220 31805 <58DA6B66.2010307@gmail.com> article Path: news.gmane.org!.POSTED!not-for-mail From: Matthew Woehlke 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 09:55:50 -0400 Lines: 51 Approved: news@gmane.org Message-ID: <58DA6B66.2010307@gmail.com> 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: text/plain; charset=UTF-8 X-Trace: blaine.gmane.org 1490709365 12733 195.159.176.226 (28 Mar 2017 13:56:05 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 28 Mar 2017 13:56:05 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC37LBFWUIFBB2OW5HDAKGQECOVDKCQ@isocpp.org Tue Mar 28 15:56:00 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f70.google.com ([209.85.214.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1csrbA-0001fc-37 for gclcip-std-proposals@m.gmane.org; Tue, 28 Mar 2017 15:55:48 +0200 Original-Received: by mail-it0-f70.google.com with SMTP id n130sf12730549ita.15 for ; Tue, 28 Mar 2017 06:55:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=subject:to:references:newsgroups:from:message-id:date:user-agent :mime-version: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=il3z16t0yykuemlPOp4yuu5S2dMT09+zLXIGM+GhW7I=; b=j1vLJYU32Ve4f8ZFyHCZW0AwASLU1wyeMvSN0x1DCJEdvUw9ejiBxn2cGALDd25lp8 hq/ncJI4PfrI/ABORD7uO9L9noe660G3/MRhWISMPcXvVeEmiOEidIzxEHVlFEog8TUy 3odd/YrDuEuict3BkjdEpLY0fDzsjDsdv4Wqjw+njgqpCKurv1jO4mwqvogdSP+a1hkr iBTgUZMCvYuG1L3mAIIXdt6BhPgwFA1MTV7OOw89u2buTUKzRSjmYE6wPPsytSfPlWnS 8UVD8jPF7gT4zXK+9ElHXJ3I2JUUv5hdTYyCplTo771HZSZ0u1xfnnxSIHqd4CmtYway wISQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:newsgroups:from:message-id :date:user-agent:mime-version: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=il3z16t0yykuemlPOp4yuu5S2dMT09+zLXIGM+GhW7I=; b=T9+JxsgOZGIxwO1ry0pf16xSPzRKBNrXfABwLiV0q7Qe1p+6ekN7lRRHnbRywD6uWN /uRekfs07tcSi1UjZcAIaxxKARiBhZrHwpBr+be6V8uI5cJNoWpMrEo6V8MnzkCLvok+ 2rpStWUhMujS8kEG6GDlE5Cz8SIQ/BmC404TjZYKxmfObbWQpVBjliMaoqeg7RTXK+Lp dQIEsXJwyjmLP3PuHnRFFsPfoOwUZx59fDi4dwtwKuD14v7iBccypEeGlBLD75Pwp4qW y1QxAuoMDI2v//+QyHRV8S8ucQbPMendEjDJ2NRgLjxmRZD/Cvqoiq/oX9XigQax2vVV fJZA== X-Gm-Message-State: AFeK/H0oL7m8XjEPYPdG8QVABuz0ATuX2p6+IFu9IuUAavYsg79luuryPMfmpGFVY81viw== X-Received: by 10.107.136.36 with SMTP id k36mr8564430iod.41.1490709353917; Tue, 28 Mar 2017 06:55:53 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.17.215 with SMTP id y23ls15700878oty.7.gmail; Tue, 28 Mar 2017 06:55:53 -0700 (PDT) X-Received: by 10.157.11.183 with SMTP id 52mr4659380oth.14.1490709353073; Tue, 28 Mar 2017 06:55:53 -0700 (PDT) Original-Received: from mail-oi0-x241.google.com (mail-oi0-x241.google.com. 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[66.194.253.20]) by smtp.googlemail.com with ESMTPSA id h10sm1686289oia.41.2017.03.28.06.55.51 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 28 Mar 2017 06:55:52 -0700 (PDT) Original-Newsgroups: gmane.comp.lang.c++.isocpp.proposals In-Reply-To: X-Original-Sender: mwoehlke.floss@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of mwoehlke.floss@gmail.com designates 2607:f8b0:4003:c06::241 as permitted sender) smtp.mailfrom=mwoehlke.floss@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:31805 Archived-At: On 2017-03-28 05:23, Alberto Barbati wrote: > 2017-03-28 11:08 GMT+02:00 Viacheslav Usov : >> This keeps coming back to this forum. For example, this: >> https://groups.google.com/a/isocpp.org/d/msg/std-proposals/ioi76TkG6g4/ >> G8WC37LVAAAJ >> >> My take on this is that we should have an operator or a keyword that >> extends the lifetime of a temporary, as discussed here >> https://groups.google.com/a/isocpp.org/d/msg/std- >> proposals/ioi76TkG6g4/bdUinF-3AQAJ and subsequent posts, notably this >> https://groups.google.com/a/isocpp.org/d/msg/std- >> proposals/ioi76TkG6g4/bdUinF-3AQAJ and this https://groups.google. >> com/a/isocpp.org/d/msg/std-proposals/ioi76TkG6g4/5JrGmugAAgAJ > > Thanks for taking the time to collect these links, I will have a look at > them. > > As for having a keyword to extend the lifetime of a temporary, there is a > formal proposal for that (http://wg21.link/p0577), which I referenced in my > draft. However I believe P0577 does not address the issue of decomposition > declarations and has a greater syntactic cost (it re-uses the "register" > keyword). It's true that P0577 provides additional use cases, though, but I > am yet to be convinced of their usefulness. The main use case for `register` as lifetime extension is that you can use it like: for (auto item : add_const(register make_list())) ....where you would otherwise need an additional declaration. The decomposition case I think would be best solved by allowing empty and nested declarations. See https://groups.google.com/a/isocpp.org/d/msg/std-proposals/gg3_eUhCuqo/HcippDFiBgAJ and following posts in the thread. This would let you write: auto [] = get_lock(); // no name auto [x, [], y] = get_tuple(); // middle element is unnamed auto [x, [a, b], y] = get_tuple(); // nested decomposition Both solve the simple case, but both also have additional but non-overlapping usefulness. I'm inclined to think that both are useful. -- Matthew -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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