220 29966 article Path: news.gmane.org!.POSTED!not-for-mail From: Richard Smith Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Rationale for why concepts can only be declared at namespace scope Date: Tue, 20 Dec 2016 17:15:17 -0800 Lines: 72 Approved: news@gmane.org Message-ID: References: <1dd1345b-0bc7-4768-8afd-fd6f4f611d8a@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a114420e8f808c6054420e313 X-Trace: blaine.gmane.org 1482282939 317 195.159.176.226 (21 Dec 2016 01:15:39 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 21 Dec 2016 01:15:39 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBDVNBJG4YAIBBOVP47BAKGQE4OD4VRY@isocpp.org Wed Dec 21 02:15:35 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f71.google.com ([209.85.215.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cJVVH-0007qw-7c for gclcip-std-proposals@m.gmane.org; Wed, 21 Dec 2016 02:15:35 +0100 Original-Received: by mail-lf0-f71.google.com with SMTP id c13sf52569076lfg.4 for ; Tue, 20 Dec 2016 17:15:40 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:sender:in-reply-to:references:from :date:message-id:subject: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=CszcqVzlKeFjpoGJ9zIcN2ZYf8lyeROiUpn1iWKfwUA=; b=Z4J9vbeWPimZ0m8QObEgwl1kESuKUllfn18Ligih7apnN1QagfDl5odCZNomVg0sYB nC4db+nL6eYKj9UVE6mWG7kmQI0Q1s3bK6V7s9KZ07fzG558TCFjxlpKOLqlZr9BZFsY jxBwlHqiPEVgl3A6gTkhDleYjZzeOgQ8hzoR1K9nt3AbK8mgOfjExlabFdCP0eaJ+0n2 bm+sIQy7G90zi426SjPWdIuOlLwC85cgm00QQ7BAwCQpaHFDeFesgVSwSjJmoC00JNWe mRU17zf0dlfnSdIETZN7zWtJWcXWX1E1zQHMl18MU2i68+piCwPyrIerRLpMeJL5wlsI 0OVQ== X-Gm-Message-State: AIkVDXJFocJd9tGMAn8lOOkrvXXRyhxTbMeKPP2+bTqiLkCMFrGvA/1eDJeTnJWe7hXryA== X-Received: by 10.46.69.135 with SMTP id s129mr186031lja.1.1482282939918; Tue, 20 Dec 2016 17:15:39 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.154.138 with SMTP id c132ls1841826wme.6.gmail; Tue, 20 Dec 2016 17:15:38 -0800 (PST) X-Received: by 10.28.211.72 with SMTP id k69mr2181662wmg.137.1482282938388; Tue, 20 Dec 2016 17:15:38 -0800 (PST) Original-Received: from mail-wm0-x244.google.com (mail-wm0-x244.google.com. [2a00:1450:400c:c09::244]) by mx.google.com with ESMTPS id hm2si25250141wjb.167.2016.12.20.17.15.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 20 Dec 2016 17:15:38 -0800 (PST) Received-SPF: pass (google.com: domain of metafoo@gmail.com designates 2a00:1450:400c:c09::244 as permitted sender) client-ip=2a00:1450:400c:c09::244; Original-Received: by mail-wm0-x244.google.com with SMTP id l2so2044695wml.2 for ; Tue, 20 Dec 2016 17:15:38 -0800 (PST) X-Received: by 10.28.142.16 with SMTP id q16mr2216677wmd.35.1482282937877; Tue, 20 Dec 2016 17:15:37 -0800 (PST) Original-Sender: metafoo@gmail.com Original-Received: by 10.80.175.37 with HTTP; Tue, 20 Dec 2016 17:15:17 -0800 (PST) In-Reply-To: <1dd1345b-0bc7-4768-8afd-fd6f4f611d8a@isocpp.org> X-Original-Sender: richard@metafoo.co.uk X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of metafoo@gmail.com designates 2a00:1450:400c:c09::244 as permitted sender) smtp.mailfrom=metafoo@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:29966 Archived-At: --001a114420e8f808c6054420e313 Content-Type: text/plain; charset=UTF-8 On 20 December 2016 at 16:25, Anthony Hall wrote: > Reading the current version of the Concepts TS, n4630, I see that both > variable and function concepts are only allowed at namespace scope, but I > don't see a reason given for this. I first stumbled upon this restriction > while trying to write concepts in the private: section of a class, because > they would be useful to me in writing the class itself, but they have no > use in the class's interface or to outside client code. > > I also would find being able to write them in > struct/class/function/lambade/basically any scope, as a way to factor out > repetitive ad-hoc 'requires' constraints. > > Does anyone know the reasons that concepts have been explicitly limited to > namespace scope? > Yes. It avoids the possibility of a dependent name resolving to a concept name. This avoids a selection of nasty problems with dependent name lookup and with partial ordering in the presence of dependent concepts. -- 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/CAOfiQq%3DDAYw2ekp1LG7Jt%2BatYeWptzHQVihOkzFzZ2_7S5sDdw%40mail.gmail.com. --001a114420e8f808c6054420e313 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On 2= 0 December 2016 at 16:25, Anthony Hall <anthrond@gmail.com>= wrote:
Reading the curr= ent version of the Concepts TS,=C2=A0n4630, I see that both variable and fu= nction concepts are only allowed at namespace scope, but I don't see a = reason given for this.=C2=A0 I first stumbled upon this restriction while t= rying to write concepts in the private: section of a class, because they wo= uld be useful to me in writing the class itself, but they have no use in th= e class's interface or to outside client code.

I also would find= being able to write them in struct/class/function/lambade/basically a= ny scope, as a way to factor out repetitive ad-hoc 'requires' const= raints.

Does anyone know the reasons that concepts have = been explicitly limited to namespace scope?
Yes. It avoids the possibility of a dependent name resolving t= o a concept name. This avoids a selection of nasty problems with dependent = name lookup and with partial ordering in the presence of dependent concepts= ..

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