220 29259 article Path: news.gmane.org!.POSTED!not-for-mail From: Peter Koch Larsen Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: explicit conversion from enum class to its underlying type Date: Sun, 30 Oct 2016 15:33:13 +0100 Lines: 81 Approved: news@gmane.org Message-ID: References: <4afed494-4fc5-4b06-b3e7-255aa293068e@isocpp.org> <1c81b80e-33b8-4de3-9bf7-94656e8b98f5@isocpp.org> <74d02121-9633-b6d1-1187-2a9ab660089d@wanadoo.fr> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1477838024 21285 195.159.176.226 (30 Oct 2016 14:33:44 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 30 Oct 2016 14:33:44 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDRIBXXKZQERBK4J3DAAKGQEKGWBDVA@isocpp.org Sun Oct 30 15:33:40 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f71.google.com ([209.85.218.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1c0rAf-0002EV-7s for gclcip-std-proposals@m.gmane.org; Sun, 30 Oct 2016 15:33:13 +0100 Original-Received: by mail-oi0-f71.google.com with SMTP id j198sf2006764oih.5 for ; Sun, 30 Oct 2016 07:33:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :content-transfer-encoding:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=NJEuzse+8zlX/DFbleAfrkVlYiY+y3rPMiMeW9pk5Jw=; b=i4+2hKu5YDti6ftedzbPJlLhjdGpRcgX0ccvEQwj4KOUAQJ4PKgBE0fJ1tg9pVsBdX XynGV9aXVp4+0q9TYltTFpCSeV28/9W4yFPtgsOziBAHbKfI4ZKsB1tQ8p2b5BH3ruTi alXRFDaO6wkuBiZnDXoYB+TX/thdccqa3VpZdqnfsnAyG7Zgxp2IasFfe7bNbAUQ7seK 5Gv7GlpHfh7WXg/SmjdTvAcBhi5pG+WJoPUhAlgp9g13HRrJQXpPigb3MscMIQpH/UxU YK12IAjVT9YNKvcW+IEd606TH1M37XmBVgvUMc4CSMHoRS4EGaooGz33gAQ76Po3Y/Jt HpvA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:content-transfer-encoding:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=NJEuzse+8zlX/DFbleAfrkVlYiY+y3rPMiMeW9pk5Jw=; b=dH8APiMnwcQP4NbViTWNrUSn/WXFFSE1qvWHPoajN3TFFuT4qmPhj7IT9X4yl2fquF IeJypPEWTcnlegPX/uZ7WN39e4Rer7fyINKvpOiYrdfcDSB2JQ9vqGdg8u2gZxTGEiHQ UMfPjdKuwPYlsnIhOlnAO1t2j8Ve1V65Xakk9R2sD3iCtAWlekS87ZfWLq/eYOjXMlLx 2q5AapGJzEcWcZ7Hx0zUXv21o1HLM3ILJ6yoftnU6PrrR7stmcvkPDS6Ht0be8snQy51 QyslSMS36gxs+x6aQxH5pes0IxwW2IWGMeciIW/ljZuzlMNuWeAou1kbPi5ENRqBvao1 UkC X-Gm-Message-State: ABUngvffnkBoFv9sMnZZYoUxr8KKsQHA2/TKTg57kWNEMBcOOHyQAaqWtaZGRL+E6bsg8g== X-Received: by 10.157.29.131 with SMTP id y3mr8575371otd.133.1477837995509; Sun, 30 Oct 2016 07:33:15 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.40.182 with SMTP id s51ls10833113ota.14.gmail; Sun, 30 Oct 2016 07:33:14 -0700 (PDT) X-Received: by 10.176.1.17 with SMTP id 17mr17396572uak.143.1477837994834; Sun, 30 Oct 2016 07:33:14 -0700 (PDT) Original-Received: from mail-vk0-x22c.google.com (mail-vk0-x22c.google.com. [2607:f8b0:400c:c05::22c]) by mx.google.com with ESMTPS id k3si9887346vkb.112.2016.10.30.07.33.14 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 30 Oct 2016 07:33:14 -0700 (PDT) Received-SPF: pass (google.com: domain of peter.koch.larsen@gmail.com designates 2607:f8b0:400c:c05::22c as permitted sender) client-ip=2607:f8b0:400c:c05::22c; Original-Received: by mail-vk0-x22c.google.com with SMTP id y123so88546498vka.3 for ; Sun, 30 Oct 2016 07:33:14 -0700 (PDT) X-Received: by 10.31.156.205 with SMTP id f196mr17824058vke.45.1477837994437; Sun, 30 Oct 2016 07:33:14 -0700 (PDT) Original-Received: by 10.103.70.156 with HTTP; Sun, 30 Oct 2016 07:33:13 -0700 (PDT) In-Reply-To: <74d02121-9633-b6d1-1187-2a9ab660089d@wanadoo.fr> X-Original-Sender: peter.koch.larsen@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of peter.koch.larsen@gmail.com designates 2607:f8b0:400c:c05::22c as permitted sender) smtp.mailfrom=peter.koch.larsen@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:29259 Archived-At: I believe bool(e) in that context was a C-style cast. A small helper function would in my opinion be the best way out for this purpose. /Peter On Sun, Oct 30, 2016 at 2:53 PM, Vicente J. Botet Escriba wrote: > Le 30/10/2016 =C3=A0 13:20, Nicol Bolas a =C3=A9crit : > > > > On Sunday, October 30, 2016 at 3:50:18 AM UTC-4, Vicente J. Botet Escriba > wrote: >> >> Le 29/10/2016 =C3=A0 23:51, Andrzej Krzemie=C5=84ski a =C3=A9crit : >> >> Hi All, >> >> One of the nice safety features of enum classes is that they cannot be >> implicitly converted to their underlying type. However, do you think we >> would lose this safety feature if we allowed an explicit conversion to t= he >> underlying type? >> >> I do not know of any practical use of explicit conversion operators exce= pt >> for the contextual conversion to bool. And it is only this conversion th= at I >> am interested in. >> >> >> This works already in a non-contextual conversion, isn't it? >> >> bool(e) > > > No, it doesn't. The only way to convert a strongly typed enum to its > underlying type is with a `static_cast`. > > > It works for clang and gcc > > http://melpon.org/wandbox/permlink/TnVrIdj3wz76l7b4 > > enum class SkipUnused : bool { No, Yes }; > > SkipUnused e{}; > bool b1 {bool(e)}; (void)b1; > bool b2 =3Dbool(e); (void)b2; > b1 =3D bool(e); > if (bool(e)) > std::cout << "Yes\n"; > else > std::cout << "No\n"; > > Maybe there is a bug in both compilers ;-) > > Vicente > > -- > 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/74d02121-963= 3-b6d1-1187-2a9ab660089d%40wanadoo.fr. --=20 You received this message because you are subscribed to the Google Groups "= ISO C++ Standard - Future Proposals" group. 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