220 37442 article Path: news.gmane.org!.POSTED!not-for-mail From: Nevin Liber Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: default assignment should be established by construction Date: Fri, 23 Mar 2018 14:03:38 -0500 Lines: 100 Approved: news@gmane.org Message-ID: References: <58813920-b8f6-4e2f-83ed-c4c299792b62@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="001a114daec260c6b50568191763" X-Trace: blaine.gmane.org 1521831742 9290 195.159.176.226 (23 Mar 2018 19:02:22 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 23 Mar 2018 19:02:22 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCE35H5S6IDBBN472XKQKGQEMNIEVWY@isocpp.org Fri Mar 23 20:02:18 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f197.google.com ([209.85.217.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1ezRxC-0002JU-Aa for gclcip-std-proposals@m.gmane.org; Fri, 23 Mar 2018 20:02:18 +0100 Original-Received: by mail-ua0-f197.google.com with SMTP id 60sf8267357uab.21 for ; Fri, 23 Mar 2018 12:04:26 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1521831865; cv=pass; d=google.com; s=arc-20160816; b=MJ1rq1gf3MlCaFhHyvJgmNWiLwcj5CYgDOsaYG2qjG4eDx/HOGNNPjXBSgdnBQ0U05 E8tLllatmdi3kK8AXNV75GvqTN4jjgoDboaN/i4cUEqsp1YYiOqWt1E1U+vMhUGvd+RW KQokE1Ot2h+BKdVKNS7JYVohlaNhyH/Kneva3lGYhEbkjcWOBxkUPCwICF2vAWOn/J8b tgDGC6LJpY1IJw9KweKzfr3AxbcknDMlFzFu2m9KmxcGTWvQX5WUmvUQ9F/95+xXtTGX h1VZH8u4tKdYhmvAUA4SHSoZQ73KkiqfunG4q3zTqKNjEtp1cBEO9EhK+6s9L6pZq+3c TGAQ== 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:to:subject:message-id:date :from:references:in-reply-to:sender:mime-version :arc-authentication-results:arc-message-signature :arc-authentication-results; bh=ekzlqyN8Try+7P0rxEzB3+1IsyDuLFAoUIOXSOPa8+c=; b=tyodQ6vfHIU/dQYO77buBWIAJFDdtmo2x3oNYnfQtkS+i6T7HXdwYIFjR7GYDIEwC3 +efmSUNKKkFHF9vcFRw/AEZx6vx6eUfW8ojbGd5OvDXOhqvfejCyaU3Kkpan17Ob99x4 +GfOsMPP8TF9eg2NDvmSAby1zAiUcRhX/IhjRBrjOHfepHJ9VEleW8QymEs6VKAwhM/c Ay7IUfqRKt+pE2BEH4qQh/yCYB1vVdUdc/ziAo6LYNKO8WIqGfZ+/UVEsAo5wvRUY7YQ BLXQE7ce3PC9N8KF0uSi1Jo1sOyKzWNcSB33UAp13/2rCx8T1jYifQxsYraJWZ/uILcw Svlw== ARC-Authentication-Results: i=2; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=PAwvxWbV; spf=pass (google.com: domain of nliber@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=nliber@gmail.com X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:sender:in-reply-to:references:from :date:message-id:subject:to: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=ekzlqyN8Try+7P0rxEzB3+1IsyDuLFAoUIOXSOPa8+c=; b=th3HjmWemvRzz7rCdxW4Ot9j1GPc2jaqIdTvQD99KrPvsVgdmEbcQFxWEOd9DKy/bu ZQ1m/XiVdmYXPRjYkPDFIm3F0/mHYjtAVLIaN7OvlE7JVZKUi0ERw7kfatKFEcBdmxet 74gXSzt8pysIjFzgKBgWqUzDNjcIOK7lUnXM+G/rsAdTZfOFNRu+v2BtZOZY29ojLA8v FHzKF8MT1gZyYqbUM+UPWRq3Glv1qKmOuGGFxKXrfFaiMks7L9DA/eCTdnDTH/0e6UhM ax6Y3O0ddRi/HXHO26Ty+7v6iaNYFTS+HWQr2d4mLZIXHkEoPn7q04sNUZb6Ewk179Ya x7Pw== X-Gm-Message-State: AElRT7EsXn5ikKLNLfhnhetPtKRGA8xk9w4FB44a93p8vHZngf6th9QB ncCinUp8pAOtQ7o7weWhHJU= X-Google-Smtp-Source: AG47ELtLWGezV73O6aqucLVyUx3czHFrQoKrpiQL8wytW4MUtPecdp/dLgbNys7YNgurkyKlbPvk3A== X-Received: by 10.31.242.74 with SMTP id q71mr9649520vkh.120.1521831865534; Fri, 23 Mar 2018 12:04:25 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.176.16.228 with SMTP id x36ls1284964uab.3.gmail; Fri, 23 Mar 2018 12:04:19 -0700 (PDT) X-Received: by 10.176.68.197 with SMTP id n63mr20284431uan.132.1521831859922; Fri, 23 Mar 2018 12:04:19 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1521831859; cv=none; d=google.com; s=arc-20160816; b=yNeUeMx1Jlskds7Oa6JIHlbY/WscHpcM2iqhfR9t7TzKfHQt6c+ePVHaQcMDkowUAu 70XO1Y2q2nvTIjk6bFWSr1RMuK33aAu2nblJvxD/OGwu+OXAIz2AV3fZyfOcdX8DWFVS r9CC133JzjeR02Nm2Gdl0SPz2DCx+gSxCGjG7E5AA6SdgU4jGvCEbj+MvuG2G41KrAdE +ttdQR2/qzWlACrTssuqhySp5rU9t3at6bZSTT2f3yl9I/t3orsUrsEbS7Nrf4zj1sY0 Lvw7/7ej2Y+84eaIyy9pB73BwYVOMIynSUGFy5Lix01owAp4Tk2jpXxYnB6r+dMvcJXQ mHfQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=to:subject:message-id:date:from:references:in-reply-to:sender :mime-version:dkim-signature:arc-authentication-results; bh=G+FByNfKSzao5hB2Y0iHaV9Hk6slrfwO5mSJRyxwo8w=; b=owBsR27XPO6uzI4gApKwz9osxuJ6Iss8sFBFrq1Sf2Bg3vpa4iATx4vy/NKvqixgos +Y6WPLMSzUX1wrZLE9SyGWX309T1x48vgTsRFs0IqljsaAgjrbO6Fc8eB1WbHHc9sug8 gJ2NZJzwvrlZ5b9ZWON3wJFPovBVwgWD5Q1C6MBDmyNhw02pRAWE6eoq1yAwveUeIBxU 0819Kww/lAbbleHMd9hNvNo4mUlXte52vmrfJhWb0alVSks7EVAxhm3ZFrz6UghH9lfh WkJgN2i9frcaEkkotqK8AqidBt13jNVz9vITxV9srqoNgUR/O4BAQ3/7935AvGnqBm16 ih/w== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=PAwvxWbV; spf=pass (google.com: domain of nliber@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=nliber@gmail.com Original-Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id l126sor1663464vkg.140.2018.03.23.12.04.19 for (Google Transport Security); Fri, 23 Mar 2018 12:04:19 -0700 (PDT) Received-SPF: pass (google.com: domain of nliber@gmail.com designates 209.85.220.41 as permitted sender) client-ip=209.85.220.41; X-Received: by 10.31.69.85 with SMTP id s82mr291069vka.162.1521831859240; Fri, 23 Mar 2018 12:04:19 -0700 (PDT) Original-Sender: nliber@gmail.com Original-Received: by 10.103.118.135 with HTTP; Fri, 23 Mar 2018 12:03:38 -0700 (PDT) In-Reply-To: <58813920-b8f6-4e2f-83ed-c4c299792b62@isocpp.org> X-Original-Sender: nevin@eviloverlord.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b=PAwvxWbV; spf=pass (google.com: domain of nliber@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=nliber@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:37442 Archived-At: --001a114daec260c6b50568191763 Content-Type: text/plain; charset="UTF-8" On Fri, Mar 23, 2018 at 2:02 PM, 'wkaras@yahoo.com' via ISO C++ Standard - Future Proposals wrote: > For a class C, if the copy constructor is not deleted or suppressed, the > default copy assignment operator should be: > > C & operator = (const C &that) > { > if (&that != this) > { > this->~C(); > new (this) C(that); > } > return *this; > } > > (with const omitted from the parameter if it is omitted in the copy > constructor). > > Likewise, if the move constructor is not deleted or surpressed, the > default move assignment operator should be: > > C & operator = (C &&that) > { > if (&that != this) > { > this->~C(); > new (this) C(std::move(that)); > } > return *this; > } > > Hypothetically this could break existing code, but I can't think of a > practical example of useful code it would break. > Only if you live in an exception-free world... -- Nevin ":-)" Liber +1-847-691-1404 -- 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/CAGg_6%2BNXH4jPHwLKqYeOJ%3DCCWsh2dJetCYOSNt8vfmMduZBPqQ%40mail.gmail.com. --001a114daec260c6b50568191763 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Fri, Mar 23, 2018 at 2:02 PM, 'wkaras@yahoo.com' via ISO C++ Standard - Future Pro= posals <std-proposals@isocpp.org> wrote:
For a class C, if the copy constructor is not deleted or = suppressed, the default copy assignment operator should be:

<= div>C & operator =3D (const C &that)
{
=C2=A0 i= f (&that !=3D this)
=C2=A0 {
=C2=A0 =C2=A0 this->= ;~C();
=C2=A0 =C2=A0 new (this) C(that);
=C2=A0 }
=
=C2=A0 return *this;
}

(with const = omitted from the parameter if it is omitted in the copy constructor).
=

Likewise, if the move constructor is not deleted or sur= pressed, the default move assignment operator should be:

C & operator =3D (C &&that)
{
= =C2=A0 if (&that !=3D this)
=C2=A0 {
=C2=A0 =C2=A0 = this->~C();
=C2=A0 =C2=A0 new (this) C(std::move(that));
=
=C2=A0 }
=C2=A0 return *this;
}
Hypothetically this could break existing code, but I can't= think of a practical example of useful code it would break.

Only if you live in an exception-free world..= ..=C2=A0
--
=C2=A0Nevin &q= uot;:-)" Liber=C2=A0 <mailto:nevin@eviloverlord.com> =C2=A0+1-847-691-1404<= /div>

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
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/CAGg_6%2BNXH4= jPHwLKqYeOJ%3DCCWsh2dJetCYOSNt8vfmMduZBPqQ%40mail.gmail.com.
--001a114daec260c6b50568191763-- .