220 31761 <5262b75e-8281-411d-2248-6be37fd52b85@wanadoo.fr> article Path: news.gmane.org!.POSTED!not-for-mail From: "Vicente J. Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allow constexpr static data members in a literal type. 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[80.12.242.125]) by mx.google.com with ESMTPS id 188si11066761wme.151.2017.03.26.09.50.35 for (version=TLS1 cipher=AES128-SHA bits=128/128); Sun, 26 Mar 2017 09:50:35 -0700 (PDT) Received-SPF: neutral (google.com: 80.12.242.125 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.125; Original-Received: from imac-de-vicente-botet-escriba.home ([2.11.188.167]) by mwinf5d57 with ME id 0gqa1v0013d8Kde03gqaZT; Sun, 26 Mar 2017 18:50:35 +0200 X-ME-Helo: imac-de-vicente-botet-escriba.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Sun, 26 Mar 2017 18:50:35 +0200 X-ME-IP: 2.11.188.167 In-Reply-To: X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.125 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) smtp.mailfrom=vicente.botet@wanadoo.fr 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:31761 Archived-At: Le 26/03/2017 =C3=A0 16:30, Avi Kivity a =C3=A9crit : > 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 =3D bool_class{true}; > > static constexpr bool_class no =3D bool_class{true}; > > }; > > > Compilation fails, I believe rightly, on clang, because by the time=20 > yes and no are parsed, bool_class is an incomplete type, and therefore=20 > not a literal type. It could be worked around by making yes and no=20 > functions. > > Should we make this legal? It seems reasonable for types to offer=20 > constants scoped under their own name, and if they are literal types,=20 > that these constants can be constexpr. > It seems that you can do template class bool_class { bool _value; public: explicit constexpr bool_class(bool v) noexcept : _value(v) {} // more emulation of bool static const bool_class yes; static const bool_class no; }; constexpr bool_class bool_class::yes =3D bool_class{true}; constexpr bool_class bool_class::no =3D bool_class{true}; Vicente --=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/5262b75e-8281-411d-2248-6be37fd52b85%40wanadoo.f= r. .