220 21323 <116a66a2-90ea-4269-ac85-3432ff7094b0@isocpp.org> article Path: news.gmane.org!not-for-mail From: Vlad from Moscow Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Conversion from lvalue to rvalue Date: Mon, 5 Oct 2015 14:37:59 -0700 (PDT) Lines: 164 Approved: news@gmane.org Message-ID: <116a66a2-90ea-4269-ac85-3432ff7094b0@isocpp.org> References: <31dedac5-7d51-402c-946e-0555c925f70d@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_3934_1473409605.1444081079692" X-Trace: ger.gmane.org 1444081084 10776 80.91.229.3 (5 Oct 2015 21:38:04 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 5 Oct 2015 21:38:04 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCXLLRHD7IDRBOG3ZOYAKGQEXPRZNTI@isocpp.org Mon Oct 05 23:38:02 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f200.google.com ([209.85.213.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZjDSM-0005gg-E5 for gclcip-std-proposals@m.gmane.org; Mon, 05 Oct 2015 23:38:02 +0200 Original-Received: by igbgg5 with SMTP id gg5sf215279113igb.1 for ; Mon, 05 Oct 2015 14:38:01 -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: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=CV0bJ9EIWmgBDgCHJ2aWePxZBdoqvFv3+N7YZyZwTV0=; b=CQKj0IUh0Slb5qy7zJ2wN1dbZs5mNeQU82VJx6U5G8q1oguCvDZwhYHmXLO4D65Dp3 LaVa58ZU5TGFQkJ+vK3kSAzDxVa/7OhDuZ8+qJM0Zpsv9LmhR1qOxtmhjyyO8v+Cx933 FAYWF/w2fLmOyqL5/JpFIFKGJ59OJC0fFCKSQzwoLDP1U4PctpvTKzwQUy3JGWymcpWv pPmuatwNdVAd54us3bm+O4GRWm3lNei2Ew3HhfzgUUfL1oYaVUJ69co+S8515lLc9DGw 0Y6rHOUM+YaN+NMEVxjWGh09ZAapc/cn8Qlc/k/p+Mj8pSoBAUD+PJql4LyrFWGAAbqV RxrQ== X-Gm-Message-State: ALoCoQncpEo6zuE9bMefdLpqTpxfRP1x1BTb1DppZgPKyosoaB0kI2PkFhYz8awbtZMRUFFh63XU X-Received: by 10.182.29.40 with SMTP id g8mr28198177obh.27.1444081081618; Mon, 05 Oct 2015 14:38:01 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.36.68 with SMTP id k65ls1782810iok.7.gmail; Mon, 05 Oct 2015 14:38:00 -0700 (PDT) X-Received: by 10.50.114.135 with SMTP id jg7mr135877igb.8.1444081080753; Mon, 05 Oct 2015 14:38:00 -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:21323 Archived-At: ------=_Part_3934_1473409605.1444081079692 Content-Type: multipart/alternative; boundary="----=_Part_3935_1237243814.1444081079692" ------=_Part_3935_1237243814.1444081079692 Content-Type: text/plain; charset=UTF-8 On Tuesday, October 6, 2015 at 12:33:16 AM UTC+3, Vlad from Moscow wrote: > > > > On Tuesday, October 6, 2015 at 12:12:22 AM UTC+3, Nicol Bolas wrote: >> >> >> >> On Monday, October 5, 2015 at 4:24:39 PM UTC-4, Vlad from Moscow wrote: >>> >>> I am suggesting to use the following general syntax >>> >>> std::tie( a, b ) = std::minmax( auto( a ), auto( b ) ); >>> >> >> So you want `auto(a)` to result in a temporary that is copy/move >> constructed from `a`, with the type having been deduced from the type of >> `a` (minus references of course). You want a shorthand for: >> >> std::remove_reference_t(a) >> >> Your basic problem in this case is that fact that the destination >> function was taking and returning references to the parameters, and you >> were trying to store those values in the variables being referenced. Your >> solution is to create a pair of temporaries, pass them, and copy the >> temporaries back into your variables. >> >> Or... you could just create variables. You could even use `auto newA = a` >> to create it. And you can use scoping to make them temporary: >> >> { >> auto oldA = a, oldB = b; >> std::tie( a, b ) = std::minmax( oldA, oldB ); >> } >> >> Is this something we really need to modify the language to do? Is it >> common enough that we need specialized syntax to solve it? >> >> Do you have any other use cases for such functionality? >> > > > I showed I bad example. I wanted to demonstrate just the idea. > > Here is a correct example > > std::vector v = { 1, 2, 3, 7, 1, 5, 4 }; > > v.erase( std::remove( v.begin(), v.end(), auto( v[0] ) ), v.end() ); > That is the idea is to do the conversion on the fly without using compound expressions. -- --- 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_3935_1237243814.1444081079692 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

On Tuesday, October 6, 2015 at 12:33:16 AM UTC+3, Vlad from Moscow = wrote:


On Tuesday, October 6, 2015 at 1= 2:12:22 AM UTC+3, Nicol Bolas wrote:


On Monday, October 5, 2015 at 4:24:39 PM UTC-4, Vlad from = Moscow wrote:
I am sugge= sting to use the following general syntax

=C2=A0= =C2=A0=C2=A0 std::tie( a, b ) =3D std::minmax(=C2=A0auto( a ),=C2=A0auto( b= =C2=A0) );

So you want `auto(a)` to re= sult in a temporary that is copy/move constructed from `a`, with the type h= aving been deduced from the type of `a` (minus references of course). You w= ant a shorthand for:

= std::remove_reference= _t<decltype(a)>(a)
=

Your basic problem in this case is that fact that the destination= function was taking and returning references to the parameters, and you we= re trying to store those values in the variables being referenced. Your sol= ution is to create a pair of temporaries, pass them, and copy the temporari= es back into your variables.

Or... you could just create variables. = You could even use `auto newA =3D a` to create it. And you can use scoping = to make them temporary:

{
=C2=A0 auto= oldA =3D a, oldB =3D b;
=C2=A0 std= ::tie( a, b ) =3D std::minmax(= oldA, oldB
}
<= /span>

Is this something we really need to modify the= language to do? Is it common enough that we need specialized syntax to sol= ve it?

Do you have any other use cases for such functionality?


I showed I bad ex= ample.=C2=A0I wanted to demonstrate just the idea.

Here is=C2=A0a correct example

=C2=A0=C2=A0=C2= =A0 std::vector<int> v =3D { 1, 2, 3, 7, 1, 5, 4 };=C2=A0
=C2=A0= =C2=A0
=C2=A0=C2=A0=C2=A0 v.erase( std::remove( v.begin(), v.end(), auto= ( v[0] )=C2=A0), v.end() );=C2=A0=C2=A0


That is the idea is to do the conversion on the fly witho= ut using compound expressions.=C2=A0

--

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