220 38011 article Path: news.gmane.org!.POSTED!not-for-mail From: Ville Voutilainen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: variant again Date: Thu, 26 Apr 2018 01:17:10 +0300 Lines: 28 Approved: news@gmane.org Message-ID: References: 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 1524694506 25020 195.159.176.226 (25 Apr 2018 22:15:06 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 25 Apr 2018 22:15:06 +0000 (UTC) To: "ISO C++ Standard - Future Proposals" Original-X-From: std-proposals+bncBC5JHI7A7ALRBZ74QPLQKGQEYYVQEQA@isocpp.org Thu Apr 26 00:15:02 2018 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 1fBSgn-0006OO-D8 for gclcip-std-proposals@m.gmane.org; Thu, 26 Apr 2018 00:15:01 +0200 Original-Received: by mail-oi0-f72.google.com with SMTP id j75-v6sf130705oib.5 for ; 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[209.85.220.41]) by mx.google.com with SMTPS id 68-v6sor8205825otj.91.2018.04.25.15.17.11 for (Google Transport Security); Wed, 25 Apr 2018 15:17:11 -0700 (PDT) Received-SPF: pass (google.com: domain of ville.voutilainen@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 2002:a9d:3644:: with SMTP id w62-v6mr22007363otb.287.1524694630747; Wed, 25 Apr 2018 15:17:10 -0700 (PDT) Original-Received: by 2002:a9d:8f6:0:0:0:0:0 with HTTP; Wed, 25 Apr 2018 15:17:10 -0700 (PDT) In-Reply-To: X-Original-Sender: ville.voutilainen@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=qn5wpoKY; spf=pass (google.com: domain of ville.voutilainen@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=ville.voutilainen@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:38011 Archived-At: On 26 April 2018 at 00:51, 'Matt Calabrese' via ISO C++ Standard - Future Proposals wrote: > Then would you or would you not be in favor of a proposal to require that we > do not enter the valueless_by_exception state here? Tony's concern is that > the current specification implies that we can get to valueless_by_exception > in an assignment even when a move constructor does not actually throw, which > is currently true. Should we "fix" this in a future standard or consider to > be fine? I would not be in favor of such a proposal. The user attempted to change the type of the object variant holds, and that can lead to a valueless state if either copy or move throws. The user didn't ask for a move, so I don't know how a non-throwing move is supposed to save the user's bacon. We can chase corner cases all we want, and entertain checking for trivial destructibility and non-throwing move and doing yet another thing in that case, but doing so would require a demonstrated benefit, and anecdotes from users who think non-throwing moves are applied to lvalues don't convince me as evidence of much anything. -- 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/CAFk2RUbc53_cc9mOJrHQLQeBBKehLsHUzJjKj6iqjmDi3RjZag%40mail.gmail.com. .