.
          You are prepared to supply all relavent header files
          and .o files from your original implementation.

         Question: after the customer derives a new sub-class
         and overrides member functions etc., how can a new
         executable be made?  How much do you need to provide
         a customer so that this type of specialization can
         be done?  Is there a better approach - say just making
         a hook in your code and allowing the customer to fill
         it


        + Suppose again, you are a company selling an all OO
          product in C++.  The customer would like to take
          your product and tightly integrate it with his own
          code but his is in C.  Again, you have some class structure
         than when instantiated can find all the work-in-progress
         and prioritize it.   The customer accepts your imple-
         mentation and just wants to get the list but in a C
         environment.   Is this possible?  Can you instantiate
         a C++ object from C?  How can the two types of object
         files be combined?

Thanks for any help, dialog, or suggestions.