220 38068 article Path: news.gmane.org!.POSTED!not-for-mail From: Phil Bouchard Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Fornux C++ Superset - Forward Declarations of Nested Structures Date: Fri, 11 May 2018 17:48:54 +0000 (UTC) Lines: 50 Approved: news@gmane.org Message-ID: References: <34fa23ed-1fab-44d5-92ab-217067b68225@isocpp.org> <75fb8736-b92a-480f-9a36-310b3e03b131@isocpp.org> <228ebe66-fa3d-40e8-a42f-37de41834977@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 1526060951 6097 195.159.176.226 (11 May 2018 17:49:11 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 11 May 2018 17:49:11 +0000 (UTC) User-Agent: NewsTap/5.3.1 (iPhone/iPod Touch) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCAYTFXFZMBBBFNQ27LQKGQEU2U4GYQ@isocpp.org Fri May 11 19:49:07 2018 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 1fHCAF-0001Sa-J1 for gclcip-std-proposals@m.gmane.org; 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Original-Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1fHCA9-0001JE-0y for std-proposals@isocpp.org; Fri, 11 May 2018 19:49:01 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 34 Original-X-Complaints-To: usenet@blaine.gmane.org Cancel-Lock: sha1:fJEzdYy4/P6avw2lIn+wt4f8NGM= X-Original-Sender: philippeb8@gmail.com 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; dmarc=fail (p=NONE sp=QUARANTINE dis=NONE) header.from=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:38068 Archived-At: Bengt Gustafsson wrote: > I'm skeptical to partial declarations as the rules would be quite=20 > complicated. What I have found lacking on various occasions is the abilit= y=20 > to declare inheritance in a forward declaration. Being able to declare=20 > inheritance relations early reduces the need of moving method=20 > implementations of methods out of the class head in certain situations. >=20 > When it comes to friend declarations it seems that you would not be helpe= d=20 > by including them in a forward declaration as their sole purpose is to=20 > allow access to private members _which have not been declared yet_. >=20 > I would favor a proposal which includes your initial possibility to decla= re=20 > a nested class after declaring the outer class (or for consistence with= =20 > namespace A::B { ... } without having to do so) plus the possibility to= =20 > declare inheritance in a forward declaration. Ok so let=E2=80=99s forget about partial declarations and consider consiste= ncy checks. But regarding inheritance; there would be no way to see if classes are virtual or not without their members. This would prevent us from using dynamic_cast on pointers. Ex.: struct Y; struct X : Y; Y * p =3D nullptr; // fine X * q =3D dynamic_cast(p); // error This might be an obscur use case but worth mentioning. Regards, -Phil --=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/pd4l26%244bv%241%40blaine.gmane.org. .