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From: "Bruno" <b.santo@free.fr>
Newsgroups: comp.lang.ada
Subject: Problem whith objects, access and abstract tagged private types
Date: Thu, 8 Jan 2004 14:58:44 +0100
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Date: 2004-01-08T14:56:43+01:00
List-Id: <comp.lang.ada>

Hello to all,

I'm newbie in Ada95 and I have some difficulties with the language.
I'll give you my specifications :

Specif (.ads) :
---------------

   package Objets is

      type Item_Type is abstract tagged private;
      -- Action
      procedure Traitement (F : in Item_Type);
      -- Allows init
      procedure Modifier (F  : in out Item_Type'Class;
                          Nb : in     Natural);

      type Item_Elmt is private;
      function To_Item_Elmt (F : in Item_Type'Class) return Item_Elmt;
      function To_Item_Type (F : in Item_Elmt) return Item_Type'Class;

   private

      type Item_Type is abstract tagged
         record
            Compteur : Natural := 0;
         end record;
      type Item_Elmt is access all Item_Type'Class;

   end Objets;

I chose private types for hiding implementation of my types and access
types.

My problem is that I can't make the function "To_Item_Elmt" that create
"Item_Elmt".

I try to write this body :

   function To_Item_Elmt (F : in Item_Type'Class) return Item_Elmt is
      My_Tag : constant Ada.Tags.Tag := F'Tag;
   begin
      return new My_Tag' (F);
   end To_Item_Elmt;

The compilation indicates the following errors :
    subtype mark required in this context
    found "My_Tag" declared at line 30

If somebody could help and explain me how to resolve my problem, thanks for
his help.

Bruno