220 23905 article Path: news.gmane.org!not-for-mail From: "Arthur O'Dwyer" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: RFC: Unpacking tuples to value sequences Date: Wed, 20 Jan 2016 15:41:55 -0800 Lines: 149 Approved: news@gmane.org Message-ID: References: <6f3ece34-e302-4d95-afd0-4c1924e8a780@isocpp.org> <6ad65a24-8a2e-4053-b9c9-80d296d98e7d@isocpp.org> <72de7daf-93af-4e55-95ea-67898bd2a5f6@isocpp.org> <22792c37-ba68-4a13-af1c-8b8247d3d22a@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a1145ab580a67110529cc8816 X-Trace: ger.gmane.org 1453333326 18082 80.91.229.3 (20 Jan 2016 23:42:06 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 20 Jan 2016 23:42:06 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDLZJYWNDQIMLNUAWUCRUBGXLKHM2@isocpp.org Thu Jan 21 00:42:00 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f69.google.com ([209.85.215.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aM2Ny-0004JW-Vk for gclcip-std-proposals@m.gmane.org; Thu, 21 Jan 2016 00:41:59 +0100 Original-Received: by mail-lf0-f69.google.com with SMTP id b134sf8956414lfe.2 for ; Wed, 20 Jan 2016 15:41:58 -0800 (PST) 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:date:message-id:subject:from:to :content-type: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=iOpLcycK7uARnUm+t30yyuDuoDurKZy7hcxb2uXHUew=; b=y42TqlKA1kheXqB6uKub/0cKi8uL+Oy8VgfVPKRVi98xZgzMd3z2ObTT6ekUFHLhjg gmkLndkiCNUoMb+u8FMpzVMWdO2JI6NcEmv35bRJ1B8KRUhr9VTCu3snp31bUds3feaj vyujSj+eHcyUKLCMxELJ/bfvd+uMmwaccdzn6fCTZRJRa6cGopcHM4cM1IQGPPAuyAN6 ePphjBuWVtWGW70hsYIaqC42D4UHoRgk3KeYyulHSgTK7o7QnHwbWJLet7HGYErYk+ZW 5hHII5zxaxrhKIOJNhjGPdghDWmlDFD0Z1eGl45yylaAOA8G185OJq3QjWOCRHAnHw75 5xPg== 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:date :message-id:subject:from:to:content-type: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=iOpLcycK7uARnUm+t30yyuDuoDurKZy7hcxb2uXHUew=; b=mG8lJKdMngigw4cDUyMnyYGyyLVRHodTxK4Omui6kd52V46K0xZQdl/TcL4merLfFv mrXGU1mLmV/z6vbHEyeFgtHUehBpUgrggj/ZbNinxIuaLjrFQtRE9tlLpsmY5f7wXe1F JMOKXaYjUR9rtZj51dddXA6rkW+03Tl6M0q34BM1ZK1BS0B19EFflFbyUvB8SUhEv32y 2yg6KYIIJXTFvAWgosEAQ0AS0WmdP70YcV1TLcxrSSXBDmFvLctp6ZMARcQDHsvqx1Dn Q43q9sG2ENBsmf7pSm13ynCEAI6gjO9mraHfQ+2d12DHFxkvb5+jmBJNrFJWYlF7mY2Z An5g== X-Gm-Message-State: ALoCoQmKmrNASAnRpo1ZMn2UxXqE8wVggTfcGeI+M1CxQwJTTnN6WOinEKJ6wo8rHRu36MLD5JeYKfkwuzsKwH9ie8e7DVu7ng== X-Received: by 10.25.15.106 with SMTP id e103mr5073031lfi.9.1453333317942; Wed, 20 Jan 2016 15:41:57 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.142.18 with SMTP id q18ls232178wmd.0.gmail; Wed, 20 Jan 2016 15:41:56 -0800 (PST) X-Received: by 10.28.63.22 with SMTP id m22mr6305220wma.59.1453333316329; Wed, 20 Jan 2016 15:41:56 -0800 (PST) Original-Received: from mail-wm0-x22e.google.com (mail-wm0-x22e.google.com. [2a00:1450:400c:c09::22e]) by mx.google.com with ESMTPS id e4si42498860wjy.109.2016.01.20.15.41.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 20 Jan 2016 15:41:56 -0800 (PST) Received-SPF: pass (google.com: domain of arthur.j.odwyer@gmail.com designates 2a00:1450:400c:c09::22e as permitted sender) client-ip=2a00:1450:400c:c09::22e; Original-Received: by mail-wm0-x22e.google.com with SMTP id 123so153125719wmz.0 for ; Wed, 20 Jan 2016 15:41:56 -0800 (PST) X-Received: by 10.28.145.204 with SMTP id t195mr6938736wmd.91.1453333316000; Wed, 20 Jan 2016 15:41:56 -0800 (PST) Original-Received: by 10.27.19.201 with HTTP; Wed, 20 Jan 2016 15:41:55 -0800 (PST) In-Reply-To: X-Original-Sender: arthur.j.odwyer@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of arthur.j.odwyer@gmail.com designates 2a00:1450:400c:c09::22e as permitted sender) smtp.mailfrom=arthur.j.odwyer@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE 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:23905 Archived-At: --001a1145ab580a67110529cc8816 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Wed, Jan 20, 2016 at 11:36 AM, Matthew Woehlke wrote: > > Okay, having said that, I *can* think of one case... can you show how > you would simplify this code? > > stream << "begin" << get<0>(x) << get<1>(x) > << ... << get(x) << "end"; > > (Rules: 'stream' must be named exactly once, and no fair creating a > helper function. Strong preference to avoid assigning 'stream' to a > scratch variable.) > Sure! // Nicol's syntax (stream << "begin" << ... << [*]x) << "end"; // Arthur's syntax (stream << "begin" << ... << x~) << "end"; > For bonus points, include `", "` between each item of `x` (okay to > include after the last item also). > This is significantly harder! I think it would have to look something like this: http://melpon.org/wandbox/permlink/oLcM3ZjH45oTbI7T template auto operator<< (std::ostream& out, F&& f) -> decltype(f(out)) // SFINAE { return f(out); // maybe C++17 should provide this overload already } template void print_to_stream(std::ostream& stream, const TupleLike& x) { auto commaize =3D [](auto&& x) { return [&x](std::ostream& out) -> std::ostream& { return out << x << ", "; }; }; (stream << "begin, " << ... << commaize(x~)) << "end"; } Messy, but not positively horrible. What would it look like in your (Matthew's) proposal? =E2=80=93Arthur --=20 ---=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. Visit this group at https://groups.google.com/a/isocpp.org/group/std-propos= als/. --001a1145ab580a67110529cc8816 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Wed, Jan 20, 2016 at 11:36 AM, Matthew Woehlke <mwoehlke.floss@gmail.com> wrote:

Okay, having said that, I *can* think of one case... can you show how
you would simplify this code?

=C2=A0 stream << "begin" << get<0>(x) << = get<1>(x)
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0<< ... << get<N>(x) <= ;< "end";

(Rules: 'stream' must be named exactly once, and no fair creating a=
helper function. Strong preference to avoid assigning 'stream' to a=
scratch variable.)

Sure!

=
=C2=A0 =C2=A0 // Nicol's= syntax
=C2=A0 =C2=A0 = (stream << "begin" << ... << [*]x) << &qu= ot;end";
=C2=A0 = =C2=A0 // Arthur's syntax
=C2=A0 =C2=A0 (stream << "begin" << ... <&= lt; x~) << "end";
=C2=A0
For bonus points, include `", "` between each item of `x` (o= kay to
include after the last item also).

This= is significantly harder!=C2=A0 I think it would have to look something lik= e this:

--

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