220 37090 article Path: news.gmane.org!.POSTED!not-for-mail From: Corentin Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: specify concept implementation Date: Mon, 26 Feb 2018 21:21:03 +0000 Lines: 151 Approved: news@gmane.org Message-ID: References: <93e7e509-edf0-4df6-9b2f-555bba92a04a@isocpp.org> <805d3933-0cf9-465f-906c-849ab25c7a63@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="001a113cd4f6f6e6bc0566241607" X-Trace: blaine.gmane.org 1519679954 15637 195.159.176.226 (26 Feb 2018 21:19:14 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 26 Feb 2018 21:19:14 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC72FQ6X7MLRBSXU2HKAKGQEQ74ZIRQ@isocpp.org Mon Feb 26 22:19:10 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f70.google.com ([209.85.218.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eqQAv-0003V7-DC for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id c145sor3767182oig.15.2018.02.26.13.21.14 for (Google Transport Security); Mon, 26 Feb 2018 13:21:14 -0800 (PST) Received-SPF: pass (google.com: domain of corentin.jabot@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.202.169.140 with SMTP id s134mr7901146oie.318.1519680073687; Mon, 26 Feb 2018 13:21:13 -0800 (PST) In-Reply-To: X-Original-Sender: corentin.jabot@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=jwTk2IV2; spf=pass (google.com: domain of corentin.jabot@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=corentin.jabot@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE 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:37090 Archived-At: --001a113cd4f6f6e6bc0566241607 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable I have a somewhat philosophical view on that. If we have a syntax to tightly couple a concept to a satisfying declaration, then is it still a concept ? Because it starts to look more like regular interface / inheritance. I see why one would want to document that a class satisfies a concept, but when it stops to do so, does that means that the class is somehow broken and should be ill-formed ? I think the implicit nature of concepts is important and obviously powerful. For this reason, I think the static_assert method is best. While not directly comparable to concepts, Go interfaces are implicit and it does seems to work even on large codebases Le lun. 26 f=C3=A9vr. 2018 =C3=A0 21:04, Nicolas Lesser a =C3=A9crit : > As for static_assert, no it's not. >> static_assert on an explicit concept call only triggers a "something wen= t >> wrong" level of informations: https://godbolt.org/g/5Hb7zP >> > > That's a quality of implementation issue. I fully expect gcc to improve > this error message in the future. > > I agree though that a whole language feature would be overkill. >> What about an attribute? >> > > Why not use requires? > > struct A requires C {}; > > It looks more like a function constraint and doesn't require any weird > language feature. Also, attributes should not change the meaning of the > program if they are ignored, so using attributes is a non-starter. > > -- > 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/CALmDwq1g4Sa= g%3D9c_eW3Qdy3KOUiHmhQTG1RB4fC1ZcgO6BfOtA%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/CA%2BOm%2BSgAn%2BacLBxzeEGPCYRw4B2FLvm5G0ZQ2Htjt= pi-%3D5sn0Q%40mail.gmail.com. --001a113cd4f6f6e6bc0566241607 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

I have a somewhat philosophical view on that.
If we have a syntax to tightly couple a concept to a satisfying decl= aration, then is it still a concept ? Because it starts to look more like r= egular interface / inheritance.

I see why one woul= d want to document that a class satisfies a concept, but when it stops to d= o so, does that means that the class is somehow broken and should be ill-fo= rmed ?

I think the implicit nature of concepts is = important and obviously powerful. For this reason, I think the static_asser= t method is best.

While not directly comparable to= concepts, Go interfaces are implicit and it does seems to work=C2=A0 even = on large codebases



<= br>

As for static_assert, no it's not.
<= div>static_assert on an explicit concept call only triggers a "somethi= ng went wrong" level of informations:=C2=A0https://godbolt.org/g/5Hb7zP

That's a quality of im= plementation issue. I fully expect gcc to improve this error message in the= future.

<= div dir=3D"ltr">
I agree though that a whole language feature would be = overkill.
What about an attribute?
<= br>
Why not use requires?

= struct A requires C<A> {};

It looks more lik= e a function constraint and doesn't require any weird language feature.= Also, attributes should not change the meaning of the program if they are = ignored, so using attributes is a non-starter.

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