220 39399 article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Alternative proposal for mapping P0709 Deterministic Exceptions into C Date: Wed, 25 Jul 2018 08:24:19 -0700 (PDT) Lines: 136 Approved: news@gmane.org Message-ID: 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_9594_1060711400.1532532259209" X-Trace: blaine.gmane.org 1532532136 526 195.159.176.226 (25 Jul 2018 15:22:16 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 25 Jul 2018 15:22:16 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBJFM4LNAKGQENIFYY6A@isocpp.org Wed Jul 25 17:22:12 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f197.google.com ([209.85.161.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fiLcA-0008R1-9j for gclcip-std-proposals@m.gmane.org; Wed, 25 Jul 2018 17:22:10 +0200 Original-Received: by mail-yw0-f197.google.com with SMTP id c204-v6sf4379478ywa.8 for ; Wed, 25 Jul 2018 08:24:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=+6MPUTEGNCYdSvzRQPey2uUCYN2IKOM3/wQPfhXKHuk=; b=OV4xElx0a36uAcfhiNAYS6v4FqjpH44ai6i1cit6JiquT6WW2+XPlgkXdugC0KURc2 UsdJOJqq8d38mwnugE6KyQhgTebEG97uxQdr/N9mqgJejrq0zDA0T0IjMfU4nQNKfuIb /gvksrMBSbyQ+6zivdIcLrrDcA5LCtlhXQ1ABXNAN5WmyIIcTJWhOTd5BCimy0kg4Ni2 BCEIz/c961Yf+9cL8U41cEGwUJWy7mzkK5BpIfSZnYWDHfbZ4KKm6g90BF1VlMtO+zpl plxIusKFhbs9sQQsOcIfikNwqGcgUYl3IjyYQs0eYDHzLIlr4Qe1nKXOkSM5U+tmAuxH yhZQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=+6MPUTEGNCYdSvzRQPey2uUCYN2IKOM3/wQPfhXKHuk=; b=QFOr5Km5fSgC0W2Xf1/x39xFVbXklLq7X9o5k+sfugvy72KrsPk5rm4X3DtoszSC/+ 7blp8SXyf2HkIt8EJ582uxzQKeBH+4bcMYclkIiF7GHiWZ23h/021YnFGYx6gzDQlwVF yFjdoZwSmjvzQNgJiZIg1D0rfGDNC7plib1QSYEE91k51zG1+k8dp/HxfkiLc6sz5yEH E4NGtcV47qxmq37ZEEfQWBNpIjM5pGwhn9hvmPTvs8e9joQWKL+hMKG98RWMaafKdUtK Sptnk6w5Dbr5T9rhZg1oMHWy0AM9C4iMg9PyVv7nwebvCTP4+jwbY2r7j87CeR4tGOx1 +VeQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:x-original-sender:reply-to:precedence :mailing-list:list-id:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=+6MPUTEGNCYdSvzRQPey2uUCYN2IKOM3/wQPfhXKHuk=; b=MdHeztp/ymUZW83kanV0FlF8MU4EpDNPYJ1jCjj2fuHQyRVxjJfvr2GI2i6gLgzFH9 jrVnJSkW5EcjllP6Vi4xda+5YjvYkaPensLGhswG6LYzBFaa8eFuKW9jTCaT7hG0TrJi l5C6/YqqLbOuHM1qn3RXX33RKV0Sn0erRXbzordhrhIkmWswKDt2Jw4fLy8q0rmcDVB9 Y5Oskc+7jCXbqCKXRebkC6SZS6BY1icbNJDXd0ZyVId7gzHN0n4RfhEvwUJPe5QhaUWX yGvvPE6ycdiKmhEAn3c0tJMvTUa2xNSI9STxdxeZQk1YOmitd9cJW2n25AHbP3JcMsJ4 rbpg== X-Gm-Message-State: AOUpUlGpk1ZLzVzl6erX0AjjOOZEnSAMYwoCN8B80mBRQGZG3ke/zHIT DAFhL/6X6ZBJ5w3ZJirWITvm9w== X-Google-Smtp-Source: AAOMgpf6uSZEQZzoI8UDXDf/yttI/mCUusQvfuJtZUMybyjZ0e51IcLC0moFTvnW2ho7qIX7wESqYA== X-Received: by 2002:a25:4e85:: with SMTP id c127-v6mr6382722ybb.32.1532532260886; Wed, 25 Jul 2018 08:24:20 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a0d:e6d7:: with SMTP id p206-v6ls2185963ywe.12.gmail; Wed, 25 Jul 2018 08:24:19 -0700 (PDT) X-Received: by 2002:a81:330a:: with SMTP id z10-v6mr386679ywz.5.1532532259748; Wed, 25 Jul 2018 08:24:19 -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:39399 Archived-At: ------=_Part_9594_1060711400.1532532259209 Content-Type: multipart/alternative; boundary="----=_Part_9595_461667012.1532532259209" ------=_Part_9595_461667012.1532532259209 Content-Type: text/plain; charset="UTF-8" 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? 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/edaab808-c155-4369-9be9-e1a0fad36265%40isocpp.org. ------=_Part_9595_461667012.1532532259209 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Wednesday, July 25, 2018 at 4:14:33 AM UTC-4, Niall Dou= glas 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 pa= rt 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 proposin= g to add `_Fails()` to C++, which I think would be a rather hard sell.

I appreciate you are probably not u= p to date, as I have not issued a new draft of=C2=A0 D1095 which incorporat= es the substantial feedback I received from WG14. And I have only very brie= fly 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(<expr>)` is a conditional throw= s declaration, much like `noexcept(<expr>)`. P0709 makes that abundan= tly clear.

What you're looking for is `throws{= T}`. Which P0709 treats as an extension, not a required part of the proposa= l. 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 sure= ly be incorporating C22 into itself, whatever goes into C also goes in C++.=

That's not how C++ has worked si= nce 1998. C++11 did not incorporate C99 wholesale; it only took specific th= ings from it. Similarly, C++14/17/20 did not adopt C11 wholesale. The two l= anguages are diverging.

So why should w= e expect C++23 to adopt C22 in this way?

I intend to propose, in fact, that = both mechanisms work perfectly in constexpr. It would let constexpr code ch= oose whether failure should be handled explicitly (_Fails) or implicitly (t= hrows), exactly the same as in non-constexpr.

Nial= l

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