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1 | /*! |
2 | @file | |
3 | Defines `boost::hana::fold_right`. | |
4 | ||
f51cf556 | 5 | Copyright Louis Dionne 2013-2022 |
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_FOLD_RIGHT_HPP | |
11 | #define BOOST_HANA_FOLD_RIGHT_HPP | |
12 | ||
13 | #include <boost/hana/fwd/fold_right.hpp> | |
14 | ||
15 | #include <boost/hana/concept/foldable.hpp> | |
16 | #include <boost/hana/config.hpp> | |
17 | #include <boost/hana/core/dispatch.hpp> | |
18 | #include <boost/hana/detail/variadic/foldr1.hpp> | |
19 | #include <boost/hana/functional/partial.hpp> | |
20 | #include <boost/hana/fwd/unpack.hpp> | |
21 | ||
22 | ||
1e59de90 | 23 | namespace boost { namespace hana { |
7c673cae FG |
24 | //! @cond |
25 | template <typename Xs, typename State, typename F> | |
26 | constexpr decltype(auto) fold_right_t::operator()(Xs&& xs, State&& state, F&& f) const { | |
27 | using S = typename hana::tag_of<Xs>::type; | |
28 | using FoldRight = BOOST_HANA_DISPATCH_IF(fold_right_impl<S>, | |
29 | hana::Foldable<S>::value | |
30 | ); | |
31 | ||
32 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
33 | static_assert(hana::Foldable<S>::value, | |
34 | "hana::fold_right(xs, state, f) requires 'xs' to be Foldable"); | |
35 | #endif | |
36 | ||
37 | return FoldRight::apply(static_cast<Xs&&>(xs), | |
38 | static_cast<State&&>(state), | |
39 | static_cast<F&&>(f)); | |
40 | } | |
41 | ||
42 | template <typename Xs, typename F> | |
43 | constexpr decltype(auto) fold_right_t::operator()(Xs&& xs, F&& f) const { | |
44 | using S = typename hana::tag_of<Xs>::type; | |
45 | using FoldRight = BOOST_HANA_DISPATCH_IF(fold_right_impl<S>, | |
46 | hana::Foldable<S>::value | |
47 | ); | |
48 | ||
49 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
50 | static_assert(hana::Foldable<S>::value, | |
51 | "hana::fold_right(xs, f) requires 'xs' to be Foldable"); | |
52 | #endif | |
53 | ||
54 | return FoldRight::apply(static_cast<Xs&&>(xs), static_cast<F&&>(f)); | |
55 | } | |
56 | //! @endcond | |
57 | ||
58 | namespace detail { | |
59 | template <typename F, typename State> | |
60 | struct variadic_foldr { | |
61 | F& f; | |
62 | State& state; | |
63 | template <typename ...T> | |
64 | constexpr decltype(auto) operator()(T&& ...t) const { | |
65 | return detail::variadic::foldr( | |
66 | static_cast<F&&>(f), | |
67 | static_cast<State&&>(state), | |
68 | static_cast<T&&>(t)... | |
69 | ); | |
70 | } | |
71 | }; | |
72 | } | |
73 | ||
74 | template <typename T, bool condition> | |
75 | struct fold_right_impl<T, when<condition>> : default_ { | |
76 | // with state | |
77 | template <typename Xs, typename S, typename F> | |
78 | static constexpr decltype(auto) apply(Xs&& xs, S&& s, F&& f) { | |
79 | return hana::unpack(static_cast<Xs&&>(xs), | |
80 | detail::variadic_foldr<F, S>{f, s} | |
81 | ); | |
82 | } | |
83 | ||
84 | // without state | |
85 | template <typename Xs, typename F> | |
86 | static constexpr decltype(auto) apply(Xs&& xs, F&& f) { | |
87 | return hana::unpack(static_cast<Xs&&>(xs), | |
88 | hana::partial( | |
89 | detail::variadic::foldr1, | |
90 | static_cast<F&&>(f) | |
91 | ) | |
92 | ); | |
93 | } | |
94 | }; | |
1e59de90 | 95 | }} // end namespace boost::hana |
7c673cae FG |
96 | |
97 | #endif // !BOOST_HANA_FOLD_RIGHT_HPP |