220 35223 article Path: news.gmane.org!.POSTED!not-for-mail From: Bo Persson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: std::vector must have strong move guarantees. Date: Wed, 1 Nov 2017 12:14:56 +0100 Lines: 63 Approved: news@gmane.org Message-ID: References: <0f1d296f-1d9c-4a63-bde0-bb1085b56e6c@isocpp.org> <1513658.MSBzcxDL38@tjmaciei-mobl1> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1509534904 11522 195.159.176.226 (1 Nov 2017 11:15:04 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 1 Nov 2017 11:15:04 +0000 (UTC) User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCZ6RLW3UIKBBOOZ43HQKGQEAWDR5NY@isocpp.org Wed Nov 01 12:15:00 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f69.google.com ([209.85.215.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1e9qz5-0002WV-06 for gclcip-std-proposals@m.gmane.org; Wed, 01 Nov 2017 12:14:59 +0100 Original-Received: by mail-lf0-f69.google.com with SMTP id a16sf643028lfk.6 for ; Wed, 01 Nov 2017 04:15:06 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1509534906; cv=pass; d=google.com; s=arc-20160816; b=VKO7dzQkCg0Nn0DyFV7Ih3qPcq2MTDGsWoS392M23nEVkalU2ezQXvaUO7lz6kjMOK kgFSCiE0MkBwKfQ1K7e2Q9yBWwadGZ3n29gJPMRk7uI1K31guwltrqLgrEZtCAZG6bb3 Qlmb6LDTg/WZwkU4EJHxU7y+L9DXe7DlQgeDXDLfJTh4WE2G2B+efsU4QVdJ0OBaVHuU PYYx6n2nBlgZ/Cxt7GY6At4iSrYbiGGdHMt9Z03Ux7c7E4izrMEipmPgXOShPQAmCXD4 SfI/H67fsKWViG7qb5PZd+IzWeejJud0AAbGqpZ1FuneI0eyZy089OYMsuei62p+t8tg Ujmg== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-unsubscribe:list-subscribe:list-archive:list-help:list-post :list-id:mailing-list:precedence:reply-to:content-language :in-reply-to:user-agent:content-transfer-encoding:mime-version :references:message-id:lines:date:subject:from:to :arc-authentication-results:arc-message-signature:dkim-signature :arc-authentication-results; bh=4h7SkOYw7Y7tZxQ24hocswKYmLMPGU2JGzW/5jGxXJQ=; b=e+8sRQhCuWv+6dY62xOdKuFl32E0wY/bIvjH4MxSb85r8fUUTDw29CIqVEKHjYx6tA EytwnBouoRxSkdcVdd6F/iKsftdLKBME/epopIHPu9K1cvB1ROy21R3xzLZU0YXGOFbb Jjm0QG9vneSlUNsuvWx3OU5aulJpdTwm3oQ2iqT7zWXxoeN4dvJSQihJIdGnyXHglmrb MpsacfdwnT2UWvDNbND0V1ZViX7GU6SrnOAacIdDKPE9dAkF5gAEGpGxfaY2gONut9Pw di8lZXXcC169lEd9hhqkMgjfArLwb0yOxCGcO61Ak5iFjU ARC-Authentication-Results: i=2; mx.google.com; spf=neutral (google.com: 195.159.176.226 is neither permitted nor denied by best guess record for domain of gclcip-std-proposals@m.gmane.org) smtp.mailfrom=gclcip-std-proposals@m.gmane.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=to:from:subject:date:lines:message-id:references:mime-version :content-transfer-encoding:user-agent:in-reply-to:content-language :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=4h7SkOYw7Y7tZxQ24hocswKYmLMPGU2JGzW/5jGxXJQ=; b=a8Dq1+z5eBUt1jghsZV7GTGzitwkM7mtiusSkg8X/BTQz1wZV259aSBzKzH46k3Fb6 K/d2981QRma9Xk5IMHDu1vG5pCM6OnUXCMPJLuo56CfvHbsWWBzfD0XnClPaLOBkcgod qcokisDO00XSH+hBJH3cSxT0sJ9g9PyqSszztOlfzkQVLQvy6POyFrbe9J2MUF9pXbVO uf5nMYRzs7om0XSzHF2sCOYxWy8hqTvP1b7cosZC0Ic6aHIHy/G/xn89w8g7MVkAv1QG rz0hE4VpyCtGTZYCh8y0U4t/WqfErad+qAd7EsVZxN28a8BdXPLO/iIpfmzfphIeRS9n X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:to:from:subject:date:lines:message-id:references :mime-version:content-transfer-encoding:user-agent:in-reply-to :content-language:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=4h7SkOYw7Y7tZxQ24hocswKYmLMPGU2JGzW/5jGxXJQ=; b=ckmkgxeRJJ840CQmO6Qm1lpHyfWnUHfohANUaFiD7Gq6tJgAYFw8UXNzffhjgPU6aX 7cEOVIYXkX0RI8+5hP6kNnCVrBBOHPzoJSxi8KCAI071yeY9+dyRqr42iWyLQ5oIAWxr 3mG5aZgKfZgIw25vxCYvnsaAcbY3hIwy4Tog7fRuGCI84r6169aQ5kymw/RmOXjK6DR+ ld/4+5Lx4opAt8CMYc5ccxYcM7zmEfK5Di9QLEpPGsqBEV5Sa9VYPaC9C9LWFrRzIdnK 3/owmlOLXxYW4efWF1DSkMUUjlkX4uJY6g6FG X-Gm-Message-State: AMCzsaXRbjfhnWWotP8bShgitKgIzi+Dv34f+EpnVQPJ5910eZu39LB1 RFu4FuNsTUFHuCTzLi6ogl4= X-Google-Smtp-Source: ABhQp+TdtTxgAnqF6e9/2upV4RkiXUft5ySc4ONSLcqiHJjk30D1dEAF2AesPHK6BOJtzLrUascg0Q== X-Received: by 10.46.95.133 with SMTP id x5mr166784lje.19.1509534906723; Wed, 01 Nov 2017 04:15:06 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.46.25.80 with SMTP id p77ls58285lje.1.gmail; Wed, 01 Nov 2017 04:15:05 -0700 (PDT) X-Received: by 10.46.64.135 with SMTP id r7mr2447132lje.111.1509534905209; Wed, 01 Nov 2017 04:15:05 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1509534905; cv=none; d=google.com; s=arc-20160816; b=TpdZHS4nnbP3Q8YhoL6jZOTSf0xy3bGRLCol8FWB9Wb2DMm0+yMm53eQBamfobqoZ4 TFtN5ZGIS+/ZlRKn3T4d2ewRWGzpc+4h8mmTH/MJkO16Pm7mRQGuXkM0nXN3kZRH6211 1vI4Gk3D027eyaxVqchysbY0Za+tCtSIbDZGY7wi2UkVNt9+Y5MxJXccXQOfsUjPMt9z MaRQQCvrSctcQkz5OHLxqRrE7dxuywQQ/XvgQBr2/KiYfVi6x3kOtMaPGRZ00/fWuc33 DMk/8Bm7LF49VYRh9AlyU3OtkNeMdvcVvbC28OPXX34biQSl579g6F0TdMbEpFNqTwEe 4A9A== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-language:in-reply-to:user-agent:content-transfer-encoding :mime-version:references:message-id:lines:date:subject:from:to :arc-authentication-results; bh=PXfJNvzQdxtJvIF57Cg84BrpKyLp+GhIO1507Ndn9b0=; b=T18ttkOEmElxwhJz33v9ui19b7dkS2zJs+WR6837uTdokxbdwNrEiwnV1dlPRrRXN+ GpqiTRdIazmQkkB5Hgsy5uhmE1ie6oSic1PcEIANbF7FiE6KaFq74E2sCvDKv38ECYSM LJ9KOxsG9qteuGeYkYBN71X/WRkGah85HB2/YJRQLPQvLFRgLvm52/DAXF5h0SAp+XUk AASrKKOO2ECqeDercmLtfPzdPXhFLjv/dMJlcHV251rOzCpCSK9Q8ETTOvGrsZtr0vRk 5Z2Ilgu57QRpWrnRclXa4kAHIn7wry1OhpU8U8mbCIUj/uGGcj4lbj+8zlo2EaAo19gs OQPg== ARC-Authentication-Results: i=1; mx.google.com; spf=neutral (google.com: 195.159.176.226 is neither permitted nor denied by best guess record for domain of gclcip-std-proposals@m.gmane.org) smtp.mailfrom=gclcip-std-proposals@m.gmane.org Original-Received: from blaine.gmane.org ([195.159.176.226]) by mx.google.com with ESMTPS id l84si179977lfi.128.2017.11.01.04.15.05 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 01 Nov 2017 04:15:05 -0700 (PDT) Received-SPF: neutral (google.com: 195.159.176.226 is neither permitted nor denied by best guess record for domain of gclcip-std-proposals@m.gmane.org) client-ip=195.159.176.226; Original-Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1e9qz0-00028g-LG for std-proposals@isocpp.org; Wed, 01 Nov 2017 12:14:54 +0100 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 49 Original-X-Complaints-To: usenet@blaine.gmane.org In-Reply-To: Content-Language: sv X-Original-Sender: gclcip-std-proposals@m.gmane.org X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 195.159.176.226 is neither permitted nor denied by best guess record for domain of gclcip-std-proposals@m.gmane.org) smtp.mailfrom=gclcip-std-proposals@m.gmane.org 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:35223 Archived-At: On 2017-11-01 12:05, Bo Persson wrote: > On 2017-10-31 17:31, Thiago Macieira wrote: >> On ter=C3=A7a-feira, 31 de outubro de 2017 08:16:53 PDT tower120@gmail.c= om=20 >> wrote: >>> What if copy ctr throwable, and move constructor noexcept (for example >>> std::vector) ? What, in this case std::vector REQUIRED=20 >>> to use >>> move? Or its juts too obvious for compiler that noexcept is faster path= ? >> >> I was hoping to find it for vector::erase(), but it says >> >> "Throws: Nothing unless an exception is thrown by the assignment=20 >> operator or >> move assignment operator of T." >> >> So that one doesn't restrict to calling the move assignment operator.=20 >> My next >> bet would be shrink_to_fit(), which means we reallocate but do not add o= r >> remove any items: I'd expect that function to be noexcept if the item=20 >> type has >> a noexcept move constructor. However, the text has a loophole: >> >> " If an exception is thrown other than by the move constructor of a non- >> CopyInsertable T there are no effects." >> >> It restricts to the noexceptness to non-copyable types only. >> >=20 > Not exactly. It's rather assumed that if the move constructor can throw,= =20 > the implementation should prefer to copy instead. A throwing copy is=20 > recoverable ("no effects"), as the original can be preserved until=20 > everything has been copied. >=20 > A throwing move halfway through a reallocation will get us in deep=20 > trouble. What are the odds that trying to move back some objects will=20 > not throw again? So the implementation is allowed to just abandon=20 > (destroy) the elements already moved, and so they are lost. >=20 > We can just hope that throwing move constructors are rare. Or that we=20 > don't need to store such objects in a vector. Or, alternatively, that=20 > losing some objects is not a big deal. YMMV. >=20 >=20 Or, reading it again, perhaps that's what you meant. :-) Bo Persson --=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/otcab8%24eqt%242%40blaine.gmane.org. .