Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!wuarchive!uunet!abvax!iccgcc!klimas
From: klimas@iccgcc.decnet.ab.com
Newsgroups: comp.object
Subject: Re: Examples of Multiple Inheritance?
Message-ID: <2277.275bdf0b@iccgcc.decnet.ab.com>
Date: 4 Dec 90 22:38:19 GMT
References: <60700005@inmet>
Lines: 33

In article <60700005@inmet>, stt@inmet.inmet.com writes:
 
> Our hypothesis is that multiple inheritance can rarely be useful
> unless planned for in advance, which seems to defeat the purpose.
> If it does require advance planning, then we anticipate that those
> situations would be amenable to other structures, perhaps, for example,
> a component with a pointer to its enclosing object.
> 
> Multiple inheritance seems to add significant overhead to an OOPL even
> when not being used in a system, so we are looking for convincing
> examples that it's benefits outweigh the cost.

	A few comments, 

	1)I have thrown out the same challenge to the Smalltalk
	community (yes ST-80 once had it and ST /V286 does support MI in the 
	hierarchy via a simple change to Behavior, and there have been 3rd 
	party add on browsers for V/286) for quite a while now, and I have 
	not gotten any substantive examples other than simple mixins to date.

	2)This is not a new topic. Per Borning and Engals 1982 "M. I. in ST-80"
	Proc. of the Ntnl. conf. on AI, "The attempts at MI have not achieved
	the elegance and simplicity of single inheritance."

        3)A lot of people claim that MI is a strength of C++, however a number
	of companies that are developing in C++ also have internal policies that
	prohibit the use of MI because of the potential for unmanageable
	complexity explosions in solutions that are of any size.  With MI in
	C++, the user must now know about how every class and method is used
	so that if he inserts a class in the hierarchy he won't break it.  This
	goes against the idea of "comprehension avoidance", i.e. for effective
	programming, limit the amount of stuff a programmer needs to know 
	about a system to interact with it. 


Brought to you by Super Global Mega Corp .com