220 19746 <383084B6-C962-4EFD-9F63-A643349DA12E@gmail.com> article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: constexpr in the era of modules. Date: Mon, 10 Aug 2015 20:14:25 +0800 Lines: 102 Approved: news@gmane.org Message-ID: <383084B6-C962-4EFD-9F63-A643349DA12E@gmail.com> References: <2671d071-9935-41fe-91d5-94423309267a@isocpp.org> <647AFA8B-6C17-44DD-9BB3-E9E0F7B9D0C6@gmail.com> <77b7c7d1-99f1-49be-925b-a43d7250fa71@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2098\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_8981BCA6-500E-4BD7-8FFB-0E595BDB5431" X-Trace: ger.gmane.org 1439208909 7287 80.91.229.3 (10 Aug 2015 12:15:09 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 10 Aug 2015 12:15:09 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBRVLUKXAKGQEKMAC7YY@isocpp.org Mon Aug 10 14:15:05 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f199.google.com ([209.85.220.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZOlyq-0005Rj-6S for gclcip-std-proposals@m.gmane.org; Mon, 10 Aug 2015 14:15:04 +0200 Original-Received: by qkfn3 with SMTP id n3sf217542877qkf.3 for ; Mon, 10 Aug 2015 05:15:03 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:content-type:message-id:mime-version :subject:date:references:to:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=4rfi0et5bwIzqcNOXmvlNbNzhyStnmvDHbwxYtJcy1Y=; b=PqPD7tMqSo/PnVCOAvvhrTrk78U0JWnJ6o1VTAh97CC3epPPL9Vn0jXn9KBRsIJnJ6 6Z0K1er/lEGMnNz8aKKNeXPVtRyNk2f8BQ2ebIj0Puat+s3oo+FEZ3XXrrY1JoGma0Z1 w2TLRBbucRDFj51O1J92962SOVdIKGohkiYnjCbJGHu6kekM1UAQhnifkf82jCkhq9yJ Ryp0WeWnxh3kSFDA2cGqIlJrs3nxBX7kjydMYUkpAJRH9QB+Uz0lCf11c1svmYnMJQGc wiA9gFhsl1HW4F+SXkQPUzgUOKOalWII1TdQBiOIvXPiiq2QgIGg7QACZ8oYKOVuCbyz xZDg== X-Gm-Message-State: ALoCoQkm33FWROO5C76XKyySIuAtntfOTqD1vrasfEIryuaPW0BenBKcTG/jw35xAVDa7ek+O14H X-Received: by 10.129.145.72 with SMTP id i69mr20685298ywg.57.1439208903155; Mon, 10 Aug 2015 05:15:03 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.13.69 with SMTP id 66ls1744765ion.68.gmail; Mon, 10 Aug 2015 05:15:02 -0700 (PDT) X-Received: by 10.68.229.195 with SMTP id ss3mr16156810pbc.100.1439208902335; Mon, 10 Aug 2015 05:15:02 -0700 (PDT) Original-Received: from mail-pa0-x235.google.com (mail-pa0-x235.google.com. [2607:f8b0:400e:c03::235]) by mx.google.com with ESMTPS id p15si15233041pdn.108.2015.08.10.05.15.02 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 10 Aug 2015 05:15:02 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c03::235 as permitted sender) client-ip=2607:f8b0:400e:c03::235; Original-Received: by pabyb7 with SMTP id yb7so105677327pab.0 for ; Mon, 10 Aug 2015 05:15:02 -0700 (PDT) X-Received: by 10.68.68.173 with SMTP id x13mr43834900pbt.143.1439208901466; Mon, 10 Aug 2015 05:15:01 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.44.91]) by smtp.gmail.com with ESMTPSA id lk4sm19882693pab.23.2015.08.10.05.14.59 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 10 Aug 2015 05:15:00 -0700 (PDT) In-Reply-To: <77b7c7d1-99f1-49be-925b-a43d7250fa71@isocpp.org> X-Mailer: Apple Mail (2.2098) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c03::235 as permitted sender) smtp.mail=potswa@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-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:19746 Archived-At: --Apple-Mail=_8981BCA6-500E-4BD7-8FFB-0E595BDB5431 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 > On 2015=E2=80=9308=E2=80=9310, at 7:27 PM, german.diago@hubblehome.com wr= ote: >=20 > "The community consensus seems to be that constexpr isn=E2=80=99t noise b= ut a useful annotation." >=20 > Well, I understand the severe limitations or that it may be technically u= nfeasible, but as a function annotation, I do not see > how it could be useful, since a function could most of the time be "poten= tially constexpr".=20 As the Q&A shows, I tend to agree with you, against the majority. At least,= when writing a constexpr metaprogramming library or a computation of some = nontrivial constant data structures, it=E2=80=99s noisy to mark every singl= e declaration as constexpr. That was the motivation of my constexpr block s= cope suggestion. Maybe, once the issue has come up for more people, a propo= sal will find support. I don=E2=80=99t think I=E2=80=99d advise anyone to just mark every function= as constexpr indiscriminately. > In D they just say: >=20 > enum auto val =3D myFunc(); >=20 > and get it done. That=E2=80=99s not quite the same. C++ constexpr allows opportunistic evalu= ation in non-constant expression contexts as well. It might cause trouble (= slow compile times, reduced compiler stability) to have the compiler specul= atively evaluating every expression, even functions of nontrivial complexit= y that weren=E2=80=99t intended for compile time. --=20 ---=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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. --Apple-Mail=_8981BCA6-500E-4BD7-8FFB-0E595BDB5431 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=UTF-8
On 2015=E2=80=9308= =E2=80=9310, at 7:27 PM, german.diago@hubblehome.com wrote:

"The community= consensus seems to be that constexpr isn=E2=80=99t noise but a useful anno= tation."

Well, I understand the severe limitat= ions or that it may be technically unfeasible, but as a function annotation= , I do not see
how it could be useful, since a function could= most of the time be "potentially constexpr".

As the Q&A shows, I tend to a= gree with you, against the majority. At least, when writing a constexpr met= aprogramming library or a computation of some nontrivial constant data stru= ctures, it=E2=80=99s noisy to mark every single declaration as constexpr. T= hat was the motivation of my constexpr block scope suggestion. Maybe, once = the issue has come up for more people, a proposal will find support.
<= div>
I don=E2=80=99t think I=E2=80=99d advise anyo= ne to just mark every function as constex= pr indiscriminately.

In D they just say:
enum auto val =3D myFunc();

and get it done.

That=E2=80=99s not quite the same. C++ constexpr allo= ws opportunistic evaluation in non-constant expression contexts as well. It= might cause trouble (slow compile times, reduced compiler stability) to ha= ve the compiler speculatively evaluating every expression, even functions o= f nontrivial complexity that weren=E2=80=99t intended for compile time.

--

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To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
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Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/<= /a>.
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