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: a07f3367d7,a41c4a2c795dbe34
X-Google-Attributes: gida07f3367d7,public,usenet
X-Google-NewGroupId: yes
X-Google-Language: ENGLISH,UTF8
Path: 
 g2news1.google.com!news1.google.com!goblin2!goblin.stu.neva.ru!aioe.org!.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Will "renames" increase program size?
Date: Wed, 15 Jun 2011 15:15:13 +0200
Organization: cbb software GmbH
Message-ID: <1ayjsy885qg2b$.13bmeo97hbau1$.dlg@40tude.net>
References: 
 <46294109-f07d-49c0-8e81-65a369a05ced@z15g2000prn.googlegroups.com>
 <it9gem$l0t$1@munin.nbi.dk> <op.vw37bq1eule2fv@douda-yannick>
Reply-To: mailbox@dmitry-kazakov.de
NNTP-Posting-Host: FbOMkhMtVLVmu7IwBnt1tw.user.speranza.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 8bit
X-Complaints-To: abuse@aioe.org
User-Agent: 40tude_Dialog/2.0.15.1
X-Notice: Filtered by postfilter v. 0.8.2
Xref: g2news1.google.com comp.lang.ada:19850
Date: 2011-06-15T15:15:13+02:00
List-Id: <comp.lang.ada>

On Wed, 15 Jun 2011 13:24:52 +0200, Yannick Duchêne (Hibou57) wrote:

> Le Wed, 15 Jun 2011 07:37:22 +0200, Randy Brukardt <randy@rrsoftware.com>  
> a écrit:
>> Some examples where there probably would be some overhead:
>>
>>              Obj : Natural renames My_Array (Some_Variable).all;
>>              Obj2 : Float renames Some_Function (A, B);
>>
> Yes, because this is more an aliasing (in the symbolic sense) than a  
> proper renaming.

Yes, Ada's renaming is not renaming. Consider this:

   Line : String renames Get_Line;

It calls Get_Line once and keeps the result object. In fact it is an
equivalent to:

   <anonymous> : constant String := Get_Line;
   Line : properly renames <anonymous>;

Consider also the effect of renaming on the visibility rules:

   package P1 is
      End_Error : exception renames Ada.Text_IO.End_Error;
   end P1;
   package P2 is
      End_Error : exception renames Ada.Text_IO.End_Error;
   end P2;
   use P1, P2;
   
   exception
      when End_Error => -- End_Error is hidden!

Ada's "renames" does not rename here, it copies, creates objects. There are
three End_Error here, all of them are equal, but not same:

exception
   when Ada.Text_IO.End_Error =>
      ...
   when P1.End_Error => -- Error! P1.End_Error has the same value
      ...
   when P2.End_Error =>
      ...

A proper renaming would create identical (x≡y) entities, Ada's renaming
sometimes creates only equal ones (x=y).

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