220 30202 article Path: news.gmane.org!.POSTED!not-for-mail From: gmisocpp@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: enum_cast proposal Date: Tue, 3 Jan 2017 15:01:15 -0800 (PST) Lines: 187 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_5498_84607148.1483484476010" X-Trace: blaine.gmane.org 1483484484 18012 195.159.176.226 (3 Jan 2017 23:01:24 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Tue, 3 Jan 2017 23:01:24 +0000 (UTC) Cc: m.cencora@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCM3TRNUXUDBBPG2WDBQKGQE7HGPBEY@isocpp.org Wed Jan 04 00:01:20 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f200.google.com ([209.85.192.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cOY4v-0003Xo-I1 for gclcip-std-proposals@m.gmane.org; Wed, 04 Jan 2017 00:01:13 +0100 Original-Received: by mail-pf0-f200.google.com with SMTP id c4sf756368627pfb.7 for ; Tue, 03 Jan 2017 15:01:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references: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=r2Qn3PKO12wPK1nEICjCZjFxOO1npkvyPWpe6K5DbnI=; b=pJrDlxhJPilR/y3oQCdF9k2+nWWx/BX1+9BPfRT4rFUJCSxFUt+jFaplZcPifSV/pF 0SQGE3tO8/yDaI47tuA6b8GJDaz4UVzXPDWcbFzPjEjBNOxuhRv3ymUPUeel1QXnsiee kcss0Le8lERyu8W6Zts4rBeehrn9g8ngTFNyfRjwQdOmdQZcukjDDTsBvIS7kmFULlmh Akke4x4pIfiFsch516aMQxzUZf+YxOpXNYocaLJDnITpuQmBfkIRF2AH58lPGDtCnmpZ crbfOFG/pcTEDp9L/nVN4sD/pSLv841RAa/TWnX8jKUiEgW0hEVd7eXvW4XrD8yMQh+c hglg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:message-id:in-reply-to:references: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=r2Qn3PKO12wPK1nEICjCZjFxOO1npkvyPWpe6K5DbnI=; b=a+iP4IxFPYTOmNbrIqWDhqxZg3yEIjkTjlTGN6iBFP4s5HUUNNo5heDpyWn5UwToqL mVFssmovMHftb4xJw3d76CvT1YsHuKxC3uNZUTXQcvGi+D2PQKaP7cNON1kr83Sq2nq5 qJEDjQ6A9Xm1SP4PD4cDDqnxZ/lbfY3G3PsKXJUBeizSnkLrVFNl10a8hZousMmnVmpT +Ksef8Jencdl6yAiZG8QSbffIZ8ix+cAHA68htPwPb8wkBjhmTNzmkA/OGfZF45I/iZQ WUMDnK3NfLvawnJEPK51veEGIjEZO8+CePdLb+apPU5yffO/eAKwl0pWX/96id0MT1yK DXOw== 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:cc:message-id:in-reply-to :references: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=r2Qn3PKO12wPK1nEICjCZjFxOO1npkvyPWpe6K5DbnI=; b=ZrsCP+Mey5uJH/u7PfIOekh/v+MMviqAOd+O2WdrJqCP5Qt1vkLPUXwh2Fz0S3v0xZ TR2RCz/egyDPvm88gw+aVSElRE6djsQYtmIpy0pQtUxaASxYCx/yKUNojG7/Paxyuxsp SaL8eHqMyNNw2nhFFwQK3fVUVYS3DOIJSR3yMvE0hMgUFI5ykxC2EKo6MrP3UjyhL/JH jOi8XzSmNeOSU3m8A8L8o4nyFlqOrjRS4TjIyldA1uCd5m3Sei9C5CQe3nL7L9TMTfLC GxVXHbrxcv1wRRvTfF5WYCvrAzZZz44XcjAiyTON/IfIiNuvOpOv5kFhu7YyX+jFPx9T jk5A== X-Gm-Message-State: AIkVDXJEDhUWJ9NoXOvz13W3aorebKtGMdx42rlWbS40KpxquwolU4W2ArnxEVwZMwg85Q== X-Received: by 10.99.23.69 with SMTP id 5mr24562659pgx.76.1483484477387; Tue, 03 Jan 2017 15:01:17 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.6.227 with SMTP id 90ls27428495otx.34.gmail; Tue, 03 Jan 2017 15:01:16 -0800 (PST) X-Received: by 10.157.17.3 with SMTP id g3mr2992450ote.8.1483484476645; Tue, 03 Jan 2017 15:01:16 -0800 (PST) In-Reply-To: X-Original-Sender: gmisocpp@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:30202 Archived-At: ------=_Part_5498_84607148.1483484476010 Content-Type: multipart/alternative; boundary="----=_Part_5499_667225547.1483484476010" ------=_Part_5499_667225547.1483484476010 Content-Type: text/plain; charset=UTF-8 How about: enum class trafflic_light{ unknown, reg, yellow, green }; traffic_light = traffic_light::unknown; // My default. bool success = make_enum(light, x); // Does not set light on failure. X of any integral type if (!success) throw std::logic_error("Error: Expected a value compatible with a traffic_light enum."); if (light == traffic_light::green) cpp20_you_are_our_only_hope(); // make_enum - Standard special funciton. Make this available in C too. On Tuesday, January 3, 2017 at 10:56:05 PM UTC+13, m.ce...@gmail.com wrote: > 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/e6c43713-ad62-4a5e-8eda-23c59bb67dd9%40isocpp.org. ------=_Part_5499_667225547.1483484476010 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

How about:

enum= class trafflic_light{ unknown, reg, yellow, green };


traffic_light =3D traffic_light::unknown; // My default.
bool success = =3D make_enum(light, x); // Does not set light on failure. X of any integra= l type
if (!success)
=C2=A0throw std::logic_error("Error: Expect= ed a value=C2=A0compatible=C2=A0with a traffic_light enum.");
if (l= ight =3D=3D traffic_light::green)
=C2=A0cpp20_you_are_our_only_hope();

// make_enum - Standard special funciton. Make= this available in C too.


On Tuesday, January 3, 2017 at 10:56= :05 PM UTC+13, m.ce...@gmail.com wrote:
<= div dir=3D"ltr">Hi,

I propose to add a enum_cast functio= n that safely casts int value to a target enum type if int value represents= a valid enumerator.

template <typename Enum, typenameInt>=
optional<Enum> enum_cast(Int value);

requires: is_enum<Enum>, is_integr= al<Int>

enum color
{
=C2=A0 =C2=A0red =3D 1,
=C2=A0= =C2=A0green =3D 200,
=C2=A0 =C2=A0blue =3D 3
};=

static_assertenum_cast<color>(200u) =3D=3D colo= r::green);
static_assert(enum_cast<color>= (3) =3D=3D colo= r::blue);<= /span>
static_assert(enum_cast<color>(4) =3D=3D= nullopt);


This should work for both scoped= and unscoped enums.
For opaque enums this would only check if va= lue fits in underlying type.

Why do we want th= is:
=C2=A0- validation of input data (e.g. coming from user o= r deserialization).
=C2=A0- other?

I kno= w 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 imp= lemented with compiler support (i.e. via __builtin_* 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/e6c43713-ad62-4a5e-8eda-23c59bb67dd9= %40isocpp.org.
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