220 28322 <47c7c8cf-13f4-4026-acf4-41ca1d2a3e53@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Casey Carter Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Trivial copyability and `optiona/variant`. Date: Thu, 22 Sep 2016 14:46:27 -0700 (PDT) Lines: 75 Approved: news@gmane.org Message-ID: <47c7c8cf-13f4-4026-acf4-41ca1d2a3e53@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_1922_579463712.1474580787221" X-Trace: blaine.gmane.org 1474580808 9948 195.159.176.226 (22 Sep 2016 21:46:48 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 22 Sep 2016 21:46:48 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBD2MLWWVRQMRBNFCSG7QKGQE75A2DQQ@isocpp.org Thu Sep 22 23:46:43 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f198.google.com ([209.85.161.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bnBpC-000104-5f for gclcip-std-proposals@m.gmane.org; Thu, 22 Sep 2016 23:46:34 +0200 Original-Received: by mail-yw0-f198.google.com with SMTP id t67sf194526862ywg.3 for ; Thu, 22 Sep 2016 14:46:36 -0700 (PDT) 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 :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=9robBnzHgK2drfRAadgTl4p2+e060RM1ShgIr4wTXEk=; b=labjFjzxoe6a/d7KXPFJkI+xfRKmXlWNvt3fSEsekr32/Q0ywC2P+qpcDmFvqgxKDY h26Pcv6UUP3OOUZLjxbPLhZHVET42DOoSLEcSeSulo4FppWtzX//lj8uzg971nGpNvFJ GugSRcLR009MgLGYSfoKfS6hs0XiJwtqrBsyZHW5wlfuOSIxmZEQihnOWnKp5rs4YzHd 9wZsdezvJ9cgSbB1zPPmBjHrCxv0BLiaCxdoKQOW1VMec9tblqe3FTm46WjixcTgoRBj pNSWq/ByM7uBOOXoki7AO0wNpaSChmuxtypgWscar0P0eWMrMViDaP0MnEDjNBWknFQp SrHg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=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=9robBnzHgK2drfRAadgTl4p2+e060RM1ShgIr4wTXEk=; b=Ltg8o6hIdAr5s3HuTGF5ZMAHOGzyCatwpXbBJ5+VP36pc4yooJz6DS2cap+cez/4B4 HRlWsDXFVoiRWxRZYsTcIumuDa0v4Sh9UWesBjjSeKt+s/3+m99+m4LwIIgc6ZaVBFHM O+jYPEP5Ss7bnbGxcVWlLJPVS5snEzXPFzUxgA54rBZX4Vm4AOhKlT6XcDp1EsZaTlWD N/oLNWR+bdInBi5/9pBMj4OlwRxS8muY7Ag127nZKzV443ZspMgAZvfzbnnfLnEbJqfd DSNTIQU/2GGhDBuRFZU40RlWRZ+79ajiKgk1YRfWo+MOOsXrtk5T4Wfztc2zHXQp5MM7 4OAA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; 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=9robBnzHgK2drfRAadgTl4p2+e060RM1ShgIr4wTXEk=; b=XiLETiu/0UVirCskvSaCfggCGzRowVg/yCWBr11wKd60i3cN3cAhTM7ktU2Zjyn1Xp sEYtv92jSaPkGDff/eyL7RgBBdEYtQA2gsPgbPD8jFrgFIoRS3nHDTmmkr4pJn1JJxvc wrePFhvdbXhtMnY4mLdcmGeUSqeoejHPx+fgMnEAmVeB3md+fOWfP0yfAR9wl2c1HXjG k7eeiKJWBfFEDyAq3e98ltRtDaNmKO00kMoOe0no0mz+526ZXJ8mRM8GiIj7dpEQKFDi WyIFbijG3nybSvsfiTwY8YHX7UAiPkcdGkl+1Vx/olU5YuhREyI6vLjiqo60foLr+7g3 gfww== X-Gm-Message-State: AE9vXwPh+f21eN7d1rYeO1Hjbv6hJxzYmSG4UPg3GvrxA/9IISA9FlBJEzJwvfbbZDGnBg== X-Received: by 10.129.123.197 with SMTP id w188mr871106ywc.111.1474580794447; Thu, 22 Sep 2016 14:46:34 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.37.1 with SMTP id l1ls6056693iol.16.gmail; Thu, 22 Sep 2016 14:46:27 -0700 (PDT) X-Received: by 10.36.60.150 with SMTP id m144mr311150ita.1.1474580787805; Thu, 22 Sep 2016 14:46:27 -0700 (PDT) In-Reply-To: X-Original-Sender: cartec69@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:28322 Archived-At: ------=_Part_1922_579463712.1474580787221 Content-Type: multipart/alternative; boundary="----=_Part_1923_1175359735.1474580787221" ------=_Part_1923_1175359735.1474580787221 Content-Type: text/plain; charset=UTF-8 On Thursday, September 22, 2016 at 12:06:04 PM UTC-7, Nicol Bolas wrote: > > `optional` is not required to be trivially copyable if `T` is trivially > copyable. And yet, I cannot imagine an implementation of `optional` where > that is not at least *possible*. After all, the bit saying whether the > `optional` is empty is likely a basic type. So why should trivial > copyability not be possible? > > Similarly, if all of the `Ts` for a `variant` are trivially copyable, it > should be possible to make the variant itself trivially copyable. > > Is there an implementation problem I'm not aware of, or was this an > oversight? Should a national body comment be filed or a defect report be > sent? > Those requirements are implementable: the Microsoft implementations of optional and variant maintain trivial copyability of the contained types. It seems to be QoI to me; I see no strong motivation to *require* that behavior. -- 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/47c7c8cf-13f4-4026-acf4-41ca1d2a3e53%40isocpp.org. ------=_Part_1923_1175359735.1474580787221 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Thursday, September 22, 2016 at 12:06:04 PM UTC-7, Nico= l Bolas wrote:
`optional` is not required to be trivially copyable if `T` is trivially co= pyable. And yet, I cannot imagine an implementation of `optional` where tha= t is not at least possible. After all, the bit saying whether the `o= ptional` is empty is likely a basic type. So why should trivial copyability= not be possible?

Similarly, if all of the `Ts` for a `variant` are = trivially copyable, it should be possible to make the variant itself trivia= lly copyable.

Is there an implementation problem I'm not aware o= f, or was this an oversight? Should a national body comment be filed or a d= efect report be sent?

Those requi= rements are implementable: the Microsoft implementations of optional and va= riant maintain trivial copyability of the contained types. It seems to be Q= oI to me; I see no strong motivation to *require* that behavior.

--
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