220 8498 article Path: news.gmane.org!not-for-mail From: Richard Smith Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: A new keyword for either a type or a variable (typical use case for variadic template template)? Date: Thu, 9 Jan 2014 17:07:21 -0800 Lines: 115 Approved: news@gmane.org Message-ID: References: <-5123564187529511709@gmail297201516> <52CB7506.1000906@gmail.com> <62bda680-3dd7-4be8-8ac5-0d2e08bf6d99@isocpp.org> <52CDFB2D.4050703@gmail.com> <-9126987679220332623@gmail297201516> <52CE0F54.5020800@gmail.com> <52CF3AB0.7090102@gmail.com> <52CF3D80.9090702@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=20cf307c9e1220d0b704ef9359f9 X-Trace: ger.gmane.org 1389316037 11928 80.91.229.3 (10 Jan 2014 01:07:17 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 10 Jan 2014 01:07:17 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDVNBJG4YAIBBSMPXWLAKGQEK5ALR6A@isocpp.org Fri Jan 10 02:07:25 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qe0-f72.google.com ([209.85.128.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1W1QZH-0004K9-Bh for gclcip-std-proposals@m.gmane.org; Fri, 10 Jan 2014 02:07:23 +0100 Original-Received: by mail-qe0-f72.google.com with SMTP id 5sf6525411qeb.3 for ; Thu, 09 Jan 2014 17:07:22 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:sender:in-reply-to:references:date :message-id:subject:from:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=BO18/wyWpXTjZm7S9C+xAMDCQzH+xeaNS6gyE4kJ9Uc=; b=CeUzZ9mAErNgILcNI9vF1HYQt18Xt+T3C5w87cE65pVjwfC/u/LK3svp7u2DqzCnOw waPlqaKgFTa+BQYoZujzri4olpomwte/Q7NanayS32B8tK9rNuhG5/BoA0bcVSf0S5B/ hJtt8IcR8DFqT6u5uUUUQzv5gvMtwyW88xAHnMVMmclJEQW4J4TkXT4TPWT24BvyxY7Q vwq/4h/WRJugyaHxTos7YFASrQVWuBktmljSVvnqacbaquCeDRY7lqhtWGxRMe+8kHhX 8kVnz9N9PkiFTlvMaOprqziCoRB4k3ElIJHVEudwVVNataUn8tvNN2Zao+qrD+kogWJj KEaQ== X-Gm-Message-State: ALoCoQnIZu69qGNWn9K8syqmyJleLouqoYy3+x2B62fFRapjPkF35QpnboirHpPAJtcTgPUh0Icz X-Received: by 10.236.228.228 with SMTP id f94mr2202742yhq.43.1389316042582; Thu, 09 Jan 2014 17:07:22 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.3.228 with SMTP id f4ls1218676qef.85.gmail; Thu, 09 Jan 2014 17:07:21 -0800 (PST) X-Received: by 10.49.40.137 with SMTP id x9mr1440655qek.18.1389316041756; Thu, 09 Jan 2014 17:07:21 -0800 (PST) Original-Received: from mail-vb0-x22b.google.com (mail-vb0-x22b.google.com [2607:f8b0:400c:c02::22b]) by mx.google.com with ESMTPS id e16si7818780qej.53.2014.01.09.17.07.21 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 09 Jan 2014 17:07:21 -0800 (PST) Received-SPF: pass (google.com: domain of metafoo@gmail.com designates 2607:f8b0:400c:c02::22b as permitted sender) client-ip=2607:f8b0:400c:c02::22b; Original-Received: by mail-vb0-f43.google.com with SMTP id p6so2762458vbe.30 for ; Thu, 09 Jan 2014 17:07:21 -0800 (PST) X-Received: by 10.52.26.148 with SMTP id l20mr4538559vdg.28.1389316041393; Thu, 09 Jan 2014 17:07:21 -0800 (PST) Original-Sender: metafoo@gmail.com Original-Received: by 10.58.136.227 with HTTP; Thu, 9 Jan 2014 17:07:21 -0800 (PST) In-Reply-To: <52CF3D80.9090702@gmail.com> X-Original-Sender: richard@metafoo.co.uk X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of metafoo@gmail.com designates 2607:f8b0:400c:c02::22b as permitted sender) smtp.mail=metafoo@gmail.com; dkim=pass header.i=@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:8498 Archived-At: --20cf307c9e1220d0b704ef9359f9 Content-Type: text/plain; charset=ISO-8859-1 On Thu, Jan 9, 2014 at 4:23 PM, David Krauss wrote: > On 1/10/14 8:11 AM, David Krauss wrote: > >> On 1/9/14 11:18 AM, Richard Smith wrote: >> >>> The useful thing about introducing a new feature is that you get to >>> specify >>> how it works =) Naturally, we would specify that passing a generic >>> template >>> argument to another template preserves the kind of template argument. >>> >> >> But how can you make that work without redoing how parsers must classify >> type-dependent expressions? And what's the benefit, given that >> overloading/partial specialization already solve the problem? >> > > I should be more specific. > > Given "?", you can peel off a fully-generic argument from a pack, and pass > it to another template. But the other template must be either > fully-generic, or overloaded/partially specialized. So you might as well > peel the pack in the target overloaded/partially specialized template. All > "?" buys you is the freedom to add a dispatcher between components which > are actually necessary. > It allows more code reuse, by allowing handling of individual elements of such a pack to be factored out. That is a valuable property, even if it only helps those people who are writing template metaprograms. > I don't see any applications for fully-generic arguments outside > metaprocessing, e.g. of packs. There is no runtime code application > parameterized over all types or all values of any type. For value-like > types, i.e. std::integral_constant, it is idiomatic (and makes perfect > sense) to deal with runtime instances of a stateless class. -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. --20cf307c9e1220d0b704ef9359f9 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
On T= hu, Jan 9, 2014 at 4:23 PM, David Krauss <potswa@gmail.com> w= rote:
On 1/10/14 8:11 AM, David = Krauss wrote:
On 1/9/14 11:18 AM, Richard Smith wrote:
The useful thing about introducing a new feature is that you get to specify=
how it works =3D) Naturally, we would specify that passing a generic templa= te
argument to another template preserves the kind of template argument.

But how can you make that work without redoing how parsers must classify ty= pe-dependent expressions? And what's the benefit, given that overloadin= g/partial specialization already solve the problem?

I should be more specific.

Given "?", you can peel off a fully-generic argument from a pack,= and pass it to another template. But the other template must be either ful= ly-generic, or overloaded/partially specialized. So you might as well peel = the pack in the target overloaded/partially specialized template. All "= ;?" buys you is the freedom to add a dispatcher between components whi= ch are actually necessary.

It allows more code reuse, by allowing han= dling of individual elements of such a pack to be factored out. That is a v= aluable property, even if it only helps those people who are writing templa= te metaprograms.
=A0
I don't see any applications for fully-generic arguments outside metapr= ocessing, e.g. of packs. There is no runtime code application parameterized= over all types or all values of any type. For value-like types, i.e. std::= integral_constant, it is idiomatic (and makes perfect sense) to deal with r= untime instances of a stateless class.

--
 
---
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-proposals+unsubscribe@isocpp.org.
To post to this group, send email to std-proposals@isocpp.org.
Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/<= /a>.
--20cf307c9e1220d0b704ef9359f9-- .