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1 | /*! |
2 | @file | |
3 | Defines `boost::hana::keys`. | |
4 | ||
5 | @copyright Louis Dionne 2013-2016 | |
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 | BOOST_HANA_NAMESPACE_BEGIN | |
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 | BOOST_HANA_NAMESPACE_END | |
47 | ||
48 | #endif // !BOOST_HANA_KEYS_HPP |