Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!iuvax!maytag!watstat!dmurdoch
From: dmurdoch@watstat.uwaterloo.ca (Duncan Murdoch)
Newsgroups: comp.lang.pascal
Subject: Re: (one way to) Copying objects in Turbo Pascal 5.5
Message-ID: <1990May25.132722.29073@maytag.waterloo.edu>
Date: 25 May 90 13:27:22 GMT
References: <4878@plains.UUCP>
Sender: daemon@maytag.waterloo.edu (Admin)
Organization: University of Waterloo
Lines: 35

In article <4878@plains.UUCP> gus@plains.UUCP (jim gustafson) writes:
>>I'd like to have a constructor for an object that just copies another instance
>>of it or one of its descendants, and (the hard part) also copies the type
>>information.  
>
>Here's one way to get part of what you want.

Thanks for your reply.  Your program works fine, but isn't quite what I wanted.
Here's some more background:  maybe I'm just approaching the problem the wrong
way entirely.

I'm trying to write some objects for representing statistical datasets.  The
simple model I have in mind is that a dataset is a one dimensional array
of pointers to cases, and cases can be just about anything, but they're all 
descended from an object that contains a pointer to some data, and a method to 
return the size of the data.  (Since they're descendants, they may contain lots
of other stuff too.)

I've got a dataset constructor called copy that can duplicate a dataset by
making copies of all the pointers to cases.  I'm trying to add a method
for making copies of the cases as well, in case I do some kind of destructive
manipulation of them, and don't want to lose the originals.

The problem is that this is a dataset method, and the dataset object only
knows about the base case object.  I guess I can give each case type a virtual
method that knows how to make a duplicate of itself, but I'd like to avoid
the work:  if I can write a method once for the base that can perform the
duplication on any descendant that sticks to the basic form described above,
it'll be that much easier to use.

By the way, since yesterday I've pored through the OOPS manual and think I
can do what I want by writing the constructor in assembler.  I'd rather 
avoid that, so I'm still hoping for alternative suggestions.

Duncan Murdoch