220 38519 article Path: news.gmane.org!.POSTED!not-for-mail From: joshua.r.marshall.1991@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Clarification of std::iterator_traits::distance_type Date: Wed, 6 Jun 2018 06:46:49 -0700 (PDT) Lines: 119 Approved: news@gmane.org Message-ID: References: <5bceda10-ca60-4100-8fb3-16fcb8713552@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_47765_2130986432.1528292809923" X-Trace: blaine.gmane.org 1528292685 15757 195.159.176.226 (6 Jun 2018 13:44:45 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 6 Jun 2018 13:44:45 +0000 (UTC) Cc: joshua.r.marshall.1991@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCFIZIPVQEORBSWL37MAKGQERJEIX2Q@isocpp.org Wed Jun 06 15:44:41 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f197.google.com ([209.85.161.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fQYjx-0003yh-3O for gclcip-std-proposals@m.gmane.org; Wed, 06 Jun 2018 15:44:41 +0200 Original-Received: by mail-yw0-f197.google.com with SMTP id a203-v6sf4498127ywe.16 for ; Wed, 06 Jun 2018 06:46:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=9P3yKkxVwgTxKIcB4/edC2mrgEE6Ikn+8uTekeAgko4=; b=kNmMT+Bc+cCe7FNyjj/HSyVm5twYD/GDvnGWuOHDtzLt/jI7PzZP+QB1hQdzNScrOR cYyz/dD9FgVJnUqgv6T+8r1Xe/BQW3d4mS0wdvIEMCWlLatGGpJMspHw7Re9m36UFLbK /VLxj7pvEf43o5wCVibbEbflY2NPYXFuzOmKSxp67GBeCbH+AFuhoJcp7Lb+I++pem3p km1jz2WTRrZMkbgS+7gWatBbilcX9XctyFFanG+j5pgoEJEZmgHvs0UDglGZquhLOvgC 0yptLsAPbbdxW1p1Evt/afUlbZxzbsB2QYtf08REQmcG9kg0AIXVaYsURbqwy3kwtSBQ 7Quw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=9P3yKkxVwgTxKIcB4/edC2mrgEE6Ikn+8uTekeAgko4=; b=sLt5bRfy1hFK8ryH8wG8ENGcX/TGqWgCq8GLM+rlvHD6XIBaisp7PBBYj69JO4+Pwl slzNJ9mSOcuSh/QDI4ogYFQK6IgxLXU7+I+5TWOEXUt3oPRHByx7H6M9jl0VwFtU6Pga d7RvTXX7eIxwOMtmLPRby/Cp7LV4KZeckDDQhgJLDibnHY4kUf0ntvYFnZIKL5DLD+3q VmPjls+0n7o+ayJIw/IA3tAAU/VwevXi2lV7443kNWtjKd7oW55dbVwgNZ4vW9jC18Ip FzzHo6NVJPvpVIgmvhe1nolAcKuOlWR+CoVJ1s+gHnTQAO0fBPpIw0Ln6enslZzq5h5b a1wQ== 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:cc: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=9P3yKkxVwgTxKIcB4/edC2mrgEE6Ikn+8uTekeAgko4=; b=bSP40UnrDkrQ2AIPBKU3OUpEw3vRPJ4BYI1IA7gRAcO/CrLKuY/dxiU1mO6E4sshNm 9/DjqV8tqtOo3m045a71qFug1OfhWHyPGWtnh6g7bSbipIUJ+wYh1i0O5rXLwQV6FzJk uIdTX45pxXOZpw6fVO6rl5JbDQbskCO3B02H20g8t4l4fXpU30K9VHkHuCxzEPSAUllN 3TtCsDGoGRC2RFmW3Cx4XCgc25JN+Rj4JX5Y04OC175O99Yn7FVZk1mP4dgoZgPFVhJu DAveWGHQseb+jZkq+IckhAtBWc86SCdokg9yi8BGZMconl+shxbCankULYyAjFDLwlYa eVFQ== X-Gm-Message-State: APt69E0skNRSMDQChF8ITcnlY7E3eT0HefYaOyQIwNrZIVIsXLjuosql JQtv0uKiEPB1Le2QXe0M+PgBtw== X-Google-Smtp-Source: ADUXVKINIkS7F3JRFF9778TT4/dVw29gZHg7lA7x7Vrge/s5VaCFVU3kXNlPeJMBsoKYIk3IH21UXQ== X-Received: by 2002:a0d:db4f:: with SMTP id d76-v6mr879817ywe.228.1528292811948; Wed, 06 Jun 2018 06:46:51 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a25:44c:: with SMTP id 73-v6ls4125868ybe.11.gmail; Wed, 06 Jun 2018 06:46:50 -0700 (PDT) X-Received: by 2002:a25:aaa1:: with SMTP id t30-v6mr135258ybi.13.1528292810325; Wed, 06 Jun 2018 06:46:50 -0700 (PDT) In-Reply-To: <5bceda10-ca60-4100-8fb3-16fcb8713552@isocpp.org> X-Original-Sender: joshua.r.marshall.1991@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:38519 Archived-At: ------=_Part_47765_2130986432.1528292809923 Content-Type: multipart/alternative; boundary="----=_Part_47766_841153955.1528292809923" ------=_Part_47766_841153955.1528292809923 Content-Type: text/plain; charset="UTF-8" It looks like this will end up needed to be a change in the next standard, mainly about C++17 27.2.1 [iterator.requirements.general] paragraph 1. On Wednesday, June 6, 2018 at 7:46:12 AM UTC-4, joshua.r.ma...@gmail.com wrote: > > There is a bug in glibc which seems to have arisen from ambiguity about > distance_type in std::iterator_traits. It does not have defined required > operators or constructors, but is implied to behave line a signed integer. > > https://en.cppreference.com/w/cpp/iterator/iterator_traits > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86015 > > This causes an issue with instrumentation of distance_type as everything > must be implicitly convertible to and from an int. This is testable by > trying to build the following project: > https://github.com/anadon/Sort-Comparisons-and-Performance-metrics > > The code of this original use case was from 1997 by David Musser and so > was permissible when the stdlib was being developed. > > I think the following clarifications are in order: > std::iterator_traits::difference_type shall not necessarily be of any > particular built in datatype, but have the following properties: > * All arithmetic operators available to signed integers must be defined > * Implicit constructor from a signed integer type (std::ptrdiff_t) to > itself shall be available > * An implicit conversion to any number type must not be present. > > This change, if found reasonable and valid, should be added backwards > through C++11 as a clarification. > -- 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/b5426ee6-f221-4342-b346-0963828a1ba9%40isocpp.org. ------=_Part_47766_841153955.1528292809923 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
It looks like this will end up needed to be a change = in the next standard, mainly about C++17 27.2.1 [iterator.requirements.gene= ral] paragraph 1.

On Wednesday, June 6, 2018 at 7:46:12= AM UTC-4, joshua.r.ma...@gmail.com wrote:
There is a bug in glibc which seems to ha= ve arisen from ambiguity about distance_type in std::iterator_traits.=C2=A0= It does not have defined required operators or constructors, but is implie= d to behave line a signed integer.


This causes an issue wit= h instrumentation of distance_type as everything must be implicitly convert= ible to and from an int.=C2=A0 This is testable by trying to build the foll= owing project:

The code of this original use case was from 199= 7 by David Musser and so was permissible when the stdlib was being develope= d.

I think the following clarifications are in ord= er:
std::iterator_traits::difference_type shall not nece= ssarily be of any particular built in datatype, but have the following prop= erties:
* All arithmetic operators available to signed integers m= ust be defined
* Implicit constructor from a signed integer type = (std::ptrdiff_t) to itself shall be available
* An implicit conve= rsion to any number type must not be present.

This= change, if found reasonable and valid, should be added backwards through C= ++11 as a clarification.

--
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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.
To view this discussion on the web visit https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/b5426ee6-f221-4342-b346-0963828a1ba9= %40isocpp.org.
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