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From: marcap@concour.CS.Concordia.CA (Marc Pawlowsky)
Newsgroups: comp.lang.eiffel
Subject: Re: PEEVES
Message-ID: <886@clyde.Concordia.CA>
Date: 9 Jun 89 12:21:07 GMT
References: <882@clyde.Concordia.CA>
Sender: news@Clyde.Concordia.CA
Reply-To: marcap@concour.CS.Concordia.CA (Marc Pawlowsky)
Organization: Concordia University, Montreal Quebec
Lines: 31

> deutsch@parcplace.com (L. Peter Deutsch) writes
>
>2) deepCopy is not a semantically useful notion.  Where do you stop?  Do
>you copy classes as well as contents?  If an object has a reference to
>some widely shared data structure, do you copy that entire structure?
>What about references to objects like Symbols (in Smalltalk), where
>there is an invariant requiring unique representation of Symbols with
>the same contents?
>
>I believe providing a deepCopy operation is a mistake.  If it were up to
>me, it would be removed from the Smalltalk-80 system.

The deepCopy of Smalltalk is the same as Clone in Eiffel.  It copies 
the first level of pointers.  A common problem I have is that I am
working with mutable objects.  I am giving one specific example, but
I have hit this trouble often.

Gene = integer
Chromosome = set of genes
Population = set of chromosomes

A permissable operation on the population is "mutation" which changes a
genes value randomly with probability p(x).

A comparison is needed between the before and
after populations.

To do the comparison it is necessary to keep a copy of the population.
So, YES, the entire data structure should be copied.  If it takes a lot
of space the programmer must be careful.  This is a normal programming
problem.