Re: Ada The Best Language?

[Lao Xiao Hai <laoxhai@ix.netcom.com>]

codesavvy wrote:

> >
> > How do _you_ write multitasking/multithreading applications in C++ ?
> > With a lot (really a lot) of system calls ? Very, very portable ;-)

However, there is no consistency checking of these system calls relative
to the underlying program.   Ada's tasking model is useful because it is
integrated into the overall program and the compiler can do full type
checking, procedure call conformance evalutation,  enforce visibility
rules (which are nearly absent in C++), and a host of other things that
require a coherent model for development.    In this regard, C++ falls
far short of Ada.

> Do you have a metric for measuring the increase in productivity that
> this brings about?

Anecdotal.  I worked with a programmer who was constantly complaining about
Ada.  He wanted to use C++.   After a couple of months he finally came to me with,
"I think I am beginning to get it.  With C and C++ I can compile anything I write and
then spend a long time debugging it.   With Ada, it takes me a long time to get my
program to successfully compile, but when it does, there is less debugging to do."

This is difficult to measure using the usual tools for software metrics.   Most metric
methods are not at a sufficient level of granularity to differentiate between the many
steps in bringing a program into production.   Most managers do not take the time to
collect metrics at that level of detail.

> I hope the compiler is consistent from OS to OS
> for Ada.  How often is portability from one system to the next
> required so that all one has to do is recompile and everything will
> work the same needed?  Not very often, almost never IMO.

Anecdote, again.   On an Army Command and Control system, the team
I was advising was developing an Ada system for a computer someone
had purchased on promises of good performance from the computer
salesperson.  The team was unable to meet its perfomance objectives,
largely because of the tasking implementation on the target platform.
Someone suggested converting the whole thing over to C.    This, of
course, would not have helped, but in a panic people will grasp at any
flimsy straw floating on the surface.

Along came a salesperson for Harris Computing, offering to run the software
on their Nighthawk.   "Oh no," thought the project manager.  "We have to convert
the Ada code to compile on their machine? "    During original design, the team
had carefully packaged all the platform-dependent code at the lowest possible
level of the design.   All the vanilla-flavored Ada code ported perfectly.  The
low-level package, consisting of a few-hundred lines, was ported easily with
the help of technicians from Harris.   Performance objectives were met and the
project came in on-time, within budget.

Prologue.   As successful as the Ada version was, another company later won
the contract.   I no longer have any association with this project, but as I am told,
they hated Ada.   No technical reasons.   Simply the usual stupidity.   My informant
tells me they sought and got funding to convert the whole thing to their favorite
language and it is still not working properly.

> > And - some of the "big" features of C++ like exception handling were
> > copied from Ada.
>
> So what?

So, it was done badly.   C++ exception handling is far more complex than necessary.
I read a three-part article about C++ exception handling  in C++ Report several
years ago that was simply scary.    The more deeply one examines C++ exception
handling, the more one wants to avoid it, especially for safety-critical software.

Richard Riehle
AdaWorks Software Engineering
richard@adaworks.com