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From: rick H <rik_nntp@dsl.pipex.com>
Subject: Re: Instantiating private types with discriminants?
Newsgroups: comp.lang.ada
References: <QD08g.28768$Nb2.521930@news1.nokia.com>
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Date: Tue, 09 May 2006 14:48:44 GMT
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Date: 2006-05-09T14:48:44+00:00
List-Id: <comp.lang.ada>

Thank you, Georg, Ludovic and Dmitri for your replies.

Now I know I won't get shouted at for asking novice questions, I have
another query for you experts, if you've got the time to have a look:

I'm trying to query the tag of a record, which I can do quite nicely,
provided I both "with Ada.Tags" and "use Ada.Tags".  Just for the sake
of it, I tried to remove the "use Ada.Tags" statement, but I can't work
out how I would then specify the XXX'Tag attribute of a variable.
Here's an example that illustrates my problem ("if Var_A'Tag..." is the
problem line):

with Ada.Integer_Text_IO;
with Ada.Float_Text_IO;
with Ada.Tags;
--  use Ada.Tags;

procedure Simple_Case is
   type General_T is tagged null record;

   type Access_T is access General_T'Class;


   type Type_A is new General_T with
   record
      Data : Integer;
   end record;


   type Type_B is new General_T with
   record
      Data : Float;
   end record;


   Var_A : Access_T; --  could be "new Type_A" or a "new Type_B"
begin
   --  Var_A := new Type_A' (Data => 100);
   Var_A := new Type_B' (Data => 100.0);

   --  problem line:
   if Var_A'Tag = Type_A'Tag then
      Ada.Integer_Text_IO.Put ( Type_A (Var_A.all).Data);
   elsif Var_A'Tag = Type_B'Tag then
      Ada.Float_Text_IO.Put ( Type_B (Var_A.all).Data);
   end if;
end Simple_Case;