220 30211 <621e1d86-492b-4ecc-96ba-4e0b74dfcb4e@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: enum_cast proposal Date: Tue, 3 Jan 2017 19:58:52 -0800 (PST) Lines: 97 Approved: news@gmane.org Message-ID: <621e1d86-492b-4ecc-96ba-4e0b74dfcb4e@isocpp.org> References: <1d5db671-8ee9-49dc-937d-10a20f48fe73@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1189_1966822393.1483502332996" X-Trace: blaine.gmane.org 1483502336 5024 195.159.176.226 (4 Jan 2017 03:58:56 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 4 Jan 2017 03:58:56 +0000 (UTC) Cc: m.cencora@gmail.com, gmisocpp@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBB7PFWHBQKGQEA4YGI6Y@isocpp.org Wed Jan 04 04:58:52 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pg0-f72.google.com ([74.125.83.72]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cOciw-0000O0-4Y for gclcip-std-proposals@m.gmane.org; Wed, 04 Jan 2017 04:58:51 +0100 Original-Received: by mail-pg0-f72.google.com with SMTP id a190sf1281692283pgc.0 for ; Tue, 03 Jan 2017 19:58:54 -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=cQzWX3zbzGRfE+AQfXy9eSrIHv9xGUc23mY4JLUnGgQ=; b=0dOaWselCX0eFSOTKtkxiwx16cSVVG2ndFSCXWqzqtJDmkLzqFAla5MBixppNPDGhw 7mRoMvG2edEAKtLtK7h4JP5OTptAJF7HX8a5rqMgA+KO8fe/lWFwxkYoARf9JDiOAIlN HrV9HGjZbfxGNoq3wiIzaHbpciuYCMrAUL+jeRJ3V614+kIlCLCOV+DL2RLNzJm+MiS/ t5EnWU2U6sPr3hDo6x6l1DvnCpt3JliHA3gLzAyPN5VMdz9zlhOkwij+cGbRt+Ak9EHt n025vrwAIMa1Lge0NUMIz5yjkLJIn7g4s2dnpfoZ0hqmLItBi7S5yETaL1SXRnTKSjN2 w/ow== 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=cQzWX3zbzGRfE+AQfXy9eSrIHv9xGUc23mY4JLUnGgQ=; b=Wv7Mm+xHL9xFTO7uYNFKZgcDaxcwuw2kK0ZsGCZ/pymhhp20F+c0ZYIXt/236omQ+8 gPgIwTkcPkJQoaoF2s7nKm1+qladXsWlYIVDEAxQG0vxrKrTce8HUIaEcChQb9rY4PJq EXfepqMRvw3DyTXuKHzivfay1ocZ26v3P9/YEN0klWCkga7ihjHvfuG6s0NT+iT8inBc 6YaW34Dq5xxfDKUstNVpUJEyAYBshErczwbbY/+ttRbwUdyCRRvqrMmvGtizSgB5rDay ACXiuWZxqYsqFkpXHxnJxFcKKMEEHeGPIWjK3MLs0lEcgyM2cyuLMYTxQVdpQZ8K3ajv fWLw== 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=cQzWX3zbzGRfE+AQfXy9eSrIHv9xGUc23mY4JLUnGgQ=; b=pUH/8BXWsOz5PSY2GW8a03pqURbUEa0SVMSTMSgqPGtEdtB5bgvy1zNA45S4Oiz7GG 1EwXs/eSPNiFVfnJ+YBLHtcE9XT1xgLHlgrTLZjt782cgdXAYIqx5B89UHz7k6vNXXPY YxhBuyptbc/7bVGr2fhbvvg3ads9C31Yzz5uSjA3nJaq70AmfhkP+9DCtalNejwww8ax +rd5FchQsOAm2hE8Fci3f8UmPHtOWMypx14IfEljnRAdllHj153po23pPb6zYsAR9xDJ HFDa8qXD64r/aSX31+XMmNQGmpeV+05z8k9jWsj5aMIsSqcjDl54I3+EeiTYXd3mjr81 WAZA== X-Gm-Message-State: AIkVDXI3Y3EoGuEyH8KlTYUiww9oC+2pjGQmOZb4EGXzXNElnYOV17aNde9VJhPGRigpRA== X-Received: by 10.99.173.12 with SMTP id g12mr40475440pgf.39.1483502334081; Tue, 03 Jan 2017 19:58:54 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.33.198 with SMTP id s64ls31277124otb.22.gmail; Tue, 03 Jan 2017 19:58:53 -0800 (PST) X-Received: by 10.157.43.243 with SMTP id u106mr2294277ota.2.1483502333439; Tue, 03 Jan 2017 19:58:53 -0800 (PST) In-Reply-To: <1d5db671-8ee9-49dc-937d-10a20f48fe73@isocpp.org> X-Original-Sender: jmckesson@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:30211 Archived-At: ------=_Part_1189_1966822393.1483502332996 Content-Type: multipart/alternative; boundary="----=_Part_1190_1757428033.1483502332996" ------=_Part_1190_1757428033.1483502332996 Content-Type: text/plain; charset=UTF-8 On Tuesday, January 3, 2017 at 6:01:16 PM UTC-5, gmis...@gmail.com wrote: > > > 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 > No, that requires the existence of `light`. C++ has too many APIs that needlessly require live objects already; we don't need another one. On Tuesday, January 3, 2017 at 6:48:25 PM UTC-5, gmis...@gmail.com wrote: > > > Just considering my earlier make_enum comment further, The ultimate > minimum for C++ is surely this?: > > traffic_light light{}; // whatever default. > bool guaranteed_success = std::can_cast_enum(x); > if (guaranteed_success) > light = reinterpret_cast(x); > // else error condition. > > It separates the validity check from the conversion > That's actually a pretty good idea. Of course, there should be "higher-level" functionality like a direct `enum_cast` that throws and so forth, as discussed. But this way, people have the lowest-level tools to build their own functionality on top of the basic question. -- 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/621e1d86-492b-4ecc-96ba-4e0b74dfcb4e%40isocpp.org. ------=_Part_1190_1757428033.1483502332996 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Tuesday, January 3, 2017 at 6:01:16 PM UTC-5, gmis...@g= mail.com wrote:

How about:

enum class trafflic= _light{ unknown, reg, yellow, green };


traffic_light= =3D traffic_light::unknown; // My default.
bool success =3D make_enum(l= ight, x); // Does not set light on failure. X of any integral type

No, that requires the existence of `light`. C++ has too many APIs that=20 needlessly require live objects already; we don't need another one.
=
On Tuesday, January 3, 2017 at 6:48:25 PM UTC-5, gmis...@gmail.com wrot= e:

Just considering my earlier make_enum comment further, The ultimat= e minimum for C++ is surely this?:

traffic_light l= ight{}; // whatever default.
bool guaranteed_success =3D std::can_cast_e= num<traffic_light>(x);
if (guaranteed_success)
=C2= =A0light =3D reinterpret_cast<traffic_light>(x);
// el= se error condition.

It separates the validity chec= k from the conversion

That's actually = a pretty good idea. Of course, there should be "higher-level" fun= ctionality like a direct `enum_cast` that throws and so forth, as discussed= .. But this way, people have the lowest-level tools to build their own funct= ionality on top of the basic question.

--
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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/621e1d86-492b-4ecc-96ba-4e0b74dfcb4e= %40isocpp.org.
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