220 21322 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 14:33:15 -0700 (PDT) Lines: 150 Approved: news@gmane.org Message-ID: 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_2048_845598811.1444080795996" X-Trace: ger.gmane.org 1444080806 5813 80.91.229.3 (5 Oct 2015 21:33:26 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 5 Oct 2015 21:33:26 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCXLLRHD7IDRBHOZZOYAKGQE3MUFWZI@isocpp.org Mon Oct 05 23:33:21 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 1ZjDNm-0001qJ-TJ for gclcip-std-proposals@m.gmane.org; Mon, 05 Oct 2015 23:33:19 +0200 Original-Received: by oiww128 with SMTP id w128sf296668091oiw.0 for ; Mon, 05 Oct 2015 14:33:18 -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=J2ZLN4ScDlXX++glfH2OeKlTshKEk/psMsyWyeUjMlE=; b=TI5pllSCje/wFJwivzQ8jKE/yLWa0X9KqZbUbuguW/L6/NUVVw2ws9RO04qWPEOBEp XAPuyzpEy0YamMNFjAUXJH6wsuvmfOjUhTtYB9Q9G8/yE+OPY1hPOghC6V/ef97Tucgx Mfwv6ndtIrejDAm6NaQR21bZ/BEoQurGY4bx/oVbIz1ZXSfnu9NzLLfiFir/78CrmkGk pdcT/N07/6dlMsIAk06tZrJtfE6gbG1DKfxlgSQA2ieJioumanhjr1SQsa0B2F9WErBx RobzBgv3yQiDGe9cAvfMyzTXMnHZuW0WzESt4OLQYY9eJl2ChivQUCotSPP+t3GrboFq RrhA== X-Gm-Message-State: ALoCoQmP555lOAON8LWbPIrItmcikEUfiWfBHPQplRFHzMRwEUrW+xzN1Yc9iPFTemnVX6+htwa8 X-Received: by 10.50.142.103 with SMTP id rv7mr13095399igb.2.1444080798042; Mon, 05 Oct 2015 14:33:18 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.158.79 with SMTP id h76ls209264ioe.104.gmail; Mon, 05 Oct 2015 14:33:17 -0700 (PDT) X-Received: by 10.50.142.9 with SMTP id rs9mr135366igb.6.1444080797099; Mon, 05 Oct 2015 14:33:17 -0700 (PDT) In-Reply-To: <31dedac5-7d51-402c-946e-0555c925f70d@isocpp.org> 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:21322 Archived-At: ------=_Part_2048_845598811.1444080795996 Content-Type: multipart/alternative; boundary="----=_Part_2049_166342910.1444080795997" ------=_Part_2049_166342910.1444080795997 Content-Type: text/plain; charset=UTF-8 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() ); -- --- 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_2049_166342910.1444080795997 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

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 sy= ntax

=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 c= onstructed from `a`, with the type having been deduced from the type of `a`= (minus references of course). You want a shorthand for:

stdremove_reference_t<decltype= (a)>(a)

Y= our basic problem in this case is that fact that the destination function w= as taking and returning references to the parameters, and you were trying t= o store those values in the variables being referenced. Your solution is to= create a pair of temporaries, pass them, and copy the temporaries back int= o your variables.

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

{
=C2=A0 auto oldA =3D a, oldB =3D b;::tie( a, b ) =3D<= /span> std::minmax( oldA, oldB );
<= span style=3D"color: rgb(102, 102, 0);">}

Is this something we really nee= d to modify the language to do? Is it common enough that we need specialize= d syntax to solve it?

Do you have any other use cases for such funct= ionality?


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

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