Re: Anybody in US using ADA ? One silly idea..

[Richard Riehle <richard@adaworks.com>]

The debate over generics versus inheritance is quite old.   Bertrand
Meyer wrote an essay on this which he included in his book, "Object
Oriented Software Construction."   The general conclusion was that
genericity could be emulated with inheritance, but inheritance could
not be emulated with genericity.

For some the objective of both concepts is software reuse.  I seen that
as a short-sighted view, but it is certainly one valid objective.

Ada has taken this a little further.  We have genericity, inheritance,
and child library units.  All three are useful tools when used for the
correct purpose.  All three provide a powerful combination of
approaches to software reuse.   Randy Brukhardt has correctly
noted that Ada /= GNAT.   Many compilers, one that I recall quite
well was TLD Ada, did not use full code expansion for generics.

Some have suggested the C++ model for generics is slightly better
than that in Ada.  I respectfully suggest that the improved flexibility
also results in a degradation of reliability.   But reliability has been
widely deprecated as less important that ease of development.

Ada generics, as well as Eiffel and C++ generics, do make the
creation of extensible containers more sensible.   In my experience,
combining genericity with inheritance in Ada is quite useful.  It
is also helpful that we can dispatch on the result of a function
when designing such containers.

Child library units have turned out to be more powerful than I
originally expected.   I now use the package body to implement
only the declarations in the specification.   All supporting
code within a body is now promoted to a child library unit.
This has provided support for creating aspects, something we
could not do easily with Ada 83, and something I see as more
challenging in C++ than in Ada (though not impossible).   As
as consequence, I see Ada as quite friendly to the new model
of Aspect-Oriented Programming, while still enforcing a
strong model of encapsulation.

Any tool, used unwisely, is a fool's tool.   Genericity, when used
intelligently, continues to be a valuable component of the Ada
language.  The addition of generic formal package parameters
in Ada 95 has proven to be an excellent addition, even though
a great many programmers are confused by it because the ALRM
does not provide a simple and fully coded example.  I do provide
such a example in "Ada Distilled."

I just returned from presenting a two week software engineering
seminar in Asia.   I used Ada to demonstrate my programming
examples.   The students, none of whom had seen Ada before,
found the examples easy to read, understand, and ask questions
about.  If I had been using C++ for a similar audience, one that
had never seen C++ before, I suspect I would have had a
classroom full of confused students.   Even my example using
an Ada generic component was easy to follow for these students,
even though English was not their native language.

Some of them plan to download GNAT and experiment with
Ada.  Everyone of them agreed that C++ is so confusing that
they spend a huge amount of time correcting errors that they
wish had been caught by the compiler.   Many had already
rejected C++ in favor of Java, Python, and other languages
because they found C++ so difficult.

Ada can be made accessible to new students.   We simply need
to learn how to present what the students need when they need
it, and to show them simple solutions they can use to work out
their own problems.

Richard Riehle