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7c673cae FG |
1 | /*! |
2 | @file | |
3 | Defines `boost::hana::unfold_right`. | |
4 | ||
b32b8144 | 5 | @copyright Louis Dionne 2013-2017 |
7c673cae FG |
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_UNFOLD_RIGHT_HPP | |
11 | #define BOOST_HANA_UNFOLD_RIGHT_HPP | |
12 | ||
13 | #include <boost/hana/fwd/unfold_right.hpp> | |
14 | ||
15 | #include <boost/hana/concept/sequence.hpp> | |
16 | #include <boost/hana/config.hpp> | |
17 | #include <boost/hana/core/dispatch.hpp> | |
18 | #include <boost/hana/empty.hpp> | |
19 | #include <boost/hana/first.hpp> | |
20 | #include <boost/hana/functional/partial.hpp> | |
21 | #include <boost/hana/optional.hpp> | |
22 | #include <boost/hana/prepend.hpp> | |
23 | #include <boost/hana/second.hpp> | |
24 | ||
25 | ||
26 | BOOST_HANA_NAMESPACE_BEGIN | |
27 | //! @cond | |
28 | template <typename S> | |
29 | struct unfold_right_t { | |
30 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
31 | static_assert(hana::Sequence<S>::value, | |
32 | "hana::unfold_right<S> requires 'S' to be a Sequence"); | |
33 | #endif | |
34 | ||
35 | template <typename State, typename F> | |
36 | constexpr auto operator()(State&& state, F&& f) const { | |
37 | return unfold_right_impl<S>::apply( | |
38 | static_cast<State&&>(state), | |
39 | static_cast<F&&>(f) | |
40 | ); | |
41 | } | |
42 | }; | |
43 | //! @endcond | |
44 | ||
45 | template <typename S, bool condition> | |
46 | struct unfold_right_impl<S, when<condition>> : default_ { | |
47 | struct unfold_right_helper { | |
48 | template <typename F, typename P> | |
49 | constexpr auto operator()(F&& f, P&& p) const { | |
50 | return hana::prepend( | |
51 | unfold_right_impl::apply( | |
52 | hana::second(static_cast<P&&>(p)), | |
53 | static_cast<F&&>(f) | |
54 | ), | |
55 | hana::first(static_cast<P&&>(p)) | |
56 | ); | |
57 | } | |
58 | }; | |
59 | ||
60 | template <typename Init, typename F> | |
61 | static constexpr auto apply(Init&& init, F&& f) { | |
62 | decltype(auto) elt = f(static_cast<Init&&>(init)); | |
63 | return hana::maybe(hana::empty<S>(), | |
64 | hana::partial(unfold_right_helper{}, static_cast<F&&>(f)), | |
65 | static_cast<decltype(elt)&&>(elt) | |
66 | ); | |
67 | } | |
68 | }; | |
69 | BOOST_HANA_NAMESPACE_END | |
70 | ||
71 | #endif // !BOOST_HANA_UNFOLD_RIGHT_HPP |