220 38183 article Path: news.gmane.org!.POSTED!not-for-mail From: Gareth Lloyd Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Restricting the valid use of certain methods upon temporary objects Date: Thu, 24 May 2018 15:48:48 -0700 (PDT) Lines: 105 Approved: news@gmane.org Message-ID: References: <81b39e17-fe78-41ab-b9c9-3b830e32dbf5@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_9727_2043010048.1527202128598" X-Trace: blaine.gmane.org 1527202003 24824 195.159.176.226 (24 May 2018 22:46:43 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 24 May 2018 22:46:43 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCTJTSELJQINDAU53ACRUBBGFLFAE@isocpp.org Fri May 25 00:46:39 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f69.google.com ([209.85.213.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fLz0J-0006Md-3n for gclcip-std-proposals@m.gmane.org; Fri, 25 May 2018 00:46:39 +0200 Original-Received: by mail-vk0-f69.google.com with SMTP id c190-v6sf2242405vke.15 for ; Thu, 24 May 2018 15:48:50 -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: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=z0Gfost9mNJNmI1gUJeILKIOVNxM9cnHL/+xX4b4L/Y=; b=owqoor17Zei2pxtsNK9A/jVUU64KmaBGyuvIRePaCu3vHVrhQdTcXfMwKK8ubrl24k 6d6omrsDNGzvgpMel2dnYrDpRtElB/5tVQ/aqVVcFY3tGYS7PcCnXHTDEf6bZbucvVXA Ct77Tc6S6JxZ9AU0os42W96uZsHOUFJagihYgREJQIKa3MMFWQ7Ed1cE7Tx/WcKa7DrI YA+WDjdZ6VHm459tSJTF6YzIF8E94aNN1hT+8RrPmxBP83eICWL8KTPweGW83XYWBi1I wejBVUfMZ1oRtHbA+ElRUSt2vs9zw+SXPeSLCv+S6KHUh0nXv/fILiJi/CxHjBbid8zw 4tHQ== 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: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=z0Gfost9mNJNmI1gUJeILKIOVNxM9cnHL/+xX4b4L/Y=; b=Ebbe6J4xmoSQIp7YWiIOKBlSYBedR9q3WQlBj48gWlVdfIlnV43RX3j9n0AE3S9Dxk /ms3isXnm00T1MZjqe7mfGA9u/SfcCy9ZXCq10fLzqGjjc0mkm5IzKKv0ezqkLwjN+XV BD2dNWNU/cKE38cosSzVs1leI+X11FW1J0cJ31ntMFMuCNFDjj6KXNaMYV0PoJoT6/Lr r9yc3ERcxR18225dAjE3uQGctEH7dNBsNOEpZdDG8cm1wTpF0k13q0DxyfKr+ENbeG0a 9ODcBhvCFRucLGM7CirJnMswjMkp0qml5YA1+mY6EeGxhJRcKMCqh34ghNf0pryYw1bI fVSA== X-Gm-Message-State: ALKqPwe6WdJyKPHHyhz3T+MGc278s0cgJ0q1oihrwv2j/3/5Bs4LLKOL aHVY50PHytU4IDOnxLP1fPu4QA== X-Google-Smtp-Source: AB8JxZpclYxHyQC04wIqHPUCfuS4GHAxzIat7q2khg5XCnLVMIwCClgehE/n8TbsLGSPY+7hOzsVNQ== X-Received: by 2002:ab0:600b:: with SMTP id j11-v6mr4015476ual.34.1527202130193; Thu, 24 May 2018 15:48:50 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a1f:19d6:: with SMTP id 205-v6ls9947667vkz.12.gmail; Thu, 24 May 2018 15:48:49 -0700 (PDT) X-Received: by 2002:a1f:9bd1:: with SMTP id d200-v6mr1377858vke.6.1527202129032; Thu, 24 May 2018 15:48:49 -0700 (PDT) In-Reply-To: <81b39e17-fe78-41ab-b9c9-3b830e32dbf5@isocpp.org> X-Original-Sender: gareth@ignition-web.co.uk 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:38183 Archived-At: ------=_Part_9727_2043010048.1527202128598 Content-Type: multipart/alternative; boundary="----=_Part_9728_79512115.1527202128599" ------=_Part_9728_79512115.1527202128599 Content-Type: text/plain; charset="UTF-8" My example which returned references should be ok as they cause a copy on assignment, which is a way of breaking the dependency chain. Bellow is a corrected example. auto e1 = example{}.dependent().dependent().dependent(); \\ fine auto e2 = example{}.dependent().not_dependent().dependent(); \\ fine auto e3 = example{}.dependent().dependent().not_dependent(); \\ fine decltype(auto) e4 = example{}.dependent().dependent().dependent(); \\ compile error decltype(auto) e5 = example{}.dependent().not_dependent().dependent(); \\ compile error decltype(auto) e6 = example{}.dependent().dependent().not_dependent(); \\ fine -- 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/a77b6fa8-985a-4d79-a53a-28f2602733b3%40isocpp.org. ------=_Part_9728_79512115.1527202128599 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
My example which returned references should be ok as they cause a = copy on assignment, which is a way of breaking the dependency chain. Bellow= is a corrected example.

auto e1 =3D example{}.de= pendent().dependent().dependent(); \\ fine
= auto e2 =3D example{}.dependent().no= t_dependent().dependent(); \\ fine
auto e3 =3D example{}.dependent()<= /span>.dependent().no= t_dependent(); \\ fine

decltype(auto) e4 =3D exampl= e{}.dependent().d= ependent().= dependent(); \\ = compile error
decltype(auto) e5 =3D = example{}= .dependent().not_dependent().dependent(); \\ compile error
de= cltype(auto) e6 =3D example{}.dependent().dependent().not= _dependent(); \\ fine
=

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