Re: "access constant" discriminant

["Randy Brukardt" <randy@rrsoftware.com>]

Lutz Donnerhacke wrote in message ...
>* Matthew Heaney wrote:
>> Access discriminants are very powerful.  No serious Ada95 program can
>> be written without them.
>
>If there is a serious program without access discriminants, let's call
it a
>Spark program, or trivial, ok?

Claw doesn't use access discriminants. That's in large part because they
cause limited 'poisoning', as they're restricted to limited types. We
prefered to use Adjust to make assignment work properly.

Indeed, I'm not aware of any real Ada program, serious or otherwise,
that actually uses access discriminants. I know that they were buggy in
Janus/Ada until very recently, and we never received any bug reports on
them. So, as a practical matter, these are a very marginal feature of
Ada with very limited uses.

In any case, Matt's statement would probably have been better if it
said:

Access discriminants are very powerful.  They are very much
underutilized, probably because hardly anybody understands them.

Sweeping statements about programming style are not likely to be
helpful. I tend to feel about finalization like Matt apparently does
about access discriminants, but the only time I would say something like
"No serious Ada program can be written without them." is when I'm
looking for fight. Even though I believe that is true, I'm well aware
that there are many, many Ada projects which have an irrational fear of
finalization, and to characterize them as not being "serious" is not
likely to make any friends.

         Randy.