220 31759 <078635c1-3de8-458b-9df3-34f4c62db1fd@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Allow constexpr static data members in a literal type. Date: Sun, 26 Mar 2017 08:22:32 -0700 (PDT) Lines: 166 Approved: news@gmane.org Message-ID: <078635c1-3de8-458b-9df3-34f4c62db1fd@isocpp.org> References: <470f86cc-36b7-4244-82dd-b795af107996@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_4926_1196441680.1490541753038" X-Trace: blaine.gmane.org 1490541766 22780 195.159.176.226 (26 Mar 2017 15:22:46 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 26 Mar 2017 15:22:46 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBONZ37DAKGQE42Z4X2I@isocpp.org Sun Mar 26 17:22:41 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f69.google.com ([209.85.218.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cs9zw-0004SK-PB for gclcip-std-proposals@m.gmane.org; Sun, 26 Mar 2017 17:22:28 +0200 Original-Received: by mail-oi0-f69.google.com with SMTP id f193sf30201099oib.1 for ; Sun, 26 Mar 2017 08:22:34 -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=BLEZ6G1mAkUpK8+5vvxQ96clKNAV1hp4Dw3pjPoVmMY=; b=SgVwjqgzrsK/vlc7B+C8d+8eHfdcSfHDjR9I4JyQ0OaCrFB9RhlVd4FtZ8z2ADfY9q 7pnCxoE9E6OtXKHtaypgp3mpKlNEh73GNlmwTDMKaoJomyMcm22g2xdeW8qr/GHFPF68 UpO96jVRnfPcWMsXZOgcUjjA3047/kVnz8dgG0MpV1uVOCELYAyXW/+1M00fz73ZGQ6U ylUEXNtnjkTRQ8nBL3d7YAEc9nYmDUbJNUFnnbALFtc/t4LGMkybytEunaJW3aoULPTn WoRLkjsFBo9UHPSGmt7Wox3MJrwbsmeym9WDm0SOV43Je+lLruMwQfx96T4UIna8bEVW IcHw== 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 :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=BLEZ6G1mAkUpK8+5vvxQ96clKNAV1hp4Dw3pjPoVmMY=; b=MjaR3ogJAtFDiPElki2ojdCL4nFPioaMFZXJST34Lq6Z3WT5nV7PWq0JycicBBia0y BO+IetiG872I+YQL4XUhXDqUTL0RIJi0zO+OgdVU+jlWOGD7STV76cX99czTd9NjYIyw NJrYrUF+MCwtHEobgNWP0XophEegqDDkEKRSwxJ0L283QfVIAypOaQh5R0xEVc6fYJaF WrlTDPWomT60VRGEvCt6y+SJw7OJTUz8UyttzZRHEKZGQ8Df0Yfi8EVORl6MENUvwHV8 Hc9PG5f4s/WWeYajn+M2g4cKi8lwywgAE1ZUVoqAkK4IVyOAxyaowUasVKUCStCWPjcw VHeQ== 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=BLEZ6G1mAkUpK8+5vvxQ96clKNAV1hp4Dw3pjPoVmMY=; b=MbxTw6AMrfLVYJnthyzj5J8HE6MxYlfGGiHKMA0liQeUjJiERUeF4Hm/N4uYgB4NNL 5NB2DWJC/e5INSTh4XHIs6eRNfAc4FMjNqlQ3OOMC6qTdk5usvTyeJtWf0SJYpyZ2QyV FpV6bAcVTThsM1nLTwEIUVNMPbDmdJeOQvfwoHS6nyoX7efhPWEKCL1StM4Otem0Lb+l D9ewEZEykL7Na1+L+CXUOwS4lUj8nhV+e9GADryL3bFgDUGFHlkE7fZd9f1VbxVoYehQ Yxr4KJM3TciFBFzhBW6kNIw3Izj5D6Zfr0n7TMTkfAL/m/6mje6BtbNKUYGe6KyKsqMz dEtg== X-Gm-Message-State: AFeK/H23wpykl1E9Ipu9lua9xGkR9vmdWAomGWHFoiFYwsHsXGNEWWbVF4rspFMRXTGeMA== X-Received: by 10.157.80.33 with SMTP id a33mr6179237oth.92.1490541754391; Sun, 26 Mar 2017 08:22:34 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.35.124 with SMTP id k57ls4623146otd.41.gmail; Sun, 26 Mar 2017 08:22:33 -0700 (PDT) X-Received: by 10.157.32.10 with SMTP id n10mr1491173ota.10.1490541753479; Sun, 26 Mar 2017 08:22:33 -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:31759 Archived-At: ------=_Part_4926_1196441680.1490541753038 Content-Type: multipart/alternative; boundary="----=_Part_4927_582499589.1490541753038" ------=_Part_4927_582499589.1490541753038 Content-Type: text/plain; charset=UTF-8 On Sunday, March 26, 2017 at 10:49:22 AM UTC-4, Avi Kivity wrote: > > > > On 03/26/2017 05:35 PM, Nicol Bolas wrote: > > On Sunday, March 26, 2017 at 10:30:29 AM UTC-4, Avi Kivity wrote: >> >> Consider this type-safe bool class: >> >> >> template >> >> class bool_class { >> >> bool _value; >> >> public: >> >> explicit constexpr bool_class(bool v) noexcept : _value(v) {} >> >> // more emulation of bool >> >> static constexpr bool_class yes = bool_class{true}; >> >> static constexpr bool_class no = bool_class{true}; >> >> }; >> >> >> Compilation fails, I believe rightly, on clang, because by the time yes >> and no are parsed, bool_class is an incomplete type, and therefore not a >> literal type. It could be worked around by making yes and no functions. >> >> Should we make this legal? It seems reasonable for types to offer >> constants scoped under their own name, and if they are literal types, >> that these constants can be constexpr. >> > > How does it seem reasonable to define variables of a type that has not yet > been defined? > > You can do that already, within an inline member function. > That's not defining a variable. That's defining a function that returns a value of a certain type. -- 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/078635c1-3de8-458b-9df3-34f4c62db1fd%40isocpp.org. ------=_Part_4927_582499589.1490541753038 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Sunday, March 26, 2017 at 10:49:22 AM UTC-4, Av= i Kivity wrote:
=20 =20 =20



On 03/26/2017 05:35 PM, Nicol Bolas wrote:
On Sunday, March 26, 2017 at 10:30:29 AM UTC-4, Avi Kivity wrote:
Consider this type-safe bool class:


=C2=A0 =C2=A0template <typename Tag>

=C2=A0 =C2=A0class bool_class {

=C2=A0 =C2=A0 =C2=A0 =C2=A0bool _value;

=C2=A0 =C2=A0public:

=C2=A0 =C2=A0 =C2=A0 =C2=A0explicit constexpr bool_class(bool v) = noexcept : _value(v) {}

=C2=A0 =C2=A0 =C2=A0 =C2=A0// more emulation of bool

=C2=A0 =C2=A0 =C2=A0 =C2=A0static constexpr bool_class yes =3D bo= ol_class{true};

=C2=A0 =C2=A0 =C2=A0 =C2=A0static constexpr bool_class no =3D boo= l_class{true};

=C2=A0 =C2=A0};


Compilation fails, I believe rightly, on clang, because by the time yes
and no are parsed, bool_class is an incomplete type, and therefore not a
literal type. =C2=A0It could be worked around by making yes and n= o functions.

Should we make this legal? =C2=A0It seems reasonable for types to offer
constants scoped under their own name, and if they are literal types,
that these constants can be constexpr.

How does it seem reasonable to define variables of a type that has not yet been defined?
=20 You can do that already, within an inline member function.

That's not defining a variable. That's defining = a function that returns a value of a certain type.

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