Re: Instanciation in a package spec.

[Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>]

On Thu, 23 Jan 2003 14:19:49 GMT, Robert A Duff
<bobduff@shell01.TheWorld.com> wrote:

>"Jean-Pierre Rosen" <rosen@adalog.fr> writes:
>
>> "Robert A Duff" <bobduff@shell01.TheWorld.com> a �crit dans le message de news: wccel752ki5.fsf@shell01.TheWorld.com...
>> > "Grein, Christoph" <christoph.grein@eurocopter.com> writes:
>> >
>> > > > * GNAT 3.15p issues:
>> > > >   pascalhe.ads:135:03: warning: cannot instantiate "Ad_hoc" before body seen
>> > > >   pascalhe.ads:135:03: warning: Program_Error will be raised at run time
>> > >
>> > > Believe Gnat. It's a RM rule to forbid instantiations before elaboration of the body.
>> >
>> > A very annoying rule, indeed.
>> >
>> ????
>> Since the body of the instance is elaborated at the point of instanciation, the body of the
>> generic has better been elaborated already....
>
>I understand the *need* for the rule in Ada.  But it's still an annoying
>restriction.  It's perfectly reasonable to want to export a generic and
>an instance of that generic from the same package.  But Ada's
>elaboration model prevents it.
>
>It's also annoying that you can't call a function in the same package:
>
>    package P is
>        function F(...) return T;
>        X: constant T;
>    private
>        X: constant T := F(...); -- raises P_E.
>    end P;
>
>The problem here is the elaboration model of Ada.  The *visibility* of
>things is too closely tied to the *elaboration* order.  I have worked
>out a different model of elaboration that doesn't have this problem (but
>still retains all the advantages of the Ada model).  Unfortunately, it's
>not Ada.

Why it cannot become Ada?

In other words, what is the price of your model?

Can  X become static (in your model), when F is pure?

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de