220 28321 article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Trivial copyability and `optiona/variant`. Date: Thu, 22 Sep 2016 12:06:04 -0700 (PDT) Lines: 60 Approved: news@gmane.org Message-ID: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_638_2086017879.1474571164175" X-Trace: blaine.gmane.org 1474571187 26862 195.159.176.226 (22 Sep 2016 19:06:27 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 22 Sep 2016 19:06:27 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBHOXSC7QKGQEFOHKO3Q@isocpp.org Thu Sep 22 21:06:23 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f72.google.com ([209.85.214.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bn9K0-0005Vx-Or for gclcip-std-proposals@m.gmane.org; Thu, 22 Sep 2016 21:06:12 +0200 Original-Received: by mail-it0-f72.google.com with SMTP id e20sf220150011itc.3 for ; Thu, 22 Sep 2016 12:06:14 -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: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=yznkDh0P98mU9qrIV7VxAEtsesy5WKIZJAuuEeCz7MQ=; b=zawg/xfM/EiR+hdOQQQhJxKncNHCUw9kSvYSVzdNfvIqh9uXHl/3qVR5Nu0umLiJkR 52Zn15QPJgkYoL5GjbRktFArNtAsZdQcAxjspMBJTaygbOLEjrYeMxJtlrrExL/Gdkcp M4m62NJvXG6IVGVZy9907CceNwAKgyXNIh4jc5pQRMdebZFAyYcPuw54cvGr41p0QzDl diIubcLOJZfuo9miTJAy6t5dpQSLz+ujI4nvz0gZ0xmH6/HTMwqGDiJTQJ8JYXj44iu5 KuGUjAg8MQzHitybUIzuxCKah0oaKhouPJtBERP03/YxnU6iJvDiNU9teLYhhBOku6k0 d1Jw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id: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=yznkDh0P98mU9qrIV7VxAEtsesy5WKIZJAuuEeCz7MQ=; b=VTkQhFRCiuip1pnRZ5VMuPiPOD9U2pzt5sca378QFeBTJbWs2VwS9v4/X5JosaB+nk UsRtzNfKUglgULu5Pnoy59hBQ7pqTZPf9SS0W/a1spd7raVFiPUGrHKbIgQlzYHWZyo9 J6D1Sv88pFRDFzQhVUjJixlSiChMEKhTD6MZgze8KaRYVnxZzlEevN78wtiQtudzmXpG lAI9rmWcGIbX+iS/4QARkPi4rkK+/25d1otwDWYfqCcoi1kkcbNTC2iaMGp/Kye77+iv 0hKKSunNW9qaK94CiqVwmhvCX1CSVHkJFQb0J4r7cLpyUNCr2zflRTl1GlT1ke+LhnH6 mWOQ== 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: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=yznkDh0P98mU9qrIV7VxAEtsesy5WKIZJAuuEeCz7MQ=; b=lAakzlZUg14fju1qYGNLT48fhcBvINo8Gs8aSlNuYJyT30lge4qzjGTjvbXnzogLUq RDDSeBd7Yo8TXTa4yCXBW3blkrZEVTjyszh/chA5uZOHWKPTpZNKuRO6iVJii2IMkn5/ N+cVWfRKkS+1MCsJy/78jL8vFXx6b9ci4gzveasUwH3kPLqXFFQeISOvPCXaADNNc949 bPiwqqKmMuIWFPrxC91PBbgdskM2K4swUdDkDdGHvfaQqPwrtwXtTh/CJWLWiDVvqY4f U2I+Drk22mjrJrrRwWyOxxg2Zn5emF33X2YN2zORiqR+K1peRhGrcemkp6dHPs24wSl1 mdDg== X-Gm-Message-State: AE9vXwMWcOAcdJlKaREYnniVfqY4CX32sZNUycDCqHg4rTCF24poxIrmLc6rfqc+cM2jbg== X-Received: by 10.36.250.67 with SMTP id v64mr622624ith.37.1474571174230; Thu, 22 Sep 2016 12:06:14 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.11.86 with SMTP id v83ls3708202ioi.3.gmail; Thu, 22 Sep 2016 12:06:05 -0700 (PDT) X-Received: by 10.36.39.214 with SMTP id g205mr254556ita.7.1474571165147; Thu, 22 Sep 2016 12:06:05 -0700 (PDT) X-Original-Sender: jmckesson@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:28321 Archived-At: ------=_Part_638_2086017879.1474571164175 Content-Type: multipart/alternative; boundary="----=_Part_639_1398756088.1474571164175" ------=_Part_639_1398756088.1474571164175 Content-Type: text/plain; charset=UTF-8 `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? -- 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/f8ccbc4e-d67c-4af5-933a-0d2822622baa%40isocpp.org. ------=_Part_639_1398756088.1474571164175 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
`optional` is not required to be trivially copyable if `T`= is trivially copyable. And yet, I cannot imagine an implementation of `opt= ional` where that is not at least possible. After all, the bit sayin= g whether the `optional` is empty is likely a basic type. So why should tri= vial copyability not be possible?

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

Is there an implementation problem I&#= 39;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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