220 39400 <61682de8-3bf2-42d4-ae19-fcf3bd1d93a0@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: inkwizytoryankes@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Alternative proposal for mapping P0709 Deterministic Exceptions into C Date: Wed, 25 Jul 2018 09:43:54 -0700 (PDT) Lines: 159 Approved: news@gmane.org Message-ID: <61682de8-3bf2-42d4-ae19-fcf3bd1d93a0@isocpp.org> References: <6a65c934-5d2a-4e75-b88d-9eaaee338bd3@isocpp.org> <1c229827-6d5d-45bd-8766-c3af818b2b0b@isocpp.org> <4ac80882-16fc-4ab4-9a12-64da1ef0e974@isocpp.org> <8866881c-ef1d-4c37-9242-5b1d3327c288@isocpp.org> <363df3db-b747-449f-b95d-81d15b6c3842@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_9634_1944432700.1532537034498" X-Trace: blaine.gmane.org 1532536911 19278 195.159.176.226 (25 Jul 2018 16:41:51 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 25 Jul 2018 16:41:51 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDDLTAGNTIBBBS6R4LNAKGQEOS3QMYQ@isocpp.org Wed Jul 25 18:41:47 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yb0-f198.google.com ([209.85.213.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fiMrB-0004r3-UQ for gclcip-std-proposals@m.gmane.org; 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Wed, 25 Jul 2018 09:43:56 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a81:ec3:: with SMTP id 186-v6ls2375985ywo.33.gmail; Wed, 25 Jul 2018 09:43:55 -0700 (PDT) X-Received: by 2002:a0d:de01:: with SMTP id h1-v6mr398057ywe.3.1532537035019; Wed, 25 Jul 2018 09:43:55 -0700 (PDT) In-Reply-To: X-Original-Sender: inkwizytoryankes@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:39400 Archived-At: ------=_Part_9634_1944432700.1532537034498 Content-Type: multipart/alternative; boundary="----=_Part_9635_11244141.1532537034498" ------=_Part_9635_11244141.1532537034498 Content-Type: text/plain; charset="UTF-8" On Wednesday, July 25, 2018 at 5:24:19 PM UTC+2, Nicol Bolas wrote: > > On Wednesday, July 25, 2018 at 4:14:33 AM UTC-4, Niall Douglas wrote: >> >> >>>>> It's a C proposal; it doesn't interact with `constexpr`. Indeed, one >>>>> of its biggest flaws is that it doesn't allow for inter-operation with C++ >>>>> static exceptions at all, despite being in part based on the same principle. >>>>> >>>> >>>> My _Fails() proposal does however work in constexpr, >>>> >>> >>> `_Fails()` is not valid C++, and `constexpr` is not valid C. How can >>> they work with one another? Unless you're proposing to add `_Fails()` to >>> C++, which I think would be a rather hard sell. >>> >> >> I appreciate you are probably not up to date, as I have not issued a new >> draft of D1095 which incorporates the substantial feedback I received from >> WG14. And I have only very briefly summarised what will go into that draft >> on std-proposals and /r/cpp/. >> >> But in short, C22 _Fails(T) maps directly onto C++ 23 throws(T). >> > > Pedantic note: `throws(T)` doesn't exist. `throws()` is a > *conditional* throws declaration, much like `noexcept()`. P0709 > makes that abundantly clear. > > What you're looking for is `throws{T}`. Which P0709 treats as an > extension, not a required part of the proposal. So there's no guarantee it > will make it into any hypothetical C++23. > > The only difference is auto-propagation, so a _Fails(T) if unhandled >> results in a failure to compile, whereas a throws(T) if unhandled >> propagates upwards. >> >> This is what WG14 asked for. As C++ 23 would surely be incorporating C22 >> into itself, whatever goes into C also goes in C++. >> > > That's not how C++ has worked since 1998. C++11 did not incorporate C99 > wholesale; it only took specific things from it. Similarly, C++14/17/20 did > not adopt C11 wholesale. The two languages are *diverging*. > > So why should we expect C++23 to adopt C22 in this way? > > To make easier to share code between? Image big C22 library that use this new calling convention in headers, if we accept this part of C22 using this library in C++23 will be trivial. This is too other way around, it allow C++ to define headers that will be easy consumable by C and other languages that will support C22 exceptions (this is major reason). > I intend to propose, in fact, that both mechanisms work perfectly in >> constexpr. It would let constexpr code choose whether failure should be >> handled explicitly (_Fails) or implicitly (throws), exactly the same as in >> non-constexpr. >> >> Niall >> > -- 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/61682de8-3bf2-42d4-ae19-fcf3bd1d93a0%40isocpp.org. ------=_Part_9635_11244141.1532537034498 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Wednesday, July 25, 2018 at 5:24:19 PM UTC+2, N= icol Bolas wrote:
On Wednesday, July 25, 2018 at 4:14:33 AM UTC-4, Niall Douglas wrote:

<= div>It's a C proposal; it doesn't interact with `constexpr`. Indeed= , one of its biggest flaws is that it doesn't allow for inter-operation= with C++ static exceptions at all, despite being in part based on the same= principle.

My _Fails() pro= posal does however work in constexpr,

`_Fails()` is not valid C++, and `constexpr` is not valid C. How can= they work with one another? Unless you're proposing to add `_Fails()` = to C++, which I think would be a rather hard sell.
=

I appreciate you are probably not up to date, as I have= not issued a new draft of=C2=A0 D1095 which incorporates the substantial f= eedback I received from WG14. And I have only very briefly summarised what = will go into that draft on std-proposals and /r/cpp/.

<= div>But in short, C22 _Fails(T) maps directly onto C++ 23 throws(T).
<= /blockquote>

Pedantic note: `throws(T)` doesn't exis= t. `throws(<expr>)` is a conditional throws declaration, much = like `noexcept(<expr>)`. P0709 makes that abundantly clear.

What you're looking for is `throws{T}`. Which P0709 tre= ats as an extension, not a required part of the proposal. So there's no= guarantee it will make it into any hypothetical C++23.

The only difference is auto-p= ropagation, so a _Fails(T) if unhandled results in a failure to compile, wh= ereas a throws(T) if unhandled propagates upwards.

This is what WG14 asked for. As C++ 23 would surely be incorporating C22 i= nto itself, whatever goes into C also goes in C++.
<= br>
That's not how C++ has worked since 1998. C++11 did not i= ncorporate C99 wholesale; it only took specific things from it. Similarly, = C++14/17/20 did not adopt C11 wholesale. The two languages are diverging= .

So why should we expect C++23 to adopt C= 22 in this way?

=C2=A0
To make easier to share code between? Image big C22 library that use = this new calling convention in headers, if we accept this part of C22 using= this library in C++23 will be trivial. This is too other way around, it al= low C++ to define headers that will be easy consumable by C and other langu= ages that will support C22 exceptions (this is major reason).
=C2=A0
=
I intend to propose= , in fact, that both mechanisms work perfectly in constexpr. It would let c= onstexpr code choose whether failure should be handled explicitly (_Fails) = or implicitly (throws), exactly the same as in non-constexpr.
Niall

--
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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/61682de8-3bf2-42d4-ae19-fcf3bd1d93a0= %40isocpp.org.
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