220 31576 <51fa0491-97aa-48c8-b361-353f5ecc7a0f@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Myriachan Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: First draft of [[unreachable]] attribute proposal Date: Mon, 13 Mar 2017 13:28:28 -0700 (PDT) Lines: 116 Approved: news@gmane.org Message-ID: <51fa0491-97aa-48c8-b361-353f5ecc7a0f@isocpp.org> References: <74928e4c-8f1e-4036-93d8-2560c27b651d@isocpp.org> <996e889d-5922-4e13-84dd-d914ec44f5a4@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_9466_2146887185.1489436908096" X-Trace: blaine.gmane.org 1489436918 30996 195.159.176.226 (13 Mar 2017 20:28:38 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 13 Mar 2017 20:28:38 +0000 (UTC) Cc: dan@soundradix.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDKLT4PURQHRB3EBTTDAKGQEXWTXMQI@isocpp.org Mon Mar 13 21:28:27 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f200.google.com ([209.85.161.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cnWZr-0006fO-W0 for gclcip-std-proposals@m.gmane.org; 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Mon, 13 Mar 2017 13:28:29 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.43.103 with SMTP id f36ls3516861otd.0.gmail; Mon, 13 Mar 2017 13:28:28 -0700 (PDT) X-Received: by 10.157.82.47 with SMTP id e47mr3241847oth.18.1489436908794; Mon, 13 Mar 2017 13:28:28 -0700 (PDT) In-Reply-To: <996e889d-5922-4e13-84dd-d914ec44f5a4@isocpp.org> X-Original-Sender: myriachan@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:31576 Archived-At: ------=_Part_9466_2146887185.1489436908096 Content-Type: multipart/alternative; boundary="----=_Part_9467_961850427.1489436908096" ------=_Part_9467_961850427.1489436908096 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Sunday, March 12, 2017 at 6:19:15 AM UTC-7, d...@soundradix.com wrote: > > I think the opposite is correct WRT tooling; if you have a separate=20 > [[unreachable]] attribute, not only does it convey the intention better t= o=20 > the reader, but it also does to any tool which sees the attribute, so for= =20 > example a static analyzer can show exactly the path in which=20 > [[unreachable]] code becomes reachable, but not necessarily show it for= =20 > failing [[assert]] attributes. > > On Saturday, March 11, 2017 at 4:24:35 PM UTC+2, Andrzej Krzemie=C5=84ski= wrote: >> >> >> Given that the expression in the assertion is a compile-time constant=20 >> only [[assert: false]] is fine. But the interaction goes beyond only=20 >> syntax. If we have attribute [[unreachable]] maybe we want it to behave= =20 >> like [[assert: false]] in every detail; that is: allow calling contract= =20 >> violation handlers in test builds, if this place in the code is reached.= =20 >> This way the hint can be used not only for optimization, but also for=20 >> instrumentation. >> >> I noticed that the draft of contractual programming does not say that=20 behavior is undefined if the expression is false past an [[assert axiom]]. = =20 I asked co-author Professor J. Daniel Garcia about why the Standardese=20 didn't say that the behavior is undefined, and his reply was: Because that is not necessarily true. It is just that the assertion is not= =20 > checked. This to me gives [[unreachable]] a niche of its own, rather than merely=20 being a simpler subset of another proposal. Melissa --=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/51fa0491-97aa-48c8-b361-353f5ecc7a0f%40isocpp.or= g. ------=_Part_9467_961850427.1489436908096 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Sunday, March 12, 2017 at 6:19:15 AM UTC-7, d...@soundr= adix.com wrote:
I think the opposite is correct WRT tooling; if you have a separate [[unr= eachable]] attribute, not only does it convey the intention better to the r= eader, but it also does to any tool which sees the attribute, so for exampl= e a static analyzer can show exactly the path in which [[unreachable]] code= becomes reachable, but not necessarily show it for failing [[assert]] attr= ibutes.

On Saturday, March 11, 2017 at 4:24:35 PM UTC+2, A= ndrzej Krzemie=C5=84ski wrote:

Given that the expression in the assertion is a compil= e-time constant only [[assert: false]] is fine. But the interaction goes be= yond only syntax. If we have attribute [[unreachable]] maybe we want it to = behave like [[assert: false]] in every detail; that is: allow calling contr= act violation handlers in test builds, if this place in the code is reached= .. This way the hint can be used not only for optimization, but also for ins= trumentation.



=C2=A0I noticed that the draft of contractual programming do= es not say that behavior is undefined if the expression is false past an [[= assert axiom]].=C2=A0 I asked co-author Professor J. Daniel Garcia about wh= y the Standardese didn't say that the behavior is undefined, and his re= ply was:

B= ecause that is not necessarily true. It is just that the assertion is not c= hecked.

This to me gives [[unreachable]] a niche of it= s own, rather than merely being a simpler subset of another proposal.
Melissa

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