Path: utzoo!attcan!uunet!mcsun!sunic!tut!tukki!sakkinen
From: sakkinen@tukki.jyu.fi (Markku Sakkinen)
Newsgroups: comp.object
Subject: Re: Evaluating "Object-Oriented" Programming Languages
Message-ID: <2669@tukki.jyu.fi>
Date: 12 Jan 90 08:01:28 GMT
References: <638@ajpo.sei.cmu.edu> <706@cui.unige.ch> <644@ajpo.sei.cmu.edu> <753@cui.unige.ch> <649@ajpo.sei.cmu.edu> <RMZ.90Jan12020729@jamhog.uio.no>
Reply-To: sakkinen@jytko.jyu.fi (Markku Sakkinen)
          SAKKINEN@FINJYU.bitnet (alternative)
Organization: University of Jyvaskyla, Finland
Lines: 49

In article <RMZ.90Jan12020729@jamhog.uio.no> rmz@jamhog.uio.no (Bjoern Remseth) writes:
>
>>  I too, would be interested in hearing from anyone with a different
>>  viewpoint, i.e., that Simula is somehow not "truly object-oriented." 
>
>I can think of two things:  
>
>First of all there  are a number  of fundamental  things that  are not
>"true" classes,  most   notably  all the  numbers and   texts.    This
>basically means  that  even  if they  are  there,  and  have a clearly
>defined protocol, a simula programmer can not make subclasses of them.

Note: This criterion applies likewise to most (if not all) OOPL's that
are extensions of conventional languages: Flavors, C++, Objective-C,
CLOS, ...  But I tend to agree that they are best regarded as
"partially object-oriented".

Question: However, isn't it actually bogus that all fundamental things
in _Smalltalk_ are first-class objects? For instance, how do you define
a use a meaningful subclass of SmallInteger, adding at least one
instance variable? (This is not a rhetorical question:
I have not used Smalltalk in practice and would be interested
to see an example.)

>Secondly it is possible  to "INSPECT" any  class instance.  This means
>that one can look into and modify the state of an object as if  it was
>a part of the local execution environment.  Since identifiers local to
>the inspected  object are used without  any form of  prefix it  is not
>possible  only by looking at  a statement inside the inspect statement
>to see if it sends a message to an object or not.
> [example deleted]

True, although in current Simula this can somehow be prevented by 'protected'
(and 'hidden') declarations. Only in very few languages is the encapsulation
of objects as tight as in Smalltalk. One can argue whether exactly
the Smalltalk model is the only right one: there are good reasons for
taking as the unit of encapsulation, either the object (as in Smalltalk)
or the class (as in most other class-based languages). 

As compared at least to C-based OOPL's, Simula has the advantage that
any protections established on the O-O level cannot be simply circumvented
on the lower level.

Markku Sakkinen
Department of Computer Science
University of Jyvaskyla (a's with umlauts)
Seminaarinkatu 15
SF-40100 Jyvaskyla (umlauts again)
Finland