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
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!mx05.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Gnat 2013 is out!
Date: Fri, 31 May 2013 09:41:56 +0200
Organization: cbb software GmbH
Message-ID: <1klsxf6xj66gd.1op1f7fzgp4l$.dlg@40tude.net>
References: <ko500n$a4v$1@dont-email.me> <lyhahl96b5.fsf@pushface.org>
 <lyd2s99324.fsf@pushface.org> <ko603g$dde$1@loke.gir.dk>
 <32d94173-533a-471e-95a0-abb73a6cdcc2@googlegroups.com>
 <ko8ao8$55i$1@loke.gir.dk>
Reply-To: mailbox@dmitry-kazakov.de
NNTP-Posting-Host: FbOMkhMtVLVmu7IwBnt1tw.user.speranza.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@aioe.org
User-Agent: 40tude_Dialog/2.0.15.1
X-Notice: Filtered by postfilter v. 0.8.2
Xref: news.eternal-september.org comp.lang.ada:15680
Date: 2013-05-31T09:41:56+02:00
List-Id: <comp.lang.ada>

On Thu, 30 May 2013 14:53:43 -0500, Randy Brukardt wrote:

> "Adam Beneschan" <adam@irvine.com> wrote in message 
> news:32d94173-533a-471e-95a0-abb73a6cdcc2@googlegroups.com...
> On Wednesday, May 29, 2013 3:39:44 PM UTC-7, Randy Brukardt wrote:
> 
>>I've always wanted some kind of feature in Ada that would allow a caller to 
>>provide a
>>"dummy" for OUT parameters, without having to declare a new variable.  The 
>>compiler
>>would allocate a temporary object (and a separate one for each use of a 
>>"dummy") and
>>then discard it after the call.  It wouldn't work well when parameter types 
>>are
>>unconstrained array or discriminant records, though.
> 
> Hmm, that seems like a good idea to me. But what would the syntax be? <> 
> maybe?
> 
>          My_Proc (Obj1, Obj2, Result => <>);

As well as function results:

   <> := My_Func (Obj1, Obj2); -- I do this for side effects!

Back in 90's I thought about null statement:

   null My_Func (Obj1, Obj2);

But for procedures it won't work:

   My_Proc (Obj1, Obj2, Result => null); -- Ambiguous

> I tried to work out a solution based on default parameters for all modes 
> (which would provide your dummy result along with other uses), but it didn't 
> work out very well. The main problem was that the default objects usually 
> had to be globals, and that could cause an unsafe use of shared variables in 
> a tasking environment.

These are two different cases. One is when the default is a named object,
another is when the default is an anonymous object allocated on the stack.

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