220 10706 article Path: news.gmane.org!not-for-mail From: Farid Mehrabi Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Forward declaring names Date: Mon, 19 May 2014 19:56:40 +0430 Lines: 200 Approved: news@gmane.org Message-ID: References: <20140509221552.GA32099@sara.home> <20140510164133.GA7642@sara.home> <73ba480c-9389-4da9-a8e8-d2ed02fd9905@isocpp.org> <20140510185607.GA9062@sara.home> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=089e013d175a38c46b04f9c265a0 X-Trace: ger.gmane.org 1400513237 9848 80.91.229.3 (19 May 2014 15:27:17 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 19 May 2014 15:27:17 +0000 (UTC) To: std-proposals Original-X-From: std-proposals+bncBC27JR6ERAOBBSGF5CNQKGQEEX3ZIBQ@isocpp.org Mon May 19 17:27:09 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wg0-f69.google.com ([74.125.82.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1WmPSz-0000U1-Hf for gclcip-std-proposals@m.gmane.org; Mon, 19 May 2014 17:27:05 +0200 Original-Received: by mail-wg0-f69.google.com with SMTP id b13sf4235044wgh.0 for ; Mon, 19 May 2014 08:27:05 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=ky1mygOlp8YWDZb6qZLb9hfgbSGA2h56sdbCMYKIMWc=; b=O5j7Ug/Vv9BEDUhxWMrfq012ecpgNjvIyN0Mr6I5kJxJ63yg3H20FMmP4uuBtHVC9x B4cV1zebweJT6lpLNaEdlbYQigVMzrWrsbaOqq0CmXR3I5FiowEo7CXL1zeK2E53LOMH XnbD8aOQFWMY0c5A+Ry6nSgMDnFBpY6jLEZkpwvi3pkMZsmlftfhv49XExtUoaNcGR/y q2PbXsEa9Q9mjz2Hpzkx+43avyoWi8kiO94IlQayAgD8Rc2vRIJmTTnpbNY1M/AeN0XY oWWbXTsUcBOx3wiEeuWkoO5zdAi4N8ud9oQuFVsJJm7WQWr+Y5vytQ23e4lRcNYXf/JJ F9nQ== X-Gm-Message-State: ALoCoQn93vAZesRHacHigUvkQTwFMca4TstUZEaL8Nrh2d0yXZMNudappblNIPaC2QQmUktPF+yV X-Received: by 10.152.36.226 with SMTP id t2mr2910693laj.1.1400513225197; Mon, 19 May 2014 08:27:05 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.24.234 with SMTP id x10ls493964wif.45.gmail; Mon, 19 May 2014 08:27:04 -0700 (PDT) X-Received: by 10.194.242.4 with SMTP id wm4mr2726785wjc.88.1400513224226; Mon, 19 May 2014 08:27:04 -0700 (PDT) Original-Received: from mail-we0-x233.google.com (mail-we0-x233.google.com [2a00:1450:400c:c03::233]) by mx.google.com with ESMTPS id ay5si9347870wjb.4.2014.05.19.08.27.04 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 19 May 2014 08:27:04 -0700 (PDT) Received-SPF: pass (google.com: domain of farid.mehrabi@gmail.com designates 2a00:1450:400c:c03::233 as permitted sender) client-ip=2a00:1450:400c:c03::233; Original-Received: by mail-we0-f179.google.com with SMTP id q59so5780761wes.10 for ; Mon, 19 May 2014 08:27:04 -0700 (PDT) X-Received: by 10.194.175.70 with SMTP id by6mr30465558wjc.3.1400513224031; Mon, 19 May 2014 08:27:04 -0700 (PDT) Original-Received: by 10.217.123.134 with HTTP; Mon, 19 May 2014 08:26:40 -0700 (PDT) In-Reply-To: X-Original-Sender: farid.mehrabi@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of farid.mehrabi@gmail.com designates 2a00:1450:400c:c03::233 as permitted sender) smtp.mail=farid.mehrabi@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:10706 Archived-At: --089e013d175a38c46b04f9c265a0 Content-Type: text/plain; charset=UTF-8 2014-05-19 19:38 GMT+04:30 Farid Mehrabi : > > > > 2014-05-18 23:28 GMT+04:30 Richard Smith : > > On Sun, May 18, 2014 at 6:17 AM, Farid Mehrabi wrote: >> >>> >>> >>> >>> 2014-05-10 23:26 GMT+04:30 Magnus Fromreide : >>> >>>> Yes, you are right, and there are also function and member pointers for >>>> more >>>> recent odd pointers so that kills the idea rather nicely. >>>> >>> >>> I should respectfully object that this one is irrelevant. Normal >>> pointers have the same size and representation - regarding the compilation >>> platform. >>> >> >> This is true on common platforms, but not in general, and the standard >> has no such requirement. >> >> > > I used to consider this as the de facto standard. > > And they are implicitly statically cast-able to void*; static_cast back >>> from this result to the original type is also well-defined behavior. >>> >> >> Yes, void* must be able to represent any object pointer, but some pointer >> types might be smaller than void*. For instance, on a word-addressable >> machine, the ABI might say that all class types have a size that is a >> multiple of one word, and all class pointers are the "normal" size for the >> machine, but char* and void* are represented as a pair of (word pointer, >> byte index). >> > > > I need a concrete practical example please. PC mainframe micro?? > A machine + OS + tool chain + relative pointer-sizes . > > Even if any platform with such design exists, the forward declared type can use pointers/references with void* layout. This is sub-optimal but yet easily implementable. And IMHO the 'typename' keyword is a good candidate for the purpose. It clearly expresses the intention. regards, FM. -- how am I supposed to end the twisted road of your hair in the dark night?? unless the candle of your face does turn a lamp up on my way!!! -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. --089e013d175a38c46b04f9c265a0 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable



2014-05-19 19:38 GMT+04:30 Farid = Mehrabi <farid.mehrabi@gmail.com>:


2014-05-18 23:28 GMT+04:30 Richard Smith <richard@metafoo.co.uk>= ;:

On Sun, May 18, = 2014 at 6:17 AM, Farid Mehrabi <farid.mehrabi@gmail.com> wrote:



2014-05-10 23:26 GMT+04:30 Magnus Fromreide <magfr@lys= ator.liu.se>:
Yes, you are right, and there= are also function and member pointers for more
recent odd pointers so that kills the idea rat= her nicely.

=
I should respectfully object that this one is irrele= vant. Normal pointers have the same size and representation - regarding the= compilation platform.

This is true on common p= latforms, but not in general, and the standard has no such requirement.
=C2=A0

I used to consider this as the de facto =C2=A0standard.

And they are i= mplicitly statically cast-able to void*; static_cast back from this result = to the original type is also well-defined behavior.=C2=A0
=

Yes, void* must be able to represent any object p= ointer, but some pointer types might be smaller than void*. For instance, o= n a word-addressable machine, the ABI might say that all class types have a= size that is a multiple of one word, and all class pointers are the "= normal" size for the machine, but char* and void* are represented as a= pair of (word pointer, byte index).

=C2=A0
I need = a concrete practical example please. PC mainframe micro??=C2=A0
A= machine + OS + tool chain + relative pointer-sizes .

<= /div>

Even if any platform with such design exists, the forward declared ty= pe can use pointers/references with void* layout. This is sub-optimal but y= et easily implementable.

And IMHO the 'typename'= keyword is a good candidate for the purpose. It clearly expresses the inte= ntion.

regards,
FM.
--
how am I supposed to end the twisted road = of=C2=A0 your hair in the dark night??
unless the candle of your face do= es turn a lamp up on my way!!!

--

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--089e013d175a38c46b04f9c265a0-- .