220 19217 article Path: news.gmane.org!not-for-mail From: Vlad from Moscow Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Overloading std::begin and std::end for std::pair Date: Thu, 23 Jul 2015 12:56:54 -0700 (PDT) Lines: 199 Approved: news@gmane.org Message-ID: References: <012fd35d-96fd-4775-835e-2105176c4f97@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_944_947749181.1437681414495" X-Trace: ger.gmane.org 1437681419 18525 80.91.229.3 (23 Jul 2015 19:56:59 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 23 Jul 2015 19:56:59 +0000 (UTC) Cc: sean.middleditch@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCXLLRHD7IDRBB4OYWWQKGQEOFLGC2Y@isocpp.org Thu Jul 23 21:56:58 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f70.google.com ([209.85.218.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZIMbx-0003v3-9A for gclcip-std-proposals@m.gmane.org; Thu, 23 Jul 2015 21:56:57 +0200 Original-Received: by oiho132 with SMTP id o132sf2835427oih.1 for ; Thu, 23 Jul 2015 12:56:56 -0700 (PDT) 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:cc:message-id:in-reply-to :references:subject:mime-version:content-type: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=wlykT0ohmv6WW2EcIGOh4U/yl8WlzZlXTgqpwUVLARM=; b=I618T8zJj/85ynQkk8dkWHKblROzubunBMXMihKUMFpsNfy+aEyuN5JTtw+1WJWtmU cNStHDaHLR5XkwS+NDJIBau54GBie8CQ8odHCptNxQ++F2lN8LzggxLUxbkHoaqymglO r0IDFKd5RstkzuvSi5zqZIW/dFBY/xc+ftKFyHXsyQgQ7vYsOBDn8tYW9GvxVozTL5Zx zTadlgW1+1MTm3GLm+B+nFMs+TNDagPxvKmVHZhpp0uIduAYBnZ/Bwes604N7LpFk4gI JdsFHT6EAHrMuQmPI9uFbT1jHeUQoRLivCyiTzwPY0RQuuIivpkexOc7m+extUb7yfg3 eGsg== X-Gm-Message-State: ALoCoQkDde8H3d1cMWCXpRvrVeIzs7UoC+ksq7MXl/ZDN8u9VpSNRT26TP4hZBSETxZrcEN3Pefy X-Received: by 10.107.164.40 with SMTP id n40mr9013743ioe.30.1437681416461; Thu, 23 Jul 2015 12:56:56 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.100.194 with SMTP id s60ls1149382qge.25.gmail; Thu, 23 Jul 2015 12:56:55 -0700 (PDT) X-Received: by 10.140.92.74 with SMTP id a68mr219763qge.14.1437681415310; Thu, 23 Jul 2015 12:56:55 -0700 (PDT) In-Reply-To: X-Original-Sender: vlad.moscow@mail.ru 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:19217 Archived-At: ------=_Part_944_947749181.1437681414495 Content-Type: multipart/alternative; boundary="----=_Part_945_1255803407.1437681414496" ------=_Part_945_1255803407.1437681414496 Content-Type: text/plain; charset=UTF-8 Or a modified previous example #include #include #include #include namespace std { template Iterator begin( const std::pair &p ) { return p.first; } template Iterator end( const std::pair &p ) { return p.second; } } int main() { std::multimap m = { { 'A', "Apple" }, { 'A', "Animal" }, { 'A', "Amigo" }, { 'B', "Bee" }, { 'B', "Beef" }, {'B', "Brother" } }; auto key = m.empty() ? '\0' : m.begin()->first; while ( key ) { auto it = m.equal_range( key ); for ( auto p : it ) std::cout << p.first << ' ' << p.second << std::endl; std::cout << std::endl; key = it.second == m.end() ? '\0' : it.second->first; }; } The program output is A Apple A Animal A Amigo B Bee B Beef B Brother And why do I have to use here some ranges? Is it that to make my life harder? On Thursday, July 23, 2015 at 10:04:27 PM UTC+3, Sean Middleditch wrote: > This is solved by ranges (there's a proposal in flight derived from > https://github.com/ericniebler/range-v3). You're trying to treat > std::pair as a range between the two iterators, which > is not semantically correct for all possible pairs of iterators. I'd rather > just leave pair alone and let the ranges proposal solve this by replacing > the handle of STL uses of pair with a range. > > In your example it's also solved by array_view, which is really just a > form of range. > > An additional nice thing about the ranges is that begin, end, size, > operator[], etc. can all be added to the range type as member functions (as > appropriate for the iterator category). > > On Thursday, July 23, 2015 at 10:36:46 AM UTC-7, Vlad from Moscow wrote: >> >> I'd like to suggest very simple and at the same time very useful >> overloaded functions std::begin and std::end for standard class std::pair. >> >> Here is a demonstrative program of the idea >> >> #include >> #include >> >> namespace std >> { >> template >> Iterator begin( const std::pair &p ) >> { >> return p.first; >> } >> template >> Iterator end( const std::pair &p ) >> { >> return p.second; >> } >> } >> > -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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Or a modified previous example

#include <iostream>
#include <utility>
#include <ma= p>
#include <string>
namespace std
{
=C2=A0=C2= =A0=C2=A0
template <class Iterator>
Iterator begin( const std:= :pair<Iterator, Iterator> &p )
{
=C2=A0=C2=A0=C2=A0 return = p.first;
}
template <class Iterator>
Iterator end( co= nst std::pair<Iterator, Iterator> &p )
{
=C2=A0=C2=A0=C2=A0= return p.second;
}
=C2=A0=C2=A0=C2=A0
}
int main()
= {
=C2=A0=C2=A0=C2=A0 std::multimap<char, std::string> m =3D
=C2= =A0=C2=A0=C2=A0 {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 { 'A= 9;, "Apple" }, { 'A', "Animal" }, { 'A'= , "Amigo" },
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 { '= ;B', "Bee" }, { 'B', "Beef" }, {'B'= , "Brother" }
=C2=A0=C2=A0=C2=A0 };
=C2=A0=C2=A0=C2=A0
= =C2=A0=C2=A0=C2=A0 auto key =3D m.empty() ? '\0' : m.begin()->fi= rst;
=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0 while ( key )
=C2=A0= =C2=A0=C2=A0 {=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 auto it =3D m.equal_range( key );
=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 for ( auto p : it ) std::cout << p.first << ' = 9; << p.second << std::endl;
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 std::cout << std::endl;
=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 key =3D it.s= econd =3D=3D m.end() ? '\0' : it.second->first;
=C2=A0=C2=A0= =C2=A0 };=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0
}=C2=A0=C2=A0=C2=A0
<= /div>

The program output is

A A= pple
A Animal
A Amigo

B Bee
B Beef
B Brother

And why do I have to use here some ranges? Is it that to = make my life harder?
On Thursday, July 23, 2015 at 10:04:27 PM UTC+3, Se= an Middleditch wrote:
Th= is is solved by ranges (there's a proposal in flight derived from https://github.com/ericniebler/range-v3). You'r= e trying to treat std::pair<iterator, iterator> as a range between th= e two iterators, which is not semantically correct for all possible pairs o= f iterators. I'd rather just leave pair alone and let the ranges propos= al solve this by replacing the handle of STL uses of pair<iterator, iter= ator> with a range<iterator>.

In your example i= t's also solved by array_view, which is really just a form of range.

An additional nice thing about the ranges is that begi= n, end, size, operator[], etc. can all be added to the range type as member= functions (as appropriate for the iterator category).

On Thursday, = July 23, 2015 at 10:36:46 AM UTC-7, Vlad from Moscow wrote:
I'd like to =C2=A0suggest very simpl= e and=C2=A0at the same time very useful=C2=A0 overloaded functions std::beg= in and std::end for standard class std::pair.

Here= is a demonstrative program of the idea

#include &= lt;iostream>
#include <utility>

namespace std
{=C2=A0=C2=A0=C2=A0
template <class Iterator>Iterator begin( const std::pair<Iterator, Iterator> &p )
{=C2=A0=C2=A0=C2=A0 return p.first;
}
template <class Iter= ator>
Iterator end( const std::pair<Iterator, Iterator> &p = )
{
=C2=A0=C2=A0=C2=A0 return p.second;
}
}

--

---
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
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.
Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/<= /a>.
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