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=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,b1ebfe7f8f5e385d
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2003-05-02 02:14:14 PST
Path: 
 archiver1.google.com!news1.google.com!newsfeed.stanford.edu!nntp.cs.ubc.ca!freenix!skynet.be!skynet.be!louie!tlk!not-for-mail
Sender: lbrenta@lbrenta.corp.emc.com
Newsgroups: comp.lang.ada
Subject: Re: Generic formal access types
References: <3eb01630@epflnews.epfl.ch> <b8pgat$1al4$1@msunews.cl.msu.edu>
 <3eb0e397@epflnews.epfl.ch> <1459423.SpdnhGgvRt@linux1.krischik.com>
 <3eb11a85@epflnews.epfl.ch>
From: Ludovic Brenta <ludovic.brenta@insalien.org>
Date: 02 May 2003 11:14:36 +0200
Message-ID: <rw2of2l4sn7.fsf@lbrenta.corp.emc.com>
User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.2
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
NNTP-Posting-Host: 213.190.149.159
X-Trace: 1051866853 reader0.news.skynet.be 723 fa058819/213.190.149.159:54369
X-Complaints-To: abuse@skynet.be
Xref: archiver1.google.com comp.lang.ada:36840
Date: 2003-05-02T11:14:36+02:00
List-Id: <comp.lang.ada>


Do you absolutely have to return null in one of the functions of your
generic package?  How about raising an exception instead?  Something
along the lines of:

generic
   type Element (<>) is private;
package List is
   No_Element_Error: Exception;
   type List is private;
   function Get_Element (L : List) return Element;
private
   type List is ... ;
end List;

package body List is
   function Get_Element (L : List) return Element is
   begin
      raise No_Element_Error; -- instead of return null
   end Get_Element;
end List;

I'm sure you've thought about that, but I'm curious to know why it
wouldn't work for you.

--
Ludovic Brenta.