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From: marti@ethz.UUCP (Robert Marti)
Newsgroups: comp.lang.c++,comp.lang.misc,comp.lang.smalltalk,comp.lang.lisp,comp.lang.modula2
Subject: Re: C++ and other OOP Languages
Keywords: C++, OOPS
Message-ID: <832@ethz.UUCP>
Date: 26 Apr 89 10:08:19 GMT
References: <823@ethz.UUCP> <5971@pdn.paradyne.com>
Organization: ETH Zuerich
Lines: 55

In article <5971@pdn.paradyne.com>, alan@rnms1.paradyne.com (Alan Lovejoy)
writes:
| In article <823@ethz.UUCP> marti@ethz.UUCP (Robert Marti) writes:
| >A language is OO if
| >1) it supports data encapsulation (information hiding, abstract data types),
| 
| It must have classes.  A class can be instantiated.  Data encapsulation is 
| just a synonym for information hiding.  Sine you mention abstract data types 
| in your definition, however, you get at least 1/2 credit.

Thanks for the 1/2 credit :-)   At any rate, class instantiation is
not all that important to me, since it can be "simulated" in a
straightforward manner within more conventional languages.  I do
agree that it's a nice feature to have, though.

| So what's the difference between a class and an abstract data type?
| Comments?

Same difference as far as I am concerned.

| >[ A language is OO if ]
| >2) it supports inheritance (subclassing, extensible record types, ... )
| >   and
| 
| Extensibilty is NOT the same thing as inheritance.  Inheritance permits
| the definition of a new class in terms of the differences between the new
| class and the superclass.  An extension is only one type of difference.

Agreed.  Ideally you'd want to extend, restrict and override definitions
inherited from a superclass.

| >[ A language is OO if ]
| >3) it supports determination of the procedure body to be executed at the
| >   time of the actual procedure call (message passing, virtual functions).
| 
| Your language is ambiguous.  "At the time of the actual procedure call" could
| mean either at run time or at compile time.

I meant at run time, of course.

| If only at compile time, then
| this is the same thing as overloading.   If also at run time, then it is
| dynamic message-to-method binding.  Your parenthetical comment indicates
| you are referring to dynamic method binding (for which overloading is a
| prerequisite).

More violent agreement here :-)

| Alan Lovejoy; alan@pdn; 813-530-2211; AT&T Paradyne: 8550 Ulmerton, Largo, FL.

-- 
Robert Marti                      Phone:      +41 1 256 52 36
Institut fur Informationssysteme
ETH-Zentrum                       CSNET/ARPA: marti%inf.ethz.ch@relay.cs.net
CH-8092 Zurich, Switzerland       UUCP:       ...uunet!mcvax!ethz!marti