Path: utzoo!attcan!uunet!odi!valens!dlw
From: dlw@valens.odi.com (Dan Weinreb)
Newsgroups: comp.lang.c++
Subject: Re: Use of inheritance for classification?
Message-ID: <329@odi.ODI.COM>
Date: 16 May 89 19:06:40 GMT
References: <30582@apple.Apple.COM> <10248@riks.csl.sony.JUNET>
Sender: news@odi.com
Followup-To: comp.lang.c++
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In-reply-to: riks@csl.sony.JUNET's message of 15 May 89 01:45:43 GMT

In article <10248@riks.csl.sony.JUNET> riks@csl.sony.JUNET (Rik Smoody) writes:
   In article <30582@apple.Apple.COM> kmcentee@Apple.COM (Kevin McEntee) writes:
   >should take place only in the context of the is-a relationship.
   >
   >    e.g.  Every dog is a mammal.
   But not all dogs are frisbeeCatchers. 
   Do I need a special sub-class?

In just about all of the popular object-oriented languages, an object
is a direct member of exactly one class.  So if you need special
behavior for frisbee_catchers, then yes, you really do need a special
class.  Of course, there's no hope here without multiple inheritance,
since ability to catch frisbees is orthagonal to biological order.
The graph would look like this:

  mammal   frisbee-catcher
    |        |
   dog       |
    |        |
    \        /
   frisb-o-pup

This is perfectly consistent with the original claim.  A frisb-o-pup is a dog,
a dog is a mammal, and a frisb-o-pup is a frisbee-catcher.