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From: sakkinen@tukki.jyu.fi (Markku Sakkinen)
Newsgroups: comp.lang.eiffel
Subject: Re: global objects
Message-ID: <3477@tukki.jyu.fi>
Date: 21 Feb 90 07:43:17 GMT
References: <925@tuewsd.lso.win.tue.nl>
Reply-To: sakkinen@jytko.jyu.fi (Markku Sakkinen)
Organization: University of Jyvaskyla, Finland
Lines: 31

In article <925@tuewsd.lso.win.tue.nl> wsineel@lso.win.tue.nl (e.vriezekolk) writes:
>
>We want to define some classes, and create only one object of
>each class. The object names must be global, so that they can
> ...
>I realize that this conflicts with the pure object oriented
>principle, but it seems to be necessary in our project.

I cannot see any necessary conflict: there can well be useful and
"natural" classes such that they always have exactly one instance.
(That's one of the main reasons why some people claim prototype-based
object models to be better than class-based ones.)
If your design truly abounds with such classes, then its object
orientation may be questionable.

>Can anyone help us out? Are such global object possible in
>Eiffel?
> ...

The largest part of your problem can probably be solved by
"once functions" (OOSC 13.3). Some Eiffel expert please suggest
an elegant way to inhibit creating additional instances of
those classes.

Markku Sakkinen
Department of Computer Science
University of Jyvaskyla (a's with umlauts)
Seminaarinkatu 15
SF-40100 Jyvaskyla (umlauts again)
Finland
          SAKKINEN@FINJYU.bitnet (alternative network address)