220 26218 <9c9cb032-a950-476b-823c-28643ef305d8@isocpp.org> article Path: news.gmane.org!not-for-mail From: Sergey Vidyuk Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: statement folding on variadic templates parameters pack Date: Wed, 8 Jun 2016 11:03:32 -0700 (PDT) Lines: 167 Approved: news@gmane.org Message-ID: <9c9cb032-a950-476b-823c-28643ef305d8@isocpp.org> References: <1e3daa7c-e10a-4589-8118-26f47bc1a0df@isocpp.org> <0aa49f06-08b0-433a-a897-720140eb7097@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1710_1167150558.1465409012569" X-Trace: ger.gmane.org 1465409315 12942 80.91.229.3 (8 Jun 2016 18:08:35 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 8 Jun 2016 18:08:35 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCB6HO5JRMARB5V34G5AKGQEXHARZ3I@isocpp.org Wed Jun 08 20:08:30 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f198.google.com ([209.85.161.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1bAhpI-0000DL-0r for gclcip-std-proposals@m.gmane.org; Wed, 08 Jun 2016 20:03:36 +0200 Original-Received: by mail-yw0-f198.google.com with SMTP id n63sf36709506ywf.3 for ; Wed, 08 Jun 2016 11:03:35 -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 :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=mRCi1Dx60cnpasOnpmS2kasLJGMlpKAyHz+0XEXkKPw=; b=ZFs6L3b/0cDFm5UT684pjeGdMmTLkYZ7+aMcFVXhbocOgw/gMoUd9QrYWAQNLTnx3l lDyP+VtSQLwM2KBxphIivYJvJQzyEulT1R9GAqGYyq6/QEJ5CfklIE8CwTgomvN+iEHH 4PpTaOUdC13UZpi0oE1ZD6IdEbwRs7FYNmnJyCroIzzz2cRDf9qFfBChBQRgaLTbne8p RV/SJHtXDpC7ABvRZJCQHzs4BFZVXp24QM8iibB16vdOB/dO+fA5YS+1YRRZzxpXFpq3 8kMCiMDAzJAAt7gaoPFXe1EIzgCvx1Ec+BKPoAuWDGYq5mioHGvPQwRN4H4T4t/hACVi +ejw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=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=mRCi1Dx60cnpasOnpmS2kasLJGMlpKAyHz+0XEXkKPw=; b=RF00fTE9vl8pFk7IssLvUDlS5ZVYMRrLeAs2FfXmKN/LUJdv2LmZkG9eCcnjWuEJV0 FCoK/F3TD8kku8Tk0+uf/o1Eo+jjY2h7dIHadTaUyJHYueKOHyV5YCuizSzMfep6ABLO Hy1KYd6OR8VfI1y8FxVQGc1jswdSuxo0zqY9EeEFf1BvRp7njyfUQfmDfFudTwRLkd1n GLK6nLdiKuYBm/sKcMp54pdXjgqUYSZM6PvMRIQqiheIUbpBuib94BAzYQGyMVAm+CJx 96lEUGqtQYtqYuLU6EI8uJe0RSTxGQBkdiQHFHyyS/tPq7q64/E5OiS4rRCNzBZlg/2h 7CLg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; 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=mRCi1Dx60cnpasOnpmS2kasLJGMlpKAyHz+0XEXkKPw=; b=V+SqMSjDpoufks80N97lqfKfny+XSccxMoMY5qVvDJiz81c+cO9/RY1VkXKDPIZAza 9QBb3T7l2cuh3aDm7U41jAorRXoueFRR1yqNnZDxG447ks5JpHi+KtUc+nF4os8tqa+k +mLpfzlLqnaQrijgfDJ8Mcc2UN7livKGkb8YLtfHASkpGRMb4vaqJlsohhAK45B6E1ck 74w1SXJf8UvQoCVN0cg6+SZNr2mpJ/WMnpn/jIjjOcJm1GVQ0zHbgLjF7j5g19AGifs6 Zvf1tZSg/rs60waIi5rvM49gYTVBD27OVeTfzX5gfV1Fg9SKR1OAG9oGi7WvuetlWkEM 0PGA== X-Gm-Message-State: ALyK8tJj3HmupSj93vqbcNPsj3uXhTSXTfyJl/XyCnv5SWbbV3yl9hXsqQzEwkHREXM02Q== X-Received: by 10.140.154.68 with SMTP id a65mr21639739qha.29.1465409014904; Wed, 08 Jun 2016 11:03:34 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.46.9 with SMTP id i9ls1451507ita.5.canary; Wed, 08 Jun 2016 11:03:33 -0700 (PDT) X-Received: by 10.36.81.79 with SMTP id s76mr371818ita.9.1465409013729; Wed, 08 Jun 2016 11:03:33 -0700 (PDT) In-Reply-To: <0aa49f06-08b0-433a-a897-720140eb7097@isocpp.org> X-Original-Sender: sir.vestnik@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:26218 Archived-At: ------=_Part_1710_1167150558.1465409012569 Content-Type: multipart/alternative; boundary="----=_Part_1711_1224358494.1465409012569" ------=_Part_1711_1224358494.1465409012569 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Foreach from the presentation you've posted allows to repeat overloaded=20 function or functor with multiple operator() for each argument from a pack= =20 by abusing coma operator. In C++17 it's even simplier since you don't need= =20 intermediate garbage initializer_list. You can perform expression folding= =20 directly and it terribly great (tried it with gcc 6.1). This kind of folding is the simpliest one. I use it a lot but always feel= =20 myself sad using such kind of haks. In the example I've shown "if (cond)=20 return foo(arg_from_pack);" statement is folded which can't be done by=20 abusing coma opertor and requires recursive templates. One more thing on=20 the syntax i propose: It allows to solve those kind of tasks without hacks= =20 or boilerplate code. It uses simple to write and understand construction=20 (simple for human and for compiler). Sergey Vidyuk =D1=81=D1=80=D0=B5=D0=B4=D0=B0, 8 =D0=B8=D1=8E=D0=BD=D1=8F 2016 =D0=B3., 21= :11:21 UTC+6 =D0=BF=D0=BE=D0=BB=D1=8C=D0=B7=D0=BE=D0=B2=D0=B0=D1=82=D0=B5= =D0=BB=D1=8C Greg Marr =D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0=D0=BB: > > On Wednesday, June 8, 2016 at 10:14:50 AM UTC-4, Sergey Vidyuk wrote: >> >> Expression folding on a variadic template parameters pack are great and= =20 >> allows to write internal function stuff inside a function instead of=20 >> writing some recursive template code which is required to be moved outsi= de=20 >> of the function. But when one want to repeat some statement for every=20 >> element of a parameter pack recursive templates or abusing of coma opera= tor=20 >> folding are stil the only options. After facing this issue several times= I=20 >> start to realize that it would be great to have the following extension = to=20 >> the C++11 range-for syntax: >> > > Have you seen Sean Parent's for_each_argument? > > template > void for_each_argument(F f, Args&&... args) { > [](...){}((f(std::forward(args)), 0)...); > } > > > > There was even a CppCon 2015 talk about it=20 > > https://www.youtube.com/watch?v=3D2l83JlqkzBk > > --=20 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 e= mail 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/9c9cb032-a950-476b-823c-28643ef305d8%40isocpp.or= g. ------=_Part_1711_1224358494.1465409012569 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Foreach from the presentation you've posted allows to = repeat overloaded function or functor with multiple operator() for each arg= ument from a pack by abusing coma operator. In C++17 it's even simplier= since you don't need intermediate garbage initializer_list. You can pe= rform expression folding directly and it terribly great (tried it with gcc = 6.1).

This kind of folding is the simpliest one. I use it a lot but = always feel myself sad using such kind of haks. In the example I've sho= wn "if (cond) return foo(arg_from_pack);" statement is folded whi= ch can't be done by abusing coma opertor and requires recursive templat= es. One more thing on the syntax i propose: It allows to solve those kind o= f tasks without hacks or boilerplate code. It uses simple to write and unde= rstand construction (simple for human and for compiler).

Sergey Vidy= uk

=D1=81=D1=80=D0=B5=D0=B4=D0=B0, 8 =D0=B8=D1=8E=D0=BD=D1=8F 2016 = =D0=B3., 21:11:21 UTC+6 =D0=BF=D0=BE=D0=BB=D1=8C=D0=B7=D0=BE=D0=B2=D0=B0=D1= =82=D0=B5=D0=BB=D1=8C Greg Marr =D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0=D0=BB:=
On Wednesday,= June 8, 2016 at 10:14:50 AM UTC-4, Sergey Vidyuk wrote:
Expression folding on a variadic te= mplate parameters pack are great and allows to write internal function stuf= f inside a function instead of writing some recursive template code which i= s required to be moved outside of the function. But when one want to repeat= some statement for every element of a parameter pack recursive templates o= r abusing of coma operator folding are stil the only options. After facing = this issue several times I start to realize that it would be great to have = the following extension to the C++11 range-for syntax:

Have you seen Sean Parent's for_each_argument?

template <class F, class... Args>
void for_each_argument(F f, Args&&... args) {
=C2=A0= [](...){}((f(std::forward<Args>(args)), 0)...= );
}=


<= /div>
There was even a CppCon 2015 talk about it=

https://www.youtube.com/watch?v=3D2l83JlqkzBk

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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/9c9cb032-a950-476b-823c-28643ef305d8= %40isocpp.org.
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