220 2816 <511AA1A2.2080409@wanadoo.fr> article Path: news.gmane.org!not-for-mail From: "Vicente J. Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: minimal enum class improvements Date: Tue, 12 Feb 2013 21:10:10 +0100 Lines: 552 Approved: news@gmane.org Message-ID: <511AA1A2.2080409@wanadoo.fr> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------010601020506020504060100" X-Trace: ger.gmane.org 1360699819 26010 80.91.229.3 (12 Feb 2013 20:10:19 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 12 Feb 2013 20:10:19 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDH67CONY4PBBJGD5KEAKGQE5DVRI2I@isocpp.org Tue Feb 12 21:10:41 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-bk0-f70.google.com ([209.85.214.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1U5MBU-0000f5-9h for gclcip-std-proposals@m.gmane.org; Tue, 12 Feb 2013 21:10:32 +0100 Original-Received: by mail-bk0-f70.google.com with SMTP id jk7sf527205bkc.1 for ; Tue, 12 Feb 2013 12:10:13 -0800 (PST) X-Received: by 10.180.14.162 with SMTP id q2mr894570wic.5.1360699812751; Tue, 12 Feb 2013 12:10:12 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.76.167 with SMTP id l7ls1204318wiw.52.canary; Tue, 12 Feb 2013 12:10:12 -0800 (PST) X-Received: by 10.194.108.229 with SMTP id hn5mr33689598wjb.8.1360699812204; Tue, 12 Feb 2013 12:10:12 -0800 (PST) X-Received: by 10.194.108.229 with SMTP id hn5mr33689595wjb.8.1360699812179; Tue, 12 Feb 2013 12:10:12 -0800 (PST) Original-Received: from smtp.smtpout.orange.fr (smtp03.smtpout.orange.fr. [80.12.242.125]) by mx.google.com with ESMTP id ft6si5335675wib.55.2013.02.12.12.10.12; Tue, 12 Feb 2013 12:10:12 -0800 (PST) Received-SPF: neutral (google.com: 80.12.242.125 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.125; Original-Received: from iMac-de-Vicente-Botet-Escriba.local ([92.139.27.229]) by mwinf5d38 with ME id zYAA1k00K4wbJms03YABm6; Tue, 12 Feb 2013 21:10:11 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:17.0) Gecko/20130107 Thunderbird/17.0.2 In-Reply-To: X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.125 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:2816 Archived-At: This is a multi-part message in MIME format. --------------010601020506020504060100 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable Le 11/02/13 14:55, ricardofabianodeandrade@gmail.com a =E9crit : > Hi all, > > > > *Request for change:* > > Inclusion of the following features in the C++ language support for enum: > > * Obtain the number of enumerators of a given enum type. > * Obtain the value of an enumerator of a given enumerator's index > (or order, or position) and its enum type. > I would add to the minimal set of features this | * obtain |the position relative of an enumeration value in the=20 enum type. This requires of course that all the enumerations have a distinct value.=20 The compiler could not provide these meta-functions if the enum doesn't=20 satisfy this condition. In addition, the allowed values of an 'ordinal' enumeration type should=20 contain only the enumerations because otherwise the pos function could=20 not be defined. This is a breaking change or require adding a specific=20 syntax for 'ordinal' enumeration. Maybe using a new *ordinal* keyword=20 instead of enum could be an option |*ordinal*classAnEnum:int{a =3D-1,b =3D1000,c =3D0}; | > *Example *(please note no syntax is being suggested initially, just a=20 > [magic] placeholder): > | > enumclassAnEnum:int{a =3D-1,b =3D1000,c =3D0}; > std::size_t enumerators =3D[magic](); > AnEnumvalue =3D[magic](0); > | > * > * I find this syntax a little bit obscure. I would prefer specific=20 functions as size, val and pos. template constexpr std::size_t size() noexcept; template constexpr EC val(std::size_t) noexcept; template constexpr std::size_t pos(EC) noexcept; | enumclassAnEnum:int{a =3D-1,b =3D1000,c =3D0}; |||| constexpr ||||std::size_t enumerators =3Dsize();||| |||||||||| ||||| ||||||||||||| constexpr AnEnume2 =3Dval(1); | |||||||std::size_t n =3D 6;|||||||| ||||||||||AnEnume2 =3Dval(n); //runtime | || ||||||||| |||||constexpr ||||std::size_t|indx =3D||pos(||||||||AnEnum::a||||||||); | |||||||||| |std::size_t|indx =3Dpos(e2); |||//runtime||| | * * ||| | The pos runtime function could use the same algorithm the compiler uses=20 for a switch. The constexpr pos function could be replaced directly at compile time. first, last, succ and pred functions can be defined easily as follows template constexpr EC first() noexcept { return val(0); } template constexpr EC last() noexcept { return val(size()-1); } template constexpr EC succ(EC e) { //assert(pos(e)!=3D(size()-1)); return val(pos(e)+1); } template constexpr EC pred(EC e) { //assert(pos(e)!=3D0); return val(pos(e)-1); } Best, 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/?hl=3Den. --------------010601020506020504060100 Content-Type: text/html; charset=ISO-8859-1
Le 11/02/13 14:55, ricardofabianodeandrade@gmail.com a écrit :
Hi all,



Request for change:

Inclusion of the following features in the C++ language support for enum:
  • Obtain the number of enumerators of a given enum type.
  • Obtain the value of an enumerator of a given enumerator's index (or order, or position) and its enum type.

I would add to the minimal set of features this
      * obtain the position relative of an enumeration value in the enum type.

This requires of course that all the enumerations have a distinct value. The compiler could not provide these meta-functions if the enum doesn't satisfy this condition.
In addition, the allowed values of an 'ordinal' enumeration type should contain only the enumerations because otherwise the pos function could not be defined. This is a breaking change or require adding a specific syntax for 'ordinal' enumeration. Maybe using a new ordinal keyword instead of enum could be an option

ordinal class AnEnum : int { a = -1, b = 1000, c = 0 };


Example (please note no syntax is being suggested initially, just a [magic] placeholder):
enum class AnEnum : int { a = -1, b = 1000, c = 0 };
std::size_t enumerators = [magic]<AnEnum>();
AnEnum value = [magic]<AnEnum>(0);

I find this syntax a little bit obscure. I would prefer specific functions as size, val and pos.

    template <typename EC>
    constexpr std::size_t size() noexcept;
    template <typename EC>
    constexpr EC val(std::size_t) noexcept;
    template <typename EC>
    constexpr std::size_t pos(EC) noexcept;


enum class AnEnum : int { a = -1, b = 1000, c = 0 };

constexpr std::size_t enumerators = size<AnEnum>();

constexpr AnEnum e2 = val<AnEnum>(1);
 std::size_t n = 6;
AnEnum e2 = val<AnEnum>(n); //runtime

constexpr std::size_t indx = pos(AnEnum::a);
std::size_t indx = pos(e2); //runtime


The pos runtime function could use the same algorithm the compiler uses for a switch.
The constexpr pos function could be replaced directly at compile time.

first, last, succ and pred functions can be defined easily as follows

    template <typename EC>
    constexpr EC first() noexcept
    {
        return val<EC>(0);
    }
    template <typename EC>
    constexpr EC last() noexcept
    {
        return val<EC>(size<EC>()-1);
    }

    template <typename EC>
    constexpr EC succ(EC e)
    {
      //assert(pos(e)!=(size<EC>()-1));
      return val<EC>(pos(e)+1);
    }
    template <typename EC>
    constexpr EC pred(EC e)
    {
      //assert(pos(e)!=0);
      return val<EC>(pos(e)-1);
    }

Best,
Vicente

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