220 11830 article Path: news.gmane.org!not-for-mail From: Ville Voutilainen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: N4078: Rvalue reference overloads for value() method returns object by value Date: Fri, 11 Jul 2014 10:35:18 +0300 Lines: 33 Approved: news@gmane.org Message-ID: References: <4DA018C3-2327-4F55-B7F8-7988EC7B789A@gmail.com> <1a858a77-310b-4591-aaf5-960c40d9f5fc@isocpp.org> <66AF41C1-CB37-4311-98EA-D47DBC6068DC@gmail.com> <66c38b61-7a95-4ace-b34f-2346bb334fb9@isocpp.org> <6F4B3C72-9962-48DC-8527-0C89EA1B9710@gmail.com> <35873CE5-ED8C-4C03-A6A1-E4132DECD91F@gmail.com> <335948E6-8140-4673-B958-930356A52070@gmail.com> <76ACA175-5A44-4BE8-B49F-BAC6DA65E6B1@gmail.com> <4D3852AD-1AEB-44BA-941C-D645BAD19405@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: ger.gmane.org 1405064127 17813 80.91.229.3 (11 Jul 2014 07:35:27 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 11 Jul 2014 07:35:27 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC5JHI7A7ALRBN5H72OQKGQEXIF6Y3I@isocpp.org Fri Jul 11 09:35:21 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ie0-f199.google.com ([209.85.223.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1X5VMW-0005Ix-Iq for gclcip-std-proposals@m.gmane.org; Fri, 11 Jul 2014 09:35:20 +0200 Original-Received: by mail-ie0-f199.google.com with SMTP id tr6sf3656137ieb.10 for ; Fri, 11 Jul 2014 00:35:19 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=IHJegJ+GI9KhrgMr1qmyytz5k0Tkoz/xcZbVQYj5gzA=; b=W4QFLM3LwSeZG1zIm+fn6V6PgWfpxYxHoNKyiykNG/QG0qPuPPrJfwJ1icAx1LIsgh DFh9yUv+X+qkXJ2F4pB43mLsuLJPF4P5TMm4uPCVNQ30IrSTdznaK/RQLPVYw0S41WTw h5xjuSeQGqKv+FjuSoZLHiZjbh01GhM3Bj1ldIG7OyDW0h1XxVN68QAN9igoMUTeZ9n8 dTTfkONqOhRG+Nm2mg5EbWgTBNiisx39c5MRR9rSrEt2cQynoWbJyquZVW3nYM2FGzOE ZDYIeoTCNTZmu/3HO/GwTwufO8ixXRfdXVeHWewopnSWpI4EBuFUI4zEW2lW7Gfv9CxE Rtmw== X-Gm-Message-State: ALoCoQlxy5Nj2Kt6JJK77Gbo+jsRoEgsvzkC6QCrREY9FWisEu07iuJBOXRniaN8R1ZrNXJff+u2 X-Received: by 10.182.181.35 with SMTP id dt3mr7175077obc.9.1405064119668; Fri, 11 Jul 2014 00:35:19 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.25.144 with SMTP id 16ls232800qgt.45.gmail; Fri, 11 Jul 2014 00:35:18 -0700 (PDT) X-Received: by 10.140.21.170 with SMTP id 39mr57103312qgl.31.1405064118939; Fri, 11 Jul 2014 00:35:18 -0700 (PDT) Original-Received: from mail-qg0-x22b.google.com (mail-qg0-x22b.google.com [2607:f8b0:400d:c04::22b]) by mx.google.com with ESMTPS id t2si169355qcq.34.2014.07.11.00.35.18 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 11 Jul 2014 00:35:18 -0700 (PDT) Received-SPF: pass (google.com: domain of ville.voutilainen@gmail.com designates 2607:f8b0:400d:c04::22b as permitted sender) client-ip=2607:f8b0:400d:c04::22b; Original-Received: by mail-qg0-f43.google.com with SMTP id a108so517493qge.16 for ; Fri, 11 Jul 2014 00:35:18 -0700 (PDT) X-Received: by 10.140.109.118 with SMTP id k109mr83338384qgf.98.1405064118811; Fri, 11 Jul 2014 00:35:18 -0700 (PDT) Original-Received: by 10.224.31.137 with HTTP; Fri, 11 Jul 2014 00:35:18 -0700 (PDT) In-Reply-To: X-Original-Sender: ville.voutilainen@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of ville.voutilainen@gmail.com designates 2607:f8b0:400d:c04::22b as permitted sender) smtp.mail=ville.voutilainen@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-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:11830 Archived-At: On 11 July 2014 08:28, wrote: > I we add the following r-value overload as originally proposed, it will > have following effect: //as always: optional f(); > 1. *std::forward(u) with optional will actually perfectly forward > 2. auto&& v = f().value() - will still create a dangling refence (as it it > will now we two dangling reference), auto will be deduced to T instead of > T&, but v still we be l-value > 3. g(f.value()), when g(const T&) accepts by cont& will work the same > 4. h(f.value()), when h(T) accepts by value, will benefit from move > 5. f().value() = 20, will no longer compile if T has l-value qualified > operator=(T const&) & //this actullay should be a true > I found this actually being good not-breaking changes, similar to one > created my adding move constructor to every feasible class in C++11. > And even adding it to the single optional will not create any surprising > effect in the code > I think adding such overloads to containers is actually possible, without > breaking many code. I think we should do what N3982 does with the addition of const-rvalue-ref-qualified overloads. With the addition of those, people who care about forwarding const-rvalues perfectly will get what they need. -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. .