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take.hpp
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1
2// Range v3 library
3//
4// Copyright Eric Niebler 2013-present
5//
6// Use, modification and distribution is subject to the
7// Boost Software License, Version 1.0. (See accompanying
8// file LICENSE_1_0.txt or copy at
9// http://www.boost.org/LICENSE_1_0.txt)
10//
11// Project home: https://github.com/ericniebler/range-v3
12//
13
14#ifndef RANGES_V3_VIEW_TAKE_HPP
15#define RANGES_V3_VIEW_TAKE_HPP
16
17#include <type_traits>
18
20
27#include <range/v3/utility/static_const.hpp>
28#include <range/v3/view/all.hpp>
30
31#include <range/v3/detail/prologue.hpp>
32
33namespace ranges
34{
37
38 template<typename Rng>
39 struct take_view : view_interface<take_view<Rng>, finite>
40 {
41 private:
42 CPP_assert(view_<Rng>);
43 Rng base_ = Rng();
44 range_difference_t<Rng> count_ = 0;
45 template<bool Const>
46 struct sentinel
47 {
48 private:
50 using CI = counted_iterator<iterator_t<Base>>;
51 sentinel_t<Base> end_ = sentinel_t<Base>();
52
53 public:
54 sentinel() = default;
55 constexpr explicit sentinel(sentinel_t<Base> last)
56 : end_(std::move(last))
57 {}
58 template(bool Other)(
59 requires Const AND CPP_NOT(Other) AND
60 convertible_to<sentinel_t<Rng>,
61 sentinel_t<Base>>)
62 constexpr sentinel(sentinel<Other> that)
63 : end_(std::move(that.end_))
64 {}
65 constexpr sentinel_t<Base> base() const
66 {
67 return end_;
68 }
69#ifdef RANGES_WORKAROUND_MSVC_756601
70 template<typename = void>
71#endif // RANGES_WORKAROUND_MSVC_756601
72 friend constexpr bool operator==(sentinel const & x, CI const & y)
73 {
74 return y.count() == 0 || y.base() == x.end_;
75 }
76#ifdef RANGES_WORKAROUND_MSVC_756601
77 template<typename = void>
78#endif // RANGES_WORKAROUND_MSVC_756601
79 friend constexpr bool operator==(CI const & y, sentinel const & x)
80 {
81 return y.count() == 0 || y.base() == x.end_;
82 }
83#ifdef RANGES_WORKAROUND_MSVC_756601
84 template<typename = void>
85#endif // RANGES_WORKAROUND_MSVC_756601
86 friend constexpr bool operator!=(sentinel const & x, CI const & y)
87 {
88 return y.count() != 0 && y.base() != x.end_;
89 }
90#ifdef RANGES_WORKAROUND_MSVC_756601
91 template<typename = void>
92#endif // RANGES_WORKAROUND_MSVC_756601
93 friend constexpr bool operator!=(CI const & y, sentinel const & x)
94 {
95 return y.count() != 0 && y.base() != x.end_;
96 }
97 };
98
99#if RANGES_CXX_IF_CONSTEXPR < RANGES_CXX_IF_CONSTEXPR_17
100 template<typename Take>
101 static auto begin_random_access_(Take & take, std::true_type)
102 {
103 return ranges::begin(take.base_);
104 }
105 template<typename Take>
106 static auto begin_random_access_(Take & take, std::false_type)
107 {
108 auto s = static_cast<range_difference_t<Rng>>(take.size());
109 return make_counted_iterator(ranges::begin(take.base_), s);
110 }
111 template<typename Take>
112 static auto begin_sized_(Take & take, std::true_type)
113 {
114 return begin_random_access_(
115 take, meta::bool_<random_access_range<decltype((take.base_))>>{});
116 }
117 template<typename Take>
118 static auto begin_sized_(Take & take, std::false_type)
119 {
120 return make_counted_iterator(ranges::begin(take.base_), take.count_);
121 }
122
123 template<typename Take>
124 static auto end_random_access_(Take & take, std::true_type)
125 {
126 return ranges::begin(take.base_) +
127 static_cast<range_difference_t<Rng>>(take.size());
128 }
129 static auto end_random_access_(detail::ignore_t, std::false_type)
130 {
131 return default_sentinel;
132 }
133 template<typename Take>
134 static auto end_sized_(Take & take, std::true_type, std::false_type) // sized
135 {
136 return end_random_access_(
137 take, meta::bool_<random_access_range<decltype((take.base_))>>{});
138 }
139 static auto end_sized_(detail::ignore_t, std::false_type,
140 std::true_type) // infinite
141 {
142 return default_sentinel;
143 }
144 static auto end_sized_(take_view & take, std::false_type, std::false_type)
145 {
146 return sentinel<false>{ranges::end(take.base_)};
147 }
148 static auto end_sized_(take_view const & take, std::false_type, std::false_type)
149 {
150 return sentinel<true>{ranges::end(take.base_)};
151 }
152#endif
153 public:
154 take_view() = default;
155
156 constexpr take_view(Rng base, range_difference_t<Rng> cnt)
157 : base_(std::move(base))
158 , count_(cnt)
159 {}
160
161 constexpr Rng base() const
162 {
163 return base_;
164 }
165
166 CPP_auto_member
167 constexpr auto CPP_fun(begin)()(
168 requires(!simple_view<Rng>()))
169 {
170#if RANGES_CXX_IF_CONSTEXPR >= RANGES_CXX_IF_CONSTEXPR_17
171 if constexpr(sized_range<Rng>)
172 if constexpr(random_access_range<Rng>)
173 return ranges::begin(base_);
174 else
175 {
176 // cannot always delegate to size() member on GCC with ConceptsTS
177#if defined(__cpp_concepts) && __cpp_concepts <= 201507
178 auto s = ranges::min(
179 static_cast<range_difference_t<Rng>>(count_),
180 static_cast<range_difference_t<Rng>>(ranges::size(base_)));
181#else
182 auto s = static_cast<range_difference_t<Rng>>(size());
183#endif
184 return make_counted_iterator(ranges::begin(base_), s);
185 }
186 else
187 return make_counted_iterator(ranges::begin(base_), count_);
188#else
189 return begin_sized_(*this, meta::bool_<sized_range<Rng>>{});
190#endif
191 }
192
193 CPP_auto_member
194 constexpr auto CPP_fun(begin)()(const //
195 requires range<Rng const>)
196 {
197#if RANGES_CXX_IF_CONSTEXPR >= RANGES_CXX_IF_CONSTEXPR_17
198 if constexpr(sized_range<Rng const>)
200 return ranges::begin(base_);
201 else
202 {
203 auto s = static_cast<range_difference_t<Rng>>(size());
204 return make_counted_iterator(ranges::begin(base_), s);
205 }
206 else
207 return make_counted_iterator(ranges::begin(base_), count_);
208#else
209 return begin_sized_(*this, meta::bool_<sized_range<Rng const>>{});
210#endif
211 }
212
213 CPP_auto_member
214 constexpr auto CPP_fun(end)()(
215 requires(!simple_view<Rng>()))
216 {
217#if RANGES_CXX_IF_CONSTEXPR >= RANGES_CXX_IF_CONSTEXPR_17
218 if constexpr(sized_range<Rng>)
219 if constexpr(random_access_range<Rng>)
220 return ranges::begin(base_) +
221 static_cast<range_difference_t<Rng>>(size());
222 else
223 return default_sentinel;
224 // Not to spec: Infinite ranges:
225 else if constexpr(is_infinite<Rng>::value)
226 return default_sentinel;
227 else
228 return sentinel<false>{ranges::end(base_)};
229#else
230 return end_sized_(*this, meta::bool_<sized_range<Rng>>{}, is_infinite<Rng>{});
231#endif
232 }
233
234 CPP_auto_member
235 constexpr auto CPP_fun(end)()(const //
236 requires range<Rng const>)
237 {
238#if RANGES_CXX_IF_CONSTEXPR >= RANGES_CXX_IF_CONSTEXPR_17
239 if constexpr(sized_range<Rng const>)
241 return ranges::begin(base_) +
242 static_cast<range_difference_t<Rng>>(size());
243 else
244 return default_sentinel;
245 // Not to spec: Infinite ranges:
246 else if constexpr(is_infinite<Rng const>::value)
247 return default_sentinel;
248 else
249 return sentinel<true>{ranges::end(base_)};
250#else
251 return end_sized_(
252 *this, meta::bool_<sized_range<Rng const>>{}, is_infinite<Rng const>{});
253#endif
254 }
255
256 CPP_auto_member
257 constexpr auto CPP_fun(size)()(
258 requires sized_range<Rng>)
259 {
260 auto n = ranges::size(base_);
261 return ranges::min(n, static_cast<decltype(n)>(count_));
262 }
263 CPP_auto_member
264 constexpr auto CPP_fun(size)()(const //
265 requires sized_range<Rng const>)
266 {
267 auto n = ranges::size(base_);
268 return ranges::min(n, static_cast<decltype(n)>(count_));
269 }
270 };
271
272 template<typename Rng>
273 RANGES_INLINE_VAR constexpr bool enable_borrowed_range<take_view<Rng>> = //
274 enable_borrowed_range<Rng>;
275
276#if RANGES_CXX_DEDUCTION_GUIDES >= RANGES_CXX_DEDUCTION_GUIDES_17
277 template<typename Rng>
278 take_view(Rng &&, range_difference_t<Rng>)
280#endif
281
282 namespace views
283 {
285 {
286 template(typename Rng)(
287 requires viewable_range<Rng>)
288 take_view<all_t<Rng>> operator()(Rng && rng, range_difference_t<Rng> n) const
289 {
290 return {all(static_cast<Rng &&>(rng)), n};
291 }
292 };
293
295 {
296 using take_base_fn::operator();
297
298 template(typename Int)(
299 requires detail::integer_like_<Int>)
300 constexpr auto operator()(Int n) const
301 {
302 return make_view_closure(bind_back(take_base_fn{}, n));
303 }
304 };
305
307 RANGES_INLINE_VARIABLE(take_fn, take)
308 } // namespace views
309
310 namespace cpp20
311 {
312 namespace views
313 {
314 using ranges::views::take;
315 }
316 template(typename Rng)(
317 requires view_<Rng>)
318 using take_view = ranges::take_view<Rng>;
319 } // namespace cpp20
321} // namespace ranges
322
323#include <range/v3/detail/epilogue.hpp>
324#include <range/v3/detail/satisfy_boost_range.hpp>
325RANGES_SATISFY_BOOST_RANGE(::ranges::take_view)
326
327#endif
The random_access_range concept.
The range concept.
The sized_range concept.
The view_ concept.
The viewable_range concept.
std::integral_constant< bool, B > bool_
An integral constant wrapper for bool.
Definition meta.hpp:168
typename detail::_cond< If >::template invoke< Then, Else > conditional_t
Select one type or another depending on a compile-time Boolean.
Definition meta.hpp:1148
Definition take.hpp:40
Definition interface.hpp:129
Definition take.hpp:285
Definition take.hpp:295