Re: Teaching new tricks to an old dog (C++ -->Ada)

[<adaworks@sbcglobal.net>]

"T Beck" <Tracy.Beck@Infineon.com> wrote in message
news:1110556310.367604.271110@g14g2000cwa.googlegroups.com...
>
> Adrien Plisson wrote:
> >
> > Ada is also used in particular rockets called missiles, and its job
> > inside is just to make them fall... but fall gracefully.
>
> Would that happen to include the now-infamous Patriot Missles (the ones
> that couldn't hit a barn after they'd been on for a while due to a
> bug?)

No.  Those missiles were not programmed in Ada.

On the other hand, there have been software failures written
in Ada, just as their have been software failures written in C,
C++, Jovial, Fortran, etc.

The use of Ada does not eliminate to potential for software failure.
No language, by itself, can guarantee there will no defects.  The
best we can hope for, in the current state of software engineering,
is to minimize the risk of failure.

Ada is designed to help reduce risk. That is a primary concern when
choosing Ada.   Still, we are always dealing with tradeoffs.

A language that allows compilers to generate some kind of result for
every syntactic expression, is likely to also permit erroneous constructs.
This is OK when that language is used in the hands of a person who
never makes mistakes.    Of course, as the size of the code grows
larger, and the number of functions increases, human comprehension
begins face more challenges in the management of the complexity.

A language that provides a set of constraints at the outset, such as
Ada, can be annoying for little programming jobs carried out by
one person.   As the software product requires more and more
people, more and more code units, and more and more time to
complete, these constraints can be useful because they prohibit
certain practices that lead to unexpected errors.

Software risk management is becoming a more and more respectable
part of software engineering practice.  Language choice is only one
part of the risk management decision matrix, and we are not going to
enumerate the many other facets of risk here.   However, language
can have an impact on risk.

I have seen software developed in many different languages over a
long period of time.   In my own view, and I don't have formal
research to support this, Ada has had value in reducing risk of
failure "when used as directed."    C++, and the C family in general,
increases the risk of failure simply because one does not have the
built-in constraints that exist in Ada.   A careful programmer can
create excellent, defect-reduced, software in C++.   A sloppy
programmer can grind out horrible, unsafe code in Ada (by
relaxing the built-in constraints).    All in all, though, I see Ada as
more risk averse than most of its competitors.

What is the cost of being risk averse?   That question is open to many
different interpretations.   There certainly is a cost.   Is that cost worth
the level of risk avoidance we hope to achieve with Ada?   The answer
to this question will also vary according to the experience, biases, and
economic decisions favored by those who must make the choices.

Richard Riehle