220 36273 <390b06f2-0c86-465e-9a11-d0ebb3501970@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Andrey Davydov Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Trivial copyability and `optiona/variant`. Date: Sat, 23 Dec 2017 04:17:01 -0800 (PST) Lines: 87 Approved: news@gmane.org Message-ID: <390b06f2-0c86-465e-9a11-d0ebb3501970@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_10310_825460880.1514031421274" X-Trace: blaine.gmane.org 1514031307 15908 195.159.176.226 (23 Dec 2017 12:15:07 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 23 Dec 2017 12:15:07 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBC7OLSNDXIHBBPUS7HIQKGQETJRZJCY@isocpp.org Sat Dec 23 13:15:03 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f70.google.com ([209.85.213.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eSihh-0003fv-CX for gclcip-std-proposals@m.gmane.org; Sat, 23 Dec 2017 13:15:01 +0100 Original-Received: by mail-vk0-f70.google.com with SMTP id l14sf3541221vki.4 for ; Sat, 23 Dec 2017 04:17:04 -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=veeVNNVsIeSoXYr7Dbzpd8mb5V9lCQlTq4rvrNhMMbY=; b=sgTOHXkEURBtUdqtFC2vVoJRlVftn/gbkm2bv25NU8jD6UE1Kw00xo8wt24UjsdcIp 51SIQxFos7TYIfR8g4VnqfEnUWbReP+GuW0n6eTNx99z9yzT0clYmLm2Y/wodk6TyEZx gSYn64YpZoJfr0j4psMgLSA/LbeBlraK0xNXtKvp4w7c/pdDYZt2XB6uBLyKuURVral2 wi74DKqHuIj6BAuRoT97AZywSw8FJPxqVQDMvUNnZeMq3Rpv/+cwuwdIx0y0Y+eq/UeW b4m4V49ohiw45q0hTqciKTYqRx/Ih3WJ8Dv6jUGTer9cNibqG8jOho5P8xCppZ7v2S5i i8Kg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; 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=veeVNNVsIeSoXYr7Dbzpd8mb5V9lCQlTq4rvrNhMMbY=; b=fcvUn6ofDV2vsFcY7lcm2ryxSb50+eqVS13ShICRhUou5KYt63PRDZU4q3mPL1q3e4 YmUKXf8jOoF/QJhIeBPtJ2VXpjVeWG7B+MyNlRM0T8MtkGCKhpeNeEr1bdJ7trycmYva EyQlECJORzy+8KgLcah3s7nllufKmxxA9BJwTIMum+K9trQCYzKwx6inW9DU+zDWLlbP ujImFXPXRbyJKujYY76KSK1mbh7vg/zngrO86ctAiaUd0+3g+y8rZc8EnubOuMvuuxOV 4/UcygjYt4oB90YnhSxSa0buunjtznQHET67gOHlexYIBUZB1dsQ5i3Xj98fTGfTXLR+ 44hg== 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=veeVNNVsIeSoXYr7Dbzpd8mb5V9lCQlTq4rvrNhMMbY=; b=KYQ4WGW376qYKz7hpP8HqY7rLjGUoHic6tvYHIaYY4qnBJktE+uPpDdeW0RdBqqSkO CEeEhVS18FI/UvQVO9rAiGCfcwkEeslCeFGYd7cmMqDKGo47lM6i7mHFEJWGM/+jJk2I G3X/c1vDW1vWpd2l/qozwLGvGoqNTerraR9Z4ldlsGNOzf1kgipzKFsDDG/o0BpjWhFv 5mlGgQFoShNpS3S2tVAzJ7mf/WMT6mwyknRXYZAFarUJYTMzlMzJU4PkbK4VP+2O3h0d qrFl3fIvCqz8SY3zmGyUTfVOEfcm3v7+cBHBpMOHCGh+y9PVsQ4jQy97G0qWrIhK7CrE aPwA== X-Gm-Message-State: AKGB3mL9f3SFu3jzhxmt+oZUPKf9OQ4rpd+GD5IVUijxuPvZ8nIPrLEu Gy9YR8byu0DoZRTFfbM0tdgxZA== X-Google-Smtp-Source: ACJfBov0t3zezMEhV3Si0jhXllt0AocByFDvCavAM7Cl4niMAQ+Co9exd+Omxjdhj2yRJEqCquppzA== X-Received: by 10.31.41.205 with SMTP id p196mr7997260vkp.71.1514031423858; Sat, 23 Dec 2017 04:17:03 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.176.69.226 with SMTP id u89ls211142uau.0.gmail; Sat, 23 Dec 2017 04:17:02 -0800 (PST) X-Received: by 10.31.171.73 with SMTP id u70mr1531536vke.10.1514031421822; Sat, 23 Dec 2017 04:17:01 -0800 (PST) In-Reply-To: X-Original-Sender: Andrey.A.Davydov@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:36273 Archived-At: ------=_Part_10310_825460880.1514031421274 Content-Type: multipart/alternative; boundary="----=_Part_10311_920418220.1514031421274" ------=_Part_10311_920418220.1514031421274 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Is there any progress being made on this? As I see now the Microsoft and=20 libc++ implementation maintain trivial copyability, but libstdc++=20 doesn't: https://godbolt.org/g/tL29Hd =D1=87=D0=B5=D1=82=D0=B2=D0=B5=D1=80=D0=B3, 22 =D1=81=D0=B5=D0=BD=D1=82=D1= =8F=D0=B1=D1=80=D1=8F 2016 =D0=B3., 22:06:04 UTC+3 =D0=BF=D0=BE=D0=BB=D1=8C= =D0=B7=D0=BE=D0=B2=D0=B0=D1=82=D0=B5=D0=BB=D1=8C Nicol Bolas=20 =D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0=D0=BB: > > `optional` is not required to be trivially copyable if `T` is trivially= =20 > copyable. And yet, I cannot imagine an implementation of `optional` where= =20 > that is not at least *possible*. After all, the bit saying whether the=20 > `optional` is empty is likely a basic type. So why should trivial=20 > copyability not be possible? > > Similarly, if all of the `Ts` for a `variant` are trivially copyable, it= =20 > should be possible to make the variant itself trivially copyable. > > Is there an implementation problem I'm not aware of, or was this an=20 > oversight? Should a national body comment be filed or a defect report be= =20 > sent? > --=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/390b06f2-0c86-465e-9a11-d0ebb3501970%40isocpp.or= g. ------=_Part_10311_920418220.1514031421274 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Is there any progress being made on this? As I see now the= Microsoft and libc++ implementation maintain trivial copyability, but libs= tdc++ doesn't:=C2=A0https://godbolt.org/g/tL29Hd

=D1=87=D0=B5=D1= =82=D0=B2=D0=B5=D1=80=D0=B3, 22 =D1=81=D0=B5=D0=BD=D1=82=D1=8F=D0=B1=D1=80= =D1=8F 2016 =D0=B3., 22:06:04 UTC+3 =D0=BF=D0=BE=D0=BB=D1=8C=D0=B7=D0=BE=D0= =B2=D0=B0=D1=82=D0=B5=D0=BB=D1=8C Nicol Bolas =D0=BD=D0=B0=D0=BF=D0=B8=D1= =81=D0=B0=D0=BB:
`optional` is not required to be trivially copyable if `T` is trivially = copyable. And yet, I cannot imagine an implementation of `optional` where t= hat is not at least possible. After all, the bit saying whether the = `optional` is empty is likely a basic type. So why should trivial copyabili= ty not be possible?

Similarly, if all of the `Ts` for a `variant` ar= e trivially copyable, it should be possible to make the variant itself triv= ially 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?

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