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=-1.3 required=5.0 tests=BAYES_00,MAILING_LIST_MULTI,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,1dd28d5040ded1f8
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2002-05-15 04:35:07 PST
Path: 
 archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news.tele.dk!small.news.tele.dk!195.25.12.36!oleane.net!oleane!freenix!enst!enst.fr!not-for-mail
From: "Grein, Christoph" <christoph.grein@eurocopter.com>
Newsgroups: comp.lang.ada
Subject: Re: Announce: Grace project site operational
Date: Wed, 15 May 2002 13:32:48 +0200 (MET DST)
Organization: ENST, France
Sender: comp.lang.ada-admin@ada.eu.org
Message-ID: <mailman.1021462505.30565.comp.lang.ada@ada.eu.org>
Reply-To: comp.lang.ada@ada.eu.org
NNTP-Posting-Host: marvin.enst.fr
Mime-Version: 1.0
Content-Type: TEXT/plain; charset=us-ascii
X-Trace: avanie.enst.fr 1021462505 65441 137.194.161.2 (15 May 2002 11:35:05
 GMT)
X-Complaints-To: usenet@enst.fr
NNTP-Posting-Date: Wed, 15 May 2002 11:35:05 +0000 (UTC)
Return-Path: <christoph.grein@eurocopter.com>
X-Authentication-Warning: mail.eurocopter.com: uucp set sender to
 <christoph.grein@eurocopter.com> using -f
Content-MD5: 2BMXcuNrTJKUdGTj8eVpjA==
X-Mailer: dtmail 1.2.1 CDE Version 1.2.1 SunOS 5.6 sun4u sparc 
Errors-To: comp.lang.ada-admin@ada.eu.org
X-BeenThere: comp.lang.ada@ada.eu.org
X-Mailman-Version: 2.0.8
Precedence: bulk
X-Reply-To: "Grein, Christoph" <christoph.grein@eurocopter.com>
List-Help: <mailto:comp.lang.ada-request@ada.eu.org?subject=help>
List-Post: <mailto:comp.lang.ada@ada.eu.org>
List-Subscribe: <http://ada.eu.org/mailman/listinfo/comp.lang.ada>,
	<mailto:comp.lang.ada-request@ada.eu.org?subject=subscribe>
List-Id: comp.lang.ada mail<->news gateway <comp.lang.ada.ada.eu.org>
List-Unsubscribe: <http://ada.eu.org/mailman/listinfo/comp.lang.ada>,
	<mailto:comp.lang.ada-request@ada.eu.org?subject=unsubscribe>
Errors-To: comp.lang.ada-admin@ada.eu.org
X-BeenThere: comp.lang.ada@ada.eu.org
Xref: archiver1.google.com comp.lang.ada:24088
Date: 2002-05-15T13:32:48+02:00

From: "Dmitry A.Kazakov" <mailbox@dmitry-kazakov.de>
> Consider:
> 
>    type Graph_Node is private;
>    No_Node : constant Graph_Node; -- Deferred, but visible
>    function Get_Next_Child
>       (Parent : Graph_Node; Child : Graph_Node := No_Node)
>          return Graph_Node;
> 
> Here I exposed No_Node, which then can be abused like:
> 
>    Get_Next_Child (No_Node);
> 
> A solution could be some sort of incomplete declaration for
> subprograms:
> 
>    type Graph_Node is private;
>    function Get_Next_Child
>       (Parent : Graph_Node; Child : Graph_Node := <>)
>          return Graph_Node;

Your caller has to have some variable Current_Parent, which might have the value 
No_Node, e.g. when it is undefined (private types should be defaulted to 
something like this so that they always have a value even when never assigned a 
value).
So you must make sure in any case that the actual for Parent is different from 
No_Node, so the abusive

  Get_Next_Child (No_Node);

is caught in any case.

There are cases where

         .---------------------------------------.
         | Information Hiding Considered Harmful |
         `---------------------------------------'


> 
> private
>    type Graph_Node is ...;
>    No_Node : constant Graph_Node := ...;
>    function Get_Next_Child
>       (Parent : Graph_Node; Child : Graph_Node := No_Node)
>          return Graph_Node;
> 
> ---
> Regards,
> Dmitry Kazakov
> www.dmitry-kazakov.de
> _______________________________________________
> comp.lang.ada mailing list
> comp.lang.ada@ada.eu.org
> http://ada.eu.org/mailman/listinfo/comp.lang.ada