boost/hana/none.hpp

0001 /*!
0002 @file
0003 Defines `boost::hana::none`.
0004
0005 Copyright Louis Dionne 2013-2022
0006 Distributed under the Boost Software License, Version 1.0.
0007 (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
0008  */
0009
0010 #ifndef BOOST_HANA_NONE_HPP
0011 #define BOOST_HANA_NONE_HPP
0012
0013 #include <boost/hana/fwd/none.hpp>
0014
0015 #include <boost/hana/concept/searchable.hpp>
0016 #include <boost/hana/config.hpp>
0017 #include <boost/hana/core/dispatch.hpp>
0018 #include <boost/hana/functional/id.hpp>
0019 #include <boost/hana/none_of.hpp>
0020
0021
0022 namespace boost { namespace hana {
0023     //! @cond
0024     template <typename Xs>
0025     constexpr auto none_t::operator()(Xs&& xs) const {
0026         using S = typename hana::tag_of<Xs>::type;
0027         using None = BOOST_HANA_DISPATCH_IF(none_impl<S>,
0028             hana::Searchable<S>::value
0029         );
0030
0031     #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
0032         static_assert(hana::Searchable<S>::value,
0033         "hana::none(xs) requires 'xs' to be a Searchable");
0034     #endif
0035
0036         return None::apply(static_cast<Xs&&>(xs));
0037     }
0038     //! @endcond
0039
0040     template <typename S, bool condition>
0041     struct none_impl<S, when<condition>> : default_ {
0042         template <typename Xs>
0043         static constexpr auto apply(Xs&& xs)
0044         { return hana::none_of(static_cast<Xs&&>(xs), hana::id); }
0045     };
0046 }} // end namespace boost::hana
0047
0048 #endif // !BOOST_HANA_NONE_HPP