220 33024 <20170629111649.5132370.85419.32148@gmail.com> article Path: news.gmane.org!.POSTED!not-for-mail From: Tony V E Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: std::optional - support for sentinel values Date: Thu, 29 Jun 2017 07:16:49 -0400 Lines: 59 Approved: news@gmane.org Message-ID: <20170629111649.5132370.85419.32148@gmail.com> References: <6e23864f-827a-4bdb-89de-a60d8f5be993@isocpp.org> <9f81f2b9-958c-4018-9f78-a6ac2e425899@isocpp.org> <730d0077-5a80-4dce-8250-19be62b1a23b@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1498735012 28730 195.159.176.226 (29 Jun 2017 11:16:52 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 29 Jun 2017 11:16:52 +0000 (UTC) To: Ville Voutilainen , ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCUZ5QWKNQIKHQ6TZICRUBFU5GRTY@isocpp.org Thu Jun 29 13:16:47 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f197.google.com ([209.85.161.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dQXRH-0007HJ-2e for gclcip-std-proposals@m.gmane.org; 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[174.95.157.190]) by smtp.gmail.com with ESMTPSA id 125sm4397326itz.7.2017.06.29.04.16.49 for (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 29 Jun 2017 04:16:49 -0700 (PDT) X-Mailer: BlackBerry Email (10.3.3.2205) In-Reply-To: X-Original-Sender: tvaneerd@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.b=BVMRkftX; spf=pass (google.com: domain of tvaneerd@gmail.com designates 2607:f8b0:4001:c06::241 as permitted sender) smtp.mailfrom=tvaneerd@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:33024 Archived-At: std::optional> Sent=C2=A0from=C2=A0my=C2=A0BlackBerry=C2=A0portable=C2=A0Babbage=C2=A0Devi= ce =C2=A0 Original Message =C2=A0 From: Ville Voutilainen Sent: Thursday, June 29, 2017 7:13 AM To: ISO C++ Standard - Future Proposals Reply To: std-proposals@isocpp.org Subject: Re: [std-proposals] std::optional - support for sentinel values On 29 June 2017 at 14:09, Igor Baidiuk wrote: >> It has nothing to do with includes. Altering the definition of >> optional to conditionally use >> a trait would be remotely feasible, but it would also be an abi-breaking >> change. >> > > Maybe I didn't express it well enough. I meant the case when someone > declares such "sentinel" locally for module, and then return that option = to > unit where sentinel is not known. > Then I realized this is well-possible even if new optional would have tra= it > parameter. Right; multiple translation units must agree, which makes it an odr-problem= , not an include-problem. The trait-approach might still work, it just requires that the trait gives the same result in every TU, but injecting such a trait-approach into the current optional is an abi break. Going for a separate type is safe from that abi break, which automatically removes some automatic opposition from the picture. --=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/CAFk2RUaVNMX9ktdTTTZywzmmOh6zJVShRcnL_ppJeFnFDpm= 0nw%40mail.gmail.com. --=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/20170629111649.5132370.85419.32148%40gmail.com. .