Path: utzoo!attcan!uunet!mcvax!enea!naggum!isncr!m2cs!frode
From: frode@m2cs.naggum.se (Frode Odegard)
Newsgroups: comp.lang.misc
Subject: Re: object oriented design decision
Summary: The trouble with multiple inheritance is perhaps an increased
	 danger of structure breakdown
Message-ID: <110@m2cs.naggum.se>
Date: 20 Nov 88 23:04:17 GMT
References: <4086@enea.se>
Organization: Modula-2 CASE Systems A.S, Oslo, Norway
Lines: 57

In article <4086@enea.se>, sommar@enea.se (Erland Sommarskog) writes:
>  
> I fail to see what is bad with multiple inheritance. If I want to
> store an object in a tree and a linked list simultaneously, what is
> wrong with my class structure?
> 
> -- 
> Erland Sommarskog
> ENEA Data, Stockholm
> sommar@enea.se
> A radio station is a four-letter word.


Some people are worried about the dependency problems and structure
implications of allowing multiple inheritance. To my knowledge,
Eiffel is the only commercial system which supports multiple inheritance
[except LISP-based systems?] and it will be interesting to see if
the reactions will continue to be so positive as they've claimed them
to be so far..

The company I work for is developing an advanced Modula-2 environment
where a lot of the effort in supporting large-scale projects (i.e.
multi-site, 200,000+ loc etc..) has gone into designing formal notations
for defining architecture and dependency demands which go beyond the
scope of the Modula-2 itself. I guess the conclusion we've reached
is that it is easier to solve structural problems (like dependency
management) when the language is simple, rather than have a HUGE
language for which it is difficult to build an equally powerful
environment [look at Ada: only Rational has been able
to come up with a decent environment, and that's 2 million lines
of Ada code, they claim].

The OOP fever has many similarities to the RISC fever. People seem
to think that as long as something is O-O it is good. This is simply
not true. Using notations which support refinement and extension of
previously written software components is going to help you in terms
of productivity, but you're still going to get maintenance problems
and in an environment like Smalltalk, you just don't go in and
fiddle too much with class dependencies :-)

National Semiconductor (which hasn't announced any RISC processor
yet) has stated that "RISC is a technology - not a product". Perhaps
it is time to be more rational about OOP, too. OOP is a new approach
to problem-solving, it's exciting, but it's not the only way of
getting good results. Sometimes it can be worth the trouble to mix
O-O approaches with others. Our Modula-2 environment, for example,
is based around a distributed object-oriented database, but we
didn't create an O-O database *programming* language. There's a new
notation for declaring database classes, but the methods are implemented
in standard Modula-2.

Sigh..I know...I know...not of all this deals with multiple inheritance,
but I got kinda carried away.

See U all on the bit-stream!

				- Frode