Re: Generic package parameters not externally visible : what's the rational ?

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

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"Hibou57 (Yannick Duch�ne)" <yannick_duchene@yahoo.fr> wrote in message 
news:7e99bb5a-26a8-4ccb-b8d0-3b6882c40ebe@k17g2000yqb.googlegroups.com...
...
>I do not mean you comment is wrong, I just attempt to reply and
>advocate an view on the situation.
>
>If I'm surely wrong on the long time, I want to know before I discover
>it myself after a (too much) long time

I don't have time to give you a detailed reply, sorry. (Well, not unless you 
want to hire me for consulting. :-)

Let me just give my general thinking on this subject. I think formal 
packages should be used sparingly, in part because they complicate the use 
of a generic package (the more instances and parameters that you have write 
before anything useful can be done, the harder it is to understand and the 
more likely that you will just forget using the generic and "roll your 
own").

Typically, when I've had to compose generics, I will nest an instantiation 
of one inside the other. (That's pretty much all you could do in Ada 83, 
after all.) Most of the time, that works fine, and the operations in the 
instance can be used directly or re-exported with renames as needed.

I also would have to agree with Dmitry (at least to a point) that generics 
can really interfere with your designs, so you need to use them sparingly. 
You can't avoid them completely when designing something like containers 
(for instance), but note that we made a strong effort to preserve the 
"single instance" model in almost all of the language-defined generics. We 
did that even at the cost of being able to have container interfaces (which 
would be really nice for abstraction purposes, but would require a second 
level of generic instances in order to be useful).

                                     Randy.