220 23686 article Path: news.gmane.org!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: n4428 and Tuple-like access interface reflection Date: Tue, 12 Jan 2016 12:15:07 -0500 Lines: 52 Approved: news@gmane.org Message-ID: References: <56770133.7070701@wanadoo.fr> <5681D877.3010101@wanadoo.fr> <43daa6cd-e152-43c1-ab51-0661779d344b@isocpp.org> <568942A9.80700@wanadoo.fr> <568B0DA1.3080704@wanadoo.fr> <7d4bd204-e4c3-4f60-8be5-63d8127daf74@isocpp.org> <487ea013-6fcb-4d2e-8bc7-8fe96cdbf0a9@isocpp.org> <568C3EC7.8070900@wanadoo.fr> <568D5959.9000501@wanadoo.fr> <568D8DD7.30303@wanadoo.fr> <568E0C83.7030609@ wanadoo.fr> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Trace: ger.gmane.org 1452618932 1770 80.91.229.3 (12 Jan 2016 17:15:32 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 12 Jan 2016 17:15:32 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC37LBFWUIFBBKHJ2S2AKGQELEQRLRI@isocpp.org Tue Jan 12 18:15:25 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f70.google.com ([209.85.215.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aJ2XU-0000Py-4T for gclcip-std-proposals@m.gmane.org; Tue, 12 Jan 2016 18:15:24 +0100 Original-Received: by mail-lf0-f70.google.com with SMTP id m196sf22403824lfe.0 for ; Tue, 12 Jan 2016 09:15:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=to:from:subject:date:lines:message-id:references:mime-version :content-type:user-agent:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=ch06VBqqBOkwMYus67whTSccNsH1DBMg38sv9nSCAXQ=; b=tAMnQdSy7FEvDkqlEDXbqOh2klEMMg7zOPiinBtLdpT0yEHqkYdMtpOyov+0Tznki7 kEAoUSDoH3cvDvzyGpbtvwAbyAdX0vDedac5T3utiGI7ohEjE+UbbqwYsY9BducZrn3p XitpDoDyJo5pDRH6/hw3ySHazFlnhp1bGDhLhbQ2Loy1W1rRqGKAkXDlTmZK7bKgxFSe 3Dr/PUzR0qu9dysA9YUzyAxwy24eYJy8alze6BRtG1qUGO9spMEfSOR9xS3W8i3cB+vZ 9M08jcLoA6VNKgyKWIh3MuyEa08Zu6Jx3HkAwIrWrCB6Y8lHCZCJoxRexveGiEzybR2G EhD X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:to:from:subject:date:lines:message-id:references :mime-version:content-type:user-agent:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=ch06VBqqBOkwMYus67whTSccNsH1DBMg38sv9nSCAXQ=; b=YajjAYAAoXJDoi14aQ+8XtUx3BSrL7+0IcaoH85DLUYNXjmvXC8xKaRNFj0m5pFfnI 3cN9n3xG/Jkfy0GncC099ImkVqQhsHtgw2tt5DUj0pTQPvd4TNfMD+baBcbNGBURk3DF L4fDIn4Yp2y8U0pHphXe6CXwJ5d9JDz3Pjd51q8BhUB2JAwhVX6Y1CSCSD4L0vPXcaE2 osMDkzpETrZL3wviqul/Ycu/Mi4eXR7VjD5kOs0/oh+GJDUeO/qg10FnmnJyX92tGPp6 YfPTYGEF2T4X+EM94HGFFipBMw4UEEKe990Vtso7FCcFiwQdlz6oBwmHfZo1L6ciDAYI X-Gm-Message-State: ALoCoQm/N5krJJGg66p/XVohHUvnNRaN4iq6ATwtEz1s9mPahPZzazQN/lztV/DMRxOaIyduMd6ibShfynhZ8tdqxLIAEuFKig== X-Received: by 10.194.201.234 with SMTP id kd10mr6151922wjc.6.1452618922203; Tue, 12 Jan 2016 09:15:22 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.25.146.10 with SMTP id u10ls307880lfd.42.gmail; Tue, 12 Jan 2016 09:15:19 -0800 (PST) X-Received: by 10.112.136.103 with SMTP id pz7mr42264263lbb.3.1452618919408; Tue, 12 Jan 2016 09:15:19 -0800 (PST) Original-Received: from plane.gmane.org (plane.gmane.org. [80.91.229.3]) by mx.google.com with ESMTPS id p15si52938343lfp.167.2016.01.12.09.15.19 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 12 Jan 2016 09:15:19 -0800 (PST) Received-SPF: pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) client-ip=80.91.229.3; Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1aJ2XN-0000LY-S1 for std-proposals@isocpp.org; Tue, 12 Jan 2016 18:15:18 +0100 Original-Received: from tripoint.kitware.com ([66.194.253.20]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 12 Jan 2016 18:15:17 +0100 Original-Received: from mwoehlke.floss by tripoint.kitware.com with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 12 Jan 2016 18:15:17 +0100 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 43 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: tripoint.kitware.com User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 In-Reply-To: X-Original-Sender: mwoehlke.floss@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) smtp.mailfrom=gclcip-std-proposals@m.gmane.org; dmarc=fail (p=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:23686 Archived-At: On 2016-01-07 14:24, Nicol Bolas wrote: > On Thursday, January 7, 2016 at 1:58:16 AM UTC-5, Vicente J. Botet Escriba > wrote: >> My question was because as I interpret >> http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0017r1.html from >> the examples, The aggregation must be nested as in >> >> struct base1 { int b1, b2 = 42; }; >> struct base2 { >> B() { >> b3 = 42; >> } >> int b3; >> }; >> struct derived : base1, base2 { >> int d; >> }; >> >> derived d1{{1, 2}, {}, 4}; // full initialization >> derived d2{{}, {}, 4}; // value-initialized bases >> >> But maybe I'm wrong. > > No, you're right. I'd forgotten that this is how it works, that base > classes are considered member-subobjects. Likewise. It... feels strange to me, but I guess it is what it is. > But my overall point stands: it should work as the exact opposite of > aggregate initialization. So in your example, the first index of the tuple > `A` should be the `A1` base class. The second index should be the `A2` base > class. Agreed. > And actually, that brings up a really good reason why we should exclude > virtual types of any kind. Because such accesses (particularly structured > binding) encourages *slicing* of types. Yup :-). -- Matthew -- --- 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. Visit this group at https://groups.google.com/a/isocpp.org/group/std-proposals/. .