220 17708 <3d85e7bb-0039-48d0-8f50-19cbd3c440ca@isocpp.org> article Path: news.gmane.org!not-for-mail From: John Yates Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: =?UTF-8?Q?=5Bstd=2Dproposals=5D_Re=3A_Proposal=3A_Class_static_=E2=80=9Cproper?= =?UTF-8?Q?ty=E2=80=9D_constants_in_vtables?= Date: Tue, 5 May 2015 12:15:08 -0700 (PDT) Lines: 107 Approved: news@gmane.org Message-ID: <3d85e7bb-0039-48d0-8f50-19cbd3c440ca@isocpp.org> References: <49c358a2-d19a-415f-a4fa-1ff67286a0ad@isocpp.org> <7b8abc94-1928-4f61-82c2-75711d0b7a50@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_5275_1046166535.1430853308825" X-Trace: ger.gmane.org 1430853314 6500 80.91.229.3 (5 May 2015 19:15:14 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 5 May 2015 19:15:14 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDW2ZOHC5EGRBPNNUSVAKGQEXG4JPTI@isocpp.org Tue May 05 21:15:14 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f197.google.com ([209.85.214.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YpiJD-0001Tk-9y for gclcip-std-proposals@m.gmane.org; Tue, 05 May 2015 21:15:11 +0200 Original-Received: by obbkp3 with SMTP id kp3sf191998053obb.0 for ; Tue, 05 May 2015 12:15:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :content-type:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=zr7llp9W2vCDUVhRQobJCo/vVwExDyn2zP2n3a8MgPs=; b=mAbDPBBisv2z5Ti6Wi4369K8NEG8lBLJMN6koCsUgtjp3B8mhbQxW0d0ii15vBX5qC KvHkxCk994++Jo1S6daWQLF4G2SoPWcsaHDJKGGuASWUOYiF2ujeUhIHPPnmvGvF8nn3 vn8I3bxaZm5uuo0MEVNv/D98phYVmEUTbmT1Z2acSrB0j0ORqJAVpc/6GkWxN3dnIZZv /nSG+walLcMwLKyTz3bl5l6bYT8OZ0tbcznTUJZZhsTTE0rQ9SNdhdwaEFUrEEEZl4lv XCSShBsebYMdcpu2ocETuodv6CveHjgGnKXT00rPO7bD4vKkH117HEm/2tjKR3qbCLVv mmVw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:content-type:x-original-sender:reply-to :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=zr7llp9W2vCDUVhRQobJCo/vVwExDyn2zP2n3a8MgPs=; b=YiuQBtdeBw5FAR+U1BJ0ttQSZRazL0dskywxEOkti+jVy4rWvY7tGENzZDSBC6W5lh oBkJemDe5wkFRHGfB7eLmucOHkyidgN1keFm8mBKqK3BVEQlV+vRa8knsNJ/AS2WiETk wCToIlWRcsELexLcQRq7hTgb/4+R43CDJcWL4kdmGdxpRA7tol5k+rVXi/toudBMpCOf PdDkVBG1zhPWzO8LjUahwBFWDchTumRVLndhSIDyEr4Hc0v7fI8nV86nIFZ+bhgn4J3C 1iELBaqhbAMEZvHrLbYFDzqEz2J8JVawIB1R5ZHScveY3RmgASrjutdu2aOWFNN4YNIC v26Q== X-Gm-Message-State: ALoCoQkQlLMzQi5D+B9FFEFVpBgUSVsUkrKGhnYHWuco2qyDZ4L96DstjXN7+niO211pn1sk1mmw X-Received: by 10.43.65.1 with SMTP id xk1mr57208484icb.32.1430853310292; Tue, 05 May 2015 12:15:10 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.95.68 with SMTP id h62ls3145453qge.55.gmail; Tue, 05 May 2015 12:15:09 -0700 (PDT) X-Received: by 10.140.95.135 with SMTP id i7mr326621qge.27.1430853309531; Tue, 05 May 2015 12:15:09 -0700 (PDT) In-Reply-To: <7b8abc94-1928-4f61-82c2-75711d0b7a50@isocpp.org> X-Original-Sender: john.yates.sheets@gmail.com 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:17708 Archived-At: ------=_Part_5275_1046166535.1430853308825 Content-Type: multipart/alternative; boundary="----=_Part_5276_1472335756.1430853308825" ------=_Part_5276_1472335756.1430853308825 Content-Type: text/plain; charset=UTF-8 On Tuesday, May 5, 2015 at 12:37:02 PM UTC-4, Igor Baidiuk wrote: > > Frankly speaking, I don't see what should it solve. > Did you read the linked to proposal? > If you know type statically, then you use template programming, static > constexpr members. > If you don't know type statically, then you'll need to go through vtable > anyway to know exact type. > Correct, the type is _not_ statically known. The first example in my document tries to be an illustrative example. If you find it inadequate perhaps you could help me improve it. > If this is a shortcut for 'virtual getSomeConstant', then please note that > constant should be allocated somewhere in vtable and be perfectly > constexpr. Not very flexible. > That is exactly the use case. It is a way of accessing efficiently class "properties". > And BTW vtable structure is implementation-defined. > Yes, I am well aware of that point. Once I have paid the price in an object to have a vtable pointer, retrieving a constant at a fixed offset is all I seek. I am not trying to control layout of the vtable, only attempting to piggyback on the the fact that my object contains a pointer to a class-specific piece of initialized readonly storageand perhaps suggesting how much storage is necessary to store my constant. -- --- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. 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On Tuesday, May 5, 2015 at 12:37:02 PM UTC-4, Igor Baidiuk= wrote:
Frankl= y speaking, I don't see what should it solve.
Did you read the linked to proposal?
 
If you know type s= tatically, then you use template programming, static constexpr members.
= If you don't know type statically, then you'll need to go through vtable an= yway to know exact type.

Correct, the type is _n= ot_ statically known.  The first example in my document tries to be an= illustrative example.  If you find it inadequate perhaps you could he= lp me improve it.
 
If this is a shortcut for 'virtual getSomeConsta= nt', then please note that constant should be allocated somewhere in vtable= and be perfectly constexpr. Not very flexible.
=
That is exactly the use case.  It is a way of accessing= efficiently class "properties". 
 
And BTW vtable structure is= implementation-defined.

Yes, I a= m well aware of that point.  Once I have paid the price in an object t= o have a vtable pointer, retrieving a constant at a fixed offset is all I s= eek.  I am not trying to control layout of the vtable, only attempting= to piggyback on the the fact that my object contains a pointer to a class-= specific piece of initialized readonly  storageand perhaps suggesting = how much storage is necessary to store my constant.

--

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