220 31816 article Path: news.gmane.org!.POSTED!not-for-mail From: Zhihao Yuan Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: This variable should not be named: an identifier (not) to remember Date: Tue, 28 Mar 2017 11:27:34 -0500 Lines: 82 Approved: news@gmane.org Message-ID: References: <985b9b2a-c734-45eb-95f4-db4dc0d309a1@isocpp.org> <7EF863A1-1454-4116-9164-676FF19BF923@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=f403045c31b0f377c1054bccef91 X-Trace: blaine.gmane.org 1490718462 1224 195.159.176.226 (28 Mar 2017 16:27:42 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 28 Mar 2017 16:27:42 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBCSKRWMD4EHBB6M55LDAKGQE3ZPYSXY@isocpp.org Tue Mar 28 18:27:38 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f72.google.com ([209.85.218.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1csty0-0007q9-24 for gclcip-std-proposals@m.gmane.org; Tue, 28 Mar 2017 18:27:32 +0200 Original-Received: by mail-oi0-f72.google.com with SMTP id r203sf62157010oib.15 for ; Tue, 28 Mar 2017 09:27:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:mime-version: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=RXifS7i+Bg0PoxCZLobRuCDdqZIjEcRpcgpKdNO+QOM=; b=dnK0kAfsvCAVnoDnKrtq8CruWHfCfTU1qNvTSBo5TDrvEDm65Czw/ISFHkncxLlwbA 0ii4grUey6r0QvoYfjDSTEcQ2/0ljd/Y4ntsBolxuY/y7uy1jK0wzi3JbV+dpDWcbu5S kthv+0ddPAULq1wVe968mZR/FY4jAvsYT+ZcQTJqdwCG9bsdAV8Vz2YT3n6fL1QWuA/j DA0CcCEBm5JxOm4DpfnZB6c6lXp05pIfl0USHfiDsFyyYosEsgOGJwg9zN1CjQKzB3V/ 9ew7XU1YAqI/w7FTmvpS/k7fmDPxHijr/P1yC4nlZswQxoDK8rb0vIuRLJyQYDwmxcra Jxyg== X-Gm-Message-State: AFeK/H2WIr9QBSSdLgtm+rDL+bCdnqHwiE+S+j2zhdC2HDYqbjpfaaSjj15vaCOK97bItA== X-Received: by 10.157.33.123 with SMTP id l56mr8123949otd.89.1490718457987; Tue, 28 Mar 2017 09:27:37 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.15.38 with SMTP id 35ls522936ott.19.gmail; Tue, 28 Mar 2017 09:27:37 -0700 (PDT) X-Received: by 10.55.16.168 with SMTP id 40mr23835518qkq.289.1490718457006; Tue, 28 Mar 2017 09:27:37 -0700 (PDT) Original-Received: from mail-s68.mailgun.info (mail-s68.mailgun.info. [184.173.153.196]) by mx.google.com with ESMTPS id a123si341595qkb.13.2017.03.28.09.27.36 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 28 Mar 2017 09:27:36 -0700 (PDT) Received-SPF: pass (google.com: domain of bounce+3f9131.69110-std-proposals=isocpp.org@miator.net designates 184.173.153.196 as permitted sender) client-ip=184.173.153.196; Original-Sender: zy@miator.net X-Mailgun-Sending-Ip: 184.173.153.196 X-Mailgun-Sid: WyI3MTBkYiIsICJzdGQtcHJvcG9zYWxzQGlzb2NwcC5vcmciLCAiNjkxMTAiXQ== Original-Received: from mail-pg0-f48.google.com (mail-pg0-f48.google.com [74.125.83.48]) by mxa.mailgun.org with ESMTP id 58da8ef7.7f801be96bf0-smtp-out-n03; Tue, 28 Mar 2017 16:27:35 -0000 (UTC) Original-Received: by mail-pg0-f48.google.com with SMTP id g2so76763152pge.3 for ; Tue, 28 Mar 2017 09:27:35 -0700 (PDT) X-Received: by 10.99.109.12 with SMTP id i12mr25702146pgc.91.1490718454671; Tue, 28 Mar 2017 09:27:34 -0700 (PDT) Original-Received: by 10.100.159.10 with HTTP; Tue, 28 Mar 2017 09:27:34 -0700 (PDT) In-Reply-To: X-Gmail-Original-Message-ID: X-Original-Sender: zy@miator.net X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@miator.net; spf=pass (google.com: domain of bounce+3f9131.69110-std-proposals=isocpp.org@miator.net designates 184.173.153.196 as permitted sender) smtp.mailfrom=bounce+3f9131.69110-std-proposals=isocpp.org@miator.net 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:31816 Archived-At: --f403045c31b0f377c1054bccef91 Content-Type: text/plain; charset=UTF-8 On Tue, Mar 28, 2017 at 4:23 AM, Alberto Barbati wrote: > However I believe P0577 does not address the issue of decomposition > declaration Because these two "use cases" imply different semantics. When you write auto __ = lock_guard(m); here you mean to *preserve* the result object, but when you write auto [__, a] = get_tuple(...); you mean to *ignore* a part of the result object, so physically, just like std::ignore, I don't expect __ here to issue a call to get(obj), nor an access to a subobject. I don't think the *preserving* semantics can fulfill the *ignoring* demand. -- Zhihao Yuan, ID lichray The best way to predict the future is to invent it. ___________________________________________________ -- 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/CAGsORuC7LZWWtCnr9Zuoqc%3DzzQOeNT-KZimy6BNO%2Bu_h3in6cA%40mail.gmail.com. --f403045c31b0f377c1054bccef91 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

= On Tue, Mar 28, 2017 at 4:23 AM, Alberto Barbati <albertobarbati@gm= ail.com> wrote:
However I b= elieve P0577 does not address the issue of decomposition declaration

Because these two "u= se cases" imply different semantics.
When you write

=C2=A0 auto __ = =3D lock_guard(m);

here you mean to= *preserve* the result object, but when
you write

=C2=A0 auto [__, a] =3D get_tuple(...);

you mean to *ignore* a part of the result object, so=
physically, just like std::ignore, I don't expect __ here
to iss= ue a call to get(obj), nor an access to a subobject.
I don't think t= he *preserving* semantics can fulfill the
*ignoring* demand.

--
Zhih= ao Yuan, ID lichray
The best way to predict the future is to invent it.<= br>___________________________________________________

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