220 29254 <1c81b80e-33b8-4de3-9bf7-94656e8b98f5@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: explicit conversion from enum class to its underlying type Date: Sun, 30 Oct 2016 05:20:39 -0700 (PDT) Lines: 104 Approved: news@gmane.org Message-ID: <1c81b80e-33b8-4de3-9bf7-94656e8b98f5@isocpp.org> References: <4afed494-4fc5-4b06-b3e7-255aa293068e@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1323_584620306.1477830040015" X-Trace: blaine.gmane.org 1477830057 18138 195.159.176.226 (30 Oct 2016 12:20:57 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 30 Oct 2016 12:20:57 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBGGL27AAKGQESIFKGXQ@isocpp.org Sun Oct 30 13:20:53 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f200.google.com ([209.85.217.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1c0p6M-0002HZ-QW for gclcip-std-proposals@m.gmane.org; Sun, 30 Oct 2016 13:20:38 +0100 Original-Received: by mail-ua0-f200.google.com with SMTP id 23sf29053644uat.4 for ; Sun, 30 Oct 2016 05:20:41 -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 :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=m7t+sgMz9TV44H52fLnNJuBcvjkbBNOfqqOgFxwKviY=; b=fNXlYkl1SJpibP5YquNwdSXKZyEa+drKk2XdpufZv2JonyOcvw5nBcQO1ZafKmUQRd q2VjEeDG0xqJwGLuy4y/alSY8iHBdXXoaVRYepMR6koBdR/Cw350BPaajj3NaRYS96vT GvQi5ovjLhW8tHNc0vuYIINDEkXVMvKu6FnUBtTqeFc+lwromXXRAQhzI8joCSKNH2ky e7YAsqmcSCUOgWMeC/zJAkFI9Q33c2dX6rTNZxCbPQbiSkigKLYxRFU9jBVzl45t113a oEwT/x9BJeb58HYJNIrBcBc++lhwNtzJdqedR0iQitVKWrs7GB06K5O4EbYOo0OgiONG BLsA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=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=m7t+sgMz9TV44H52fLnNJuBcvjkbBNOfqqOgFxwKviY=; b=YhYNdQLCAHr6nkTei8aJuftJWxQ16ZqQgWBQDdmb9NTrsDzxWlSfMe27yel9YtjWmX 2odpFryGVp+F7HpG8aAtdT0trFfVSGGJQE/NWqNvBdMujnD7w42cewqb9JHP+7J6GKWI Ga9u5nbWPLCGm5/4jpXSyB/lCbZfDgyDGLpGTp/i5df6yy18lFJn2YerxZ8zI1YL3Pdq m8SRB49sqbJOoO/gdm/usz5h+ahH8qBXiganweqCcCaNnXoMcroJreuPoUPHWjC6db6K fpVif0qBHJLo0k3fkJPkbrZA88HD5mkAXK6IwgTjoX00Ckg+Xmv7ekOfXe2lkJtUDV65 9d7A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; 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=m7t+sgMz9TV44H52fLnNJuBcvjkbBNOfqqOgFxwKviY=; b=Zj6NerzxhcCYbLyGxRRIHIXIws/tq1Y++WJiuwJH2butNNd7eMj7y6gNs+BC0uEKvK kCjmLcS28RHo/17Sx4mQ0PXSXHku7tS2W3zaf6u9rZGd2luVJqXBOd79YI3TTb0/CNk7 cJgpVPKBVUz1AppladfsGCCZlts0YqRA9WxKAwcCXuA9mSWp9ADC9+liHADkoBua6Fp9 o+Pkkp9drcIPs+RDqihqBW6b3B38dwdyMYWx9Jj6GB+doXT7Pi3IgBHlIynz9C8kykTb Kis7FSXZ8YhJTewhIwkS4ysZ30Rkjqmn9wc+TwScuRil1Wd0qodpOIM92C3VzCZmPro6 mczw== X-Gm-Message-State: ABUngvfJp7JpEg0+RttLwlf5jMgSnXTwjyvdOwZnrBcNjA6HoOL0ee0xOrFp1N+f/JlE6Q== X-Received: by 10.176.6.37 with SMTP id f34mr8055751uaf.40.1477830041214; Sun, 30 Oct 2016 05:20:41 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.44.3 with SMTP id f3ls10423022otb.45.gmail; Sun, 30 Oct 2016 05:20:40 -0700 (PDT) X-Received: by 10.157.15.143 with SMTP id d15mr2463596otd.2.1477830040582; Sun, 30 Oct 2016 05:20:40 -0700 (PDT) In-Reply-To: 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:29254 Archived-At: ------=_Part_1323_584620306.1477830040015 Content-Type: multipart/alternative; boundary="----=_Part_1324_1011137650.1477830040015" ------=_Part_1324_1011137650.1477830040015 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Sunday, October 30, 2016 at 3:50:18 AM UTC-4, Vicente J. Botet Escriba= =20 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=20 > implicitly converted to their underlying type. However, do you think we= =20 > would lose this safety feature if we allowed an explicit conversion to th= e=20 > underlying type? > > I do not know of any practical use of explicit conversion operators excep= t=20 > for the contextual conversion to bool. And it is only this conversion tha= t=20 > 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=20 underlying type is with a `static_cast`. --=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/1c81b80e-33b8-4de3-9bf7-94656e8b98f5%40isocpp.or= g. ------=_Part_1324_1011137650.1477830040015 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Sunday, October 30, 2016 at 3:50:18 AM UTC-4, V= icente J. Botet Escriba wrote:
=20 =20 =20
Le 29/10/2016 =C3=A0 23:51, Andrzej Krzemie=C5=84ski a =C3=A9crit=C2=A0:
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 the underlying type?

I do not know of any practical use of explicit conversion operators except for the contextual conversion to bool. And it is only this conversion that I am interested in.

This works already in a non-contextual conversion, isn't it?

=C2=A0=C2=A0=C2=A0 bool(e)

No, it doesn&= #39;t. The only way to convert a strongly typed enum to its underlying type= is with a `static_cast`.

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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/1c81b80e-33b8-4de3-9bf7-94656e8b98f5= %40isocpp.org.
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