220 26590 article Path: news.gmane.org!not-for-mail From: Jonathan Coe Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allow zero size arrays and let them occupy zero bytes. 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[2a00:1450:400c:c09::22d]) by mx.google.com with ESMTPS id j142si368066wmg.142.2016.07.06.06.25.10 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 06 Jul 2016 06:25:10 -0700 (PDT) Received-SPF: pass (google.com: domain of jonathanbcoe@gmail.com designates 2a00:1450:400c:c09::22d as permitted sender) client-ip=2a00:1450:400c:c09::22d; Original-Received: by mail-wm0-x22d.google.com with SMTP id z126so111670797wme.0 for ; Wed, 06 Jul 2016 06:25:10 -0700 (PDT) X-Received: by 10.194.11.5 with SMTP id m5mr20706563wjb.119.1467811509460; Wed, 06 Jul 2016 06:25:09 -0700 (PDT) Original-Received: from [10.120.227.94] ([213.205.195.94]) by smtp.gmail.com with ESMTPSA id vs4sm1140553wjb.24.2016.07.06.06.25.08 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 06 Jul 2016 06:25:08 -0700 (PDT) In-Reply-To: X-Mailer: iPhone Mail (13F69) X-Original-Sender: jonathanbcoe@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of jonathanbcoe@gmail.com designates 2a00:1450:400c:c09::22d as permitted sender) smtp.mailfrom=jonathanbcoe@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-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:26590 Archived-At: --Apple-Mail-9097D46E-DDCE-45CF-ACDC-74A4191AF82A Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable > On 6 Jul 2016, at 13:06, Mathias Gaunard wrote: >=20 >> On 4 July 2016 at 16:15, Bengt Gustafsson wrote: >> I have been following the recent thread about empty base optimization, o= r rather, the lack of empty member optimization possibility. And today I ag= ain fell in the 0 sized array trap in metaprogramming, noticing that it cre= ates quite a few problems requiring extra coding. >>=20 >> This idea struck me to solve both of these issues at once by a few small= changes: >>=20 >> 1. Allow zero sized arrays in C++. >>=20 >> 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. >>=20 >> 2. Define that a zero size array occupies zero bytes. >>=20 >> As zero size arrays have never been allowed in C++ it can't be a breakin= g change to define that the now allowed zero size arrays actually consume n= o bytes regardless of the size of the element. >=20 > So you want >=20 > struct Foo > { > char array[0]; > int value; > }; >=20 > to be well-formed? >=20 > That's problematic for a number of reasons. Could you elaborate? > --=20 > 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/isoc= pp.org/d/msgid/std-proposals/CALnjya-8Kn7VR3J0yxfPoR%2BzpDGDNxXSUwh4ZpD-t1K= dbN9Prw%40mail.gmail.com. --=20 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 e= mail 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/DA1D891D-5D63-44A8-BA31-A8D9BCC9E684%40gmail.com= .. --Apple-Mail-9097D46E-DDCE-45CF-ACDC-74A4191AF82A Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On 6= Jul 2016, at 13:06, Mathias Gaunard <mathias@gaunard.com> wrote:

On 4 July 2016 at 16:15, Bengt Gustafsson <bengt.gustafss= on@beamways.com> 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, noti= cing that it creates quite a few problems requiring extra coding.

This idea struck me to solve both of these issues at once b= y a few small changes:

1. Allow zero sized arrays = in C++.

No code would break by just allowing somet= hing previously forbidden. The problem with allowing this could have been t= o 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 ca= n't be a breaking change to define that the now allowed zero size arrays ac= tually consume no bytes regardless of the size of the element.
<= /blockquote>

So you want

struct Foo
{
   char array[0];
   int = value;
};

to be well-formed?

That= 's problematic for a number of reasons.

Could you elaborate?

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