220 36355 article Path: news.gmane.org!.POSTED!not-for-mail From: Ville Voutilainen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Default assignment operators for std::pair and std::tuple Date: Tue, 26 Dec 2017 15:50:55 +0200 Lines: 27 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 1514296139 14716 195.159.176.226 (26 Dec 2017 13:48:59 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 26 Dec 2017 13:48:59 +0000 (UTC) To: "ISO C++ Standard - Future Proposals" Original-X-From: std-proposals+bncBC5JHI7A7ALRBQFHRHJAKGQE5EBWO6Q@isocpp.org Tue Dec 26 14:48:55 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f71.google.com ([209.85.218.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eTpbC-0003PK-No for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id w53sor1694393otd.193.2017.12.26.05.50.55 for (Google Transport Security); Tue, 26 Dec 2017 05:50:55 -0800 (PST) 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 10.157.91.37 with SMTP id x34mr20544113oth.176.1514296255427; Tue, 26 Dec 2017 05:50:55 -0800 (PST) Original-Received: by 10.157.43.248 with HTTP; Tue, 26 Dec 2017 05:50:55 -0800 (PST) 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=EtgU0pPU; 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=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-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:36355 Archived-At: On 26 December 2017 at 15:46, mrpi via ISO C++ Standard - Future Proposals wrote: > Given that the copy and move constructors of both std::pair and std::tuple > are defaulted, why shouldn't we enforce the same for their respective > assignment operators? It seems strange that assigning these types would > invoke non-trivial work compared to just copy constructing them, and as a > result of this difference, currently both types are not considered trivially > copyable. > > Based on an old discussion, it seems that this discrepancy in the > requirement caused some compilers to make std::pair trivially > copyable while others don't. Furthermore, someone on StackOverflow hacked up > an implementation for std::tuple that was trivially copyable. It would be > nice if future proposals can provide some potential guarantees on this > matter. The assignment operators need to be user-provided for reference elements. Both pair and tuple can be made conditionally trivial when there are no reference elements, but doing so is an ABI break. -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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