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take.hpp
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1 // 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 
19 #include <range/v3/range_fwd.hpp>
20 
27 #include <range/v3/utility/static_const.hpp>
28 #include <range/v3/view/all.hpp>
29 #include <range/v3/view/view.hpp>
30 
31 #include <range/v3/detail/prologue.hpp>
32 
33 namespace 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>)
199  if constexpr(random_access_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>)
240  if constexpr(random_access_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 
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>
325 RANGES_SATISFY_BOOST_RANGE(::ranges::take_view)
326 
327 #endif
CPP_concept random_access_range
\concept random_access_range
Definition: concepts.hpp:140
RANGES_INLINE_VARIABLE(detail::to_container_fn< detail::from_range< std::vector >>, to_vector) template< template< typename... > class ContT > auto to(RANGES_HIDDEN_DETAIL(detail
For initializing a container of the specified type with the elements of an Range.
Definition: conversion.hpp:399
std::integral_constant< bool, B > bool_
An integral constant wrapper for bool.
Definition: meta.hpp:168
defer< bind_back, Fn, Ts... > bind_back
Definition: meta.hpp:994
meta::size_t< L::size()> size
An integral constant wrapper that is the size of the meta::list L.
Definition: meta.hpp:1696
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