220 31540 article Path: news.gmane.org!.POSTED!not-for-mail From: Morwenn Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: First draft of [[unreachable]] attribute proposal Date: Fri, 10 Mar 2017 04:41:05 -0800 (PST) Lines: 167 Approved: news@gmane.org Message-ID: References: <74928e4c-8f1e-4036-93d8-2560c27b651d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_2161_913442477.1489149665587" X-Trace: blaine.gmane.org 1489149685 32305 195.159.176.226 (10 Mar 2017 12:41:25 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 10 Mar 2017 12:41:25 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBC2ZP4V74IFBBYV5RLDAKGQEMYVZWBA@isocpp.org Fri Mar 10 13:41:15 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f199.google.com ([209.85.161.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cmJr2-00062H-Dk for gclcip-std-proposals@m.gmane.org; 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Fri, 10 Mar 2017 04:41:07 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.4.119 with SMTP id 110ls8105821otc.44.gmail; Fri, 10 Mar 2017 04:41:06 -0800 (PST) X-Received: by 10.157.13.82 with SMTP id 76mr2060988oti.6.1489149666193; Fri, 10 Mar 2017 04:41:06 -0800 (PST) In-Reply-To: <74928e4c-8f1e-4036-93d8-2560c27b651d@isocpp.org> X-Original-Sender: morwenn29@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:31540 Archived-At: ------=_Part_2161_913442477.1489149665587 Content-Type: multipart/alternative; boundary="----=_Part_2162_1258772651.1489149665587" ------=_Part_2162_1258772651.1489149665587 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Le vendredi 10 mars 2017 13:04:37 UTC+1, Andrzej Krzemie=C5=84ski a =C3=A9c= rit : > > > > W dniu czwartek, 9 marca 2017 04:49:35 UTC+1 u=C5=BCytkownik Myriachan na= pisa=C5=82: >> >> I wrote up a proposal document for a new attribute, [[unreachable]],=20 >> which lets you mark locations in code as being unreachable for optimizat= ion=20 >> purposes, or to suppress certain warnings. >> >> This has been discussed on the mailing list before; there's a link to=20 >> that thread in the .pdf. >> >> https://1drv.ms/b/s!Agwy_QljRwlGgcoJeZMiimuq3H36Ww=20 >> >> >> I have no idea what to do with it now. If you have any comments on the= =20 >> content, or how to actually proceed, let me know! =3D^-^=3D >> >> Melissa >> > > Melissa, the functionality you propose is definitely useful. However, it= =20 > looks to me that it is already contained in the contracts proposal:=20 > http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/p0542r0.html > > Under the contract proposal, anywhere where the statement is expected, yo= u=20 > can type: > > [[assert: false]]; > > Which is somewhat similar to old macro assert(), but is not a macro=20 > anymore and is allowed to be a hint for optimizations and warning=20 > generation, and additionally is allowed to be static-analysis-tested for= =20 > correctness. > > If contracts get accepted [[unreachable]] will become redundant. However= =20 > contracts are a big and novel feature, which makes it likely for them to= =20 > miss the place in C++20. Your proposal is small, so it has bigger chances= =20 > of succeeding. > > Anyway, it would be fair to put a comparison with contracts in your=20 > proposal. > > Good luck. > &rzej; =20 > While [[assert axiom: false]] is probably semantically equivalent to the=20 proposed [[unreachable]], the former doesn't really convey the meaning. I would be more confortable adding [[unreachable]] to the default branch of= =20 a switch than the equivalent [[assert axiom: false]]. --=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/cc73faa8-2e33-4314-b50b-cf715b4e7ccf%40isocpp.or= g. ------=_Part_2162_1258772651.1489149665587 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Le vendredi 10 mars 2017 13:04:37 UTC+1, Andrzej Krzemie= =C5=84ski a =C3=A9crit=C2=A0:
<= div dir=3D"ltr">

W dniu czwartek, 9 marca 2017 04:49:35 UTC+1 u=C5= =BCytkownik Myriachan napisa=C5=82:
I wrote up a proposal document for a new attribute, [[unr= eachable]], which lets you mark locations in code as being unreachable for = optimization purposes, or to suppress certain warnings.

This has bee= n discussed on the mailing list before; there's a link to that thread i= n the .pdf.

https://1drv.ms/b/s!Agwy_<= wbr>QljRwlGgcoJeZMiimuq3H36Ww

I have no idea what to do with it = now.=C2=A0 If you have any comments on the content, or how to actually proc= eed, let me know! =3D^-^=3D

Melissa

M= elissa, the functionality you propose is definitely useful. However, it loo= ks to me that it is already contained in the contracts proposal: http://www.open-st= d.org/jtc1/sc22/wg21/docs/papers/2017/p0542r0.html

Und= er the contract proposal, anywhere where the statement is expected, you can= type:

[[assert: false]];
=

Which is somewhat similar to old macro assert(), but is not a mac= ro anymore and is allowed to be a hint for optimizations and warning genera= tion, and additionally is allowed to be static-analysis-tested for correctn= ess.

If contracts get accepted [[unreachable]] will become redundant= .. However contracts are a big and novel feature, which makes it likely for = them to miss the place in C++20. Your proposal is small, so it has bigger c= hances of succeeding.

Anyway, it would be fair to put a comparison w= ith contracts in your proposal.

Good luck.
&rzej;=C2=A0
<= /div>

While [[assert axiom: false]] is probably semantically equ= ivalent to the proposed [[unreachable]], the former doesn't really convey the meaning.<= br>
I would be more confortable adding [[unreachable]] to the default branch of a switch than the equivalent [[assert axiom: false]].

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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.
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/cc73faa8-2e33-4314-b50b-cf715b4e7ccf= %40isocpp.org.
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