220 31192 <69c0683c-3b36-4de4-941d-9487366615d6@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Arthur O'Dwyer Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Removing forward references ("universal" references) from the standard Date: Mon, 27 Feb 2017 11:51:45 -0800 (PST) Lines: 126 Approved: news@gmane.org Message-ID: <69c0683c-3b36-4de4-941d-9487366615d6@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_7050_1470126613.1488225105152" X-Trace: blaine.gmane.org 1488225109 27131 195.159.176.226 (27 Feb 2017 19:51:49 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 27 Feb 2017 19:51:49 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDLZJYWNDQINDBWSYUCRUBCR4MKU2@isocpp.org Mon Feb 27 20:51:43 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-it0-f70.google.com ([209.85.214.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ciRKe-0006Kk-Pj for gclcip-std-proposals@m.gmane.org; Mon, 27 Feb 2017 20:51:41 +0100 Original-Received: by mail-it0-f70.google.com with SMTP id 203sf99535112ith.3 for ; Mon, 27 Feb 2017 11:51:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :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=p1I+S37amhuRSvwZGCT/ugRH8I4mBlV9RhQ8h13KUG8=; b=cL2i55TAp7gKCvtUq63F5nST2n8cCNKmy92la6LJXL281yYh0s5gP7cUmI202VkBfN dMEKNcxO05EA3GU3ZefsuDqPsZhwMbeNJEL4zDyhTBqYlOFo2h5EhibYHMEynet1uyCH ycKw/dK4NJBQldHFrkHCkaVS7Ws49T+02PTIjpWh8+L2SVox7ihYfu3s4TJK6V3DFfmX gS+SW8RIgOO0/+CpSPtqaoD55xzXsUgFcDEwy6J631BWipIQhW0/EuXgzX2xhU2YxOAR 465xsuEls7ezWycOCuvo9iyOewIgHNKNEurLa2I6+apHVQxKxGgu1GH/lQL2/dXVERbp spsw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :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=p1I+S37amhuRSvwZGCT/ugRH8I4mBlV9RhQ8h13KUG8=; b=R4KRCdvSIz0cAzo5rbPNfTMCL7UebPVFnl4g91PIUZdJ+Ac9L7oLSWV7ZijWKmPBUp sSQ+pjlubyV9DgjeU7xgVkzBNcY0FMwwfwrTyYdgcd3L9phmrEnW7JlBG/Rt70NwTfXN fTJstscx/aikxXhOSPEhIVQzoIKJcJMs62dUEk7duK56OwupLvpxEPUlhPBqup+MYsKS vrFf0gyXt1k74IYUwrEL2meGyDi1nADCvInang6pZwPh2DhdxdzkEfEiiDn5Ixrno8Uk QL2tw+6gYJcM/8mBG9W+AHLfagVKZ4oZKW52xpyxxoH6kEi26cNJn8uVHXVbys89O8rj O0+w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; 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:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=p1I+S37amhuRSvwZGCT/ugRH8I4mBlV9RhQ8h13KUG8=; b=Jn4B86JvSyJSltWXWks7kPOTYxsuRsOe89wdVLr817xWTo1slDz+maNtLjCI4l3KMH tm68FH7F9dxwP5+T1hc/96rbYc7pWhGYBtU8DrzUuy3yL4jOFAfN+1YVosW0YpsiIFnM ETeTPeDSemOnZeoM/8ginA/N2YJHM+UXKhCCJ3Fn6tWpNTX2a/AcbkAQLFpFQtTOztyJ Vsf6lt0Anza0PeIRgsvagz3eFO1gnVxX+fBQa7FMdRXHlAn5iUCAobgG9lkmOsZJEdHS piPu1IXq+ZtnCoWfkC47Jcu+JS8yB8gaqy/8XkKFxu2HFPsCHCOazTxrn1QeeK8d3P6R OLbg== X-Gm-Message-State: AMke39njduXoenQrzTKjvz85sX+/x1B+lLh2WxEvoed+YEeqD+SJrAcNsoHWKcJXw1DWLw== X-Received: by 10.36.117.11 with SMTP id y11mr846847itc.3.1488225106480; Mon, 27 Feb 2017 11:51:46 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.8.69 with SMTP id 63ls14292342oty.0.gmail; Mon, 27 Feb 2017 11:51:45 -0800 (PST) X-Received: by 10.157.32.3 with SMTP id n3mr1047412ota.1.1488225105710; Mon, 27 Feb 2017 11:51:45 -0800 (PST) In-Reply-To: X-Original-Sender: arthur.j.odwyer@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:31192 Archived-At: ------=_Part_7050_1470126613.1488225105152 Content-Type: multipart/alternative; boundary="----=_Part_7051_1106779844.1488225105153" ------=_Part_7051_1106779844.1488225105153 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Saturday, February 25, 2017 at 11:43:16 PM UTC-8, Denis Kotov wrote: > > > My proposal is very simple. Just remove completely forward references=20 > because of confusion that it makes until it is not too late !! > Basically if we have the following example: > > template > void setItem(T && t) > { > ... > // T can be *lvalue *or *rvalue *reference as all of you know = =20 > =20 > } > > But it confuses ( I think ) all of us. > Nope! Reference collapsing has been in the language since 1998, although= =20 its exact semantics were not standardized until 2011 as far as I know. If you find reference collapsing confusing, I suggest that you watch my=20 CppCon 2016 talk "Template Normal Programming"[1], which covers the=20 difference between lvalue and rvalue references and explains the rule for= =20 collapsing them together. (In short: if anyone else in the world claims to= =20 care about an object, you're not allowed to disembowel that object.) Once= =20 you understand reference collapsing, "forwarding references" (formerly=20 known as "universal references", formerly known as "just this particular=20 syntax for exploiting reference collapsing in template contexts") falls out= =20 naturally. So it would be reasonable (IMHO) to say that the term "forwarding=20 reference" is unnecessary and therefore confusing; but personally I find it= =20 useful to have a term for the thing that's less cumbersome than "this=20 particular syntax for exploiting reference collapsing" or "an rvalue=20 reference to a cv-unqualified template parameter that does not represent a= =20 template parameter of a class template" or whatever. HTH, =E2=80=93Arthur [1] - https://www.youtube.com/watch?v=3DvwrXHznaYLA (circa the 35-minute ma= rk) --=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/69c0683c-3b36-4de4-941d-9487366615d6%40isocpp.or= g. ------=_Part_7051_1106779844.1488225105153 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Saturday, February 25, 2017 at 11:43:16 PM UTC-8, Denis= Kotov wrote:
=

My proposal is very simple. Just remove completely=C2= =A0forward references because of confusion that it makes until it is not to= o late !!
Basically if we have the following example:
<= br>
=C2=A0 =C2=A0 template<typename T>
=C2=A0 =C2= =A0 void setItem(T && t)
=C2=A0 =C2=A0 {
=C2=A0= =C2=A0 =C2=A0 =C2=A0 ...
=C2=A0 =C2=A0 =C2=A0 =C2=A0 // T can be= lvalue or rvalue reference as all of you know =C2=A0 =C2=A0 = =C2=A0 =C2=A0
=C2=A0 =C2=A0 }

But it con= fuses ( I think ) all of us.

No= pe! =C2=A0Reference collapsing has been in the language since 1998, althoug= h its exact semantics were not standardized until 2011 as far as I know.
If you find reference collapsing confusing, I suggest that you watc= h my CppCon 2016 talk "Template Normal Programming"[1], which cov= ers the difference between lvalue and rvalue references and explains the ru= le for collapsing them together. (In short: if anyone else in the world cla= ims to care about an object, you're not allowed to disembowel that obje= ct.) =C2=A0Once you understand reference collapsing, "forwarding refer= ences" (formerly known as "universal references", formerly k= nown as "just this particular syntax for exploiting reference collapsi= ng in template contexts") falls out naturally.

So it would be reasonable (IMHO) to say that the term "forwarding re= ference" is unnecessary and therefore confusing; but personally I find= it useful to have a term for the thing that's less cumbersome than &qu= ot;this particular syntax for exploiting reference collapsing" or &quo= t;an rvalue reference to a cv-unqualified template parameter that does not = represent a template parameter of a class template" or whatever.
=

HTH,
=E2=80=93Arthur

[1] -=C2=A0https://www.youtube.com/watch?v=3DvwrXHznaYLA (circa the 35-min= ute mark)

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
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.
To view this discussion on the web visit https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/69c0683c-3b36-4de4-941d-9487366615d6= %40isocpp.org.
------=_Part_7051_1106779844.1488225105153-- ------=_Part_7050_1470126613.1488225105152-- .