220 24911 <92a6bfcf-0100-40b2-8946-a9c634783ec9@isocpp.org> article Path: news.gmane.org!not-for-mail From: "'Walt Karas' via ISO C++ Standard - Future Proposals" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: "Components" template with implicitly defined partial specializations for all classes Date: Thu, 3 Mar 2016 21:01:14 -0800 (PST) Lines: 83 Approved: news@gmane.org Message-ID: <92a6bfcf-0100-40b2-8946-a9c634783ec9@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_369_153204546.1457067674823" X-Trace: ger.gmane.org 1457067678 4244 80.91.229.3 (4 Mar 2016 05:01:18 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 4 Mar 2016 05:01:18 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDFLZXWOVYIBBHFN4S3AKGQECNCOFFY@isocpp.org Fri Mar 04 06:01:18 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f198.google.com ([209.85.213.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1abhrZ-00061N-Vt for gclcip-std-proposals@m.gmane.org; Fri, 04 Mar 2016 06:01:18 +0100 Original-Received: by mail-ig0-f198.google.com with SMTP id o1sf22529983igz.1 for ; Thu, 03 Mar 2016 21:01:17 -0800 (PST) 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 :x-spam-checked-in-group:list-post:list-help:list-archive:sender :list-subscribe:list-unsubscribe; bh=+XgKjYs5cv+ug/NC8VvnHGpXDLuUw0Gp08aLtT0LTOI=; b=REUbI96YYsQeSZCUkutm58Fn/+er8l3nXXA8D2TqIozAmn+PptPhZ7T7DLEqH+eEl7 Tmb0p0eu7YomJpBCv5VYJYPMPbNz7VzueDxbbC5Ci9eKBsRoUdbLT1SY7xi8+PfKKssE Wd2NqjPKL6pGHITbMzvh/6dziiyrN0XDuNQeTwKITahNsnSzMnqKXPE6H5Ly78AkLkBa +Hm0BaEuXNWlmiYZLsLOHSDjKs3eB9dFDGJcnrxMfDFH7I23bIHHj8zaRaOP13G5jno5 RlNBwoxE1dr1uwWQkSWGMXAAdjs2lufgKunYndpOe1cUkk2OyWTyLb9lWQhAv0v19QRE cp6Q== 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:x-original-sender:reply-to:precedence :mailing-list:list-id:x-spam-checked-in-group:list-post:list-help :list-archive:sender:list-subscribe:list-unsubscribe; bh=+XgKjYs5cv+ug/NC8VvnHGpXDLuUw0Gp08aLtT0LTOI=; b=YXQ6RBYtEex8gdLlPBPPqG4EnfS+gcLuMwT3WZDqVvAUYMk01yt/UEEw3rmGokcuNG eETEwMu09ZMPtLlCIbNVziflgyaI3tdGFO9wn5s3vhfUE3ftlpOvRkEvfuCKZ84OPrT6 LrWYp4bztmBUDcoaEIeiHOaoAHdB+FHkEo3UF5c03gAdqxu3QVxO3oKkQAj2fulPEa4U j3yxgowwnDUosRCxdpoDDWtYVDJFJ1Ut804RCoOEejY+oiBoNyggg/M944WBvjG0Nt11 qsnOilIimGJSo2mTWm66T/UPTC2UtXBNSUi1+BtFBJ9Qyobvw1dbuMoMfvxbCtLi+7ku A79A== X-Gm-Message-State: AD7BkJLMDNpzExB7zTQfG6wZN8DorNStP7Fh1wm1M6vIdRudv/WVT27zMBgVn0eW8CMKJQ== X-Received: by 10.182.247.68 with SMTP id yc4mr4548908obc.34.1457067677024; Thu, 03 Mar 2016 21:01:17 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.93.72 with SMTP id cs8ls172784igb.29.canary; Thu, 03 Mar 2016 21:01:15 -0800 (PST) X-Received: by 10.50.117.10 with SMTP id ka10mr87755igb.1.1457067675835; Thu, 03 Mar 2016 21:01:15 -0800 (PST) In-Reply-To: X-Original-Sender: wkaras@yahoo.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: Original-Sender: std-proposals@isocpp.org List-Subscribe: , List-Unsubscribe: , X-Original-From: Walt Karas Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:24911 Archived-At: ------=_Part_369_153204546.1457067674823 Content-Type: multipart/alternative; boundary="----=_Part_370_661324883.1457067674823" ------=_Part_370_661324883.1457067674823 Content-Type: text/plain; charset=UTF-8 Another possible approach generic mapping of operations to components would be to accept the idiom ++C , C a class name, as a template parameter. The compiler would implicitly expand ++C to multiple parameters, namely C itself, followed by a pair of parameters for each component of C. Each pair would consist of the type T of the component, followed by the member pointer of type T C::* to the component. (The reason for using ++ is to suggest iteration of over the components.) For example, for this class: struct A { int i, j; double x; }; the template instantiation: X<++A> would be equivalent to: X This hopefully would allow variadic templates to create reasonable default comparison, input and display, persistence, endiance swap, hashing, etc. operations for many classes. A difficult issue would be wether the context where X<++A> is instantiated would be required to have access to all the implicitly reverenced component types and components themselves. Perhaps the compiler could also except the idiomatic template parameter --C, which would lay out the components in reverse order (of destruction) rather than forward order (of construction). -- 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/92a6bfcf-0100-40b2-8946-a9c634783ec9%40isocpp.org. ------=_Part_370_661324883.1457067674823 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Another possible approach generic mapping of operations to= components would be to accept the idiom ++C , C a class name, as a templat= e parameter.=C2=A0 The compiler would implicitly expand ++C to multiple par= ameters, namely C itself, followed by a pair of parameters for each compone= nt of C.=C2=A0 Each pair would consist of=C2=A0 the type T of the component= , followed by the member pointer of type T C::* to the component.=C2=A0 (Th= e reason for using ++ is to suggest iteration of over the components.)=C2= =A0 For example, for this class:

struct A { int i, j; double x; };
the template instantiation:

X<++A>

would be equiv= alent to:

X<A, int, &C::i, int, &C::j, double, &C::x&= gt;

This hopefully would allow variadic templates to create reasonab= le default comparison, input and display, persistence, endiance swap, hashi= ng, etc. operations for many classes.=C2=A0 A difficult issue would be weth= er the context where X<++A> is instantiated would be required to have= access to all the implicitly reverenced component types and components the= mselves.

Perhaps the compiler could also except the idiomatic templa= te parameter --C, which would lay out the components in reverse order (of d= estruction) rather than forward order (of construction).

--
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