| 1 | /*! |
|---|---|
| 2 | @file |
| 3 | Defines `boost::hana::keys`. |
| 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_KEYS_HPP |
| 11 | #define BOOST_HANA_KEYS_HPP |
| 12 | |
| 13 | #include <boost/hana/fwd/keys.hpp> |
| 14 | |
| 15 | #include <boost/hana/accessors.hpp> |
| 16 | #include <boost/hana/concept/struct.hpp> |
| 17 | #include <boost/hana/config.hpp> |
| 18 | #include <boost/hana/core/dispatch.hpp> |
| 19 | #include <boost/hana/first.hpp> |
| 20 | #include <boost/hana/transform.hpp> |
| 21 | |
| 22 | |
| 23 | namespace boost { namespace hana { |
| 24 | //! @cond |
| 25 | template <typename Map> |
| 26 | constexpr auto keys_t::operator()(Map&& map) const { |
| 27 | return keys_impl<typename hana::tag_of<Map>::type>::apply( |
| 28 | static_cast<Map&&>(map) |
| 29 | ); |
| 30 | } |
| 31 | //! @endcond |
| 32 | |
| 33 | template <typename T, bool condition> |
| 34 | struct keys_impl<T, when<condition>> : default_ { |
| 35 | template <typename ...Args> |
| 36 | static constexpr auto apply(Args&& ...) = delete; |
| 37 | }; |
| 38 | |
| 39 | template <typename S> |
| 40 | struct keys_impl<S, when<hana::Struct<S>::value>> { |
| 41 | template <typename Object> |
| 42 | static constexpr auto apply(Object const&) { |
| 43 | return hana::transform(hana::accessors<S>(), hana::first); |
| 44 | } |
| 45 | }; |
| 46 | }} // end namespace boost::hana |
| 47 | |
| 48 | #endif // !BOOST_HANA_KEYS_HPP |
| 49 |