From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Thread: 103376,dad94612ff745427
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news2.google.com!news2.google.com!fu-berlin.de!newsfeed.arcor.de!news.arcor.de!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Instantiating private types with discriminants?
Newsgroups: comp.lang.ada
User-Agent: 40tude_Dialog/2.0.15.1
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Reply-To: mailbox@dmitry-kazakov.de
Organization: cbb software GmbH
References: <QD08g.28768$Nb2.521930@news1.nokia.com>
 <gZ18g.28779$Nb2.521756@news1.nokia.com>
Date: Tue, 9 May 2006 18:01:09 +0200
Message-ID: <jun15ub0lkbv$.lzbor2gy7cz7.dlg@40tude.net>
NNTP-Posting-Date: 09 May 2006 18:00:57 MEST
NNTP-Posting-Host: bbd86641.newsread2.arcor-online.net
X-Trace: 
 DXC=8LdE5P7]NYBC;_l<5e4khAQ5U85hF6f;DjW\KbG]kaMH[NGU2GAcMGJfn`O1iBMRjNWRXZ37ga[7JjTA67ckJ=XE[G\7LRj5O5E
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news2.google.com comp.lang.ada:4161
Date: 2006-05-09T18:00:57+02:00
List-Id: <comp.lang.ada>

On Tue, 09 May 2006 14:48:44 GMT, rick H wrote:

> 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;

You can do:

   if Var_A.all in Type_A then

which is cleaner, and requires no reference to tags.

BTW, You should probably make Put a primitive operation of General_T. Then
the whole could look like simply:

   Put (Var_A.all); -- Do what have to be done

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