220 34984 <1643738.UGnyhZm5To@tjmaciei-mobl1> article Path: news.gmane.org!.POSTED!not-for-mail From: Thiago Macieira Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Contra P0722R0 "destroying operator-delete" Date: Tue, 17 Oct 2017 11:03:55 -0700 Lines: 62 Approved: news@gmane.org Message-ID: <1643738.UGnyhZm5To@tjmaciei-mobl1> References: <89c7d198-0eec-4099-ba31-bad92706ebae@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1508263460 25496 195.159.176.226 (17 Oct 2017 18:04:20 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 17 Oct 2017 18:04:20 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBEUMTHHQKGQEMQSAINY@isocpp.org Tue Oct 17 20:04:14 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wr0-f197.google.com ([209.85.128.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1e4WDc-0003sy-Tq for gclcip-std-proposals@m.gmane.org; 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[2a01:4f8:d13:f81:21c:14ff:fe01:12a3]) by mx.google.com with ESMTP id q22si7996996wrc.186.2017.10.17.11.04.02 for ; Tue, 17 Oct 2017 11:04:02 -0700 (PDT) Received-SPF: pass (google.com: domain of thiago@macieira.org designates 2a01:4f8:d13:f81:21c:14ff:fe01:12a3 as permitted sender) client-ip=2a01:4f8:d13:f81:21c:14ff:fe01:12a3; Original-Received: from tjmaciei-mobl1.localnet (jfdmzpr03-ext.jf.intel.com [134.134.139.72]) by gondolin.macieira.info (Postfix) with ESMTPSA id 2CDB911B47B for ; Tue, 17 Oct 2017 11:04:00 -0700 (PDT) In-Reply-To: X-Original-Sender: thiago@macieira.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of thiago@macieira.org designates 2a01:4f8:d13:f81:21c:14ff:fe01:12a3 as permitted sender) smtp.mailfrom=thiago@macieira.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:34984 Archived-At: On ter=C3=A7a-feira, 17 de outubro de 2017 10:02:11 PDT 'Richard Smith' via= ISO C++=20 Standard - Future Proposals wrote: > Please read to the end of the paper; that alternative is discussed and we > explain why it is not entirely satisfactory. And I agree. My first reaction was, "why not just add a class operator dele= te",=20 which is answered in the paper. I like the idea of the destroying operator delete. Can we have a constructing operator new too? That is, the dual of what the= =20 paper proposes. That would allow for the object to have a public constructo= r=20 too. This has been a request in QObject for some time, but we have never fo= und=20 a satisfactory (i.e., non-hacky or inefficient) solution. Almost all class types using private implementations would benefit from thi= s.=20 Take this from actual code : QObject::QObject(QObject *parent) : d_ptr(new QObjectPrivate) You'll find that QObject is roughly even divided between stack / member obj= ects=20 and those created with new QObject (or one of the derived classes). It would be grand to have: QObject *QObject::operator new(/* implicit size */) { size_t full_size =3D sizeof(QObject) + sizeof(QObjectPrivate); auto obj =3D static_cast(::operator new(full_size)); auto d =3D reinterpret_cast(obj + 1); // call a private or protected constructor return new (obj) QObject(InPlaceTag{}, d); } Coupled with a member operator delete (not necessarily the destroying delet= e),=20 the only other things we need is 1 bit indicating that the main class does = not=20 own the private object and should not delete it. --=20 Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org Software Architect - Intel Open Source Technology Center --=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/1643738.UGnyhZm5To%40tjmaciei-mobl1. .