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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: generic child class
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Date: Tue, 7 Mar 2006 12:31:35 +0100
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On 7 Mar 2006 02:44:09 -0800, nblanpain@hotmail.com wrote:

> I have a compilation error that i not understand. This is my example :
> 
> ## Vec package ##
> generic
> type T_Real is digits <>;
> package Vec is
> end Vec;
> 
> ## Mat package ##
> with Vec;
> generic
> with package Vector is new Vec (<>);
> package Mat is
> end Mat;
> 
> ## Mat.Child package ##
> generic
> type T_Tab is array (Integer) of Vector.T_Real;
> package Mat.Child is
> end Mat.Child;
> 
> ## Test package ##
> with Vec;
> with Mat;
> with Mat.Child;
> package Test is
>    package Vec_Float is new Vec (T_Real => Float);
>    package Mat_Float is new Mat (Vector => Vec_Float);
>    type T_Tableau is array (Integer) of Float;
>    package Mat_Child_Float is new Mat_Float.Child (T_Tab => T_Tableau);
> ---- error !!!!!!!!!!
> end Test;
> 
> The error message is :
> "component subtype of actual does not match that of formal T_Tab "
> 
> have you an explaining ?

GNAT has numerous bugs in generics. As for your example, one trick I know
works with GNAT 3.15p is:
-----------------------------
with Vec;
generic
   with package Vector is new Vec (<>);
package Mat is
   subtype Mat_Float is Vector.T_Real;
       -- Fake subtype to make "type renaming"
end Mat;
------------------------------
generic
   type T_Tab is array (Integer) of Mat_Float;
      -- Refers to the "rename"
package Mat.Child is
end Mat.Child;
-----------------------------
with Vec;
with Mat;
with Mat.Child;
package Test is
   package Vec_Float is new Vec (T_Real => Float);
   package Mat_Float is new Mat (Vector => Vec_Float);
   type T_Tableau is array (Integer) of Float;
   package Mat_Child_Float is new Mat_Float.Child (T_Tab => T_Tableau);
      -- This should be OK with GNAT 3.15p
end Test;

Alas, at some point this all tricks stop to work. BTW, one "nice" feature
of GNAT is to successfully compile generic specifications and bodies and
then, upon instantiation, to report bugs in already compiled specifications
and bodies.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de