220 26317 article Path: news.gmane.org!not-for-mail From: "'Edward Catmur' via ISO C++ Standard - Future Proposals" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: statement folding on variadic templates parameters pack Date: Mon, 13 Jun 2016 15:14:18 +0100 Lines: 105 Approved: news@gmane.org Message-ID: References: <1e3daa7c-e10a-4589-8118-26f47bc1a0df@isocpp.org> <2d8458f8-27b2-464f-a16e-fc866ccfd2cd@isocpp.org> <55892254-d646-4cc3-b10c-a0f0a5eb665c@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a11479a861893ea05352981a7 X-Trace: ger.gmane.org 1465827268 20817 80.91.229.3 (13 Jun 2016 14:14:28 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 13 Jun 2016 14:14:28 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDZLZTXF7UJBBO777K5AKGQENRDKACA@isocpp.org Mon Jun 13 16:14:28 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f72.google.com ([209.85.214.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1bCSdG-0006AW-8I for gclcip-std-proposals@m.gmane.org; Mon, 13 Jun 2016 16:14:26 +0200 Original-Received: by mail-it0-f72.google.com with SMTP id z189sf102158718itg.2 for ; Mon, 13 Jun 2016 07:14:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=inEWHLgX1t4QI4w0IqzxnuMJ67fGl5kTBMzZsg2qcno=; b=aqwgvCG6QsFh/zHM7obUgSMpeAbZezLQiROHFNwAA1p6kkDDOjhGu5aGbX9ZHoNmPF Gu6Te9gXXvMxk32MrdBd2qQGFjyQkzjfQztr2+uKt37x5yjDKZJBNnRIdMM+BJN1jjxX mJWbS1U/y5WyTIE3XADTHXalljmbpIU8GSI053B2SPa+Ic/rRmrb4spHo7zE+P3vEbiF B6Nh8ZIWdweZjw8zxLhEdVYrduQbZsUpm/NNNYQb0VKCp+4cHOB1fU5wQe8X+399rP2L mOqIjuMBXnlhSCO7nYLAZxpcKPquoApWoZ2lMph1iH9HChrMvVzy9OMrPSS1vQfHOQzc uXcg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=inEWHLgX1t4QI4w0IqzxnuMJ67fGl5kTBMzZsg2qcno=; b=VIDk+yJGn00cAW3DNYuHRSFXkDO2BNwFvdPUnzWV9xKsDsdwckZOoUMlkA/et9mMTP /7N0oZXiensr2cfP6d/A8Sk7x/iTuxhQGmbsKTnhlsnwQ7NPk5paOw1jxvnH2OSrQ4df 6WnvCV248fCXCDLT1aQTMwJjX4KyQ0e5/s50aOJojbjqHblsY2EYF83qnn04Tj/erJLD wFsQJDT46Hg+Pn4MwUFNZXPGhhVqsjB7Md65NdK+mvstqDgocs0xb+X0tqcOwgAQMotd uTHuQxukLxtiXdIPZdcx45zixTNVfKvAms8RubIHRKjNZdgP/aZWVwJNYQk1+nfTCOfP 2zXA== X-Gm-Message-State: ALyK8tIQH6bz5UTU//HCwfILkftIVJc5V7xRxC15FpZne2c3anLZfYnjkq5fuRbMSZGcfA== X-Received: by 10.107.13.77 with SMTP id 74mr12572772ion.4.1465827260389; Mon, 13 Jun 2016 07:14:20 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.80.170 with SMTP id c39ls3309505qgd.28.gmail; Mon, 13 Jun 2016 07:14:19 -0700 (PDT) X-Received: by 10.55.124.130 with SMTP id x124mr14962937qkc.113.1465827259537; Mon, 13 Jun 2016 07:14:19 -0700 (PDT) Original-Received: from mail-qk0-x22d.google.com (mail-qk0-x22d.google.com. [2607:f8b0:400d:c09::22d]) by mx.google.com with ESMTPS id s5si15276047qkc.169.2016.06.13.07.14.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 13 Jun 2016 07:14:19 -0700 (PDT) Received-SPF: pass (google.com: domain of ecatmur@googlemail.com designates 2607:f8b0:400d:c09::22d as permitted sender) client-ip=2607:f8b0:400d:c09::22d; Original-Received: by mail-qk0-x22d.google.com with SMTP id p10so39457413qke.3 for ; Mon, 13 Jun 2016 07:14:19 -0700 (PDT) X-Received: by 10.55.217.148 with SMTP id q20mr15050433qkl.62.1465827259354; Mon, 13 Jun 2016 07:14:19 -0700 (PDT) Original-Received: by 10.237.55.198 with HTTP; Mon, 13 Jun 2016 07:14:18 -0700 (PDT) In-Reply-To: <55892254-d646-4cc3-b10c-a0f0a5eb665c@isocpp.org> X-Original-Sender: ecatmur@googlemail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@googlemail.com; spf=pass (google.com: domain of ecatmur@googlemail.com designates 2607:f8b0:400d:c09::22d as permitted sender) smtp.mailfrom=ecatmur@googlemail.com; dmarc=pass (p=QUARANTINE dis=NONE) header.from=googlemail.com X-Original-From: Edward Catmur 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:26317 Archived-At: --001a11479a861893ea05352981a7 Content-Type: text/plain; charset=UTF-8 On Mon, Jun 13, 2016 at 10:33 AM, Giovanni Piero Deretta < gpderetta@gmail.com> wrote: > On Sunday, June 12, 2016 at 11:25:50 AM UTC+1, Ville Voutilainen wrote: >> >> On 12 June 2016 at 13:23, wrote: >> > This code should be fast as manually written switch, it would be >> trivial for >> > compiler to create jump table to have best performance. >> >> >> I'm sure the open-source compilers will happily accept an extension >> patch that shows how trivial it is. >> > > For what is worth, you can abuse GCC statement expressions plus variadics > to get variadic expansion of switch statements. Although 'case' in > statement expressions is explicitly documented not to be supported, it does > work in practice (nothing I would use in production of course). > That's amazing! I couldn't get it to work in any version after 4.9.2, though; is there a trick I'm missing? switch (i) { ([](...){})(({ case I : g(), ({ return; }), 0; })... ); } > So, while I wouldn't call it trivial, it seems to me that it souldn't be > too hard to implement the extension in GCC, and you could even consider > statement expressions as existing practice. > Absolutely; it'd be a nice hack to work on. -- 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/CAJnLdObbLAvViULXGAq%3DR7oP%2B%2BY5%2BWHNKu0C2BapoZwDXLnR4A%40mail.gmail.com. --001a11479a861893ea05352981a7 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On M= on, Jun 13, 2016 at 10:33 AM, Giovanni Piero Deretta <= gpderetta@gmail.co= m> wrote:
On Sunday, Jun= e 12, 2016 at 11:25:50 AM UTC+1, Ville Voutilainen wrote:<= blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-l= eft-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;pa= dding-left:1ex">On 12 June 2016 at 13:23, =C2=A0<ink= wizyt...@gmail.com> wrote:
> This code should be fast as manually written switch, it would be t= rivial for
> compiler to create jump table to have best performance.


I'm sure the open-source compilers will happily accept an extension
patch that shows how trivial it is.

For what is worth, you can abuse GCC state= ment expressions plus variadics to get variadic expansion of switch stateme= nts. Although 'case' in statement expressions is explicitly documen= ted not to be supported, it does work in practice (nothing I would use in p= roduction of course).

That&= #39;s amazing! I couldn't get it to work in any version after 4.9.2, th= ough; is there a trick I'm missing?

=C2=A0 switch (i) {
=C2=A0 =C2=A0 ([](...){})(({ case I : g<I&g= t;(), ({ return; }), 0; })... );
=C2=A0 }
=C2=A0
So, while I wouldn't call it trivial, it seems to me= that it souldn't be too hard to implement the extension in GCC, and yo= u could even consider statement expressions as existing practice.
=

Absolutely; it'd be a nice hack = to work on.

--
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