220 29389 article Path: news.gmane.org!.POSTED!not-for-mail From: Shi Yan Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: why not formally support meta programming. Date: Wed, 9 Nov 2016 12:11:55 -0800 Lines: 202 Approved: news@gmane.org Message-ID: References: <668e0a04-c988-4354-ae32-30f626f75403@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a11418c705ea4ba0540e3de7c X-Trace: blaine.gmane.org 1478722353 26681 195.159.176.226 (9 Nov 2016 20:12:33 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 9 Nov 2016 20:12:33 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBD7JLV7X6MLRBDMGR3AQKGQEAYQERGY@isocpp.org Wed Nov 09 21:12:29 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f71.google.com ([74.125.82.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1c4ZDu-00029f-E0 for gclcip-std-proposals@m.gmane.org; Wed, 09 Nov 2016 21:11:54 +0100 Original-Received: by mail-wm0-f71.google.com with SMTP id r68sf109815466wmd.0 for ; Wed, 09 Nov 2016 12:11:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=zikE1YnbZzpnwqdWDwPMV0OV1ge7o5MnN1TBxetuDJs=; b=JrR0CZRjd0IsShY+NgHApKuwSwTmZc0QfLspfI7qtrLzKvrZ8D7aov41CcHSYEiXsv LFWmckHfXYRc+EBxl5WESTD0ie1U17JIvOU3r8/tRhrtBxl2mBXy5dP4gk3hEJKvvMCJ zSKVl1Ir80Brs4OQaF44DDDXJHZaa26aF1RatMxdQ/9ZmbZVzUPmzTS1T+3EKOBvzkpt S2MMo4LTBTZpc6mtbnrBNkG8741JkJSrqpC0C1sGtC/jQ4I1tQBs7xr3U6XTrzZQOy8J pJpS4si9KLPmDRa0sFW6nxQkQ05VdYil+kLBTfX8bzMlfZMEXAd2zZALuQ8YP6aQU2kp XTkw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=zikE1YnbZzpnwqdWDwPMV0OV1ge7o5MnN1TBxetuDJs=; b=RHV8NLOpaN/A6cKG4LaZpMnqJqirqHlTT3lP67EamjyrzCyj4N4EZcncNRlbus1bYZ HOmBA4iIAubkLs+y9kHuWOkrJFLsBTZPoeLp1NsRp6xqXawGR1WBlcFoxlllsBgwg6tq mPyLBAH11RzFwMGle3ILIyj+bb/Mzzdhntr/nD4g9/60MHr53CRll1857781wv4j6A90 yR/ILKTJ/OE0vxCS8AL7lYtas7bHJG3Cootvu1T8BkaQZHEuHo9Ztk4yIAziyzaeGj1S 6VrN03H6+uRNOalNr/mfI9dqzOGyyeIrl9AMLkqugiNYDtdjBYTdHjiRhlcOdpJJPkSE BuyA== X-Gm-Message-State: ABUngvcDzeQMWlwH26pCacKvP6RQ+dATOIfV3AUxr8uNx2+mEGUpzVZVXgBN7PN60bhJYA== X-Received: by 10.28.167.9 with SMTP id q9mr3418797wme.1.1478722317773; Wed, 09 Nov 2016 12:11:57 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.18.133 with SMTP id 127ls1288239wms.10.canary-gmail; Wed, 09 Nov 2016 12:11:56 -0800 (PST) X-Received: by 10.194.85.107 with SMTP id g11mr1264609wjz.82.1478722316465; Wed, 09 Nov 2016 12:11:56 -0800 (PST) Original-Received: from mail-wm0-x241.google.com (mail-wm0-x241.google.com. [2a00:1450:400c:c09::241]) by mx.google.com with ESMTPS id ga4si1300272wjb.93.2016.11.09.12.11.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Nov 2016 12:11:56 -0800 (PST) Received-SPF: pass (google.com: domain of billconan@gmail.com designates 2a00:1450:400c:c09::241 as permitted sender) client-ip=2a00:1450:400c:c09::241; Original-Received: by mail-wm0-x241.google.com with SMTP id g23so209253wme.1 for ; Wed, 09 Nov 2016 12:11:56 -0800 (PST) X-Received: by 10.28.125.3 with SMTP id y3mr2387818wmc.30.1478722316049; Wed, 09 Nov 2016 12:11:56 -0800 (PST) Original-Received: by 10.28.72.193 with HTTP; Wed, 9 Nov 2016 12:11:55 -0800 (PST) In-Reply-To: X-Original-Sender: billconan@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of billconan@gmail.com designates 2a00:1450:400c:c09::241 as permitted sender) smtp.mailfrom=billconan@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:29389 Archived-At: --001a11418c705ea4ba0540e3de7c Content-Type: text/plain; charset=UTF-8 So what's the reason for rejection? On Wed, Nov 9, 2016 at 11:46 AM, Mikhail Maltsev wrote: > On Wed, Nov 9, 2016 at 11:32 AM, wrote: > > I'm trying to design a library for different hardware (CPU and GPU) > > > > For users, I want the interface looks like this: > > > > > > Blah b(); > > > > or > > > > Blah c(); > > > > > > ideally inside the class of Blah, I want to do this to avoid duplication > and > > reduce workload: > > > > > > > > template > > class Blah > > { > > DataType shared_member; > > > > > > #Meta_if(deviceUsed == GPU) //some kind of meta programming > syntax > > to enable code based on template > > #{ > > DataType member_only_used_by_gpu; > > void function_on_gpu(); > > #} > > > > > > #Meta_if(deviceUsed == CPU) > > #{ > > DataType member_only_used_by_cpu; > > void function_on_cpu(); > > #} > > > > > > > > > > void shared_function() > > { > > .... > > #Meta_if(deviceUsed = GPU) { > > .... > > #} > > } > > }; > > > C++17 will have constexpr if. It can be used in a function, but not in > a class definition. Actually the latter has been proposed earlier, but > rejected: https://isocpp.org/files/papers/n3613.pdf > > -- > Regads, > Mikhail Maltsev > > -- > You received this message because you are subscribed to a topic in the > Google Groups "ISO C++ Standard - Future Proposals" group. > To unsubscribe from this topic, visit https://groups.google.com/a/ > isocpp.org/d/topic/std-proposals/dxjR3T_uGAk/unsubscribe. > To unsubscribe from this group and all its topics, 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/CAOqAUTiRxwtmzM-_ > tSyTUKbyiJhivCbVmUgQ749ByD%3Dh-SAF4A%40mail.gmail.com. > -- 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/CAKO7S%3DJZi-v%3DEZiXFmUZnkMxARbVK5EJ6wmnC3NkqT_oSEQjOQ%40mail.gmail.com. --001a11418c705ea4ba0540e3de7c Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
So what's the reason for rejection?=C2=A0

On Wed, Nov 9, 2016 at 1= 1:46 AM, Mikhail Maltsev <maltsevm@gmail.com> wrote:
On Wed,= Nov 9, 2016 at 11:32 AM,=C2=A0 <= billconan@gmail.com> wrote:
> I'm trying to design a library for different hardware (CPU and GPU= )
>
> For users, I want the interface looks like this:
>
>
> Blah<GPU, float> b();
>
> or
>
> Blah<CPU, double> c();
>
>
> ideally inside the class of Blah, I want to do this to avoid duplicati= on and
> reduce workload:
>
>
>
> template<DeviceType deviceUsed, typename DataType>
> class Blah
> {
>=C2=A0 =C2=A0 =C2=A0 =C2=A0DataType shared_member;
>
>
>=C2=A0 =C2=A0 =C2=A0 =C2=A0#Meta_if(deviceUsed =3D=3D GPU)=C2=A0 =C2=A0= //some kind of meta programming syntax
> to enable code based on template
>=C2=A0 =C2=A0 =C2=A0 =C2=A0#{
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 DataType member_only_used_by_= gpu;
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 void function_on_gpu();
>=C2=A0 =C2=A0 =C2=A0 =C2=A0#}
>
>
>=C2=A0 =C2=A0 =C2=A0 =C2=A0#Meta_if(deviceUsed =3D=3D CPU)
>=C2=A0 =C2=A0 =C2=A0 =C2=A0#{
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0DataType member_only_used_by_c= pu;
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0void function_on_cpu();
>=C2=A0 =C2=A0 =C2=A0 =C2=A0#}
>
>
>
>
>=C2=A0 =C2=A0 =C2=A0 =C2=A0void shared_function()
>=C2=A0 =C2=A0 =C2=A0 =C2=A0{
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0....
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0#Meta_if(deviceUsed =3D= GPU) {
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 ....
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0#}
>=C2=A0 =C2=A0 =C2=A0 =C2=A0}
> };
>
C++17 will have constexpr if. It can be used in a function, but= not in
a class definition. Actually the latter has been proposed earlier, but
rejected: https://isocpp.org/files/papers/n3613.pdf

--
Regads,
=C2=A0 =C2=A0Mikhail Maltsev

--
You received this message because you are subscribed to a topic in the Goog= le Groups "ISO C++ Standard - Future Proposals" group.
To unsubscribe from this topic, visit https://groups.google.com/a/isocpp.org/d/topic/s= td-proposals/dxjR3T_uGAk/unsubscribe.
To unsubscribe from this group and all its topics, send an email to std-proposals+unsubscrib= e@isocpp.org.
To post to this group, send email to std-proposals@isocpp.org.
To view this discussion on the web visit htt= ps://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAOqAUT= iRxwtmzM-_tSyTUKbyiJhivCbVmUgQ749ByD%3Dh-SAF4A%40mail.gmail.com.

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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/CAKO7S%3DJZi-= v%3DEZiXFmUZnkMxARbVK5EJ6wmnC3NkqT_oSEQjOQ%40mail.gmail.com.
--001a11418c705ea4ba0540e3de7c-- .