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: 103376,33ed4ca582c945fc
X-Google-Attributes: gid103376,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news4.google.com!feeder1-2.proxad.net!proxad.net!feeder1-1.proxad.net!club-internet.fr!feedme-small.clubint.net!news.teledata-fn.de!newsfeed.arcor.de!newsspool4.arcor-online.net!news.arcor.de.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Limited returns
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: <pt291p6yh4g9.1iey97ygy74vl.dlg@40tude.net>
 <7ab69a86-cfcf-4dba-9280-e0fce906ed76@x1g2000prh.googlegroups.com>
Date: Mon, 23 Jun 2008 19:03:24 +0200
Message-ID: <umf8uvw0rac1.ocs4eq7gbyde.dlg@40tude.net>
NNTP-Posting-Date: 23 Jun 2008 19:03:28 CEST
NNTP-Posting-Host: 992db569.newsspool2.arcor-online.net
X-Trace: 
 DXC=cK\TYnSOiR6NTD<CL>55K=A9EHlD;3Yc24Fo<]lROoR18kF<OcfhCO;n>J``68^M;=[6LHn;2LCV>COgUkn_?_Y?4RhJRkCnE@454PGBcl:<L0
X-Complaints-To: usenet-abuse@arcor.de
Xref: g2news1.google.com comp.lang.ada:823
Date: 2008-06-23T19:03:28+02:00
List-Id: <comp.lang.ada>

On Mon, 23 Jun 2008 08:15:12 -0700 (PDT), Adam Beneschan wrote:

> On Jun 23, 7:21 am, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
>> Let's consider this:
>>
>>    with Ada.Finalization;
>>    procedure Test_Limited_Stuff is
>>       type I is limited interface;
>>
>>       type T is new Ada.Finalization.Limited_Controlled with record
>>          A : Integer;
>>       end record;
>>
>>       type S is new T and I with record
>>          Self : not null access S'Class := S'Unchecked_Access;
>>       end record;
>>
>>       function Factory return I'Class is
>>       begin
>>          return X : S;
>> -- GNAT: wrong type for return_subtype_indication
>>       end Factory;
>>    begin
>>       null;
>>    end Test_Limited_Stuff;
>>
>> Is it illegal? I am surprised why? S is in I'Class.
> 
> It's illegal, but hopefully not for long.  See:
> 
> http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AI05s/AI05-0032-1.TXT?rev=1.4

It would be nice, because this "feature" is extremely boring.

> Perhaps you could ask your compiler to go ahead and implement that AI
> (or at least the part of it that allows the specific return type as
> you've done).  I think it was just an oversight in Ada 2005 not to
> allow this.

Is there an AI to finally fix a similar problem with pool-specific access
types? I mean this:

procedure Test_Access is
   type T is tagged null record;
   type S is new T with null record;
   
   type T_Ptr is access T'Class;
   type S_Ptr is access S'Class;

   function Factory return T_Ptr is
      X : S_Ptr := new S;
   begin
      .. -- Do something with X
      return T_Ptr (X); -- Illegal!???
   end Factory;
begin
   null;
end Test_Access;

The only workaround is to cast:

   function Factory return T_Ptr is
      Result : P_Ptr := new S;
      X : S'Class renames S'Class (Result.all);
   begin
      .. -- Do something with X
      return Result;
   end Factory;

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