Re: Software Reuse -- do we really know what it is ?

[crowl@rochester.arpa (Lawrence Crowl)]

In article <371@dcl-csvax.comp.lancs.ac.uk>
craig@comp.lancs.ac.uk (Craig Wylie) writes:
>...  The scale of software that Ada allows the programmer to reuse seems to be
>primarily that of the package. Is this sufficient?

Personal opinion:  It is not.  The mechanism is sufficient if the programmer
of a package is very thorough and very disciplined.  However, programmers are
often under too much presure to be so.

Modula-II mechanisms are insufficient because they do not provide generics.

>1.	We don't really know what it is.

Well, I find a glimering of re-use in reading Knuth's books.  I will point at
an analogy though.  Board level designers constantly use circuits designed by
others.  They are packaged in integrated circuits.

>2.	It probably isn't a thing at all, but rather a collection of things
>	depending on the scale at which the reuse is to take place.

I agree.  However, I consider discipline and investment as necessary things.

>3.	Languages such as Ada and Modula-2, and imperative languages in
>	general are unsuitable for writing reusable software because of
>	their concentration on the HOW rather than the WHAT.

Clearly, we need more concentration on WHAT, but we should not abandon the
efficiency of HOW.

>4.	Reuse of Design isn't considered at all by any current applications
>	language.

The separation of abstract type from implementation in Trellis/Owl and Emerald
helps.  In addition the pre/post conditions of Eiffel provide some (though
not enough) facilities for ensuring the WHAT.  (See Proceedings OOPSLA'86 in
the November 1986 SIGPLAN.)

>5.	Nobody can force programmers to write good reusable code.

True.  But no one need buy code that is not both good and reusable.  I believe
there is a market for such code.

>6.	Even if they do write reusable code how the **** do we ever find it
>	again so that we can reuse it ?

Well, libraries do a somewhat reasonable job of reusing intellectual work in
other forms.  Perhaps they could be drafted into this task also.
-- 
  Lawrence Crowl		716-275-5766	University of Rochester
			crowl@rochester.arpa	Computer Science Department
 ...!{allegra,decvax,seismo}!rochester!crowl	Rochester, New York,  14627