Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!asuvax!intertel!wohlenbe
From: wohlenbe@intertel.UUCP (Greg Wohlenberg)
Newsgroups: comp.lang.c++
Subject: Abstract Base Class Enforcement
Keywords: class, abstract, c++
Message-ID: <358@intertel.UUCP>
Date: 22 Mar 91 22:01:24 GMT
Organization: Inter-Tel, Inc., Chandler, AZ
Lines: 23

Hi,

     I've  got  a question.   Say you have  a base  class that  you want to be
abstract.  But, for one reason or another, it  isn't convenient to make any of
the  class's virtual functions  pure.  (This would happen  if all your virtual
functions actually "do something" in the base class.)  Given that you  want to
disallow instances of  the abstract base  class from  being created, which  of
these alternatives is best?

1. Create a extra do-nothing function in the base class that is pure virtual.

2. Make the base class's no-parameter constructor "protected".  This  makes it
so only  derived classes  are able to create instances  of the base class (and
therefore enforces the abstract characteristic of the base class).

     Or, is there another alternative that I am not aware of?

Thanks,

Greg Wohlenberg          |    Voice: (602) 961-9000
Inter-tel, Inc.          |      Fax: (602) 961-1370
6505 W. Chandler Blvd.   | INTERNET: wohlenbe%intertel.uucp@asuvax.eas.asu.edu
Chandler, Arizona, 85226 |     UUCP: intertel!wohlenbe@asuvax.eas.asu.edu