220 38518 <5bceda10-ca60-4100-8fb3-16fcb8713552@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: joshua.r.marshall.1991@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Clarification of std::iterator_traits::distance_type Date: Wed, 6 Jun 2018 04:46:12 -0700 (PDT) Lines: 84 Approved: news@gmane.org Message-ID: <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_47106_1069134468.1528285572033" X-Trace: blaine.gmane.org 1528285450 4054 195.159.176.226 (6 Jun 2018 11:44:10 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 6 Jun 2018 11:44:10 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCFIZIPVQEORBBMT37MAKGQEJIKMJGI@isocpp.org Wed Jun 06 13:44:06 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yb0-f199.google.com ([209.85.213.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fQWrD-0000t1-5O for gclcip-std-proposals@m.gmane.org; Wed, 06 Jun 2018 13:44:03 +0200 Original-Received: by mail-yb0-f199.google.com with SMTP id f141-v6sf4486605yba.15 for ; Wed, 06 Jun 2018 04:46:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=RGW/lCe4Jxv/g2KCoF7u0Mirb7FtuiZ0pgCEirvfy3c=; b=KQo47B/gnCraPBcwrRvnt9zfRs/FSVmtTVDopDZ+D4mfPZq8aeUqkBY3i/V3DEujuv HeLrJeIzXpWdNS+AxL2dmkHDk5/K9QAOIxRS3jTBeWhxQouSKUCwIhcFxf5RM1Y/ECuy XnhqQWMRdzJmjoHvq3iIHrtbVF/3DR+5akRIXIW6uDm7K+km1PaIHQvgRP6kwt2xYcFD AfvlaRwUTdmtYClkK6QnSJO1sehJ8ZtYrynP+II0kdr6/vL17klhT1YliKHK1Gj5wTAl /cOI3RHq80OTRVcLgg/pC+abheTSEaccaZw5+YRhoxV3ZyN33nEGZKVZOfQHLq5WTEG6 nq3Q== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=RGW/lCe4Jxv/g2KCoF7u0Mirb7FtuiZ0pgCEirvfy3c=; b=R8m3nTZQ0OJNBA1CkkLN8Ac4YgDZyD2001w+mvLQtef6jVDZoAIw7hMcd2M7MvcaDC ZtfXq3fIVlKrx4oMVYcL709FiMsMJws+VM2BcFlQt/3cnCnYUmE4iZ+jBgPe10zIYO/P Q+Fqvwd5dQ1xHSRJn3tk+wbebA8OHxZ/LmQRJzqx+KDq2+d7x/xDGAzbYfjbR00JWmFQ VfQwh/rS2Oqaeo0QQuNyS3wuTDGmVL/eUUHaUteChvxRUNr5xZCcWQ8yEY2moZJQ0Muq mxzEQJ0CVu5QlVKKhM5SmFGi6tgGbWe4jUhNWU+WLwgDTAPG+rDIWS12Uwh0/J+DjRQn 4XqQ== 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: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=RGW/lCe4Jxv/g2KCoF7u0Mirb7FtuiZ0pgCEirvfy3c=; b=NFZG5eyaPelfzJ1Oxu1s2Bsm1+PZ3M4yDSrVGN6R3sBDVFXpFxRxVTlZTFnx6ynCLe P8I8355Ys7suyh17SzHH21UNTUNbUXDDlGwwNA+RzEO/4Sr7oh1vNwNOhHWgA0PWewOH TEa7crThzN0uzec3wryxwq0El0PEVQ1l3igbnpkhPRGyune6U/mi5fpY9Dhb03dERjCN 6/GnlmtRdKu6/UfLEHew2U03BN0WRTvLk4t64SmKfclvGn5y7VXLGeOcWAguDdqO/1XT mkgYJgMNDygcFczbxaTKDGSBIxsbVV8c9qxRPwM+NIiohH6X2i/msILFO9gR197IGmMC cClA== X-Gm-Message-State: APt69E2v1cSv5w8ZkwrweHctqumpse0LgcipismU4UoUOEK47Z3B+fpx X6YUf3cFrvisBY0vWwUpFnKqBQ== X-Google-Smtp-Source: ADUXVKJPm0V4DH6jMw8vj0XQzuC5bRAFvW4XeSipmK4M+QHUfupMTxTombAmSp0tnNDjfUyi7gQXlQ== X-Received: by 2002:a25:be12:: with SMTP id h18-v6mr737254ybk.62.1528285573965; Wed, 06 Jun 2018 04:46:13 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a0d:ddd7:: with SMTP id g206-v6ls3628060ywe.28.gmail; Wed, 06 Jun 2018 04:46:12 -0700 (PDT) X-Received: by 2002:a81:9c58:: with SMTP id t85-v6mr115892ywg.12.1528285572652; Wed, 06 Jun 2018 04:46:12 -0700 (PDT) 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:38518 Archived-At: ------=_Part_47106_1069134468.1528285572033 Content-Type: multipart/alternative; boundary="----=_Part_47107_824776385.1528285572033" ------=_Part_47107_824776385.1528285572033 Content-Type: text/plain; charset="UTF-8" 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/5bceda10-ca60-4100-8fb3-16fcb8713552%40isocpp.org. ------=_Part_47107_824776385.1528285572033 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
There is a bug in glibc which seems to have arisen fr= om ambiguity about distance_type in std::iterator_traits.=C2=A0 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.gn= u.org/bugzilla/show_bug.cgi?id=3D86015

This causes= an issue with instrumentation of distance_type as everything must be impli= citly convertible to and from an int.=C2=A0 This is testable by trying to b= uild the following project:
https://github.com/anadon/Sort-Compar= isons-and-Performance-metrics

The code of this= original use case was from 1997 by David Musser and so was permissible whe= n the stdlib was being developed.

I think the foll= owing clarifications are in order:
std::iterator_traits::diff= erence_type shall not necessarily be of any particular built in datatype, b= ut have the following properties:
* All arithmetic operators avai= lable to signed integers must be defined
* Implicit constructor f= rom 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.

--
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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/5bceda10-ca60-4100-8fb3-16fcb8713552= %40isocpp.org.
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