220 11856 article Path: news.gmane.org!not-for-mail From: tomaszkam@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: N4078: Rvalue reference overloads for value() method returns object by value Date: Fri, 11 Jul 2014 02:56:24 -0700 (PDT) Lines: 105 Approved: news@gmane.org Message-ID: References: <4DA018C3-2327-4F55-B7F8-7988EC7B789A@gmail.com> <1a858a77-310b-4591-aaf5-960c40d9f5fc@isocpp.org> <66AF41C1-CB37-4311-98EA-D47DBC6068DC@gmail.com> <66c38b61-7a95-4ace-b34f-2346bb334fb9@isocpp.org> <6F4B3C72-9962-48DC-8527-0C89EA1B9710@gmail.com> <35873CE5-ED8C-4C03-A6A1-E4132DECD91F@gmail.com> <335948E6-8140-4673-B958-930356A52070@gmail.com> <76ACA175-5A44-4BE8-B49F-BAC6DA65E6B1@gmail.com> <4D3852AD-1AEB-44BA-941C-D645BAD19405@gmail.com> <6a4b6425-1167-40c1-acd8-3945c8cd4c74@isocpp.org> <13DD0D7A-A146-4667-9F30-6FB3739CDBE0@gmail.com> <7411f096-742f-4e9b-a265-1b05a1af5521@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_154_13869155.1405072585090" X-Trace: ger.gmane.org 1405072595 22557 80.91.229.3 (11 Jul 2014 09:56:35 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 11 Jul 2014 09:56:35 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDNPVXXG6IGBBSXJ72OQKGQENKWE5YQ@isocpp.org Fri Jul 11 11:56:27 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vc0-f199.google.com ([209.85.220.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1X5XZ5-0007HB-Gb for gclcip-std-proposals@m.gmane.org; Fri, 11 Jul 2014 11:56:27 +0200 Original-Received: by mail-vc0-f199.google.com with SMTP id ij19sf2923931vcb.10 for ; Fri, 11 Jul 2014 02:56:26 -0700 (PDT) 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 :list-post:list-help:list-archive:list-subscribe:list-unsubscribe :content-type; bh=0Ev7ybJzgnRLQq2Vyhp8ohnxH7aTZw6ghNiuc9TctPM=; b=cVK2iSumYAmFsUGjqy9nTtwpeu+B27XrWwFnT6rybRIhYKVvXM82Q1yZqc9jnm/JLh 8Bczypmnsyo/6IRjScDcibc1SR8kCeGRhyByNdBK94KyQvH12GiTKHQ+Nc9sSRnuGXHv FQtcRFYhR0GN8uWwSbmeRy9ogMYFip6MzPPUPJdpbi2sx78/2RxhiQsJC8X1G2oyZhpX U1ptBXsaDLNviRx7AWrBRXztwv51S0JbN3PBm2kZGkVFF7JYctDCT7YPBnx1CR9oBBK4 mtP4gIF5HIv2jiHEDW2mPZxJ4Iyl/XooUJOBRb0+hPRNLYBIJmkmfiPqCgctKQKfYuls cj4w== 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:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=0Ev7ybJzgnRLQq2Vyhp8ohnxH7aTZw6ghNiuc9TctPM=; b=ksha4iP4HBQjHFNCfZ9Ssh4PLDAWfrdC1nP8g1NG2mDAuhPZDao2FUpgLvq9wyBj2A 8q6Ep8rnaZ1ZI9fUpSQdfG1KcaMVtmqXZPCLXIY0ubrXo9bIfJ2xvYCVZ7Hhe0OBZN3v rSDZASdWqNlz/ZD8CCu1WIaV4FMn2tIvpB2C87ZQ3XV4a5mKiYow+vVyFxP1gjnA68hx Cf831srxo6B31A/CEIg2P69vgdeNHe7FwZFp5fpOjtOy2sh0vKnQiNVUM5tQx8j7AuK9 /RK3df4QSVl9iUDH2eKk4fayLYJoYQCHnBVZtdxgMmx63B17E0CqBii+5nPIqmDBtXyz 5MPw== X-Gm-Message-State: ALoCoQl/K+gzT6subAvOrBg8lHc9vu8uYBX/oVj6Y09iaZK7FyNSfwVxQdsG76FbdKZhBtV6YdDG X-Received: by 10.58.93.162 with SMTP id cv2mr23407677veb.11.1405072586711; Fri, 11 Jul 2014 02:56:26 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.182.246.199 with SMTP id xy7ls366744obc.83.gmail; Fri, 11 Jul 2014 02:56:25 -0700 (PDT) X-Received: by 10.182.143.4 with SMTP id sa4mr1038obb.38.1405072585966; Fri, 11 Jul 2014 02:56:25 -0700 (PDT) In-Reply-To: <7411f096-742f-4e9b-a265-1b05a1af5521@isocpp.org> X-Original-Sender: tomaszkam@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: 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:11856 Archived-At: ------=_Part_154_13869155.1405072585090 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable And the really funny think. Your code will not work if container_handle is= =20 a lazy evaluator and * std::forward< container_handle >( ch ) acutally=20 returns the container by value, ortogonalny to the fact if we have &&=20 overloads and the solutions presented by me will actually fix the code.=20 Because the * std::forward< container_handle >( ch ) will be created and=20 used in one expression. The auto&& will create dangling reference. W dniu pi=C4=85tek, 11 lipca 2014 11:49:09 UTC+2 u=C5=BCytkownik toma...@gm= ail.com=20 napisa=C5=82: > > Acutall case does even need susbtitute: > template< typename container_handle > > void operate_on_fifth_thing( container_handle && ch ) { > process_for_a_long_time( * std::forward< container_handle >( ch ) )[ 5 = ]=20 > ); > } > > That willl work with any body: > template > void with(T&& t, FV&& fv) { std::forward(fv)(std::forward(t)); } > > template< typename container_handle > > void operate_on_fifth_thing( container_handle && ch ) { > with(( * std::forward< container_handle >( ch ) )[ 5 ], [](auto &&=20 > fifth_thing) { > // This is illustrated as a function call, but there might as well= =20 > be a loop here. > process_for_a_long_time( std::forward< decltype( thing ) >(=20 > fifth_thing ) ); > }); > } > --=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 http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. ------=_Part_154_13869155.1405072585090 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
And the really funny think. Your code will not work if con= tainer_handle is a lazy evaluator and * std::forward= < container_handle >( ch ) acutally returns the container by value, o= rtogonalny to the fact if we have && overloads and the solut= ions presented by me will actually fix the code. Because the * std::forward< container_handle >( ch ) will be crea= ted and used in one expression. The auto&& will create dangling ref= erence.

W dniu pi=C4=85tek, 11 lipca 2014 11:49:09 UTC+2 u=C5=BCytko= wnik toma...@gmail.com napisa=C5=82:
Acutall case does even need susbtitute:
template< typename container_handle ><= /div>
void operate_on_fifth_thing( container_han= dle && ch ) {
  proces= s_for_a_long_time( * s= td::forward< container_handle >( ch ) )[ 5 ] );
}

That willl work with any bo= dy:
template<typename T, typename F>
void with(T&& t, F= V&& fv) { std::forward<FV>(fv)(std::forward<T>(t))= ; }

template< typename container_hand= le >
void operate_on_fifth_thing= ( container_handle && ch ) {
    with(( * std::forward< container_handle >( ch ) )[ 5 ],= [](auto && fifth_thing) {
=
      // This is illustrated as a function call, but t= here might as well be a loop here.
=       process_for_a_long_time( std::forward< decltype( th= ing ) >( fifth_thing ) );
    });
}

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