220 9888 <6F532E62-C10A-404A-8F0D-662B7EA3D202@gmail.com> article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Explicitly-defaulted enumeration operators Date: Tue, 18 Mar 2014 12:29:46 +0800 Lines: 104 Approved: news@gmane.org Message-ID: <6F532E62-C10A-404A-8F0D-662B7EA3D202@gmail.com> References: <3B09C97E-7ADE-49ED-8C31-B5B41CD3DDE7@gmail.com> <781009e3-cd3c-4cb8-b034-b51a7c97c750@isocpp.org> <10450602-fee9-48c4-9fa2-d000e434f5fb@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 7.2 \(1874\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_59B47583-253A-4CC5-808C-AFB17D9AAFE7" X-Trace: ger.gmane.org 1395116992 6765 80.91.229.3 (18 Mar 2014 04:29:52 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 18 Mar 2014 04:29:52 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRBRMXT6MQKGQEDYXYATI@isocpp.org Tue Mar 18 05:30:01 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ie0-f199.google.com ([209.85.223.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1WPlf5-0004hF-9K for gclcip-std-proposals@m.gmane.org; Tue, 18 Mar 2014 05:29:59 +0100 Original-Received: by mail-ie0-f199.google.com with SMTP id rl12sf24414717iec.6 for ; Mon, 17 Mar 2014 21:29:58 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:message-id:mime-version:subject:date :references:to:in-reply-to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=66PW3LaN3Klw+pTChOhfG0Oe2TcE9RUAQGEjwfykUe0=; b=fSArmxTRYiCe3WYZsHIPwfsUOteUV5hdgU+C0QCPDO+B8IkGOpt1kmrT8OWhPYe7Fh ELaw9t41icDmd4Xve9BCWJuuvAqVpXK6/fRkGU6r/AS6U0Anlx6EdOA0S0RUBmZKuvB5 skLFZtkFDnRkn/lgmF/R/0y5xfveoo9P9Of0n+6a5JdgyU314zldZnRSdocgN/NCv6E6 9+yt+kFwStH4Dwuy2FhO5U1CE3FOPu6L4a3jYjsFz9PVg3i2PYmP5fYL8OTCoUIZA+pj /mwl9TFes2hUTaaxtxUc7mxM7FQUT7AMHdE3hOwHhwmK0zxYCzF6jyouLvyZT44UF3Zy aOIA== X-Gm-Message-State: ALoCoQkOuU4pF8aMuolBNzgH19+JL/EwVPDQGzpUROLD3ne1iH0oTgsN4CvNWcAcpJTk74yCGAx6 X-Received: by 10.42.53.135 with SMTP id n7mr10130726icg.11.1395116998213; Mon, 17 Mar 2014 21:29:58 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.57.104 with SMTP id h8ls1321698igq.0.gmail; Mon, 17 Mar 2014 21:29:57 -0700 (PDT) X-Received: by 10.68.228.138 with SMTP id si10mr30199539pbc.13.1395116997220; Mon, 17 Mar 2014 21:29:57 -0700 (PDT) Original-Received: from mail-pb0-x22c.google.com (mail-pb0-x22c.google.com [2607:f8b0:400e:c01::22c]) by mx.google.com with ESMTPS id w4si828352paa.239.2014.03.17.21.29.57 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 17 Mar 2014 21:29:57 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c01::22c as permitted sender) client-ip=2607:f8b0:400e:c01::22c; Original-Received: by mail-pb0-f44.google.com with SMTP id rp16so6666149pbb.31 for ; Mon, 17 Mar 2014 21:29:57 -0700 (PDT) X-Received: by 10.68.159.228 with SMTP id xf4mr30274610pbb.74.1395116997094; Mon, 17 Mar 2014 21:29:57 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.49]) by mx.google.com with ESMTPSA id np9sm48252407pbc.31.2014.03.17.21.29.54 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Mon, 17 Mar 2014 21:29:56 -0700 (PDT) In-Reply-To: <10450602-fee9-48c4-9fa2-d000e434f5fb@isocpp.org> X-Mailer: Apple Mail (2.1874) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c01::22c as permitted sender) smtp.mail=potswa@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:9888 Archived-At: --Apple-Mail=_59B47583-253A-4CC5-808C-AFB17D9AAFE7 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=ISO-8859-1 On 2014-03-18, at 12:19 PM, Matheus Izvekov wrote: >=20 > On Tuesday, March 18, 2014 1:06:31 AM UTC-3, David Krauss wrote: >=20 > It proposes a feature that would supersede some uses of enumerations, but= even if it is adopted, the problem of correct usage of enumerations would = still remain. >=20 > A bitfield-like enumeration class wouldn't want to define addition and su= btraction, except maybe as bitwise operations OR and ANDNOT. Not every enum= eration with operators wants to be an opaque typedef. >=20 > Actually, the feature as proposed there would allow you to default and de= lete operator definitions, so you could have what you want, an int opaque a= lias which has operator+ deleted, and so you can't do addition. Oh, now I see. It's a bit of a radical approach. The problem is that for "custom scalar" types we sometimes want intrinsical= ly named values (enumerators) for things like bitsets, but other times we w= ant floating-point underlying type, which is incompatible with named values= or often any specific values at all. Perhaps now with opaque enum declarations, the use cases can be reconciled = by allowing floating-point enumerations with the caveat that no enumerators= are allowed. Or perhaps the lack of implicit operators (and comparability = to the underlying FP type) already provides sufficient safety and the langu= age is ready for floating-point enumerations. Anyway, my instinct is that building on the existing enumeration framework = would be simpler than starting with typedefs. I should contact Walter, than= ks again. --=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/. --Apple-Mail=_59B47583-253A-4CC5-808C-AFB17D9AAFE7 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1
On 2014&= ndash;03–18, at 12:19 PM, Matheus Izvekov <mizvekov@gmail.com> wrote:


On Tuesda= y, March 18, 2014 1:06:31 AM UTC-3, David Krauss wrote:

It pr= oposes a feature that would supersede some uses of enumerations, but even i= f it is adopted, the problem of correct usage of enumerations would still r= emain.

A bitfield-like enumeration class wouldn’t want = to define addition and subtraction, except maybe as bitwise operations OR a= nd ANDNOT. Not every enumeration with operators wants to be an opaque typed= ef.

Actually, the feature as proposed ther= e would allow you to default and delete operator definitions, so you could = have what you want, an int opaque alias which has operator+ deleted, and so= you can't do addition.

Oh,= now I see. It’s a bit of a radical approach.

The problem is that for “custom scalar” types we sometimes wa= nt intrinsically named values (enumerators) for things like bitsets, but ot= her times we want floating-point underlying type, which is incompatible wit= h named values or often any specific values at all.

Perhaps now with opaque enum declarations, the use cases can be reconcile= d by allowing floating-point enumerations with the caveat that no enumerato= rs are allowed. Or perhaps the lack of implicit operators (and comparabilit= y to the underlying FP type) already provides sufficient safety and the lan= guage is ready for floating-point enumerations.
Anyway,= my instinct is that building on the existing enumeration framework would b= e simpler than starting with typedefs. I should contact Walter, thanks agai= n.

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