220 31196 article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Removing forward references ("universal" references) from the standard Date: Mon, 27 Feb 2017 16:32:45 -0800 (PST) Lines: 106 Approved: news@gmane.org Message-ID: References: <69c0683c-3b36-4de4-941d-9487366615d6@isocpp.org> <77fd5ab0-76dc-47d5-b0cc-cd7f0a32f921@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_2301_1104877832.1488241965212" X-Trace: blaine.gmane.org 1488241967 21182 195.159.176.226 (28 Feb 2017 00:32:47 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 28 Feb 2017 00:32:47 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBLUK2PCQKGQEUD55OKA@isocpp.org Tue Feb 28 01:32:41 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f200.google.com ([209.85.161.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ciVib-00050Z-Cp for gclcip-std-proposals@m.gmane.org; Tue, 28 Feb 2017 01:32:41 +0100 Original-Received: by mail-yw0-f200.google.com with SMTP id 2sf167498876ywn.1 for ; Mon, 27 Feb 2017 16:32:47 -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=pvFbM2ghypv7cnKCfM/QPi61zqdEryuG+HMn5TbiFTI=; b=uy9dq8FlJOoCw5nAi6GXvd3akv5d2OqYHHAae24FDhMwecGuoUHtW4zO2zOnLYA6Ja OXhJL7UuvXe9m8I7m4deVePO8Z8gj3+sOB7Z0EAYxTYVZpnEF1tNOAqReYC7dsWVjHGG shPUlk11Nm76MIzYb14oqNudhDJ8wLZCC1G7a41gzuoz8K4VveFCWC1AqQSv2WGbK8Wk 1T0FBeNFea5BKELNZto4neLvF+OaYGXmaPkQ/KbLvq3K2BoWRu9G5nZBbsjZ7bzH5KRe /Xgq6nTgnNjALj6iQBPnFtQtTXfQna82FeZ/fSTy0tmP2mCuR+KH7csyeH01E4I6k5Ra JGdQ== 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=pvFbM2ghypv7cnKCfM/QPi61zqdEryuG+HMn5TbiFTI=; b=TVEkhl8bAP1kjg3OiEJQ2QrBjnG0zda2cSdNLfrThynKqnOTVN8YXle+hxFDmQtC+i MZd2gBt4OKytuwBtOJNnQUXyszEIfQvrmygIJDmDe1pUdgypht4qMJN0AfioQxZE2r/6 OSzk2NtlU8Uy1ffjLckf8M3k3WbglZ55zIKM/cCwA4cZ0qjjoQ87sUPWlw3I2j3djbl0 aunMAWqU/gpnNm87412IiT70ErIX7IwyXiDaAeh1J/hQtpvHVVHuHUx6ot38hOJSzuz5 4H90/WyWaC0XcDoUgivZDZsLcaQfLPvZigGj3kx2lLJF+ix5r1526rUCghE40Fu9VX3t 0ecg== 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=pvFbM2ghypv7cnKCfM/QPi61zqdEryuG+HMn5TbiFTI=; b=S81HhX2NsUj+W9PBB+0k4yBs4uWBqN79GfqFn4lpe2UP9I1QdB2fkI+eb5Wq/eKq/n zJhcpt9PCMmQrS5vnGy0wpTcN8b7UXHH9Hn6Ay5nKPo/MR45BVYZ3fKjh0hAuJp4Ro6+ w9UJur84qnvshzpNDchbvtymZa/3a1RkoSzOIK+FxbdWfypMkrzYOXWVkwRK9hBCugQ/ Xm8lM/R/UkjeSmamRwQVpTBJY/a2EBaJgDBKvIKUSUtjs0pS4DPNhv2UyaykMvf56qqd mqBw2nrxyXoj+vk/LOz2omUPN42CsrLve0lgZmdUtbGsqIpyo2ZJP7j7zIwJdjIG8TAy G2iA== X-Gm-Message-State: AMke39lQoGeJ/gms4c1UtANL+R90fMDx45SgvxVuaBrVQaeonFwDWZIK/99whhZIGwETXQ== X-Received: by 10.129.175.31 with SMTP id n31mr7502324ywh.30.1488241967093; Mon, 27 Feb 2017 16:32:47 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.18.240 with SMTP id g103ls13738644otg.39.gmail; Mon, 27 Feb 2017 16:32:45 -0800 (PST) X-Received: by 10.157.68.226 with SMTP id p34mr1129776otg.8.1488241965938; Mon, 27 Feb 2017 16:32:45 -0800 (PST) In-Reply-To: <77fd5ab0-76dc-47d5-b0cc-cd7f0a32f921@isocpp.org> X-Original-Sender: jmckesson@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:31196 Archived-At: ------=_Part_2301_1104877832.1488241965212 Content-Type: multipart/alternative; boundary="----=_Part_2302_2132747203.1488241965212" ------=_Part_2302_2132747203.1488241965212 Content-Type: text/plain; charset=UTF-8 On Monday, February 27, 2017 at 3:39:16 PM UTC-5, Denis Kotov wrote: > > 3) If you anyway think that forwarding reference is useful, can you give > an example of usefulness ? > .... oh, now I get what the problem is. It now seems apparent that you are under the impression that forwarding references are some kind of accident. That nobody really thought about the reference collapsing and template argument deduction of rvalues. That forwarding references were something effect that came out of the natural growth of rvalue references and template deduction. Forwarding references didn't happen by accident; the specific reference collapsing rules that led to forwarding references were added *deliberately and purposefully* to C++0x's rvalue reference system (which in its original form didn't behave like this). They were added to solve a specific and pernicious problem. Namely the forwarding problem, which is why these rules (and `std::forward`) are often collectively referred to as "perfect forwarding". Proper use of forwarding references solves the forwarding problem, thus allowing *numerous* C++ functions to exist and do their jobs correctly and without creating unnecessary copies or inhibiting moves. If you want to understand the forwarding problem in detail, read the paper that introduced these reference collapsing rules to C++ . But until you understand the purpose that forwarding references *currently serve*, we cannot effectively discuss whether or not it is reasonable to remove them. In order to remove forwarding references, you would need to re-solve the forwarding problem. Because we're not going to give up our only solution to that just because it confuses you. Also, please stop top-posting. -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/fb147f1a-a9c1-4a7e-b783-e91ee51d5532%40isocpp.org. ------=_Part_2302_2132747203.1488241965212 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Monday, February 27, 2017 at 3:39:16 PM UTC-5, Denis Ko= tov wrote:
3) = If you anyway think that forwarding reference is useful, can you give an ex= ample of usefulness ?

... oh, now I get what the= problem is.

It now seems apparent that you are under the impression= that forwarding references are some kind of accident. That nobody really t= hought about the reference collapsing and template argument deduction of rv= alues. That forwarding references were something effect that came out of th= e natural growth of rvalue references and template deduction.

Forwar= ding references didn't happen by accident; the specific reference colla= psing rules that led to forwarding references were added deliberately an= d purposefully to C++0x's rvalue reference system (which in its original form didn= 9;t=20 behave like this). They were added to solve a specific and pernicious=20 problem. Namely the forwarding problem, which is why these rules (and=20 `std::forward`) are often collectively referred to as "perfect forward= ing". Proper use of forwarding references solves the forwarding problem, thus allowing n= umerous C++ functions to exist and do their jobs correctly and without = creating unnecessary copies or inhibiting moves.

If you want to unde= rstand the forwarding problem in detail, read the paper that introduced = these reference collapsing rules to C++. But until you understand the p= urpose that forwarding references currently serve, we cannot effecti= vely discuss whether or not it is reasonable to remove them.

In orde= r to remove forwarding references, you would need to re-solve the forwardin= g problem. Because we're not going to give up our only solution to that= just because it confuses you.

Also, please stop top-posting.
<= /div>

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