220 37357 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 10:54:11 -0400 Lines: 70 Approved: news@gmane.org Message-ID: References: <71ed1718-d272-4920-92fe-3b59750e6fb8@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="001a114975742fea86056788c9c2" X-Trace: blaine.gmane.org 1521211954 17129 195.159.176.226 (16 Mar 2018 14:52:34 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 16 Mar 2018 14:52:34 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDKJJPVBQMKRBKNVV7KQKGQEEZWMZZQ@isocpp.org Fri Mar 16 15:52:30 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 1ewqiZ-0004L6-NW for gclcip-std-proposals@m.gmane.org; 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[209.85.220.41]) by mx.google.com with SMTPS id b9sor3566097wrh.54.2018.03.16.07.54.33 for (Google Transport Security); Fri, 16 Mar 2018 07:54:33 -0700 (PDT) Received-SPF: pass (google.com: domain of hyman.rosen@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.223.134.210 with SMTP id 18mr2100477wry.232.1521212072125; Fri, 16 Mar 2018 07:54:32 -0700 (PDT) Original-Received: by 10.28.55.19 with HTTP; Fri, 16 Mar 2018 07:54:11 -0700 (PDT) In-Reply-To: <71ed1718-d272-4920-92fe-3b59750e6fb8@isocpp.org> 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=cDhyh3aU; spf=pass (google.com: domain of hyman.rosen@gmail.com designates 209.85.220.41 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:37357 Archived-At: --001a114975742fea86056788c9c2 Content-Type: text/plain; charset="UTF-8" On Thu, Mar 15, 2018 at 11:55 PM, Nicol Bolas wrote: > > The problem I'm talking about here is that if you have a `std.cstddef` > module, without the ability to export macros, it cannot export anything > which is compatible with `offsetof` usage. So even if we make an operator > for this or empower member pointers or whatever, the existence of such a > feature won't allow you to switch from `#include ` to `import > std.cstddef` without changing your code. > You just need to simultaneously modify C++ so that there is a built-in equivalent to offsetof, and make offsetof a pre-defined macro that expands to that. Why is that difficult? Are you imagining that modular C++ isn't going to have a preprocessor at all? Users of __FILE__, __LINE__, __PRETTY_FUNCTION__, and __COUNTER__ may want to have a word with you. -- 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/CAHSYqdaG06U9DwCW57%3DUM5GrUHkXWV9Ah5u%2B1wDrisBSo_nQig%40mail.gmail.com. --001a114975742fea86056788c9c2 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On T= hu, Mar 15, 2018 at 11:55 PM, Nicol Bolas <jmckesson@gmail.com> wrote:
The proble= m I'm talking about here is that if you have a `std.cstddef` module, wi= thout the ability to export macros, it cannot export anything which is comp= atible with `offsetof` usage. So even if we make an operator for this or em= power member pointers or whatever, the existence of such a feature won'= t allow you to switch from `#include <cstddef>` to `import std.cstdde= f` without changing your code.

You just ne= ed to simultaneously modify C++ so that there is a built-in equivalent
t= o offsetof, and make offsetof a pre-defined macro that expands to that.=C2= =A0 Why is
that difficult?

Are you imagining that modular C++ isn= 't going to have a preprocessor at all?
Users of __FILE__, __LINE__,= __PRETTY_FUNCTION__, and __COUNTER__
may want to have a word with you.<= /div>

--
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