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From: Richard Riehle <rriehle@nunic.nu.edu>
Subject: Re: PL/I Versus Ada (Was: Arianne ...)
Date: 1996/08/28
Message-ID: <Pine.GSO.3.92.960828172250.8140A-100000@nunic.nu.edu>#1/1
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Date: 1996-08-28T00:00:00+00:00
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On 21 Aug 1996, Tony Konashenok wrote:

> What exactly is an "object-oriented version" of a language? Why is PL/I
> not object-oriented? IMHO, one can do object-oriented programming even in
> assembly language, given enough skill and dedication. Too many people are
> confusing object-oriented programming as a method with the usage of
> C++/Ada-specific features.

  Well you may have your own idea of object-oriented programming.
  We usually think of encapsulated classes which support extensible
  inheritance, dynamic binding, and polymorphism.  We ordinarily do not
  consider the heroic efforts of a star programmer as being sufficient
  to implement the method.  There are specific, widely-accepted criteria
  for object-oriented programming which are not language-specific.
  So I will rephrase the question.

  Is there a version of PL/I which:

     1) has explicit syntactic support for extensible inheritance
        of encapsulated classes (i. e., supports Meyer's "open/closed
        principle") ?

     2) supports dynamic selection of class object based on run-time
        evaluation of class membership  (dynamic binding and
        polymorphism)?

     3) permits the definition of a type/class with hidden data
        structures that are visible only via their exported
        methods?  (a la "programming by contract")?

     4) allows the definition of "abstract classes" (deferred classes)
        for implementation, through extensible inheritance and
        polymorphism, of variants of that class.  This should include
        the capability for late binding?

   None of these characteristics are language-specific, but each is
   included in any language defined, by contemporary usage, as an
   object-oriented programming language.  How does PL/I compare?

   Richard Riehle