220 37366 article Path: news.gmane.org!.POSTED!not-for-mail From: Myriachan Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: `offsetof` in a macro-less, modular world Date: Fri, 16 Mar 2018 11:56:29 -0700 (PDT) Lines: 161 Approved: news@gmane.org Message-ID: References: <2034613.rN3AoRdNao@tjmaciei-mobl1> <2319008.6H3YVR8kxN@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_2119_1204606126.1521226589362" X-Trace: blaine.gmane.org 1521226475 1524 195.159.176.226 (16 Mar 2018 18:54:35 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 16 Mar 2018 18:54:35 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDKLT4PURQHRBXVGWDKQKGQEP2AEO3Q@isocpp.org Fri Mar 16 19:54:31 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f199.google.com ([209.85.217.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ewuUi-0000Ab-K8 for gclcip-std-proposals@m.gmane.org; Fri, 16 Mar 2018 19:54:24 +0100 Original-Received: by mail-ua0-f199.google.com with SMTP id w9sf6791911uaa.17 for ; Fri, 16 Mar 2018 11:56:32 -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 :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=7/nL6ZN8gohFZEctBmwAdZVrn+ictTxZu8HtsUJbehA=; b=kHQ8/qY3CcfrkzYSbblEaxoDzMar9IQ0W57Dk34Um4g/Ycmzh8tuFCD2wdsi6oCocl Kv3+fDa2BiyKY59P5YYQUK2dNi748u8tylkUc3h/CBa+ARLgdNnTLEYABikrdB5hON3l Gc8rLwkJ0MAdSKHofPFn+7a9Siq4b678rLAwne8fmVOA4dyN0q68co8JF0c5mq7WiewZ veYStGlomlVk8NEGs5x7DgWSAPbMYG9i7pV9t1l65Amu+A12zFLa3ToXQcHdead/Ts26 spVm43CCtsj+cGc2ei8Ox4DnvKU1cTTy9aa5qD6Ph8pBCrdiFDsC//uMOIGAPS1rF3tC DEyA== 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=7/nL6ZN8gohFZEctBmwAdZVrn+ictTxZu8HtsUJbehA=; b=dD7Jzim1lzCI2U5WXdP44ay/rzogQZ7Ufec7mFIbvpJxxijR5uR26QEO2xJ8QtuK7/ z6UsF+F7b+H4OvNmOrxArTQ/Xi1o8N69mgpS9Yg9lzf4EhF2aRuWX6gYKNESEgZnfYMo +Qld6jBz8Ny6tSBnng070It3FJKIQGFYvW1aw7F9N7lcqOQOwV0aynge/s1GUcVfufa3 DXXwU3aHwLwnLsVlhnsh/oJVNZxE4Slhjq7dLW3ePmrRcdGk35nNi7y/xhkHU1zlprGC uppx0Czd4OMGfE5SG8/z4CEG1zkmGwf0QZFAXwlP9JGP+rzE2bmPPpz5tdtWG7SJ2iYI u89Q== 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=7/nL6ZN8gohFZEctBmwAdZVrn+ictTxZu8HtsUJbehA=; b=N0VCQebmoMK3ki4L8gBiCZDhmHHx2xi1lziBs6fQelGMgHXj+goXsZJc/YuDIGRiYL 9xoHVoPliIwa255w8WCmfnvvlIA6aIj5goeeVphjSwNEHF1odxLdABht/Bqk3Hzds4C9 ENYnubIgd4XKSMTEM0Uo+2ZKc6BXu2r0lvu18S0e+8auXNuS5pm2SWBijzcE8b4asZAd SbaE2LDMli0y/EDX5VMomjC33hVP/ZBJm7pshNlc4xbz7TzNZhaByV7xm9VVHcclD2Q8 TytNUO8WWeFsBTAhMz+Ay98cn+3ImL9BL/rI/iXHNRRoEiJ7pIDvoVDh3jMZj1PgVAJ1 txMw== X-Gm-Message-State: AElRT7GpD1i5mnT+xCVx0gEEqQSK5phmlkdXedVfKyOoiTZ4hyuHHppR zVkB8AcXL1uyOi7W0h7wG1BDnw== X-Google-Smtp-Source: AG47ELvUBGg3zUddbCGpE6x0rVVgwF9pSMFLywUFDi+XkBLuUFCR2I/AclSNiMgkKVcPdTCdaKR6Hw== X-Received: by 10.159.57.214 with SMTP id p22mr1205613uag.20.1521226591500; Fri, 16 Mar 2018 11:56:31 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.146.138 with SMTP id u132ls4300275vkd.13.gmail; Fri, 16 Mar 2018 11:56:30 -0700 (PDT) X-Received: by 10.31.193.140 with SMTP id r134mr330143vkf.6.1521226590055; Fri, 16 Mar 2018 11:56:30 -0700 (PDT) In-Reply-To: X-Original-Sender: myriachan@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:37366 Archived-At: ------=_Part_2119_1204606126.1521226589362 Content-Type: multipart/alternative; boundary="----=_Part_2120_2045095458.1521226589362" ------=_Part_2120_2045095458.1521226589362 Content-Type: text/plain; charset="UTF-8" On Friday, March 16, 2018 at 8:13:44 AM UTC-7, Hyman Rosen wrote: > > > struct A { int x[10]; }; > struct B { A a; }; > int B::*number_5 = &B::a.x[5]; > Careful here: this is a breaking change. Consider this currently-legal code: struct W { int x[10]; }; struct X { W w; }; struct Y { W w; }; struct Z : X, Y { void f(); }; void Z::f() { int *p = &Y::w.x[5]; *p = 4; } You'd need to use parentheses and define operators . and [] on member operators in order to solve this: (&B::a).x[5] I really like Thiago's proposal regarding data member pointers, but it has a major problem: it's an ABI break. Some proposed constructions would allow data member pointers with a negative offset (pointing to the containing class's members), and both the Microsoft and Itanium ABIs encode null member pointers as -1. Melissa -- 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/dcd5b3da-0018-4eca-b7a6-b94e950de2de%40isocpp.org. ------=_Part_2120_2045095458.1521226589362 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Friday, March 16, 2018 at 8:13:44 AM UTC-7, Hyman Rosen= wrote:
<= div class=3D"gmail_quote">
=C2= =A0 =C2=A0 struct A { int x[10]; };
=C2=A0 =C2=A0 struct B { A a; };
= =C2=A0 =C2=A0 int B::*number_5 =3D &B::a.x[5];
=

Careful here: this is a breaking change.=C2=A0 = Consider this currently-legal code:

struct W { int = x[<= span style=3D"color: #066;" class=3D"styled-by-prettify">10]; };
struct X { W= w;= };
struct Y { W w;= };=
struct Z : X, Y
{
=C2=A0 =C2=A0 void f();<= /span>
= };

void Z::f()
{
= =C2=A0 =C2=A0 int *p =3D &Y::w= ..x<= span style=3D"color: #660;" class=3D"styled-by-prettify">[5];
=C2=A0 =C2=A0 *p =3D 4;=
}

You'd need to use parentheses and define operators . and= [] on member operators in order to solve this:

(&B::a).x[5]
=
I really like Thiago's proposal regarding data member pointers, but= it has a major problem: it's an ABI break.=C2=A0 Some proposed constru= ctions would allow data member pointers with a negative offset (pointing to= the containing class's members), and both the Microsoft and Itanium AB= Is encode null member pointers as -1.

Melissa

--
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/dcd5b3da-0018-4eca-b7a6-b94e950de2de= %40isocpp.org.
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