Re: Virtualization of a 'protected interface'

=?ISO-8859-1?Q?Marcel_M=FCller?= <>
Mon, 04 May 2009 22:04:45 +0200
Michael Doubez wrote:

An ugly way to do it is to add a static member function in MyBase that
calls InternalService on its parameter:

class MyBase
  static void DoInternalService(MyBase& b)

Hmm, this it is not only ugly but also seems to be the only solution
without a significant overhead. I would say it is OK to me. The nice
part is that it does not mess the public interface. I think I will go
that way.

And use it in MyImplementation:
    void InternalService()

Note that this kind of design if brittle and it breaks encapsulation.

Well, there is almost no application out there that does not break any
design rule. :-/
As long as the ugly parts are safely encapsulated, it will not be the
source of many maintenance problems. I did really more ugly core logic
in this application. First of all the virtualization of an C-style
plug-in interface that required me to infer an object instance from a
callback function's address. But I have a type safe template wrapper
that transforms a member functions pointers and an object instance into
a static function pointer with the same signature. This really dirty and
non portable hack have not been the source of any problem in the last years.



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