Re: Good Design Strategies <Was comments on comments>

[sdl@linus.UUCP (Steven D. Litvintchouk)]

In article <4574@hubcap.UUCP> billwolf@hubcap.clemson.edu (William Thomas Wolfe,2847,) writes:

> From article <4343@enea.se>, by sommar@enea.se (Erland Sommarskog):
> > What I like to stress is: Ada is *not* an object-oriented language.
> > [it lacks] inheritance and dynamic typing.....
> 
>       Software Productivity Solutions, Inc., has announced a new product,
>       Classic-Ada (tm), which allows Ada software developers to use
>       inheritance and dynamic binding in object-oriented Ada designs.

Lest anyone get the wrong impression about Classic-Ada, let me
clarify: The Classic-Ada language is *not* legal Ada.  It is a unique
dialect, which consists of Ada extended (nicely) with a new
construct--the class--with inheritance and dynamic binding.

SPS, Inc., is to be commended for attempting to improve Ada's support for
object oriented programming.  But the resulting Classic-Ada language
is not legal Ada.  Classic-Ada programs must be put thru SPS'
translator to generate legal Ada.

Mr. Sommarskog is quite correct.  Ada lacks any specific mechanism for
defining relationships among classes; the Classic-Ada language
provides just this mechanism.  

Eiffel does manage to provide inheritance in a reasonably
strongly-typed framework.  In their zeal to facilitate object-oriented
programming, SPS added both inheritance and dynamic binding to
Classic-Ada.  Was dynamic binding necessary?  It seems to entirely
defeat the safety and reliability that was a goal of Ada.

I believe that Eiffel tries to provide both separate compilation and
generics, just like Ada.  And, just like Ada, I would suspect that the
early Eiffel compilers will have "teething problems."  (At OOPSLA '88,
I recall that several Eiffel users reported problems with the Eiffel
library manager; a real case of deja vu for us veteran Ada
programmers.)


Steven Litvintchouk
MITRE Corporation
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