1/*!
2@file
3Defines `boost::hana::unfold_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_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
26namespace boost { namespace hana {
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}} // end namespace boost::hana
70
71#endif // !BOOST_HANA_UNFOLD_RIGHT_HPP
72

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