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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Declaring private packages to instantiate generics?
Date: Wed, 16 May 2012 07:36:27 -0700 (PDT)
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Date: 2012-05-16T07:36:27-07:00
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On Wednesday, May 16, 2012 7:21:24 AM UTC-7, Markus Sch=F6pflin wrote:
> I just found myself wanting to write the following code, which Gnat doesn=
't like:
>=20
> ---%<---
> package FOO is
>    procedure P;
> end FOO;
>=20
> package body FOO is
>    package BAR is new SOME_GENERIC_PACKAGE;
>    procedure P is new BAR.P;
> end FOO;
> --->%---
>=20
> Can I somehow provide the body of P without writing a procedure which jus=
t=20
> forwards to an instantiation of BAR.P, IOW without having to write:
>=20
> ---%<---
> package body FOO is
>    package BAR is new SOME_GENERIC_PACKAGE;
>    procedure BAR_P is new BAR.P;
>    procedure P is begin BAR_P; end;
> end FOO;
> --->%---
>=20
> Regards,
> Markus

You can change the last to

   procedure P renames BAR_P;

But that's the best you can do.  If you have an incomplete declaration (i.e=
. the declaration of P in the *spec* of FOO), you can't complete it with a =
generic instantiation---that's the rule.  (I think he reason is that a gene=
ric instantiation is equivalent to a declaration of the instance followed b=
y the body of the instance, and doing that here would mean you're declaring=
 P twice, which isn't allowed.  It can be argued that the language rules sh=
ould be relaxed in this case, since it's tripped up more than one person, a=
nd offhand I don't see any complications that would arise if it were allowe=
d.)

                          -- Adam