1/*!
2@file
3Defines `boost::hana::fold_right`.
4
5Copyright Louis Dionne 2013-2022
6Distributed 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
23namespace boost { namespace hana {
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 };
95}} // end namespace boost::hana
96
97#endif // !BOOST_HANA_FOLD_RIGHT_HPP
98

source code of boost/libs/hana/include/boost/hana/fold_right.hpp