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From: graulich@cadis.de (Robert Graulich)
Newsgroups: comp.lang.beta,comp.lang.eiffel,comp.object
Subject: Re: On why BETA does not have multiple inheritance
Date: 22 Sep 1994 12:33:57 +0200
Organization: Cadis GmbH
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References: <358nrv$bpf@engnews2.Eng.Sun.COM> <DERWAY.94Sep15123648@alumni.ndc.com> <35jb33$3q1@engnews2.Eng.Sun.COM>
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olm@Eng.Sun.COM (Ole Lehrmann Madsen) writes:

>derway@ndc.com (D. Erway) writes:


...

>> Ole> As a final example, consider the following well-know MI case:


>> Ole> 			Window
>> Ole> 	               /       \	
>> Ole> 	WindowWitBorder		WindowWithTitle
>> Ole> 		      \		/	
>> Ole> 		WindowWithTitleAndBorder

Hi!

Please excuse me intruding your discussion, but I want to point out
the following.

With inheritance you express the relationship "A is B"
(in C++ class A : public B {}).
But in this example you want to model WindowWithTitleAndBorder HAS
WindowWithBorder and WindowWithTitle or even better
WindowWithTitleAndBorder HAS Border and Title.
But you say that WindowWithTitleAndBorder IS WWB and WWT.
Thats not true. When a class wants to HAVE something, this should
be layered.

(in C++:
class WindowWithTitleAndBorder
{
  Border b;
  Title  t;
};)

What do you think about this? I think using MI at the right point is
good, but this is the situation, which can nobody predict.
(Because in C++ you must say if a base class is virtual or not.
But a library designer cannot predict it all. So why using
MI where it is no needed???)

Greetings,
Robert Graulich