220 30163 article Path: news.gmane.org!.POSTED!not-for-mail From: m.cencora@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: enum_cast proposal Date: Tue, 3 Jan 2017 01:56:05 -0800 (PST) Lines: 179 Approved: news@gmane.org Message-ID: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_2059_164701516.1483437365479" X-Trace: blaine.gmane.org 1483437369 19587 195.159.176.226 (3 Jan 2017 09:56:09 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 3 Jan 2017 09:56:09 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBD7YFUMJRYMBBNPKVXBQKGQEZ6RV4HY@isocpp.org Tue Jan 03 10:56:05 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yb0-f199.google.com ([209.85.213.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cOLp4-0004Zg-IF for gclcip-std-proposals@m.gmane.org; Tue, 03 Jan 2017 10:56:02 +0100 Original-Received: by mail-yb0-f199.google.com with SMTP id n141sf237243589ybf.0 for ; Tue, 03 Jan 2017 01:56:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=WrsZGnL8rl4QRG/1ZMF9z0ZNopndY1CWpGW+ENhZVtU=; b=tF8LAKfTVXsXZ3ensEez3JP6dqcDspUXDvhpn4sJN678JDfkMOlXx+mw1agSWxDPRV lxjnJCLCsHdLkTDo1QzUOaPtFkhYfU8LEDm27RuE3EDMg/SIXbkMSTMpuJwkeNX9/ahM OZoEve+07b+DrfbDyeG1Ihy+VD9VOFDf9/TOW1kwK+bjnBp1ZfDhUVriffZ20uLXZzYG ALPlx3GPZBkwhFXGXkmAJMPY5QRABwVyJR+oGkp93GDgk4Mdtq952gLi2dE9ET+haGHO WmKfcMmcXYF58d8JhGjPfrgIkHgfk5BkCFYZlCJFbZU/z9fEjrzok9xTOEEdMdiKh6eC CAlA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:x-spam-checked-in-group :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=WrsZGnL8rl4QRG/1ZMF9z0ZNopndY1CWpGW+ENhZVtU=; b=YYISvKKdQxABJJWnQP40DmvxZY+xmz4G3zNmLbKCh8JgEufq55k8eXByqWzd1T7MEu iIzMfIbrjqOORD3YHbVwUGc5gvZTCF2PDiCMJN+kko5Fn/ITvX0ebv1sERX9eWHX/W5Q 32yWbAYuRLdrHGxKj5FRm/JY9aX0uQQygIW1zI+D8RY/LIkQAeNoqmENHVrd4qu0J9EW BOO3+qcFR1TvzLz7uZ5nVTA9taHUyDqM8lA3lwnbdMQ/PUUo+zFyDAdgQH0z+YBBaEFA Os3LzY/pqDW10Ni68XsuxQSRrvpX3ChDlw3GS9aPmd80a3XdlmpAeeoerklr7oDDHa86 98cQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=WrsZGnL8rl4QRG/1ZMF9z0ZNopndY1CWpGW+ENhZVtU=; b=dEVbzmCGuyfFSkVZNW2HDtt1duz7nv6DDnWnzl5E0YwoBTj1IAmp3SXVvskAVazXiR QnlpToGtxF815ZREPfn9VCtInFvd/uuLbO4EhT0ykrglauB+i9FTtoJ+GCq93lE/BcOc b5PceX6GjQLjJQ0AlkTE/DgYEKM5CVAQtN4MKUw1NIVULDJfYRMymLIinmp0FmFos7oU rLst7D26VuVQq9raNtxW2s57xlABJEczFmn3MYmDvZVE/N790bKDJqldSvgaMnHWkD3T hbAtoYmoq7bIfiruqXmrZFawKTTZsDGkiee/3HsmTRInAQg9WtB2W1axonFnB33y7rrS enew== X-Gm-Message-State: AIkVDXIrB+8T/hId2Q+CIb0Vrt+EgcPJFtazyEZPcT2I+f0FRKQ7XTD2OgUx8lYCGp/o+w== X-Received: by 10.129.166.216 with SMTP id d207mr19537737ywh.120.1483437366415; Tue, 03 Jan 2017 01:56:06 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.15.106 with SMTP id 97ls41610363ott.11.gmail; Tue, 03 Jan 2017 01:56:05 -0800 (PST) X-Received: by 10.157.49.66 with SMTP id v2mr2715240otd.19.1483437365827; Tue, 03 Jan 2017 01:56:05 -0800 (PST) X-Original-Sender: m.cencora@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:30163 Archived-At: ------=_Part_2059_164701516.1483437365479 Content-Type: multipart/alternative; boundary="----=_Part_2060_263266050.1483437365480" ------=_Part_2060_263266050.1483437365480 Content-Type: text/plain; charset=UTF-8 Hi, I propose to add a enum_cast function that safely casts int value to a target enum type if int value represents a valid enumerator. template optional enum_cast(Int value); requires: is_enum, is_integral enum color { red = 1, green = 200, blue = 3 }; static_assert(enum_cast(200u) == color::green); static_assert(enum_cast(3) == color::blue); static_assert(enum_cast(4) == nullopt); This should work for both scoped and unscoped enums. For opaque enums this would only check if value fits in underlying type. Why do we want this: - validation of input data (e.g. coming from user or deserialization). - other? I know this could be purely library extension if based on reflection, but since we don't know when we will get reflection, and implementation based on reflection may not be optimal, I think it should be implemented with compiler support (i.e. via __builtin_* intrinsic). Regards, Maciej -- 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/efdf2357-00a6-408a-8772-12f99135a880%40isocpp.org. ------=_Part_2060_263266050.1483437365480 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Hi,

I propose to add a enum_cast functi= on that safely casts int value to a target enum type if int value represent= s a valid enumerator.

templ= ate <typename Enum, typename Int= >
op= tional<= Enum> enum_cast(Int value);

requires: is_enum<Enum>, is_integral<Int>

enum color
{
=C2=A0 =C2=A0red =3D 1= ,
=C2=A0 =C2=A0gr= een =3D 200,
=C2=A0 =C2=A0blue =3D 3
};

static_assert(enum_cast<color>(200u) =3D=3D = color::green);
s= tatic_assert(enum_ca= st<colo= r>(3) =3D=3D color::blue);
st= atic_assert(enum_cas= t<color= >(4) =3D=3D nullopt);


Th= is should work for both scoped and unscoped enums.
For opaque enu= ms this would only check if value fits in underlying type.
Why do we want this:
=C2=A0- validation of input= data (e.g. coming from user or deserialization).
=C2=A0- other?<= /div>

I know this could be purely library extension if b= ased on reflection, but since we don't know when we will get reflection= ,
and implementation based on reflection may not be optimal,
I think it should be implemented with compiler support (i.e. via __bu= iltin_* intrinsic).

Regards,
Maciej

--
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/efdf2357-00a6-408a-8772-12f99135a880= %40isocpp.org.
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