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-Thread: 103376,85c4b961f840b5ab
X-Google-Attributes: gid103376,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news2.google.com!proxad.net!news.cs.univ-paris8.fr!informatik.uni-bremen.de!cs.tu-berlin.de!uni-duisburg.de!not-for-mail
From: Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>
Newsgroups: comp.lang.ada
Subject: Re: Zero length Objects
Date: Thu, 1 Jul 2004 01:28:02 +0000 (UTC)
Organization: GMUGHDU
Message-ID: <cbvpb2$rqp$1@a1-hrz.uni-duisburg.de>
References: <mailman.1.1088614449.375.comp.lang.ada@ada-france.org>
 <PSFEc.50650$aJ3.17580@nwrdny02.gnilink.net> <2kh2leF2ct4hU1@uni-berlin.de>
NNTP-Posting-Host: l1-hrz.uni-duisburg.de
X-Trace: a1-hrz.uni-duisburg.de 1088645282 28505 134.91.1.34 (1 Jul 2004
 01:28:02 GMT)
X-Complaints-To: usenet@news.uni-duisburg.de
NNTP-Posting-Date: Thu, 1 Jul 2004 01:28:02 +0000 (UTC)
User-Agent: tin/1.5.8-20010221 ("Blue Water") (UNIX) (HP-UX/B.11.00
 (9000/800))
Xref: g2news1.google.com comp.lang.ada:2015
Date: 2004-07-01T01:28:02+00:00
List-Id: <comp.lang.ada>

Nick Roberts <nick.roberts@acm.org> wrote:
: "Frank J. Lhota" <NOSPAM.lhota.adarose@verizon.net> wrote in message
: news:PSFEc.50650$aJ3.17580@nwrdny02.gnilink.net...
: 
:> No object is really of zero length. The reason is that every object should
:> have a unique address. Therefore, most Ada compilers will allocate at
: least
:> one storage element to each object, in order to insure that if we declare
:>
:>        A, B : Empty_Type;
:>
:> then A and B do not both refer to the same location.
: 
: Yes indeed.

One might add that the full story has zero size things if not
objects:

with Ada.Text_IO;

procedure sz is
   type Nothing is null record;
   for Nothing'size use 0;

   type What is record
      thing: Natural := 1_000_000;
      more: Nothing;
   end record;

   type Then_Again is record
      uhm: Nothing;
   end record;

   package TIO renames Ada.Text_IO;

   x: What;
   y: Then_Again;
begin
   TIO.put_line("size of Natural: " & Natural'image(Natural'size));
   TIO.put_line("size of x of type What: " & Natural'image(x'size));
   TIO.put_line("size of y of type Then_Again: " & Natural'image(y'size));
end sz;

$ ./sz
size of Natural:  31
size of x of type What:  32
size of y of type Then_Again:  8
$

So the size of the .more component is no greater than 1, I think.


Georg