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Date: Tue, 31 Jul 2012 09:48:04 +0200
From: Georg Bauhaus <rm.dash-bauhaus@futureapps.de>
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Newsgroups: comp.lang.ada
Subject: Re: Access to generic formal parameters in an generic package
 instantiation
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Date: 2012-07-31T09:48:02+02:00
List-Id: <comp.lang.ada>

On 29.07.12 20:16, Florian Weimer wrote:
> It seems that generic formal packages are unusual because GNAT shows
> some strange effects (and the occasional bug box).

Compilers seem to differ on this one, which should be Ada 95.
I am not sure the generics are properly addressing the issue
of type comparison (well, of convertibility).

With GNAT's bug boxes currently in the way I can't try the
Ada 2012 features. (Something about failures when testing entity
node kinds.)

generic
    type T is private;
    Fst, Snd : in T;
package Same_Type is end;

with Same_Type;
generic
    type Ancestor is private          ;
    type T1 is new Ancestor;
    type T2 is new Ancestor;
    X : T1;
    Y : T2;
--   with package Comparison is new Same_Type (T1, T1'(X), T1 (Y));
package Ops is

private
    package Comparison_1 is new Same_Type (T1, T1'(X), T1 (Y));
    package Comparison_2 is new Same_Type (T2, T2 (X), T2'(Y));
end;

with Same_Type, Ops;
procedure Test_G is

    type Int is new Integer;
    type Chr is new Character;

    Two : constant Int := 2;
    C : constant Chr := 'c';

    package Test_1 is new Ops (Int, Int, Int, Two, Two);

--!GNAT!   package Test_2 is new Ops (Int, Int, Chr, Two, C);

    package PK is
       type root is tagged null record;
       type left is new root with null record;
       type right is new root with null record;
    end PK;
    use pK;

    L : Left;
    R : Right;
    package test_3 is new ops (Root, Left, Right, L, R);
begin
    null;
end Test_G;