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Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: std::degenerate<> class template : primitive/enum types with a special "undefined" value Date: Wed, 04 Sep 2013 18:05:44 +0200 Lines: 157 Approved: news@gmane.org Message-ID: <52275A58.502@wanadoo.fr> References: <18ab4801-260a-4228-8a7b-a71248b624e2@isocpp.org> <77a1bdf8-1e0d-4294-b528-d08ba5403c98@isocpp.org> <023111c2-c983-407d-918f-39be42aa2949@isocpp.org> <88ef15f1-6942-476e-b26c-6873ef6e6f0b@isocpp.org> <01900060-3aac-4645-a4a8-93b4e8760e42@isocpp.org> <5e63fe81-ab33-4bbb-ab4c-305f8b90140a@isocpp.org> <51a05a5a-ad56-4ffa-81d8-759953a93766@isocpp.org> <787f2f45-1fbc-4ce5-90fc-d8f0d8c2b8f4@isocpp.org> <6da8e8d3-7c26-4841-bc3f-40dd0715e92b@isocpp.org> <5226D6A4.4040707@wanadoo.fr> <90eb2850-ff75-47b6-979d-ac7400146b0b@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------070808090102030307020204" X-Trace: ger.gmane.org 1378310751 4367 80.91.229.3 (4 Sep 2013 16:05:51 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 4 Sep 2013 16:05:51 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDH67CONY4PBBYFUTWIQKGQE3V5FJJI@isocpp.org Wed Sep 04 18:05:53 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lb0-f200.google.com ([209.85.217.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1VHFab-0002KQ-DN for gclcip-std-proposals@m.gmane.org; Wed, 04 Sep 2013 18:05:53 +0200 Original-Received: by mail-lb0-f200.google.com with SMTP id y6sf518523lbh.7 for ; Wed, 04 Sep 2013 09:05:53 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=message-id:date:from:user-agent:mime-version:to:subject:references :in-reply-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=rkVkJX5/uc9pSKl+PlZ9uNhtgEtIFtWmKcHdz7nVcq4=; b=IsS0qr4dvwkAB+fQ8PY61GqYZl70NYY+SCPh8DTDV77iFBEdNvPSwacbdr2itIcFl+ XAmuedDqfzSw5nUmfnCn6dltNYn32acS07kAB/Q8yMninryjW38Wkme2ByJY7OqfXy5h PgFhoqF2DG6ZSLwcJ94EZ1rA1fACwREP3DKIpCNYd5gVRnaKsi72sRiB+vkzR+8Qv+qr eOibzOZBn4/F3dipXsoiTVLjm7RhB6B3B9qPFCu+20DpA8qqbDMFiKszwiNzdYbfhsge t8MgmeUXHTkbonhVB81swHiDENlmUteiBgpmaTfZQPSm3XZOZ21C5rZy/8J9TvhDfTVj xMlA== X-Received: by 10.112.141.232 with SMTP id rr8mr662010lbb.11.1378310752853; Wed, 04 Sep 2013 09:05:52 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.2.39 with SMTP id 7ls20412lar.11.gmail; Wed, 04 Sep 2013 09:05:51 -0700 (PDT) X-Received: by 10.152.116.82 with SMTP id ju18mr674897lab.54.1378310751882; Wed, 04 Sep 2013 09:05:51 -0700 (PDT) Original-Received: from smtp.smtpout.orange.fr (smtp10.smtpout.orange.fr. [80.12.242.132]) by mx.google.com with ESMTP id 6si10917280lay.88.1969.12.31.16.00.00; Wed, 04 Sep 2013 09:05:51 -0700 (PDT) Received-SPF: neutral (google.com: 80.12.242.132 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.132; Original-Received: from pc3.home ([2.10.128.70]) by mwinf5d20 with ME id M45n1m0031XFuXW0345pJW; Wed, 04 Sep 2013 18:05:51 +0200 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 In-Reply-To: <90eb2850-ff75-47b6-979d-ac7400146b0b@isocpp.org> X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.132 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) smtp.mail=vicente.botet@wanadoo.fr 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:6152 Archived-At: This is a multi-part message in MIME format. --------------070808090102030307020204 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable Le 04/09/13 14:37, Nicol Bolas a =E9crit : > > > On Tuesday, September 3, 2013 11:43:48 PM UTC-7, Vicente J. Botet=20 > Escriba wrote: > > Le 04/09/13 06:48, the.ultim...@gmail.com a =E9crit : > > What do you think about defining the degenerate class empty > > template > struct degenerate > { > typedef T value_type; > typedef DegenerateValue degenerate_value_type; > }; > > and use it to make specialization of optional > > template > struct optional > > { > // include here the degenerated specialization > } > > In this way optional doesn't changes its interface (preserv only > one template parameter), and we are able to have > > optional > > and > > optional> > > > That seems way too much like a kludge. Sure, you can `template using=3D`= =20 > your way around it, but we shouldn't /have/ to do things like that=20 > just to make something useable. What is so wrong with just making=20 > `optional` as a variation? We do something similar for=20 > `unique_ptr`. > There is nothing wrong. Just this must be done quickly as once in C++14=20 it would be not so easy to change the std::optional interface. My=20 suggestion could be adopted just after c++14 is released. Vicente --=20 ---=20 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 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-proposa= ls/. --------------070808090102030307020204 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
Le 04/09/13 14:37, Nicol Bolas a =E9crit=A0:


On Tuesday, September 3, 2013 11:43:48 PM UTC-7, Vicente J. Botet Escriba wrote:
Le 04/09/13 06:48, the.ultim...@gmail.c= om a =E9crit=A0:

What do you think about defining the degenerate class empty

template <typename T, typename DegenerateValue>
struct degenerate
{
=A0 typedef T value_type;
=A0 typedef DegenerateValue degenerate_value_type;
};

and use it to make=A0 specialization of optional

template <typename T, typename DegenerateValue>
struct optional <degenerate<T,DegenerateValue>>= ;
{
=A0// include here the degenerated specialization
}

In this way optional doesn't changes its interface (preserv only one template parameter), and we are able to have

optional<T>

and

optional<degenerate<Player, integral_constant<Player, Player(-1)>>

That seems way too much like a kludge. Sure, you can `template using=3D` your way around it, but we shouldn't have to do things like that just to make something useable. What is so wrong with just making `optional<T, Tester>` as a variation? We do something similar for `unique_ptr`.

There is nothing wrong. Just this must be done quickly as once in C++14 it would be not so easy to change the std::optional interface. My suggestion could be adopted just after c++14 is released.

Vicente

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