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From: wmueller@herodotus.rdrc.rpi.edu
Newsgroups: comp.lang.lisp
Subject: change-class and additional parameters
Message-ID: <=1+$+~^@rpi.edu>
Date: 29 May 90 15:04:06 GMT
Article-I.D.: rpi.=1+$+~^
Reply-To: wmueller@herodotus.rdrc.rpi.edu ()
Organization: Rensselaer Polytechnic Institute, Troy NY
Lines: 26

Hi, netlanders !

I have a problem to change the class of some of my objects. Especially the
initialization of the new instance via update-instance-for-different-class makes 
some problems. In some of my cases the initialization after a change-class depends 
on the local environment, from where the change of the class was ordered. You might 
think here of a time dependent initialization, where the time belongs to a local
environment. The problem is how can I tell update-instance-for-different-class
about the time. However, change-class accepts only the old instance and the new class
as parameters. So far, the only apparent solutions for this problem:

	- temporary storage of the environment information in global variables

	- storage of the needed environment variables in the instances

	- update of the instances outside of change-class (this means the status
	  of the instance is undefined after a change-class !)

	- rewrite of change-class to accept additional parameters

None of these solutions makes me very happy. Is there a cleaner solution 
for this problem?
-------------------------------------------------------------------------------
Wolfgang Mueller                                          wmueller@rdrc.rpi.edu
Rensselaer Design Research Center
Rensselaer Polytechnic Institute, Troy, NY 12180-3590   Phone:   (518) 276-2733