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From: dag@control.lth.se (Dag Bruck)
Newsgroups: comp.object
Subject: Re: the need for classes as objects
Message-ID: <1990Aug29.071345.11084@lth.se>
Date: 29 Aug 90 07:13:45 GMT
References: <2259@esquire.UUCP>
Sender: newsuser@lth.se (LTH network news server)
Organization: Department of Automatic Control, Lund, Sweden
Lines: 58

In article <2259@esquire.UUCP> yost@esquire.UUCP (David A. Yost) writes:
>I've heard lispers and smalltalkers say that
>the ability of their languages to create
>classes at runtime is very powerful
>
>... I'm sure dynamic classes must
>make development environments better, but I'm
>particularly interested in examples not
>related to issues of the development
>environment.

I work on a research project aimed at developing a modelling and
simulation environment for control systems.  This is a development
environment, but at least not restricted to software...

Object-oriented concepts are used to describe models of control
systems (class hierarchies, component hierarchies, etc).

Because we use C++ as implementation language, we have had to
implement an additional layer for representing the models.  The reason
is just that C++ does not allow creation of classes at run-time. I
believe that limiting ourselves to a domain with some inherent
structure (control systems) has made the mechanisms for maintaining
and instantiating class hierarchies simpler, compared to the very
general mechanisms needed in a general-purpose programming language.

A discussion of why C++ classes cannot be used directly is found in:

	Bruck, Dag M (1988): "Modelling of Control Systems with C++
	and PHIGS," Proc. USENIX C++ Conference, Denver, CO, USA.

A follow-up paper (with some additional details, and new graphics) is:

	Bruck, dag M (1989): "Experiences of Object-Oriented
	Development in C++ and InterViews," Proc. TOOLS '89, Paris,
	France.

The ideas and concepts for describing control systems with OO
technology may in fact be the most interesting to you:

	Andersson, Mats (1989): "An Object-Oriented Modelling
	Environment," Proc. of the 1989 Simulation Multiconference,
	Rome. Italy.

	Andersson, Mats (1990): "Omola - An Object-Oriented Language
	for Model Representation," Technical Report TFRT-3208, Dept.
	of Automatic Control, Lund Institute of Technology, Box 118,
	S-221 00 Lund, Sweden.

Any comments or feedback are of course gratefully accepted.


Dag M. Bruck
--
Department of Automatic Control		Internet:  dag@control.lth.se
Lund Institute of Technology
P. O. Box 118				Phone:	+46 46-108779
S-221 00 Lund, SWEDEN			Fax:    +46 46-138118