1/*!
2@file
3Defines `boost::hana::group`.
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_GROUP_HPP
11#define BOOST_HANA_GROUP_HPP
12
13#include <boost/hana/fwd/group.hpp>
14
15#include <boost/hana/at.hpp>
16#include <boost/hana/concept/sequence.hpp>
17#include <boost/hana/config.hpp>
18#include <boost/hana/core/dispatch.hpp>
19#include <boost/hana/core/make.hpp>
20#include <boost/hana/detail/algorithm.hpp>
21#include <boost/hana/detail/array.hpp>
22#include <boost/hana/detail/nested_by.hpp> // required by fwd decl
23#include <boost/hana/equal.hpp>
24#include <boost/hana/length.hpp>
25
26#include <cstddef>
27#include <utility>
28
29
30namespace boost { namespace hana {
31 //! @cond
32 template <typename Xs>
33 constexpr auto group_t::operator()(Xs&& xs) const {
34 using S = typename hana::tag_of<Xs>::type;
35 using Group = BOOST_HANA_DISPATCH_IF(group_impl<S>,
36 hana::Sequence<S>::value
37 );
38
39 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
40 static_assert(hana::Sequence<S>::value,
41 "hana::group(xs) requires 'xs' to be a Sequence");
42 #endif
43
44 return Group::apply(static_cast<Xs&&>(xs));
45 }
46
47 template <typename Xs, typename Predicate>
48 constexpr auto group_t::operator()(Xs&& xs, Predicate&& pred) const {
49 using S = typename hana::tag_of<Xs>::type;
50 using Group = BOOST_HANA_DISPATCH_IF(group_impl<S>,
51 hana::Sequence<S>::value
52 );
53
54 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
55 static_assert(hana::Sequence<S>::value,
56 "hana::group(xs, predicate) requires 'xs' to be a Sequence");
57 #endif
58
59 return Group::apply(static_cast<Xs&&>(xs),
60 static_cast<Predicate&&>(pred));
61 }
62 //! @endcond
63
64 namespace detail {
65 template <typename Xs, std::size_t ...i>
66 constexpr auto get_subsequence_(Xs&& xs, std::index_sequence<i...>) {
67 using S = typename hana::tag_of<Xs>::type;
68 return hana::make<S>(hana::at_c<i>(static_cast<Xs&&>(xs))...);
69 }
70
71 template <std::size_t offset, typename Indices>
72 struct offset_by;
73
74 template <std::size_t offset, std::size_t ...i>
75 struct offset_by<offset, std::index_sequence<i...>> {
76 using type = std::index_sequence<(offset + i)...>;
77 };
78
79 template <bool ...b>
80 struct group_indices {
81 static constexpr bool bs[sizeof...(b)] = {b...};
82 static constexpr std::size_t n_groups =
83 detail::count(bs, bs + sizeof(bs), false) + 1;
84
85 static constexpr auto compute_info() {
86 detail::array<std::size_t, n_groups> sizes{}, offsets{};
87 for (std::size_t g = 0, i = 0, offset = 0; g < n_groups; ++g) {
88 offsets[g] = offset;
89
90 sizes[g] = 1;
91 while (i < sizeof...(b) && bs[i++])
92 ++sizes[g];
93
94 offset += sizes[g];
95 }
96 return std::make_pair(offsets, sizes);
97 }
98
99 static constexpr auto info = compute_info();
100 static constexpr auto group_offsets = info.first;
101 static constexpr auto group_sizes = info.second;
102
103 template <typename S, typename Xs, std::size_t ...i>
104 static constexpr auto finish(Xs&& xs, std::index_sequence<i...>) {
105 return hana::make<S>(
106 detail::get_subsequence_(
107 static_cast<Xs&&>(xs),
108 typename offset_by<
109 group_offsets[i],
110 std::make_index_sequence<group_sizes[i]>
111 >::type{}
112 )...
113 );
114 }
115 };
116 } // end namespace detail
117
118 template <typename S, bool condition>
119 struct group_impl<S, when<condition>> : default_ {
120 template <typename Xs, typename Pred, std::size_t ...i>
121 static constexpr auto
122 group_helper(Xs&& xs, Pred&& pred, std::index_sequence<0, i...>) {
123 using info = detail::group_indices<static_cast<bool>(decltype(
124 pred(hana::at_c<i - 1>(static_cast<Xs&&>(xs)),
125 hana::at_c<i>(static_cast<Xs&&>(xs)))
126 )::value)...>;
127 return info::template finish<S>(static_cast<Xs&&>(xs),
128 std::make_index_sequence<info::n_groups>{}
129 );
130 }
131
132 template <typename Xs, typename Pred>
133 static constexpr auto
134 group_helper(Xs&& xs, Pred&&, std::index_sequence<0>) {
135 return hana::make<S>(static_cast<Xs&&>(xs));
136 }
137
138 template <typename Xs, typename Pred>
139 static constexpr auto
140 group_helper(Xs&&, Pred&&, std::index_sequence<>) {
141 return hana::make<S>();
142 }
143
144 template <typename Xs, typename Pred>
145 static constexpr auto apply(Xs&& xs, Pred&& pred) {
146 constexpr std::size_t len = decltype(hana::length(xs))::value;
147 return group_helper(static_cast<Xs&&>(xs),
148 static_cast<Pred&&>(pred),
149 std::make_index_sequence<len>{});
150 }
151
152 template <typename Xs>
153 static constexpr auto apply(Xs&& xs)
154 { return group_impl::apply(static_cast<Xs&&>(xs), hana::equal); }
155 };
156}} // end namespace boost::hana
157
158#endif // !BOOST_HANA_GROUP_HPP
159

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