Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!rochester!pt.cs.cmu.edu!wb1.cs.cmu.edu!ram
From: ram@wb1.cs.cmu.edu (Rob MacLachlan)
Newsgroups: comp.sw.components
Subject: Re: Inheritance vs. component efficienc
Message-ID: <5186@pt.cs.cmu.edu>
Date: 11 Jun 89 13:42:52 GMT
References: <130200002@p.cs.uiuc.edu> <5731@hubcap.clemson.edu>
Organization: Carnegie-Mellon University, CS/RI
Lines: 27


Far be it from me to for a university research programmer to tell a real
software engineer about how to develop reusable maintainable software.
But...  It seems to me that anyone trying to develop highly reusable
software components has a thing or two to learn from object-oriented
development systems.

As I see it, the key barrier to reusing software is that systems don't
naturally break down into atomic reusable components.  Supposing I had this
whizzy indexed library of frobs, and I wanted a green frobboz.  But when I
look, I probably won't find one.  I could maybe make do with the
yellow-green one, but I would have to work around it or modify it.  

The advantage of an o-o inheritance system is that it makes it very easy to
reuse a component *with modifications*.  If you have to modify a component
without understanding how it works, then you are much better off with the
structured modification techniques of inheritance and method combination
than if you attempted arbitrary modification of the code.

I personally think you are wacko if you think that there are going to be
very many components reusable millions of times without modification, at
least if defined in Ada.  I can conceive of there being a "programming
environment" someday that could substantially automate the process of
customizing components, but it's going to have to pay a lot more attention to
semantics than Ada does.

  Rob
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