220 14518 article Path: news.gmane.org!not-for-mail From: Brent Friedman Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Range-based if Date: Wed, 12 Nov 2014 20:52:06 -0600 Lines: 127 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a1137d89e04f47e0507b4998a X-Trace: ger.gmane.org 1415847135 29065 80.91.229.3 (13 Nov 2014 02:52:15 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 13 Nov 2014 02:52:15 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCHLPXGUXMJBBVVZSCRQKGQEHY63PRQ@isocpp.org Thu Nov 13 03:52:09 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ie0-f199.google.com ([209.85.223.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XokW0-0001Gw-F2 for gclcip-std-proposals@m.gmane.org; Thu, 13 Nov 2014 03:52:08 +0100 Original-Received: by mail-ie0-f199.google.com with SMTP id x19sf72526945ier.10 for ; Wed, 12 Nov 2014 18:52:07 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=+uaGToJcF68vD6I10aIOKMpuG0kctBVITeMoJ89yYmE=; b=QUI9zSOB9bIfsTXkJyVj9MitFDb2Etxx32ZMCThEzIek5Uadl6JLgrAysnkDVbE4bn wP1t34x9yoVoXuSvdcoaHaIwxsZ5gIjVxSM3XYxwkl4bo9g87ZZB0cS3EGkjVLE4JjxO pL8ZDXZ248d+jqzSp+41FOR9lI3Y7BwrCXFXaxiQtVM4kXO4+9mal/wHokBxS1SdyEhd pcH6L//ghvqlPpAqJCYqjpZbgbDUf/hag878urR7Vt8n+h0r7BwLlfg2bHf0A2FP4A/a +lGEbTvm38Thm9qUifQbriee7gREtgqUWQG9alSd6B9RhTF5vAe8aSGLA34nqygrD3ke 9BLA== X-Gm-Message-State: ALoCoQmoYfdJaX7ywq6NtLyIHuS2fMWJOieR+470vyIj7BBUrEnfT6q4ZbxDNQz2ViwKMxd1avT1 X-Received: by 10.42.203.136 with SMTP id fi8mr47517313icb.18.1415847127544; Wed, 12 Nov 2014 18:52:07 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.182.225.130 with SMTP id rk2ls1134228obc.32.gmail; Wed, 12 Nov 2014 18:52:06 -0800 (PST) X-Received: by 10.202.4.5 with SMTP id 5mr5457397oie.22.1415847126419; Wed, 12 Nov 2014 18:52:06 -0800 (PST) Original-Received: from mail-oi0-x230.google.com (mail-oi0-x230.google.com. [2607:f8b0:4003:c06::230]) by mx.google.com with ESMTPS id g74si16605446oic.44.2014.11.12.18.52.06 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 12 Nov 2014 18:52:06 -0800 (PST) Received-SPF: pass (google.com: domain of fourthgeek@gmail.com designates 2607:f8b0:4003:c06::230 as permitted sender) client-ip=2607:f8b0:4003:c06::230; Original-Received: by mail-oi0-f48.google.com with SMTP id x69so9653887oia.35 for ; Wed, 12 Nov 2014 18:52:06 -0800 (PST) X-Received: by 10.202.203.66 with SMTP id b63mr13140oig.60.1415847126297; Wed, 12 Nov 2014 18:52:06 -0800 (PST) Original-Received: by 10.202.232.77 with HTTP; Wed, 12 Nov 2014 18:52:06 -0800 (PST) In-Reply-To: X-Original-Sender: fourthgeek@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of fourthgeek@gmail.com designates 2607:f8b0:4003:c06::230 as permitted sender) smtp.mail=fourthgeek@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:14518 Archived-At: --001a1137d89e04f47e0507b4998a Content-Type: text/plain; charset=UTF-8 > The idea is, it is a pointer (how can it not be?). It absolutely doesn't have to be a pointer. We use range adaptors in our code for filtering, mapping, dynamic_casting, and the like. These iterators are not pointers, and cannot be constructed from nullptr_t. We also have counting iterators that store and increment a number, so there's not even a notion of some underlying memory location at all. A function like first_or_null which returns an optional could probably work alright for our purposes with only a bit of extra syntax over this range-if idea. On Wed, Nov 12, 2014 at 8:47 PM, Benjamin Lindley wrote: > > > On Wednesday, November 12, 2014 8:31:37 PM UTC-6, Brent Friedman wrote: >> >> > It doesn't assume that the iterators are pointers, if that's what you >> mean. >> It assumes that it is possible to convert from nullptr_t to decltype(&range.begin()). >> It also assumes that this value constructed from nullptr necessarily >> represents an invalid value (converts to false) for that iterator type. >> >> > Well, I'm pretty sure that Matthew wrote that in a hurry, and it should > really be decltype(std::addressof(*std::begin(range)). The idea is, it is a > pointer (how can it not be?). In which case, it can of course convert from > nullptr_t. > > -- > > --- > 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/. > -- --- 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/. --001a1137d89e04f47e0507b4998a Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
>=C2=A0The idea is, it is a pointer (how can it not be?).=C2=A0=

It absolutely doesn't have= to be a pointer. We use range adaptors in our code for filtering, mapping,= dynamic_casting, and the like. These iterators are not pointers, and canno= t be constructed from nullptr_t. We also have counting iterators that store= and increment a number, so there's not even a notion of some underlyin= g memory location at all.

A function like fir= st_or_null which returns an optional<T&> could probably work alri= ght for our purposes with only a bit of extra syntax over this range-if ide= a.=C2=A0

On Wed, Nov 12, 2014 at 8:47 PM, Benjamin Lindley <benja= meslindley@gmail.com> wrote:


On Wednesday, November 12, 2014= 8:31:37 PM UTC-6, Brent Friedman wrote:
>=C2=A0It doesn't assume that the iterators are pointers, if = that's what you mean.
It assumes that it is possible to convert from nullpt= r_t to=C2=A0decltype(&range.begin()). It also assumes that this value construct= ed from nullptr necessarily represents an invalid value (converts to false)= for that iterator type.


Well, I'm pretty sure that Matthew wrote that in a hurry, a= nd it should really be decltype(std::addressof(*std::begin(range)). The ide= a is, it is a pointer (how can it not be?). In which case, it can of course= convert from nullptr_t.

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