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[209.85.220.65]) by mx.google.com with SMTPS id k33-v6sor1875827pld.14.2018.03.15.11.11.00 for (Google Transport Security); Thu, 15 Mar 2018 11:11:00 -0700 (PDT) Received-SPF: pass (google.com: domain of gasper.azman@gmail.com designates 209.85.220.65 as permitted sender) client-ip=209.85.220.65; X-Received: by 2002:a17:902:b582:: with SMTP id a2-v6mr9266881pls.353.1521137459639; Thu, 15 Mar 2018 11:10:59 -0700 (PDT) Original-Received: by 10.236.133.141 with HTTP; Thu, 15 Mar 2018 11:10:39 -0700 (PDT) In-Reply-To: X-Original-Sender: gasper.azman@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=RyvrW8ii; spf=pass (google.com: domain of gasper.azman@gmail.com designates 209.85.220.65 as permitted sender) smtp.mailfrom=gasper.azman@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:37340 Archived-At: --000000000000efb9fa0567776971 Content-Type: text/plain; charset="UTF-8" ooo offsetof that works on members of virtual base classes :) On Thu, Mar 15, 2018 at 6:09 PM, wrote: > I think we should leave this macro alone and add new operator with > different name that will be available everywhere. > And then optionally define `offsetof ` with use this new operator. > > On Thursday, March 15, 2018 at 6:21:19 PM UTC+1, Nicolas Lesser wrote: >> >> Not that I know of. This was mentioned in passing while discussing P0908, >> where it was suggested to make it an operator. >> >> EWG then went back and forth a bit, as making offsetof an operator would >> mean incompatibilities with POSIX headers but better for modules. >> >> You might want to write a proposal for this. >> >> There is the Atom proposal which proposes to have a "module header" which >> can also solve this issue in a relatively clean way (P0947). >> >> On Thu, Mar 15, 2018, 12:12 PM Nicol Bolas wrote: >> >>> The C standard library defines a large number of things that are macros. >>> In the vast majority of cases, these are constants or functions, which can >>> in C++ code be converted into `constexpr` variables or actual functions. >>> For all intents and purposes, such constructs can be drop-in replacements >>> for the C macros, which allows us to still work with them in a modular >>> standard library that doesn't allow macros. >>> >>> `offsetof` is a special case because it's not a function. Or at least, >>> it's not a function that C++ at present allows you to write. Without >>> reflection, there is no way to pass a typename or member variable as a >>> function parameter. And while there are ways we can work around it, none of >>> those ways would be drop-in replacements for `offsetof`; the user would >>> have to change their code. >>> >>> And even ignoring the non-drop-in part, there is currently no C++ >>> replacement for `offsetof`. As modules moves forward, are there plans to >>> resolve this issue and similar ones (beside the "let's get modules to >>> export macros" plan)? >>> >>> -- >>> 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-proposal...@isocpp.org. >>> To post to this group, send email to std-pr...@isocpp.org. >>> To view this discussion on the web visit https://groups.google.com/a/is >>> ocpp.org/d/msgid/std-proposals/c5f5ccc4-3267-442d-8cb2- >>> de1ae103a38e%40isocpp.org >>> >>> . >>> >> -- > 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/e7a864e9-a866-40d6- > 9688-95219dc34d92%40isocpp.org > > . > -- 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/CAANG%3DkUKSnNQ%3DdcKB-oeDdap7ydGNUy4dM9p4LOBZCrLdGL%3DUw%40mail.gmail.com. --000000000000efb9fa0567776971 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
ooo offsetof that works on members of virtual base classes= :)

On Thu, = Mar 15, 2018 at 6:09 PM, <inkwizytoryankes@gmail.com> wrote:
I think we sh= ould leave this macro alone and add new operator with different name that w= ill be available everywhere.
And then optionally define `offsetof ` with= use this new operator.

On Thursday, March 15, 2018= at 6:21:19 PM UTC+1, Nicolas Lesser wrote:
Not that I know of. This = was mentioned in passing while discussing P0908, where it was suggested to = make it an operator.

EWG then = went back and forth a bit, as making offsetof an operator would mean incomp= atibilities with POSIX headers but better for modules.

You might want to write a proposal for this.=

There is the Atom propo= sal which proposes to have a "module header" which can also solve= this issue in a relatively clean way (P0947).

On Thu, Mar 15, 2018= , 12:12 PM Nicol Bolas <jmck...@gmail.com> wr= ote:
The C standard library defines a large number of things that are= macros. In the vast majority of cases, these are constants or functions, w= hich can in C++ code be converted into `constexpr` variables or actual func= tions. For all intents and purposes, such constructs can be drop-in replace= ments for the C macros, which allows us to still work with them in a modula= r standard library that doesn't allow macros.

`offsetof` is a sp= ecial case because it's not a function. Or at least, it's not a fun= ction that C++ at present allows you to write. Without reflection, there is= no way to pass a typename or member variable as a function parameter. And = while there are ways we can work around it, none of those ways would be dro= p-in replacements for `offsetof`; the user would have to change their code.=

And even ignoring the non-drop-in part, there is currently no C++ r= eplacement for `offsetof`. As modules moves forward, are there plans to res= olve this issue and similar ones (beside the "let's get modules to= export macros" plan)?

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 To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposal...@isocpp.org.
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