220 21333 <42447957-4276-4f59-89b6-ab4be37c47c6@isocpp.org> article Path: news.gmane.org!not-for-mail From: "T. C." Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Conversion from lvalue to rvalue Date: Mon, 5 Oct 2015 17:12:57 -0700 (PDT) Lines: 172 Approved: news@gmane.org Message-ID: <42447957-4276-4f59-89b6-ab4be37c47c6@isocpp.org> References: <31dedac5-7d51-402c-946e-0555c925f70d@isocpp.org> <116a66a2-90ea-4269-ac85-3432ff7094b0@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_0_2130957191.1444090377381" X-Trace: ger.gmane.org 1444090504 2297 80.91.229.3 (6 Oct 2015 00:15:04 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 6 Oct 2015 00:15:04 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCQ43G7NQIIRBDFEZSYAKGQEVVOJYYY@isocpp.org Tue Oct 06 02:15:04 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yk0-f197.google.com ([209.85.160.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZjFsW-00083W-U2 for gclcip-std-proposals@m.gmane.org; Tue, 06 Oct 2015 02:13:13 +0200 Original-Received: by ykdz138 with SMTP id z138sf262846831ykd.3 for ; Mon, 05 Oct 2015 17:13:01 -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 :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=l1V1yZNxkQWbLIcTIDYP9X/Koi43qnI7UVTNSSurSSs=; b=KuNIMh+fiqrCo0NSyPcb/VW9rkACw0SsSXT3E7iLPo/Zbw596JSEU30heXyljKryqm 4xqB7CNtNZqUkwSSfFf68dlvcc2EzPADd4YgZnAf/cw+gqOxzGiPAsjKWZGX4NCrLFkw FuNd9lPwuIDT+6BhUqpZh5A7/8/O0UqImffDdA8OA3/LkQhlx3HZoLBzfWXzSDuDUTya r3eZB87xt4Er7G9eaF8GEL5XMp14onf6kb3vAkHM6j8AugK3u7cK4fn6xXRCoIupvlzC l6eZNdHKCtzegge5cI0Efpx+iL2DscI3jwf+jsAg+CpNWDaMYZF+4TN5wZ2J3yqhphz9 RI8g== 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=l1V1yZNxkQWbLIcTIDYP9X/Koi43qnI7UVTNSSurSSs=; b=VKkssNd3MYs6fxgfjMatIfdDeNs7nCZeVLcufcLM5Usomi3JlOXS+cEoFyLcW59VYq IbfWCoONZUhGY9/f48OiATR+xyHgeQ43TLyjjMkcKBtGCUQ41tR0z1qg3lujNcsl42JE z1wRyvgWxW5iS1U2jw1HZxdg6ZxHO7VirZsZVULcEXwyn8TWMPwEnqEXBposSsVQkgJf dg0u6v/tjkMDIaEEmXomh5HIzfrzgey8J6t5EHaBubkKiMwIY5A0mkmiN550Ab5TDBoK gUC9X8ZI1+BTXT0nGCF4vEYrB6dFHlE4Fz1zsKlesiNQe6bpief0Xs41cyhc6qslrYjb t8zg== X-Gm-Message-State: ALoCoQlwhN1qU9iH1ej+Rsk3zMW5VsLFHbBin/P5U2aUXCxCxIpS6/EcZoONtKrv6m8wa//R14Ae X-Received: by 10.13.220.4 with SMTP id f4mr12454520ywe.22.1444090381481; Mon, 05 Oct 2015 17:13:01 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.16.166 with SMTP id 38ls1063609ioq.71.gmail; Mon, 05 Oct 2015 17:13:00 -0700 (PDT) X-Received: by 10.50.114.36 with SMTP id jd4mr164307igb.6.1444090380475; Mon, 05 Oct 2015 17:13:00 -0700 (PDT) In-Reply-To: <116a66a2-90ea-4269-ac85-3432ff7094b0@isocpp.org> X-Original-Sender: rs2740@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:21333 Archived-At: ------=_Part_0_2130957191.1444090377381 Content-Type: multipart/alternative; boundary="----=_Part_1_1734711264.1444090377389" ------=_Part_1_1734711264.1444090377389 Content-Type: text/plain; charset=UTF-8 http://cplusplus.github.io/EWG/ewg-active.html#188 Although LWG might get to it first with decay_copy. On Monday, October 5, 2015 at 5:38:00 PM UTC-4, Vlad from Moscow wrote: > > > > 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_1_1734711264.1444090377389 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
http://cplusplus.github.io/EWG/ewg-active.html#188
Although LWG might get to it first with decay_copy.
On Monday, October 5, 2015 at 5:38:00 PM UTC-4, Vlad from Moscow wrote:

On Tuesday, October 6, 20= 15 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 U= TC-4, Vlad from Moscow wrote:
I am suggesting 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 result in a= temporary that is copy/move constructed from `a`, with the type having bee= n deduced from the type of `a` (minus references of course). You want a sho= rthand for:

std<= /span>::remove_reference_t<= ;decltype(a= )>(a)
<= /div>
Your basic problem in this case is that fact that the destination = function was taking and returning references to the parameters, and you wer= e trying to store those values in the variables being referenced. Your solu= tion is to create a pair of temporaries, pass them, and copy the temporarie= s back into your variables.

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

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

Is this something we really need to modify the languag= e 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.= =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


<= /div>
That is the idea is to do the conversion on the fly without using= compound expressions.=C2=A0

--

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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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