220 31913 <9523C82E-3AF8-40ED-9102-B89084FC7D26@gmail.com> article Path: news.gmane.org!.POSTED!not-for-mail From: Alberto Barbati Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: This variable should not be named: an identifier (not) to remember Date: Fri, 31 Mar 2017 08:49:43 +0200 Lines: 72 Approved: news@gmane.org Message-ID: <9523C82E-3AF8-40ED-9102-B89084FC7D26@gmail.com> References: <985b9b2a-c734-45eb-95f4-db4dc0d309a1@isocpp.org> <2235919.4GAIbDEcRC@tjmaciei-mobl1> <3760122.IY8cFr858X@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 (1.0) Content-Type: multipart/alternative; boundary=Apple-Mail-8BD016DC-4DF2-4AB4-81DA-85B1E644EB70 Content-Transfer-Encoding: 7bit X-Trace: blaine.gmane.org 1490942992 28509 195.159.176.226 (31 Mar 2017 06:49:52 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 31 Mar 2017 06:49:52 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCPY5DV6RIMBBCXY67DAKGQE4BNC3RI@isocpp.org Fri Mar 31 08:49:48 2017 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 1ctqNR-0006Iu-0Z for gclcip-std-proposals@m.gmane.org; Fri, 31 Mar 2017 08:49:41 +0200 Original-Received: by mail-lf0-f71.google.com with SMTP id f66sf14029065lfe.23 for ; Thu, 30 Mar 2017 23:49:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=content-transfer-encoding:from:mime-version:date:message-id:subject :in-reply-to:references: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=XKrpKtzFtzybQcZGhq/v8d4wyctm4HEVDUUlcoXXxl4=; b=ESwaQnTnZsXVK1vsqmLAnbfQCUtn2y80Q3pF4x56IxH9DkTIQkdMGoH5JON2Gy5PH6 mPfnAOvmMyfuXd66mwIMUMZl+WepIGS8Bv0QxVqxJQAOdTKC91V4vGsrZdmbbno4NDNQ FloDTqyVruBI/2gf98s/f5HSXMydJb3bl8Iq9pOa4VlO/cwHOVocgzk6LsFvQshVqq+b Qrs1aZVuKmO6rBc5Dfx7eY5thLSFBKeo/jZlbw+TBrTuH0RikIycISPDoNg7BQTcVDFs gqVVp8SjJUaGCgQZFjjKr2rJDZgIBZb/QJr0mLHq+CnNrjN9AmWmQVnPlXRRH2lwxGqf KHPA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:content-transfer-encoding:from:mime-version:date :message-id:subject:in-reply-to:references: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=XKrpKtzFtzybQcZGhq/v8d4wyctm4HEVDUUlcoXXxl4=; b=Z29epXSpjh84bRFqZI372epDAYWt5L5N00VXP7q0tmx1eIOTUUKiVrKwea4XasTGxp QvwJTl3XbaoDaRUxmj1CoFqb3GmKgMXprY6KXNY9CX5b9DPFChYzBctu+2Lh/Bqql6zI T97S9NioZWia+mtnVlQrbeqdUSvl7r9yE35pfLi0cTOwCf8xrnR7e1N2Wz9cigvhJGLG jv4NX59dgIFpoYt4/CNjoQYp22iLhyw9fxgljzek4O0xy8Q9vS+EoPXYrqK6mBv7dmhV RS9HZnygQL2TDQYwq3ModHW8NqWmx3HkeFz3kN0qB/8f1BVLp6JfwnMRJEriwVAAowr5 DMf X-Gm-Message-State: AFeK/H0nGUHzc9KeuIXgHrPVwLu1Ed6Ze/5hQaVPo4GxxLZvgHpvgAVuqG4ZarNUPtfmSg== X-Received: by 10.46.71.19 with SMTP id u19mr426485lja.7.1490942987275; Thu, 30 Mar 2017 23:49:47 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.184.4 with SMTP id i4ls3177503wmf.21.gmail; Thu, 30 Mar 2017 23:49:45 -0700 (PDT) X-Received: by 10.28.214.149 with SMTP id n143mr1569518wmg.127.1490942985744; Thu, 30 Mar 2017 23:49:45 -0700 (PDT) Original-Received: from mail-wr0-x22a.google.com (mail-wr0-x22a.google.com. [2a00:1450:400c:c0c::22a]) by mx.google.com with ESMTPS id m197si2095299wmd.63.2017.03.30.23.49.45 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 30 Mar 2017 23:49:45 -0700 (PDT) Received-SPF: pass (google.com: domain of albertobarbati@gmail.com designates 2a00:1450:400c:c0c::22a as permitted sender) client-ip=2a00:1450:400c:c0c::22a; Original-Received: by mail-wr0-x22a.google.com with SMTP id w11so90204908wrc.3 for ; Thu, 30 Mar 2017 23:49:45 -0700 (PDT) X-Received: by 10.28.113.12 with SMTP id m12mr1741622wmc.18.1490942985188; Thu, 30 Mar 2017 23:49:45 -0700 (PDT) Original-Received: from [1.137.172.222] ([91.253.168.84]) by smtp.gmail.com with ESMTPSA id c8sm5482188wrd.57.2017.03.30.23.49.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 30 Mar 2017 23:49:44 -0700 (PDT) In-Reply-To: X-Mailer: iPhone Mail (14D27) X-Original-Sender: AlbertoBarbati@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of albertobarbati@gmail.com designates 2a00:1450:400c:c0c::22a as permitted sender) smtp.mailfrom=albertobarbati@gmail.com; dmarc=pass (p=NONE sp=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:31913 Archived-At: --Apple-Mail-8BD016DC-4DF2-4AB4-81DA-85B1E644EB70 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable > Il giorno 30 mar 2017, alle ore 23:41, Vitali Lovich = ha scritto: >=20 > Ah. But I forgot now that with structured binding there's a hidden local = variable anyway for the tuple itself. I was thinking the compiler was smar= t and applied RVO to the individual elements directly. Exactly. All RAII logic is (or at least should be) performed by the "main" = hidden object that is being decomposed. No get() function should ever depen= d on the side effects of other get() function on the same object, because o= therwise the following valid code would become problematic: auto x =3D getstr(); auto v =3D get<1>(x); A.=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/9523C82E-3AF8-40ED-9102-B89084FC7D26%40gmail.com= .. --Apple-Mail-8BD016DC-4DF2-4AB4-81DA-85B1E644EB70 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

Il giorno 30 mar 2017, alle ore 23:41, Vitali Lovich <vlovich@gmail.com> ha scritto:

Ah. But I forgot now that with struc= tured binding there's a hidden local variable anyway for the tuple itself.&= nbsp; I was thinking the compiler was smart and applied RVO to the individu= al elements directly.

Exactly. All R= AII logic is (or at least should be) performed by the "main" hidden object = that is being decomposed. No get() function should ever depend on the side = effects of other get() function on the same object, because otherwise the f= ollowing valid code would become problematic:

auto x =3D=  getstr();
auto v =3D get<1>(x);

A.&nbs= p;

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