220 21174 article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: P0007R0: Constant View: A proposal for a std::as_const helper function template Date: Fri, 2 Oct 2015 22:55:54 +0800 Lines: 96 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2104\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_D9C1848B-833F-449D-8E99-E4A4ECEC163F" X-Trace: ger.gmane.org 1443797770 4571 80.91.229.3 (2 Oct 2015 14:56:10 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 2 Oct 2015 14:56:10 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBAFWXKYAKGQEDLQINTQ@isocpp.org Fri Oct 02 16:56:05 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yk0-f198.google.com ([209.85.160.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Zi1kh-0002q5-OO for gclcip-std-proposals@m.gmane.org; Fri, 02 Oct 2015 16:56:03 +0200 Original-Received: by ykft14 with SMTP id t14sf139581862ykf.0 for ; Fri, 02 Oct 2015 07:56:03 -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=n4CyD50GcD8IonL30AhKqERhupoB3IuvTKzjOtcdFSQ=; b=ZpxRK4J/AQnojXdyhNvA0rRITTQt2SBIWlEXMfShjsWEP1YXNK39ZuptdEuYGbltu6 uoE+1xcysxAcMtTybcjlZyaaWw1qe8Htec9BYJDVNqF7eoX81mkTQ7nAElNH0LRvtL6s j0kFTbbLt6P3zrSxU1vgAYYNiQm955THPbB6brszB7/pUp6I0iXkd13EIxO3AeO9y2b/ OEvaHhDWuFI2KSTXBBDe5jw2iIgCCn24Z4OKPvqaoIIwKNLcjozsvtEJgVEEO5sY3tkr GWwpXebnAn7POlvTgu3NHjbjtpFoiuUGVuDtjBwwWOGXhnAMpdT3XHY+TIELUh9BfMzN AAhA== X-Gm-Message-State: ALoCoQmQdaIJ2IDYrkxLvfo7QrNhEqD8IxqOEHvZROUmt9CWUhnFqlHDmmsRMCodNzeZLI0PfVPm X-Received: by 10.129.125.130 with SMTP id y124mr12963580ywc.14.1443797763125; Fri, 02 Oct 2015 07:56:03 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.130.157 with SMTP id m29ls967415ioi.33.gmail; Fri, 02 Oct 2015 07:56:00 -0700 (PDT) X-Received: by 10.107.128.106 with SMTP id b103mr20360609iod.116.1443797760166; Fri, 02 Oct 2015 07:56:00 -0700 (PDT) Original-Received: from mail-pa0-x236.google.com (mail-pa0-x236.google.com. [2607:f8b0:400e:c03::236]) by mx.google.com with ESMTPS id y42si8959199ioi.100.2015.10.02.07.56.00 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 02 Oct 2015 07:56:00 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c03::236 as permitted sender) client-ip=2607:f8b0:400e:c03::236; Original-Received: by pablk4 with SMTP id lk4so107978483pab.3 for ; Fri, 02 Oct 2015 07:55:59 -0700 (PDT) X-Received: by 10.67.5.66 with SMTP id ck2mr20537078pad.137.1443797759843; Fri, 02 Oct 2015 07:55:59 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.177]) by smtp.gmail.com with ESMTPSA id y5sm12406887pbt.77.2015.10.02.07.55.57 for (version=TLSv1/SSLv3 cipher=OTHER); Fri, 02 Oct 2015 07:55:59 -0700 (PDT) In-Reply-To: X-Mailer: Apple Mail (2.2104) 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::236 as permitted sender) smtp.mailfrom=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:21174 Archived-At: --Apple-Mail=_D9C1848B-833F-449D-8E99-E4A4ECEC163F Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 > On 2015=E2=80=9310=E2=80=9302, at 10:45 PM, Ville Voutilainen wrote: >=20 > On 2 October 2015 at 17:38, Matthew Woehlke wr= ote: >> While it's true that we want lifetime extension anyway, the reality is >> that std::as_const *also* doesn't work without core language changes, >> i.e. as a library-only solution it is incomplete. Moreover, I don't see >> that it cannot be made to work at all for an rvalue of a type that is >> not {copy,move}able without introducing mandatory copy elision. (The >=20 > Ah, yes, the rvalue overload is returning by value, which doesn't work fo= r > forwarding cases. Then again, for forwarding cases, one can forward() > so perhaps that wasn't important. If T is a reference type, then const will be ignored in forward. It=E2=80=99s another use case for generalized lifetime extension (P0066) bu= t I=E2=80=99m not sure whether that proposal is getting closer or further := P A core language feature, const(expr) or const{expr} parsed as if const was = a simple-type-specifier, would produce temporary expressions=E2=80=A6 --=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=_D9C1848B-833F-449D-8E99-E4A4ECEC163F Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=UTF-8
On 2015=E2=80=9310= =E2=80=9302, at 10:45 PM, Ville Voutilainen <ville.voutilainen@gmail.com> wrote:
On 2 October 20= 15 at 17:38, Matthew Woehlke <mwoehlke.floss@gmail.com> wrote:
While it's true that we want lifetime extensio= n anyway, the reality is
that std::as_const *also* doesn't wo= rk without core language changes,
i.e. as a library-only solu= tion it is incomplete. Moreover, I don't see
that it cannot b= e made to work at all for an rvalue of a type that is
not {co= py,move}able without introducing mandatory copy elision. (The

Ah, yes, the rvalue overload is returning by v= alue, which doesn't work for
forwarding cases. Then again, fo= r forwarding cases, one can forward<const T>()
so perha= ps that wasn't important.

If T=  is a reference type, then const will be ignored in forward<const T>.

It=E2=80=99s another use case for generalized lifetime extensio= n (P0066) but I=E2=80=99m not sure whether that proposal is getting closer = or further :P

A c= ore language feature, const(expr) = or const{expr} parsed as if&n= bsp;const was = a simple-type-specifier, would produce temporary expressions=E2=80=A6
=

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