Path: utzoo!attcan!uunet!husc6!rutgers!att!ulysses!hector!jss
From: jss@hector.UUCP (Jerry Schwarz)
Newsgroups: comp.lang.c++
Subject: Re: C++, Objectivce-C and projects..
Message-ID: <10854@ulysses.homer.nj.att.com>
Date: 14 Nov 88 18:15:26 GMT
References: <5155@thorin.cs.unc.edu> <6639@spool.cs.wisc.edu> <5263@thorin.cs.unc.edu>
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Reply-To: jss@hector.UUCP (Jerry Schwarz)
Organization: AT&T Bell Laboratories
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In article <5263@thorin.cs.unc.edu> coggins@cs.unc.edu (Dr. James Coggins) writes:
>
>This is an interesting comment since the (in-person) discussion that
>led to my original posting arrived at a concensus that C++ classes are
>NOT ADTs and that Smalltalk classes are closer to ADTs.
>
>(an ADT consists of data, procedures, and axioms that define consistent
>states of the structure.  Most discussions and all implementations forget
>about the axioms.)
>

I do not think this is a correct description of Abstract Data Types.
The usual presentations of ADT involve axioms (commonly in the form
of equations) that say something about the abstract values and do not
refer to the internal state of data structures.  There will also be
some way of relating the "concrete" representation to the "abstract"
value being represented.  The aspect that most clearly distinguishes
ADT from OO is that using an ADT approach one does not define
operations that modify the state of a value.  (It makes no more sense
to modify the state of an abstract value than it does to modify the
number 2.)

For the record, I believe both ADT and OO, (and some other
programming frameworks I won't name here) are each appropriate for
certain problems.   One of the attractive aspects of C++ is that it
allows a wide variety of approaches to be used efficiently.

Jerry Schwarz
AT&T Bell Labs, Murray Hill