220 24348 <1604CAB7-DF4D-45B4-A5F8-E21F70491CB7@gmail.com> article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: [tuple] extracting tuples out of a tuple Date: Sat, 13 Feb 2016 18:03:26 +0800 Lines: 126 Approved: news@gmane.org Message-ID: <1604CAB7-DF4D-45B4-A5F8-E21F70491CB7@gmail.com> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 9.1 \(3096.5\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_6A8ED708-663E-4191-8621-BBFEA03F8D91" X-Trace: ger.gmane.org 1455357825 22461 80.91.229.3 (13 Feb 2016 10:03:45 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 13 Feb 2016 10:03:45 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRB5767O2QKGQEKBUICBQ@isocpp.org Sat Feb 13 11:03:39 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f200.google.com ([209.85.220.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1aUX3B-0001rT-BM for gclcip-std-proposals@m.gmane.org; Sat, 13 Feb 2016 11:03:37 +0100 Original-Received: by mail-qk0-f200.google.com with SMTP id u128sf159679383qkh.0 for ; Sat, 13 Feb 2016 02:03:37 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=from:content-type:message-id:mime-version:subject:date:references :to:in-reply-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=LQAZ2KFoYJ5Zk92kdwZuUA9i2ejRpmqJYp96/mile5g=; b=LREu90iyLvjFSWAkmUWK5k4AeF3c4oJCz4G/xSaXbZ7eQGYqNLQoF9DqTPMUfmDA3s nCZlUfzWh4Ad//J2wqqFqnYVm1ZvnBPvqI9KEKLDLbVI96UHvdPQ3BYatZTm+h0aEZGK EIIhPxafnab7tqhqoSNhTrW5J6Qyp9jQh26WlkbdB5n5HeHCq0JyVm8z8DFIij+xR/qy 4J7chKbThdVXOkrQS/LRaq2bX0CbJF3I2V5DlCtRZU+6pRCf57A6gGDUhMGcHkV4zG5a eEMJjRHFIHEORw9OHfMxRojlPuA0lvvP17Pz+rSN1y8WUHNXi5EwcX9u0snn6iW225Jk u6Jw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:content-type:message-id:mime-version :subject:date:references:to:in-reply-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=LQAZ2KFoYJ5Zk92kdwZuUA9i2ejRpmqJYp96/mile5g=; b=Zqm4FLJxxNyRW6ETx1mxETU+odzvz4rnsLjWU7MxVzJ54oQg2w5VWw2iExlgYT4/OD iMnnieKKsAiPCE3kbG/xa9LzlvMqc/usQxiTkp0c1kd07QHSO9nEGjgeiFi5R3YQ2lY+ 8LyvYSwboJwMPecbYDolIMglQdSoPDGeO4jBOLVXrAkKDoF8S9YumXNcHcJ6R24G0R+H pA4lR3jNI8w6i3kzF/RySmmqdTokdukylKbtybzboRzebtMxtz49ZsVhjH3CIbRNP5OQ HR0eEOwy2ueHpNOvACm/umBuMdhlRDrars46XPeIkVEpg2eSWujNaAJre348IKYE1cEB X6vA== X-Gm-Message-State: AG10YOTOQ/IdU52OeeYb4OVbSfVDCs8DFm5MGtxL9Ayjf0WLJg4EQjFx5i8/WjXYQzA5aw== X-Received: by 10.129.130.71 with SMTP id s68mr6040570ywf.29.1455357816446; Sat, 13 Feb 2016 02:03:36 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.128.69 with SMTP id b66ls1121896iod.101.gmail; Sat, 13 Feb 2016 02:03:35 -0800 (PST) X-Received: by 10.98.14.79 with SMTP id w76mr8770331pfi.1.1455357815510; Sat, 13 Feb 2016 02:03:35 -0800 (PST) Original-Received: from mail-pa0-x22e.google.com (mail-pa0-x22e.google.com. [2607:f8b0:400e:c03::22e]) by mx.google.com with ESMTPS id tg6si26615064pab.0.2016.02.13.02.03.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sat, 13 Feb 2016 02:03:35 -0800 (PST) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c03::22e as permitted sender) client-ip=2607:f8b0:400e:c03::22e; Original-Received: by mail-pa0-x22e.google.com with SMTP id yy13so59404033pab.3 for ; Sat, 13 Feb 2016 02:03:35 -0800 (PST) X-Received: by 10.66.124.170 with SMTP id mj10mr8738987pab.92.1455357815393; Sat, 13 Feb 2016 02:03:35 -0800 (PST) Original-Received: from [172.20.10.2] ([121.54.54.157]) by smtp.gmail.com with ESMTPSA id 70sm25040321pfs.78.2016.02.13.02.03.31 for (version=TLSv1/SSLv3 cipher=OTHER); Sat, 13 Feb 2016 02:03:34 -0800 (PST) In-Reply-To: X-Mailer: Apple Mail (2.3096.5) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c03::22e as permitted sender) smtp.mailfrom=potswa@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:24348 Archived-At: --Apple-Mail=_6A8ED708-663E-4191-8621-BBFEA03F8D91 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 > On 2016=E2=80=9302=E2=80=9313, at 12:30 AM, Oliver Kowalke wrote: >=20 > I've had std::tie() in mind, The special feature of tie is generating references. That seems orthogonal = to slicing a sequence. Reference semantics should be used sparingly in gene= ral. How about a function to get a pack of references from a tuple, template< typename ... t > std::tuple< t & ... > tuple_ref( std::tuple< t ... > & ); and a generic slice function, template< std::size_t first, std::size_t last, typename tuple_like > std::tuple< std::tuple_element_t< tuple_like, N > ... > // N goes from firs= t to last. tuple_slice( tuple_like const & ); Then the example looks like, std::tuple< int, std::string, std::string, double > tpl{ -1, "abc", "xyz", = ..5 }; std::tuple< int, std::string, std::string > tpl1; std::tuple< std::string, double > tpl2; tpl1 =3D tuple_slice< 0, 3 >( tpl ); tpl2 =3D tuple_slice< 2, 2 >( tpl ); std::tuple_cat( tuple_ref( tpl1 ), tuple_ref( tpl2 ) ) =3D tpl; The bounds of the slice are explicit, but that looks more like a feature th= an a bug. --=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/. --Apple-Mail=_6A8ED708-663E-4191-8621-BBFEA03F8D91 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=UTF-8
On 2016=E2=80=9302= =E2=80=9313, at 12:30 AM, Oliver Kowalke <oliver.kowalke@gmail.com> wrote:

I've had std::tie() in mind,

The special f= eature of tie is generating refere= nces. That seems orthogonal to slicing a sequence. Reference semantics shou= ld be used sparingly in general.

=
How about a function to get a pack of references from a tup= le,

template< typename ... t >
std::tuple< t & ... > tu= ple_ref( std::tuple< t ... > & );
and a generic slice function,

template< std::size_t first, std::size_t last, typename tuple= _like >
std::tuple< std::tuple_element_t< t= uple_like, N > ... > // N goes from first to last.
tuple_slice( tuple_like const &= amp; );

Then the example looks like,

std::tuple< int, std::string, std::string, double > = tpl{ -1, "abc", "xyz", .5 };
std::tuple< int, std::string, std:= :string > tpl1;
std::tuple< std::string, double > tpl2;
tpl1 =3D tuple_slice< 0, 3 >( tpl );
tpl2 =3D = ;tuple_slice< 2, 2 >( tpl );
std::tuple_cat( tuple_ref( tpl1 ), tuple_ref( tpl2 = ) ) =3D tpl;

The bounds of the slice are explicit, but that look= s more like a feature than a bug.

--

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