220 37363 <64578641-a89f-4b60-82ce-5183a54a3630@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: `offsetof` in a macro-less, modular world Date: Fri, 16 Mar 2018 10:23:11 -0700 (PDT) Lines: 120 Approved: news@gmane.org Message-ID: <64578641-a89f-4b60-82ce-5183a54a3630@isocpp.org> References: <71ed1718-d272-4920-92fe-3b59750e6fb8@isocpp.org> <22ef47e6-e957-4519-820f-1decb09a116d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1850_1285662006.1521220991948" X-Trace: blaine.gmane.org 1521220873 6093 195.159.176.226 (16 Mar 2018 17:21:13 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 16 Mar 2018 17:21:13 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBAP3V7KQKGQESJF4IAI@isocpp.org Fri Mar 16 18:21:09 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f200.google.com ([209.85.217.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ewt2R-0001Si-Bd for gclcip-std-proposals@m.gmane.org; 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Fri, 16 Mar 2018 10:23:13 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.50.79 with SMTP id y76ls4094901vky.7.gmail; Fri, 16 Mar 2018 10:23:12 -0700 (PDT) X-Received: by 10.31.158.83 with SMTP id h80mr291429vke.9.1521220992673; Fri, 16 Mar 2018 10:23:12 -0700 (PDT) In-Reply-To: X-Original-Sender: jmckesson@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:37363 Archived-At: ------=_Part_1850_1285662006.1521220991948 Content-Type: multipart/alternative; boundary="----=_Part_1851_1871515636.1521220991948" ------=_Part_1851_1871515636.1521220991948 Content-Type: text/plain; charset="UTF-8" On Friday, March 16, 2018 at 11:34:02 AM UTC-4, Hyman Rosen wrote: > > On Fri, Mar 16, 2018 at 11:16 AM, Nicol Bolas > wrote: >> >> 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. >>> >> >> And if modules can't export macros, how will `import std.cstddef` give me >> access to that module? >> > > What module? I don't understand. > > Let me try again: > > - Change C++ so that there is a built-in version of offsetof under a > different name, say __offsetof. > - __offsetof is available for use in all C++ code without any header > or module needed, just as sizeof is. > - Also change C++ so that offsetof is a pre-defined macro that expands > to __offsetof. > > Oh, when you said "built-in" you meant like "supplied by the compiler". So... what happens with people's code that *don't* include or that happens to use the `offsetof` identifier? Admittedly this is a minor issue, as I rather doubt someone's going to make a class or function that conflicts with a fairly widely known C macro that gets included by quite a few things (even if only because of other useful things). -- 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/64578641-a89f-4b60-82ce-5183a54a3630%40isocpp.org. ------=_Part_1851_1871515636.1521220991948 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Friday, March 16, 2018 at 11:34:02 AM UTC-4, Hyman Rose= n wrote:
=
On Fri, Mar 16, 2018 at 11:16 AM, Nicol Bolas <jmck...@gmail.com> wrote:
You just need to simult= aneously modify C++ so that there is a built-in equivalent
to offsetof, = and make offsetof a pre-defined macro that expands to that.

And if modules can't export macros= , how will `import std.cstddef` give me access to that module?
<= /blockquote>

What module?=C2=A0 I don't understand.

Let me try again:<= br>
  • Change C++ so that there is a built-in version of offsetof under a different name, say __offsetof.
  • __offsetof=C2=A0is available for use in all C++ code without any header o= r module needed, just as sizeof = is.
  • Also change C++ so that off= setof=C2=A0is a pre-defined macro that expands to __offsetof.

Oh, wh= en you said "built-in" you meant like "supplied by the compi= ler".

So... what happens with people's code that don'= ;t include <cstddef> or <stddef> that happens to use the `o= ffsetof` identifier? Admittedly this is a minor issue, as I rather doubt so= meone's going to make a class or function that conflicts with a fairly = widely known C macro that gets included by quite a few things (even if only= because of other useful things).

--
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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/64578641-a89f-4b60-82ce-5183a54a3630= %40isocpp.org.
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