220 19215 <792fab39-5af7-4d95-b9ba-a5cc4aed8544@isocpp.org> 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 12:31:59 -0700 (PDT) Lines: 185 Approved: news@gmane.org Message-ID: <792fab39-5af7-4d95-b9ba-a5cc4aed8544@isocpp.org> 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_1075_1516249200.1437679919783" X-Trace: ger.gmane.org 1437679929 26502 80.91.229.3 (23 Jul 2015 19:32:09 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 23 Jul 2015 19:32:09 +0000 (UTC) Cc: sean.middleditch@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCXLLRHD7IDRBMECYWWQKGQEE64OQ7Y@isocpp.org Thu Jul 23 21:32:04 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yk0-f198.google.com ([209.85.160.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZIMDq-0007hy-Rn for gclcip-std-proposals@m.gmane.org; Thu, 23 Jul 2015 21:32:03 +0200 Original-Received: by ykek23 with SMTP id k23sf2846749yke.2 for ; Thu, 23 Jul 2015 12:32:01 -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=TOic4dS+/Lb4VR/oQoGi9hctPE0qTRp7ocsDf9sedmU=; b=HPwUTqpMRVi8zLvkczCidzCUrvc2xlfIQwyoZ0g3vXsaDSvPhfCzVMb/nX+Rb5XQlW zqcwircniVjJkcvvRqRzSHo2JRHGS70P0pTshVJxr44UYe2yVoCY85gxwrm6up45tgWn tISCy1fcjhVYy1HN2d+lXuMMUGadVdcN0TuKc/0M3VuDZ7ww23byuFtrXFEljoyG5S/t ZshLUIrAWSSKB6DHpGzFjBqgRlWa2mIPsjK2b18Gd2HI8IMrlov5HDgl9k9uoYprU8S1 x1CxETRPShXaK5R+uzKjCtzalKevX4dAvFmFoZLiElV0fSIot5o6+4n8t/AKBtkkl+w5 78yA== X-Gm-Message-State: ALoCoQniHRIK+ixvPJrAEO7I5vxskkiYYm6ayei5wDj6cLCMAXUWTb4pkzUT9pzYLJmkZnCF1fXb X-Received: by 10.13.244.2 with SMTP id d2mr10138066ywf.34.1437679921471; Thu, 23 Jul 2015 12:32:01 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.35.199 with SMTP id n65ls1144147qgn.21.gmail; Thu, 23 Jul 2015 12:32:00 -0700 (PDT) X-Received: by 10.140.19.46 with SMTP id 43mr224056qgg.13.1437679920545; Thu, 23 Jul 2015 12:32:00 -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:19215 Archived-At: ------=_Part_1075_1516249200.1437679919783 Content-Type: multipart/alternative; boundary="----=_Part_1076_1409815911.1437679919784" ------=_Part_1076_1409815911.1437679919784 Content-Type: text/plain; charset=UTF-8 Could you explain why do I need some ranges when this program looks clear and nice without any ranges? #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 it = m.equal_range( 'A' ); for ( auto p : it ) std::cout << p.first << ' ' << p.second << std::endl; } The program output is A Apple A Animal A Amigo 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. 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. ------=_Part_1076_1409815911.1437679919784 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Could you explain why do I need some ranges when this= program looks clear and nice without any ranges?

= #include <iostream>
#include <utility>
#include <map&g= t;
#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 Iterat= or>
Iterator end( const std::pair<Iterator, Iterator> &p )<= br>{
=C2=A0=C2=A0=C2=A0 return p.second;
}
=C2=A0=C2=A0=C2=A0
= }

int main()
{
=C2=A0=C2=A0=C2=A0 std::multi= map<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', "Apple" }, { 'A= ', "Animal" }, { 'A', "Amigo" },
=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 { 'B', "Bee" }, { &#= 39;B', "Beef" }, {'B', "Brother" }
=C2= =A0=C2=A0=C2=A0 };
=C2=A0=C2=A0=C2=A0
=C2=A0=C2=A0=C2=A0 auto it =3D= m.equal_range( 'A' );
=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 <= < ' ' << p.second << std::endl;
}=C2=A0=C2=A0=C2= =A0

The program output is

A Apple
A Animal
A Amigo



On Th= ursday, 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://g= ithub.com/ericniebler/range-v3). You're trying to treat std::pair&l= t;iterator, iterator> as a range between the two iterators, which is not= semantically correct for all possible pairs of iterators. I'd rather j= ust leave pair alone and let the ranges proposal solve this by replacing th= e handle of STL uses of pair<iterator, iterator> with a range<iter= ator>.

In your example it's also solved by array_= view, which is really just a form of range.

An addit= ional 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 fo= r 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 simple and=C2=A0at the same time v= ery useful=C2=A0 overloaded functions std::begin and std::end for standard = class std::pair.

Here is a demonstrative program o= f the idea

#include <iostream>
#in= clude <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 Iterator>
Iterator end( co= nst std::pair<Iterator, Iterator> &p )
{
=C2=A0=C2=A0=C2=A0= return p.second;
}
}

--

---
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