1 /*! 2 @file 3 Defines `boost::hana::none`. 4 5 @copyright Louis Dionne 2013-2017 6 Distributed under the Boost Software License, Version 1.0. 7 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) 8 */ 9 10 #ifndef BOOST_HANA_NONE_HPP 11 #define BOOST_HANA_NONE_HPP 12 13 #include <boost/hana/fwd/none.hpp> 14 15 #include <boost/hana/concept/searchable.hpp> 16 #include <boost/hana/config.hpp> 17 #include <boost/hana/core/dispatch.hpp> 18 #include <boost/hana/functional/id.hpp> 19 #include <boost/hana/none_of.hpp> 20 21 22 BOOST_HANA_NAMESPACE_BEGIN 23 //! @cond 24 template <typename Xs> operator ()(Xs && xs) const25 constexpr auto none_t::operator()(Xs&& xs) const { 26 using S = typename hana::tag_of<Xs>::type; 27 using None = BOOST_HANA_DISPATCH_IF(none_impl<S>, 28 hana::Searchable<S>::value 29 ); 30 31 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS 32 static_assert(hana::Searchable<S>::value, 33 "hana::none(xs) requires 'xs' to be a Searchable"); 34 #endif 35 36 return None::apply(static_cast<Xs&&>(xs)); 37 } 38 //! @endcond 39 40 template <typename S, bool condition> 41 struct none_impl<S, when<condition>> : default_ { 42 template <typename Xs> applynone_impl43 static constexpr auto apply(Xs&& xs) 44 { return hana::none_of(static_cast<Xs&&>(xs), hana::id); } 45 }; 46 BOOST_HANA_NAMESPACE_END 47 48 #endif // !BOOST_HANA_NONE_HPP 49