Path: utzoo!mnetor!uunet!husc6!mailrus!ames!claris!apple!dan
From: dan@Apple.COM (Dan Allen)
Newsgroups: comp.lang.c++
Subject: Critique of Wiener/Pinson
Message-ID: <8063@apple.Apple.Com>
Date: 12 Apr 88 18:15:19 GMT
Reply-To: dan@apple.UUCP (Dan Allen)
Organization: Apple Computer Inc, Cupertino, CA
Lines: 83
Keywords: Object-oriented,abstract data types,C++,definitions

A brief critique of:

        "An Introduction to Object-Oriented Programming and C++"
        (Richard S. Wiener & Lewis J. Pinson.  Addison-Wesley.
        ISBN 0-201-15413-7.)

follows.

Wiener & Pinson is definitely a needed book, as Stroustrup's book is
somewhat hard to read, a fact admitted by many on the network.  However,
Wiener & Pinson (W&P) has a few flaws itself...

My main concerns are with some of the definitions of object-oriented
programming.  At the last main conference on object-oriented
programming, OOPSLA '87, Peter Wegner's paper entitled "Dimensions of
Object-Based Language Design" gave the following definition of what it
means for a language to be object-oriented:

  object oriented = objects + classes + inheritance

Further definitions of these terms define objects to be instances of a
class, and classes to be an organizational tool that allows inherited
qualities to be passed to subclasses, etc.

Now for the problems.  Wegner goes on to define data-abstraction as an
ORTHOGONAL attribute to object-orientedness, for the following
reason(s):  data abstraction and the notion of abstract data types
provide for the description of a data structure and some associated
function and procedures that have sole access to the data structure.
Wegner's point is that object-oriented languages allow access to the
underlying data structures BY DIRECT REFERENCE rather than only through
the (to use OO language) associated methods of the class.  OO languages
can also use functions and procedures to access the data structure as
well.

Well, W&P do not make this distinction.  Pages 1,2, and 57-58
particulary are full of definitions that are not in keeping with the
main body of OO language designers.

Now, what is C++ then?  Well, C++ is interesting in that its classes
are, by default, supportive of abstract data types and the data
abstraction paradigm by making fields of a class private.  (Remember,
private data = Data Abstraction.)

C++ also supports object-oriented programming by allowing fields to be
declared public.  (Public data = Object-Oriented if inheritance is also
supported, which it is in C++).

Now there is a definitional problem at hand: what if some fields are
public and some fields are private?  C++ has created a new definitional
problem.

I must point out that W&P is fairly consistent internally with the
definitions that are used.  My gripe is that they are using the same
terms as the mainline Object-Oriented world, but with new and changed
definitions.

A few more guidelines with the definitions that I subscribe to:

**	Ada is NOT object-oriented.  Ada does support data abstraction.

**	Object Pascal IS object-oriented, but does NOT support data ab.

**	Modula-2 is NOT object-oriented.  It does support ADTs.

**	C++ supports both object-oriented programming & ADTs, though not
	at the same time.  (Stroustrup's definitions are more in line,
	by the way, with mine and Wegner's than with W&P.)

Sorry for the long flame about definitional problems, but I have been
working with object-oriented languages for several years here at Apple
and have found them a little hard to teach to people because of problems
such as these.

When Stroustrup came to Apple recently, he spoke about such matters and
he seems to have a good understanding of these issues.  His talk also
was much more understandable than his book, so if you ever get the
chance to hear him, make sure to take advantage of it.  You'll enjoy it.
I did.

Dan Allen
Software Explorer
Apple Computer