220 29388 article Path: news.gmane.org!.POSTED!not-for-mail From: Mikhail Maltsev Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: why not formally support meta programming. Date: Wed, 9 Nov 2016 11:46:40 -0800 Lines: 64 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: text/plain; charset=UTF-8 X-Trace: blaine.gmane.org 1478720806 5920 195.159.176.226 (9 Nov 2016 19:46:46 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 9 Nov 2016 19:46:46 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCTMPSET54IRBIX2RXAQKGQE7W4KJNI@isocpp.org Wed Nov 09 20:46:42 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f72.google.com ([74.125.82.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1c4YpU-0000sW-CI for gclcip-std-proposals@m.gmane.org; Wed, 09 Nov 2016 20:46:40 +0100 Original-Received: by mail-wm0-f72.google.com with SMTP id g23sf38685996wme.4 for ; Wed, 09 Nov 2016 11:46:43 -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=0Ub3fgQdBstYBtwGuhsoYgFWA8PpCUAt8NrUnZRXbs4=; b=hHcMsdvikK8wbkbwSmnVBFfoRH2odExS/Wp5fjDvAvD/tgJtS2edhyR3FaEcWfzj9t wjm5SGVDjKdXdTnLHQ1vR1wtL3F1n5Cza0CuG2xZi9PdynsyqVu34Umtv/a/0CwO1QdQ twXKd+mkJMTk4cUjW+AeWztx6ybAr5OQcnQxFlUPOzD6yg7BbVqXBT7MI8BJycB/PCix c0Z6kTt6F0MO8owyffxvVokQKO9606bnn0XHBDSYbuTgApHT3RmqDsZWaYJDeOTibyWo Ml1RuHfhm38jtxW6+Ax+5S8DKDD5MusEV2yMIDjjjajXNs1QJUVIsAwMA0+WotxrBY6W XGmw== 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=0Ub3fgQdBstYBtwGuhsoYgFWA8PpCUAt8NrUnZRXbs4=; b=aSYZ0JuThCVMIYKCKZIyGtMrCvnu8fh1Sh1LLehgrtp5jFlK3a5Eg+8UuejpCTs+c/ lpfygURnJ5J6XSk2ezQVPwXkL5wk2UdxxOsuFvACyYISHTJL94RDGLhfvDAOlKaT2I0C O8Z0WVS4CDGp9gjzlXhfCYarBsqUrILqSB4OWGKCKPffMoARYcuShxc3o0NnLBIBa4Fl Ooey+5/9OOsLFNam84CuGyjDgabC+7QUrZcwjJClTCDIUJRlnSqSTkht9i6NumE264fD kbWZmEwdejSa67UtFj2wAUT06VHJFgGdLmulUOQvjRIdfxW5+My5BirvVPjxjfLOFs22 EhGQ== X-Gm-Message-State: ABUngvfYoYOTFO7N3leEmgMvkD5UZ/VPGHSxzt0kfJwqEFR/N6nIVIzxTUBPLcU3cCLucQ== X-Received: by 10.28.63.213 with SMTP id m204mr322617wma.21.1478720803487; Wed, 09 Nov 2016 11:46:43 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.228.136 with SMTP id b130ls1568215wmh.0.gmail; Wed, 09 Nov 2016 11:46:42 -0800 (PST) X-Received: by 10.28.109.87 with SMTP id i84mr2052827wmc.100.1478720802194; Wed, 09 Nov 2016 11:46:42 -0800 (PST) Original-Received: from mail-wm0-x22d.google.com (mail-wm0-x22d.google.com. [2a00:1450:400c:c09::22d]) by mx.google.com with ESMTPS id xy10si1127940wjb.253.2016.11.09.11.46.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Nov 2016 11:46:42 -0800 (PST) Received-SPF: pass (google.com: domain of maltsevm@gmail.com designates 2a00:1450:400c:c09::22d as permitted sender) client-ip=2a00:1450:400c:c09::22d; Original-Received: by mail-wm0-x22d.google.com with SMTP id f82so263287573wmf.1 for ; Wed, 09 Nov 2016 11:46:42 -0800 (PST) X-Received: by 10.194.109.168 with SMTP id ht8mr1211315wjb.36.1478720801632; Wed, 09 Nov 2016 11:46:41 -0800 (PST) Original-Received: by 10.80.175.4 with HTTP; Wed, 9 Nov 2016 11:46:40 -0800 (PST) In-Reply-To: <668e0a04-c988-4354-ae32-30f626f75403@isocpp.org> X-Original-Sender: maltsevm@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of maltsevm@gmail.com designates 2a00:1450:400c:c09::22d as permitted sender) smtp.mailfrom=maltsevm@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:29388 Archived-At: 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 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/CAOqAUTiRxwtmzM-_tSyTUKbyiJhivCbVmUgQ749ByD%3Dh-SAF4A%40mail.gmail.com. .