220 29177 article Path: news.gmane.org!.POSTED!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Initializer list for move-only types Date: Fri, 28 Oct 2016 08:14:41 +0800 Lines: 100 Approved: news@gmane.org Message-ID: References: <34f09dd5-e231-4a0b-a218-48c8eabe73c5@isocpp.org> <6030c88d-626c-4cf9-a0e6-963ae3fbe708@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 (Mac OS X Mail 9.1 \(3096.5\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_F6124A75-E701-4889-B14A-19BC37C5D640" X-Trace: blaine.gmane.org 1477613673 5020 195.159.176.226 (28 Oct 2016 00:14:33 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 28 Oct 2016 00:14:33 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBYNQZLAAKGQES6TYI2Q@isocpp.org Fri Oct 28 02:14:29 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f200.google.com ([209.85.161.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bzuoV-0000dL-GH for gclcip-std-proposals@m.gmane.org; Fri, 28 Oct 2016 02:14:27 +0200 Original-Received: by mail-yw0-f200.google.com with SMTP id u124sf55968753ywg.3 for ; Thu, 27 Oct 2016 17:14:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=from: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=ei/SOZVDiciVMPhvG5qWE85riFdEbS2kUo/JTShn+lw=; b=Tt2ru/rkrithgVwfwAZZJxJaLuoS/nddOqnmOMCtg+BFIKZraa/lmH6vnck2Ir+fS1 Vts/+Sp/dh/wytS7f/OTJpFCtT4M9am5pNGI1n7UlTHVdnSyl8qzb0kwPSU7U2OCTXi/ GDdXhO3Ls+SF5y3NxzlbFXg/RVjOJUGEhiIatr8PMIhdhlVS0czAUei3Czxe5wFDUXj2 gUtNgC49dEAmxwVdWBtPKvmJ7/otZo9kseG55q/gZzqb3j9Nri9Ajp6Cg3SuKKpaU4zn Z37t6E5R+l3l+R/430bZgl27bG/0XM8PFh0R8iHzCHpqJk60JVofKeAgclfAKJOKuLX+ XrZQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from: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=ei/SOZVDiciVMPhvG5qWE85riFdEbS2kUo/JTShn+lw=; b=Hxq8AllY8HD1rRlkoWSEQNfl28vm1ggnC7WbsXmXvGVhykGDLlyFwbExI9pt4cIKcF FMu3cvvdFAqfjk+bLF3BtKoTMx0dQEFnlx0wFHbQ1dfa8/iOd27hyWcLu8qf30Vx2w8Q UJLA8UcHlmp4sHpF/wAL8l5b/TCup93evvdRYiKpKeGXkvhE120yN+r3WQvkwMrDoiVg XSdIOiVRtXldDCOT+Fq6DeWd+J3998MReAZ6+8HmJfgDP37Jns/uIkN26aPWmo50ZLMh VATe1Wh25vCw7ooGZ7/c6Ouf3LoPMYk6FQBHUYKbhH5AcnP00eJ42zqL/C/E1kc7xCog t0eg== X-Gm-Message-State: ABUngvdGcGt0xhrBS0/ProaxwbKsthuOXtIbwcY9debPmLrM5AjECuXp4ey4UeApFhWS7w== X-Received: by 10.36.216.198 with SMTP id b189mr30175itg.30.1477613669635; Thu, 27 Oct 2016 17:14:29 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.134.168 with SMTP id q40ls1359857ioi.23.gmail; Thu, 27 Oct 2016 17:14:25 -0700 (PDT) X-Received: by 10.98.44.212 with SMTP id s203mr19493849pfs.84.1477613665288; Thu, 27 Oct 2016 17:14:25 -0700 (PDT) Original-Received: from mail-pf0-x22e.google.com (mail-pf0-x22e.google.com. [2607:f8b0:400e:c00::22e]) by mx.google.com with ESMTPS id mj3si8584455pab.275.2016.10.27.17.14.25 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 27 Oct 2016 17:14:25 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c00::22e as permitted sender) client-ip=2607:f8b0:400e:c00::22e; Original-Received: by mail-pf0-x22e.google.com with SMTP id 197so26429414pfu.0 for ; Thu, 27 Oct 2016 17:14:25 -0700 (PDT) X-Received: by 10.98.20.146 with SMTP id 140mr19519814pfu.51.1477613664867; Thu, 27 Oct 2016 17:14:24 -0700 (PDT) Original-Received: from [172.20.10.2] ([175.158.200.92]) by smtp.gmail.com with ESMTPSA id yk6sm14196080pab.43.2016.10.27.17.14.22 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 27 Oct 2016 17:14:24 -0700 (PDT) In-Reply-To: X-Mailer: Apple Mail (2.3096.5) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c00::22e as permitted sender) smtp.mailfrom=potswa@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:29177 Archived-At: --Apple-Mail=_F6124A75-E701-4889-B14A-19BC37C5D640 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 > On 2016=E2=80=9310=E2=80=9327, at 3:16 PM, Ville Voutilainen wrote: >=20 > I don't necessarily know of cases outside those two examples, because tho= se > two examples are what changes meaning. The paper provides a similar examp= le, >=20 > auto ls =3D { std::string( "hello" ) }; // ls has type > std::own_initializer_list< std::string > This is the controversial case. In particular, a subsequent auto qs =3D ls;= goes from well-formed to ill-formed. I=E2=80=99m certainly open to changin= g it, but given the variety of opinions in Kona, there should be a discussi= on to be sure everyone=E2=80=99s on the same page. Also, the range-for case= may be considered separately from general deduction. Depending on whether = the loop declaration is auto&& or an object, meaning changes only by removi= ng constness or only by changing copy operations to moves, respectively. Ei= ther of which is potentially breaking, but much less risky than ripping out= copy-constructibility. > and also >=20 > std::vector< std::string > vs =3D { "yizzo" }; // OK: move from sequence This only changes meaning with a library change. Also, I was instructed to = add motivation with a performance micro-benchmark graph showing the improve= ment on this example. So while there may be some controversy, a proposal ch= ange is less likely and may not touch EWG anyway. --=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/EFFD45A5-AB48-47F9-93D7-B90F85BB0789%40gmail.com= .. --Apple-Mail=_F6124A75-E701-4889-B14A-19BC37C5D640 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=UTF-8
On 2016=E2=80=9310= =E2=80=9327, at 3:16 PM, Ville Voutilainen <ville.voutilainen@gmail.com> wrote:
= I don't necessarily know of cases outside those two examples, because those=
two examples are what changes meaning. The paper provides a = similar example,

auto ls =3D { std::string( "h= ello" ) }; // ls has type
std::own_initializer_list< std::= string >

This is the controversial case. In particular, a subsequent auto qs =3D ls; goes from well-formed to i= ll-formed. I=E2=80=99m certainly open to changing it, but given the variety= of opinions in Kona, there should be a discussion to be sure everyone=E2= =80=99s on the same page. Also, the range-for case may be considered separa= tely from general deduction. Depending on whether the loop declaration is&n= bsp;auto&&&= nbsp;or an object, meaning changes only by removing constness or only = by changing copy operations to moves, respectively. Either of which is pote= ntially breaking, but much less risky than ripping out copy-constructibilit= y.

and also

std::vector< std:= :string > vs =3D { "yizzo" }; // OK: move from sequence

This only chang= es meaning with a library change. Also, I was instructed to add motivation = with a performance micro-benchmark graph showing the improvement on this ex= ample. So while there may be some controversy, a proposal change is less li= kely and may not touch EWG anyway.

--
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