1/*!
2@file
3Defines `boost::hana::sort`.
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_SORT_HPP
11#define BOOST_HANA_SORT_HPP
12
13#include <boost/hana/fwd/sort.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/nested_by.hpp> // required by fwd decl
21#include <boost/hana/length.hpp>
22#include <boost/hana/less.hpp>
23
24#include <utility> // std::declval, std::index_sequence
25
26
27namespace boost { namespace hana {
28 //! @cond
29 template <typename Xs, typename Predicate>
30 constexpr auto sort_t::operator()(Xs&& xs, Predicate&& pred) const {
31 using S = typename hana::tag_of<Xs>::type;
32 using Sort = BOOST_HANA_DISPATCH_IF(sort_impl<S>,
33 hana::Sequence<S>::value
34 );
35
36 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
37 static_assert(hana::Sequence<S>::value,
38 "hana::sort(xs, predicate) requires 'xs' to be a Sequence");
39 #endif
40
41 return Sort::apply(static_cast<Xs&&>(xs),
42 static_cast<Predicate&&>(pred));
43 }
44
45 template <typename Xs>
46 constexpr auto sort_t::operator()(Xs&& xs) const {
47 using S = typename hana::tag_of<Xs>::type;
48 using Sort = BOOST_HANA_DISPATCH_IF(sort_impl<S>,
49 hana::Sequence<S>::value
50 );
51
52 #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
53 static_assert(hana::Sequence<S>::value,
54 "hana::sort(xs) requires 'xs' to be a Sequence");
55 #endif
56
57 return Sort::apply(static_cast<Xs&&>(xs));
58 }
59 //! @endcond
60
61 namespace detail {
62 template <typename Xs, typename Pred>
63 struct sort_predicate {
64 template <std::size_t I, std::size_t J>
65 using apply = decltype(std::declval<Pred>()(
66 hana::at_c<I>(std::declval<Xs>()),
67 hana::at_c<J>(std::declval<Xs>())
68 ));
69 };
70
71 template <typename Left, typename Right>
72 struct concat;
73
74 template <std::size_t ...l, std::size_t ...r>
75 struct concat<std::index_sequence<l...>, std::index_sequence<r...>> {
76 using type = std::index_sequence<l..., r...>;
77 };
78
79 template <typename Pred, bool PickRight, typename Left, typename Right>
80 struct merge;
81
82 template <
83 typename Pred,
84 std::size_t l0,
85 std::size_t l1,
86 std::size_t ...l,
87 std::size_t r0,
88 std::size_t ...r>
89 struct merge<
90 Pred,
91 false,
92 std::index_sequence<l0, l1, l...>,
93 std::index_sequence<r0, r...>
94 > {
95 using type = typename concat<
96 std::index_sequence<l0>,
97 typename merge<
98 Pred,
99 (bool)Pred::template apply<r0, l1>::value,
100 std::index_sequence<l1, l...>,
101 std::index_sequence<r0, r...>
102 >::type
103 >::type;
104 };
105
106 template <
107 typename Pred,
108 std::size_t l0,
109 std::size_t r0,
110 std::size_t ...r>
111 struct merge<
112 Pred,
113 false,
114 std::index_sequence<l0>,
115 std::index_sequence<r0, r...>
116 > {
117 using type = std::index_sequence<l0, r0, r...>;
118 };
119
120 template <
121 typename Pred,
122 std::size_t l0,
123 std::size_t ...l,
124 std::size_t r0,
125 std::size_t r1,
126 std::size_t ...r>
127 struct merge<
128 Pred,
129 true,
130 std::index_sequence<l0, l...>,
131 std::index_sequence<r0, r1, r...>
132 > {
133 using type = typename concat<
134 std::index_sequence<r0>,
135 typename merge<
136 Pred,
137 (bool)Pred::template apply<r1, l0>::value,
138 std::index_sequence<l0, l...>,
139 std::index_sequence<r1, r...>
140 >::type
141 >::type;
142 };
143
144 template <
145 typename Pred,
146 std::size_t l0,
147 std::size_t ...l,
148 std::size_t r0>
149 struct merge<
150 Pred,
151 true,
152 std::index_sequence<l0, l...>,
153 std::index_sequence<r0>
154 > {
155 using type = std::index_sequence<r0, l0, l...>;
156 };
157
158 template <typename Pred, typename Left, typename Right>
159 struct merge_helper;
160
161 template <
162 typename Pred,
163 std::size_t l0,
164 std::size_t ...l,
165 std::size_t r0,
166 std::size_t ...r>
167 struct merge_helper<
168 Pred,
169 std::index_sequence<l0, l...>,
170 std::index_sequence<r0, r...>
171 > {
172 using type = typename merge<
173 Pred,
174 (bool)Pred::template apply<r0, l0>::value,
175 std::index_sequence<l0, l...>,
176 std::index_sequence<r0, r...>
177 >::type;
178 };
179
180 // split templated structure, Nr represents the number of elements
181 // from Right to move to Left
182 // There are two specializations:
183 // The first handles the generic case (Nr > 0)
184 // The second handles the stop condition (Nr == 0)
185 // These two specializations are not strictly ordered as
186 // the first cannot match Nr==0 && empty Right
187 // the second cannot match Nr!=0
188 // std::enable_if<Nr!=0> is therefore required to make sure these two
189 // specializations will never both be candidates during an overload
190 // resolution (otherwise ambiguity occurs for Nr==0 and non-empty Right)
191 template <std::size_t Nr, typename Left, typename Right, typename=void>
192 struct split;
193
194 template <
195 std::size_t Nr,
196 std::size_t ...l,
197 std::size_t ...r,
198 std::size_t r0>
199 struct split<
200 Nr,
201 std::index_sequence<l...>,
202 std::index_sequence<r0, r...>,
203 typename std::enable_if<Nr!=0>::type
204 > {
205 using sp = split<
206 Nr-1,
207 std::index_sequence<l..., r0>,
208 std::index_sequence<r...>
209 >;
210 using left = typename sp::left;
211 using right = typename sp::right;
212 };
213
214 template <std::size_t ...l, std::size_t ...r>
215 struct split<0, std::index_sequence<l...>, std::index_sequence<r...>> {
216 using left = std::index_sequence<l...>;
217 using right = std::index_sequence<r...>;
218 };
219
220 template <typename Pred, typename Sequence>
221 struct merge_sort_impl;
222
223 template <typename Pred, std::size_t ...seq>
224 struct merge_sort_impl<Pred, std::index_sequence<seq...>> {
225 using sequence = std::index_sequence<seq...>;
226 using sp = split<
227 sequence::size() / 2,
228 std::index_sequence<>,
229 sequence
230 >;
231 using type = typename merge_helper<
232 Pred,
233 typename merge_sort_impl<Pred, typename sp::left>::type,
234 typename merge_sort_impl<Pred, typename sp::right>::type
235 >::type;
236 };
237
238 template <typename Pred, std::size_t x>
239 struct merge_sort_impl<Pred, std::index_sequence<x>> {
240 using type = std::index_sequence<x>;
241 };
242
243 template <typename Pred>
244 struct merge_sort_impl<Pred, std::index_sequence<>> {
245 using type = std::index_sequence<>;
246 };
247 } // end namespace detail
248
249 template <typename S, bool condition>
250 struct sort_impl<S, when<condition>> : default_ {
251 template <typename Xs, std::size_t ...i>
252 static constexpr auto apply_impl(Xs&& xs, std::index_sequence<i...>) {
253 return hana::make<S>(hana::at_c<i>(static_cast<Xs&&>(xs))...);
254 }
255
256 template <typename Xs, typename Pred>
257 static constexpr auto apply(Xs&& xs, Pred const&) {
258 constexpr std::size_t Len = decltype(hana::length(xs))::value;
259 using Indices = typename detail::merge_sort_impl<
260 detail::sort_predicate<Xs&&, Pred>,
261 std::make_index_sequence<Len>
262 >::type;
263
264 return apply_impl(static_cast<Xs&&>(xs), Indices{});
265 }
266
267 template <typename Xs>
268 static constexpr auto apply(Xs&& xs)
269 { return sort_impl::apply(static_cast<Xs&&>(xs), hana::less); }
270 };
271}} // end namespace boost::hana
272
273#endif // !BOOST_HANA_SORT_HPP
274

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