220 36356 <4110e47f-a021-4ccc-9e03-53e4ebdb8c21@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: "mrpi via ISO C++ Standard - Future Proposals" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Default assignment operators for std::pair and std::tuple Date: Tue, 26 Dec 2017 07:02:05 -0800 (PST) Lines: 109 Approved: news@gmane.org Message-ID: <4110e47f-a021-4ccc-9e03-53e4ebdb8c21@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_18603_155550226.1514300525168" X-Trace: blaine.gmane.org 1514300412 5494 195.159.176.226 (26 Dec 2017 15:00:12 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 26 Dec 2017 15:00:12 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDH2LIF7UEOBB3WIRHJAKGQEANPK5WA@isocpp.org Tue Dec 26 16:00:08 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f69.google.com ([209.85.213.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eTqi4-0000vN-VP for gclcip-std-proposals@m.gmane.org; Tue, 26 Dec 2017 16:00:05 +0100 Original-Received: by mail-vk0-f69.google.com with SMTP id q198sf11642627vkh.18 for ; Tue, 26 Dec 2017 07:02:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=fmLCR1reHI89ivoyZ1VStw1cbSA9F3GMXWl7KzoLGSE=; b=o4Ur0wuVxE28BwNDJkDgYYLnDmztBS+HDqINjnqHSUiBGmef31Ari6Y5jzAXMgAWwJ /pTx399VT5tIYEEP0yyuSyC2B8VW3lmXKgCkQMhcXaCCyr1Z7w4rPPtlNmft+glhAgNv 3vR+sSzqwn9Ze4WPFBGvyOMBNokVVbBgn4VGCTmwYOD6cJkqqlHQZLsA826S1B8CNOee qEpMjCo8vwSEvB17Nn13OyZ6XUgGdGtjb0CdnxO1LnOyhLPAfAejZeXnZDZYzWbpHc3v O5qes4LuCaks74hWBBBlJGgjFu3tHK4SCUX77OKcOOZsGgdvuqlbj2nfTcVPD6p8pm4g jeZw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:x-original-sender:reply-to:precedence :mailing-list:list-id:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=fmLCR1reHI89ivoyZ1VStw1cbSA9F3GMXWl7KzoLGSE=; b=ufz43/7dUkNK+Z7fs+eOLHoopA9rqBT/3fPcZaev1dJXcrcxXMS6GMB6K6ZaWI0wNh hArxSmoCN0SkW9TAZZXjCuYtLBkUItURsfMSp5dq2nCI/6dgHKUI1YdUwPL7KcT+wWuT dnRLagAFJN6mEf3ZUZgYUJEpttDAS7LM7oEsUt5I4Z9p62hyVL+p8LKalFdFXjeF8A6A lqYZYPk5te1cLDm2RQ/XGOhAa1TAb8HTovCumw3Z7aVE1RVvNSEd4c8qGLQ3bcHsWR4R RzLnU1wYSQGGe1EjQkpt6gzErwOpO5yJPUMNa22XU6bZtif8lnMCAsE1aj02V/CMViB2 HRFg== X-Gm-Message-State: AKGB3mKmdZl0hhipK8xOfESte9jMpKab9F69aEbg4C+LuDE3/JmzrM4+ U/dSuS7G3FPXzqhSYCa7STYXUA== X-Google-Smtp-Source: ACJfBouJRS5OtUNBlW4V6/UxPtJO8/lKA40HycrSF2xR9P9Pe0UoQugGhOrdhEEKU9JFeCTxyU8zUQ== X-Received: by 10.31.2.208 with SMTP id 199mr11940279vkc.3.1514300527424; Tue, 26 Dec 2017 07:02:07 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.176.69.226 with SMTP id u89ls1860871uau.0.gmail; Tue, 26 Dec 2017 07:02:06 -0800 (PST) X-Received: by 10.31.171.73 with SMTP id u70mr2384974vke.10.1514300525636; Tue, 26 Dec 2017 07:02:05 -0800 (PST) In-Reply-To: X-Original-Sender: mrpi@google.com X-Original-From: mrpi@google.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:36356 Archived-At: ------=_Part_18603_155550226.1514300525168 Content-Type: multipart/alternative; boundary="----=_Part_18604_1016768534.1514300525168" ------=_Part_18604_1016768534.1514300525168 Content-Type: text/plain; charset="UTF-8" Sorry, I might not be understanding it correctly, but in what way would it be an ABI break, given that reference types are not trivially copyable anyways? On Tuesday, December 26, 2017 at 5:50:57 AM UTC-8, Ville Voutilainen wrote: > > 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. 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/4110e47f-a021-4ccc-9e03-53e4ebdb8c21%40isocpp.org. ------=_Part_18604_1016768534.1514300525168 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Sorry, I might not be understanding it correctly, but in w= hat way would it be an ABI break, given that reference types are not trivia= lly copyable anyways?

On Tuesday, December 26, 2017 at 5:50:57 AM UT= C-8, Ville Voutilainen wrote:
O= n 26 December 2017 at 15:46, mrpi via ISO C++ Standard - Future
Proposals <std-pr...@isocpp.org> wrote:
> Given that the copy and move constructors of both std::pair and st= d::tuple
> are defaulted, why shouldn't we enforce the same for their res= pective
> assignment operators? It seems strange that assigning these types = would
> invoke non-trivial work compared to just copy constructing them, a= nd 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<scalar> = trivially
> copyable while others don't. Furthermore, someone on StackOver= flow hacked up
> an implementation for std::tuple that was trivially copyable. It w= ould 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 &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/4110e47f-a021-4ccc-9e03-53e4ebdb8c21= %40isocpp.org.
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