220 40117 <67f2bf5e-14cf-487f-8d87-9171f49f2ffe@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Chris Hallock Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: enumerator duplicated value attribute Date: Fri, 7 Sep 2018 13:13:34 -0700 (PDT) Lines: 104 Approved: news@gmane.org Message-ID: <67f2bf5e-14cf-487f-8d87-9171f49f2ffe@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_444_2067409423.1536351214745" X-Trace: blaine.gmane.org 1536351091 9094 195.159.176.226 (7 Sep 2018 20:11:31 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 7 Sep 2018 20:11:31 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCHINCHEQEFBB35XZPOAKGQEK57AH5I@isocpp.org Fri Sep 07 22:11:27 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw1-f70.google.com ([209.85.161.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fyN6E-0002DE-Lg for gclcip-std-proposals@m.gmane.org; Fri, 07 Sep 2018 22:11:26 +0200 Original-Received: by mail-yw1-f70.google.com with SMTP id q141-v6sf9485369ywg.5 for ; Fri, 07 Sep 2018 13:13:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=jT2o34xFFom882aiivs2FE6MWYcw4QD6236aJnGe+l0=; b=SJwamN6j9FegLoM7THWr/1BVMzJXNL7NlPp8WkZRGGL/70O78bZI607rOZNMRS3+tL 2lH6GRDSoSdAzLPV984/9tHFRQdaa5BQtcfuazle6EkXFxqqwtZEn7GawmMbenLqefKR UoqBloBP/Ee30mVTG7cp1LwPWRUKSTMK2v/K30AnMDjHQJaLwOKMXgfZnNM0l6AxMw10 Emu5mRsdFGLPFnCr4QZFVNi6dxtoqb3ZDwvAlKtD+DhXcoHcgIaAqJ8iE5RA0uzKPdnp RmSSGb07P6+xJCsydaaxU1BZsceyA+vv4Nz3eV8fsMdnPAHvwyGINFAstIcvQJAIlJnt Ibpw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe; bh=jT2o34xFFom882aiivs2FE6MWYcw4QD6236aJnGe+l0=; b=kfYxfwjFokRPBgZ2MELeNvgHEPSKICRIq0ZeGBk/AjUFN5dFMc2JpomjiTB7nyy9eL zDsjBERLGQx7qxcEs0VRILuS9lKSs+dCFymNCwHBKcW5ChmVAvFS6KXp1zEY8xK4aNNC pbbrKZP/iu5MpJ96eEUxg9AVAUAq0dOyHJBs3gFZtqcTfI8n7Dj/OKqy4Z0cSkFXSSMt P40WW/HrLWOgWiBgsVcxAwXZAR/ieP5WakYk+L+WNwFIJDHVBdgtyteWxIXNqP6jewQj Dx/TJRtsmQiPtNBsli4Wdbsb+iYLuut/IxM4x9iuNuGoc0yydMwPriLXpXip/OIEjZAV /sHg== 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: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=jT2o34xFFom882aiivs2FE6MWYcw4QD6236aJnGe+l0=; b=ru0g6WO9KrcXeCAHgnZqNStMyR2WAG5UIZVj8q0w8Sahp5ehQ/tkJ1eJnS0QCLXr31 f0Pz3yFSFvvV1hkPB/J+b67lXUtrwdoH4z9WB0p3HxfyTqxB3lgPje4qUWWqIpcfJoKA EKqHATbiGKoQcSApDD+PPwhbt+83aYRXgM2vdGLAfkPx5sJw1CCYK4nhv6/JMn9VADmW M7Xze8b/TQbKDrbrNuwMyQluxGvuJ3GOlN2LVVwKJtRORcJyvr6NSovC59rcsGKjQp12 ++F4rYBfKTaYry8uxunalywAy/qnrXS1ISDKzVky+3imvF6nwgHhalCnYvtMticyxJ89 D95A== X-Gm-Message-State: APzg51CbZf0MTuJ5icDVNTrhipvRiI+X5ZvqGJ3Li4FmZQmy+bP35Dxd Kd0IoZx+Ie4yCb49QMcFskUNdQ== X-Google-Smtp-Source: ANB0VdYoigPLykhAT8CyC1Z8wJewv/CergJMyhemg98/5sFM3nLXvtPZJnoOsSIKn0wj+zVW5eEhGA== X-Received: by 2002:a81:3b07:: with SMTP id i7-v6mr2512869ywa.228.1536351216692; Fri, 07 Sep 2018 13:13:36 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a0d:ec93:: with SMTP id v141-v6ls842897ywe.42.gmail; Fri, 07 Sep 2018 13:13:35 -0700 (PDT) X-Received: by 2002:a81:6e04:: with SMTP id j4-v6mr96404ywc.6.1536351215315; Fri, 07 Sep 2018 13:13:35 -0700 (PDT) In-Reply-To: X-Original-Sender: christopherhallock@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:40117 Archived-At: ------=_Part_444_2067409423.1536351214745 Content-Type: multipart/alternative; boundary="----=_Part_445_1561369125.1536351214745" ------=_Part_445_1561369125.1536351214745 Content-Type: text/plain; charset="UTF-8" On Friday, September 7, 2018 at 2:55:57 PM UTC-4, Daniel Gutson wrote: > > Hi, > > sometimes is important to prevent duplication of enumerators in the > enumerations. That's why some compilers such as clang has the > -Wduplicate-enum. > However there are cases such as ranges within enums, where enumerators > define a category and then are followed by the first element of the > category, with the same value. > > enum Ranges > { > CategoryX = 100, > X1 = CategoryX, > X2, > X3 > CategoryY = 200 > // ... > }; > > In order to allow such cases coexist with the useful diagnostic, I propose > adding an enumerator attribute, such as [[allow_duplicate]] > > enum Ranges > { > CategoryX = 100 [[allow_duplicate]], > X1 = CategoryX, > X2, > X3 > CategoryY = 200 [[allow_duplicate]] > // ... > }; > > This way, we can have the diagnostic and also explicit the intention that > in those cases it is OK to have a repeated value. > That warning triggers only on *implicit* duplicates, so you're all good. -- 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/67f2bf5e-14cf-487f-8d87-9171f49f2ffe%40isocpp.org. ------=_Part_445_1561369125.1536351214745 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Friday, September 7, 2018 at 2:55:57 PM UTC-4, = Daniel Gutson wrote:
Hi,

=C2=A0 =C2=A0sometimes is important to prev= ent duplication of enumerators in the enumerations. That's why some com= pilers such as clang has the -Wduplicate-enum.
However there are = cases such as ranges within enums, where enumerators define a category and = then are followed by the first element of the category, with the same value= ..

enum Ranges
{
=C2=A0 =C2=A0 = CategoryX =3D 100,
=C2=A0 =C2=A0 =C2=A0 =C2=A0X1 =3D CategoryX,
=C2=A0 =C2=A0 =C2=A0 =C2=A0X2,
=C2=A0 =C2=A0 =C2=A0 =C2= =A0X3
=C2=A0 =C2=A0 =C2=A0CategoryY =3D 200
=C2=A0 =C2= =A0 =C2=A0 =C2=A0// ...
};

In order to a= llow such cases coexist with the useful diagnostic, I propose adding an enu= merator attribute, such as [[allow_duplicate]]

enum Ranges
{
=C2=A0 =C2=A0 CategoryX =3D 100 [[allow= _duplicate]],
=C2=A0 =C2=A0 =C2=A0 =C2=A0X1 =3D CategoryX,
<= div>=C2=A0 =C2=A0 =C2=A0 =C2=A0X2,
=C2=A0 =C2=A0 =C2=A0 =C2=A0X3<= /div>
=C2=A0 =C2=A0 =C2=A0CategoryY =3D 200 [[allow_duplicate]]
=C2=A0 =C2=A0 =C2=A0 =C2=A0// ...
};

= This way, we can have the diagnostic and also explicit the intention that i= n those cases it is OK to have a repeated value.

That warning triggers only on implicit duplicates, so y= ou're all good.

--
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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/67f2bf5e-14cf-487f-8d87-9171f49f2ffe= %40isocpp.org.
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