220 37367 article Path: news.gmane.org!.POSTED!not-for-mail From: Hyman Rosen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: `offsetof` in a macro-less, modular world Date: Fri, 16 Mar 2018 15:25:28 -0400 Lines: 209 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/alternative; boundary="001a1143dd1e614aac05678c9348" X-Trace: blaine.gmane.org 1521228229 22261 195.159.176.226 (16 Mar 2018 19:23:49 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 16 Mar 2018 19:23:49 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDKJJPVBQMKRBPVUWDKQKGQELYDKD4Q@isocpp.org Fri Mar 16 20:23:45 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wr0-f197.google.com ([209.85.128.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ewux6-0005gb-A4 for gclcip-std-proposals@m.gmane.org; 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[209.85.220.65]) by mx.google.com with SMTPS id 74sor2075418wmf.39.2018.03.16.12.25.49 for (Google Transport Security); Fri, 16 Mar 2018 12:25:49 -0700 (PDT) Received-SPF: pass (google.com: domain of hyman.rosen@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; X-Received: by 10.28.146.2 with SMTP id u2mr2514672wmd.79.1521228349260; Fri, 16 Mar 2018 12:25:49 -0700 (PDT) Original-Received: by 10.28.55.19 with HTTP; Fri, 16 Mar 2018 12:25:28 -0700 (PDT) In-Reply-To: X-Original-Sender: hyman.rosen@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=ixb7rxkG; spf=pass (google.com: domain of hyman.rosen@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=hyman.rosen@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE 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:37367 Archived-At: --001a1143dd1e614aac05678c9348 Content-Type: text/plain; charset="UTF-8" On Fri, Mar 16, 2018 at 2:56 PM, Myriachan wrote: > 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; > } > > I swear, C++ drives me more crazy every time I look at it. Notice the obvious corollary to your code: void Z::f() { int *p = &(Y::w.x[5]); // OK int *q = & Y::w.x[5] ; // OK W *r = &(Y::w) ; // OK W *s = & Y::w ; // Error } C++ syntax is a horrible hodgepodge mess caused by too much "it would be nice if *this* meant *that*" without any consideration of making everything globally consistent. -- 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/CAHSYqda43Vo0%2BvhY3i39JT1%2BcBaumAwynsJ%3D-NjGu7Nm3Yd9-A%40mail.gmail.com. --001a1143dd1e614aac05678c9348 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On F= ri, Mar 16, 2018 at 2:56 PM, Myriachan <myriachan@gmail.com> wrote:
On Friday, March 16, 2018 at 8:13:44 AM UTC-7, Hyman Rosen wrote:

=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];
<= /span>

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

struct W { int x[10]; };
struct X { W w; };
stru= ct Y { W w; };=
struct Z : X, Y=
{
=C2=A0 =C2=A0 void f(= );
};

void Z= ::f()
{
=C2=A0 =C2=A0 = int *p =3D <= span style=3D"color:#660" class=3D"m_6940945667384060895styled-by-prettify"= >&Y::w.x[<= span style=3D"color:#066" class=3D"m_6940945667384060895styled-by-prettify"= >5];
=C2=A0 =C2=A0 *p =3D 4;
}


I swear, C++ drives me more crazy e= very time I look at it.=C2=A0 Notice the obvious corollary to your code:
=C2=A0 =C2=A0 void Z::f()=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 int *p =3D &(Y::w.x[5]);=C2=A0 // OK
=C2=A0 =C2=A0 =C2=A0 =C2=A0 int *q =3D & = Y::w.x[5] ;=C2=A0 // OK
=C2=A0 = =C2=A0 =C2=A0 =C2=A0 W=C2=A0 =C2=A0*s =3D & Y::w=C2=A0 =C2=A0 =C2=A0 ;= =C2=A0 // Error
=C2=A0 =C2=A0= }

C++ syntax is = a horrible hodgepodge mess caused by too much "it would be nice if = this meant that"
without any consideration of making eve= rything globally consistent.

--
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--001a1143dd1e614aac05678c9348-- .