220 37372 <6725bbc8-a8db-40e1-a3f4-98ac05e23862@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 15:12:24 -0700 (PDT) Lines: 158 Approved: news@gmane.org Message-ID: <6725bbc8-a8db-40e1-a3f4-98ac05e23862@isocpp.org> References: <71ed1718-d272-4920-92fe-3b59750e6fb8@isocpp.org> <22ef47e6-e957-4519-820f-1decb09a116d@isocpp.org> <64578641-a89f-4b60-82ce-5183a54a3630@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_2699_671267481.1521238344610" X-Trace: blaine.gmane.org 1521238224 5018 195.159.176.226 (16 Mar 2018 22:10:24 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 16 Mar 2018 22:10:24 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBSMCWHKQKGQEPI5DRZQ@isocpp.org Fri Mar 16 23:10:20 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f70.google.com ([209.85.213.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ewxYJ-0001Dr-RX for gclcip-std-proposals@m.gmane.org; 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Fri, 16 Mar 2018 15:12:26 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.67.2 with SMTP id q2ls775656vka.0.gmail; Fri, 16 Mar 2018 15:12:25 -0700 (PDT) X-Received: by 10.31.178.81 with SMTP id b78mr398144vkf.14.1521238345176; Fri, 16 Mar 2018 15:12:25 -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:37372 Archived-At: ------=_Part_2699_671267481.1521238344610 Content-Type: multipart/alternative; boundary="----=_Part_2700_1124475017.1521238344610" ------=_Part_2700_1124475017.1521238344610 Content-Type: text/plain; charset="UTF-8" On Friday, March 16, 2018 at 6:02:16 PM UTC-4, Marcin Jaczewski wrote: > > > > On Friday, March 16, 2018 at 6:23:12 PM UTC+1, Nicol Bolas wrote: >> >> 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). >> > > People who use `` will still use `` we don not change > antything (this why I suggest leaving it alone). > We add new keyword `real_super_offsetof` that will be available everywhere. > Only problem would be migration of heder to modules usage but because > offsetof is macro we can safely use text replace to change it to new > keyword. > If it's going to be a direct, drop-in replacement, such that code which uses `offsetof` can be changed to use `new_offsetof` with no other changes... why make it a new identifier at all? Just have `offsetof` become a C++ keyword, and have the C++ versions of `` and `stddef.h` simply not define them. I thought the whole point of using a new keyword was to give them a (presumably) better interface. -- 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/6725bbc8-a8db-40e1-a3f4-98ac05e23862%40isocpp.org. ------=_Part_2700_1124475017.1521238344610 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Friday, March 16, 2018 at 6:02:16 PM UTC-4, Marcin Jacz= ewski wrote:
<= br>
On Friday, March 16, 2018 at 6:23:12 PM UTC+1, Nicol Bolas wrote:
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 <jmc= k...@gmail.com> 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?
<= br>What module?=C2=A0 I don't understand.

Let me try again:
  • Change C++ s= o that there is a built-in version of o= ffsetof 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).

Peop= le who use=C2=A0 `<cstddef>` will still use `<cstddef>` we don = not change antything (this why I suggest leaving it alone).
We add new k= eyword `real_super_offsetof` that will be available everywhere.
Only pro= blem would be migration of heder to modules usage but because offsetof is m= acro we can safely use text replace to change it to new keyword.
<= /div>

If it's going to be a direct, drop-in replac= ement, such that code which uses `offsetof` can be changed to use `new_offs= etof` with no other changes... why make it a new identifier at all? Just ha= ve `offsetof` become a C++ keyword, and have the C++ versions of `<cstdd= ef>` and `stddef.h` simply not define them.

I thought the whole p= oint of using a new keyword was to give them a (presumably) better interfac= e.

--
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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/6725bbc8-a8db-40e1-a3f4-98ac05e23862= %40isocpp.org.
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