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From: snorri@rhi.hi.is (Snorri Agnarsson)
Newsgroups: comp.object
Subject: Re: Evaluating "Object-Oriented" Programming Languages
Message-ID: <1443@krafla.rhi.hi.is>
Date: 4 Jan 90 12:21:45 GMT
References: <638@ajpo.sei.cmu.edu>
Organization: University of Iceland
Lines: 69

From article <638@ajpo.sei.cmu.edu>, by eberard@ajpo.sei.cmu.edu (Edward Berard):
>         ...
> 	- Static Versus Dynamic Binding: Binding is the association of
> 	  allowable operands (i.e., objects) with operations. Binding
> 	  may be either static (or early), i.e., accomplished at
> 	  compile time, or dynamic (or late), i.e., accomplished at
> 	  run-time. Until the introduction of Objective-C ([Cox,
> 	  1986]), there was little, if any, discussion of "binding"
> 	  within the object-oriented community.

I agree that binding is an important issue in evaluating OO programming
languages; in fact I suggest that a programming language should not
be considered object oriented unless it has dynamic binding of methods
to messages, the binding being on a per-object basis.  All the programming
languages I would consider object orientet have this feature, including
for example Smalltalk, Eiffel, Turbo Pascal 5.5 and C++.
Offhand, I think dynamic binding is more important than inheritance.
Inheritance is more easily simulated by "buying".  If Ada had dynamic
binding I would agree to call it an object oriented programming language,
but if it had inheritance and no dynamic binging, I be very reluctant
to do so.

> 
> 	  Static binding is usually associated with strongly typed
> 	  programming languages, and dynamic binding with weakly-typed
> 	  programming languages. Smalltalk and Objective-C support
> 	  dynamic binding.

Some object oriented programming languages have both dynamic binding
and object orientation, for example C++, Turbo Pascal 5.5 and Eiffel.
I have not used Eiffel, but what I have seen about it suggests it has
a much better typing scheme than other object oriented programming
languages I know of.

>         ...[more features defining oo-languages]

I would like to add a feature to the list which I believe has great
effect on the way it can be used:

- Automatic memory deallocation: Smalltalk and Eiffel are examples
  of OO-programming languages having this feature.  It is much easier
  to do encapsulation in a language having this feature since we
  do not have to spend as much effort on describing memory management
  issues in the use of the encapsulated thing (in most cases we can
  entirely ignore the issue).  Taking the memory management burden
  from the shoulders of the programmer and placing it on the run-time
  system is a prerequisite for elegant programming-in-the-large,
  in my opinion.
  C++ has a more restricted form of automatic deallocation, where
  the object is deallocated as it goes out of scope.  This is more
  work for the programmer, who has to supply destructor methods for
  deallocation.  Also, this can lead to more memory use, since sharing
  memory in different structures is hindered.

> 
> This is probably the biggest article I have submitted to comp.object.
> I'll try to cut back on the size of future articles. Thank you for
> listening.
> 
> 				-- Ed Berard

Please don't cut back on my account, at least.  And thanks for
all the thought-provoking articles.

	-- Snorri Agnarsson
-- 
Snorri Agnarsson		|  Internet:	snorri@rhi.hi.is
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