220 26589 article Path: news.gmane.org!not-for-mail From: Mathias Gaunard Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allow zero size arrays and let them occupy zero bytes. 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[188.165.36.253]) by mx.google.com with ESMTPS id n4si140058wja.210.2016.07.06.05.06.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 06 Jul 2016 05:06:35 -0700 (PDT) Received-SPF: pass (google.com: domain of mathias@gaunard.com designates 188.165.36.253 as permitted sender) client-ip=188.165.36.253; Original-Received: from player735.ha.ovh.net (b9.ovh.net [213.186.33.59]) by mo4.mail-out.ovh.net (Postfix) with ESMTP id C074A1024B38 for ; Wed, 6 Jul 2016 14:06:34 +0200 (CEST) Original-Received: from mail-lf0-f44.google.com (mail-lf0-f44.google.com [209.85.215.44]) (Authenticated sender: mathias@gaunard.com) by player735.ha.ovh.net (Postfix) with ESMTPSA id 8989B160080 for ; Wed, 6 Jul 2016 14:06:34 +0200 (CEST) Original-Received: by mail-lf0-f44.google.com with SMTP id l188so153049642lfe.2 for ; Wed, 06 Jul 2016 05:06:34 -0700 (PDT) X-Received: by 10.25.215.20 with SMTP id o20mr4565940lfg.18.1467806794028; Wed, 06 Jul 2016 05:06:34 -0700 (PDT) Original-Received: by 10.25.87.141 with HTTP; Wed, 6 Jul 2016 05:06:33 -0700 (PDT) In-Reply-To: <51e6aec9-a745-4fd9-94f7-bdd78b5798ca@isocpp.org> X-Gmail-Original-Message-ID: X-Ovh-Tracer-Id: 17602882097674106495 X-VR-SPAMSTATE: OK X-VR-SPAMSCORE: 0 X-VR-SPAMCAUSE: gggruggvucftvghtrhhoucdtuddrfeeltddrvdeigdegfecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfqggfjnecuuegrihhlohhuthemuceftddtnecu X-Original-Sender: mathias@gaunard.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of mathias@gaunard.com designates 188.165.36.253 as permitted sender) smtp.mailfrom=mathias@gaunard.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:26589 Archived-At: --001a11401ac28ea1130536f66634 Content-Type: text/plain; charset=UTF-8 On 4 July 2016 at 16:15, Bengt Gustafsson wrote: > I have been following the recent thread about empty base optimization, or > rather, the lack of empty member optimization possibility. And today I > again fell in the 0 sized array trap in metaprogramming, noticing that it > creates quite a few problems requiring extra coding. > > This idea struck me to solve both of these issues at once by a few small > changes: > > 1. Allow zero sized arrays in C++. > > No code would break by just allowing something previously forbidden. The > problem with allowing this could have been to make up ones mind about what > size such an array should report. > > 2. Define that a zero size array occupies zero bytes. > > As zero size arrays have never been allowed in C++ it can't be a breaking > change to define that the now allowed zero size arrays actually consume no > bytes regardless of the size of the element. > So you want struct Foo { char array[0]; int value; }; to be well-formed? That's problematic for a number of reasons. -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CALnjya-8Kn7VR3J0yxfPoR%2BzpDGDNxXSUwh4ZpD-t1KdbN9Prw%40mail.gmail.com. --001a11401ac28ea1130536f66634 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On 4= July 2016 at 16:15, Bengt Gustafsson <bengt.gustafsson@beamwa= ys.com> wrote:
I have been following the recent thread about empty base optimiza= tion, or rather, the lack of empty member optimization possibility. And tod= ay I again fell in the 0 sized array trap in metaprogramming, noticing that= it creates quite a few problems requiring extra coding.

This idea struck me to solve both of these issues at once by a few s= mall changes:

1. Allow zero sized arrays in C++.

No code would break by just allowing something prev= iously forbidden. The problem with allowing this could have been to make up= ones mind about what size such an array should report.

2. Define that a zero size array occupies zero bytes.

<= /div>
As zero size arrays have never been allowed in C++ it can't b= e a breaking change to define that the now allowed zero size arrays actuall= y consume no bytes regardless of the size of the element.

So you want

struct Foo
{
=C2=A0 =C2=A0char array[0];
=C2=A0 =C2=A0int value= ;
};

to be well-formed?

That'= s problematic for a number of reasons.

--
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