| 1 | /*! |
|---|---|
| 2 | @file |
| 3 | Defines `boost::hana::is_empty`. |
| 4 | |
| 5 | Copyright Louis Dionne 2013-2022 |
| 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_IS_EMPTY_HPP |
| 11 | #define BOOST_HANA_IS_EMPTY_HPP |
| 12 | |
| 13 | #include <boost/hana/fwd/is_empty.hpp> |
| 14 | |
| 15 | #include <boost/hana/concept/iterable.hpp> |
| 16 | #include <boost/hana/config.hpp> |
| 17 | #include <boost/hana/core/dispatch.hpp> |
| 18 | |
| 19 | |
| 20 | namespace boost { namespace hana { |
| 21 | //! @cond |
| 22 | template <typename Xs> |
| 23 | constexpr auto is_empty_t::operator()(Xs const& xs) const { |
| 24 | using It = typename hana::tag_of<Xs>::type; |
| 25 | using IsEmpty = BOOST_HANA_DISPATCH_IF(is_empty_impl<It>, |
| 26 | hana::Iterable<It>::value |
| 27 | ); |
| 28 | |
| 29 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS |
| 30 | static_assert(hana::Iterable<It>::value, |
| 31 | "hana::is_empty(xs) requires 'xs' to be an Iterable"); |
| 32 | #endif |
| 33 | |
| 34 | return IsEmpty::apply(xs); |
| 35 | } |
| 36 | //! @endcond |
| 37 | |
| 38 | template <typename It, bool condition> |
| 39 | struct is_empty_impl<It, when<condition>> : default_ { |
| 40 | template <typename ...Args> |
| 41 | static constexpr auto apply(Args&& ...) = delete; |
| 42 | }; |
| 43 | }} // end namespace boost::hana |
| 44 | |
| 45 | #endif // !BOOST_HANA_IS_EMPTY_HPP |
| 46 |