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drop.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_DROP_HPP
15 #define RANGES_V3_VIEW_DROP_HPP
16 
17 #include <type_traits>
18 
19 #include <meta/meta.hpp>
20 
21 #include <range/v3/range_fwd.hpp>
22 
29 #include <range/v3/utility/box.hpp>
31 #include <range/v3/utility/static_const.hpp>
32 #include <range/v3/view/all.hpp>
35 #include <range/v3/view/view.hpp>
36 
37 #include <range/v3/detail/prologue.hpp>
38 
39 namespace ranges
40 {
43  template<typename Rng>
44  struct RANGES_EMPTY_BASES drop_view
45  : view_interface<drop_view<Rng>,
46  is_finite<Rng>::value ? finite : range_cardinality<Rng>::value>
47  , private detail::non_propagating_cache<iterator_t<Rng>, drop_view<Rng>,
48  !random_access_range<Rng>>
49  {
50  private:
51  using difference_type_ = range_difference_t<Rng>;
52  Rng rng_;
53  difference_type_ n_;
54 
55  template(bool Const = true)(
56  requires Const AND range<meta::const_if_c<Const, Rng>>)
58  get_begin_(std::true_type, std::true_type) const
59  {
60  CPP_assert(random_access_range<meta::const_if_c<Const, Rng>>);
61  return next(ranges::begin(rng_), n_, ranges::end(rng_));
62  }
63  iterator_t<Rng> get_begin_(std::true_type, std::false_type)
64  {
65  CPP_assert(random_access_range<Rng>);
66  return next(ranges::begin(rng_), n_, ranges::end(rng_));
67  }
68  iterator_t<Rng> get_begin_(std::false_type, detail::ignore_t)
69  {
70  CPP_assert(!random_access_range<Rng>);
71  using cache_t =
72  detail::non_propagating_cache<iterator_t<Rng>, drop_view<Rng>>;
73  auto & begin_ = static_cast<cache_t &>(*this);
74  if(!begin_)
75  begin_ = next(ranges::begin(rng_), n_, ranges::end(rng_));
76  return *begin_;
77  }
78 
79  public:
80  drop_view() = default;
81  drop_view(Rng rng, difference_type_ n)
82  : rng_(std::move(rng))
83  , n_(n)
84  {
85  RANGES_EXPECT(n >= 0);
86  }
87  iterator_t<Rng> begin()
88  {
89  return this->get_begin_(meta::bool_<random_access_range<Rng>>{},
90  std::false_type{});
91  }
92  sentinel_t<Rng> end()
93  {
94  return ranges::end(rng_);
95  }
96  template(bool Const = true)(
97  requires Const AND random_access_range<meta::const_if_c<Const, Rng>>)
99  {
100  return this->get_begin_(std::true_type{}, std::true_type{});
101  }
102  template(bool Const = true)(
103  requires Const AND random_access_range<meta::const_if_c<Const, Rng>>)
104  sentinel_t<meta::const_if_c<Const, Rng>> end() const
105  {
106  return ranges::end(rng_);
107  }
108  CPP_auto_member
109  auto CPP_fun(size)()(const //
110  requires sized_range<Rng const>)
111  {
112  auto const s = ranges::size(rng_);
113  auto const n = static_cast<range_size_t<Rng const>>(n_);
114  return s < n ? 0 : s - n;
115  }
116  CPP_auto_member
117  auto CPP_fun(size)()(
118  requires sized_range<Rng>)
119  {
120  auto const s = ranges::size(rng_);
121  auto const n = static_cast<range_size_t<Rng>>(n_);
122  return s < n ? 0 : s - n;
123  }
124  Rng base() const
125  {
126  return rng_;
127  }
128  };
129 
130  template<typename Rng>
131  RANGES_INLINE_VAR constexpr bool enable_borrowed_range<drop_view<Rng>> = //
132  enable_borrowed_range<Rng>;
133 
134 #if RANGES_CXX_DEDUCTION_GUIDES >= RANGES_CXX_DEDUCTION_GUIDES_17
135  template<typename Rng>
136  drop_view(Rng &&, range_difference_t<Rng>)
138 #endif
139 
140  namespace views
141  {
143  {
144  private:
145  template<typename Rng>
146  static auto impl_(Rng && rng, range_difference_t<Rng> n, input_range_tag)
148  {
149  return {all(static_cast<Rng &&>(rng)), n};
150  }
151  template(typename Rng)(
152  requires borrowed_range<Rng> AND sized_range<Rng>)
153  static subrange<iterator_t<Rng>, sentinel_t<Rng>> //
154  impl_(Rng && rng, range_difference_t<Rng> n, random_access_range_tag)
155  {
156  return {begin(rng) + ranges::min(n, distance(rng)), end(rng)};
157  }
158 
159  public:
160  template(typename Rng)(
161  requires viewable_range<Rng> AND input_range<Rng>)
162  auto operator()(Rng && rng, range_difference_t<Rng> n) const
163  {
164  return drop_base_fn::impl_(
165  static_cast<Rng &&>(rng), n, range_tag_of<Rng>{});
166  }
167  };
168 
170  {
171  using drop_base_fn::operator();
172 
173  template(typename Int)(
174  requires detail::integer_like_<Int>)
175  constexpr auto operator()(Int n) const
176  {
177  return make_view_closure(bind_back(drop_base_fn{}, n));
178  }
179  };
180 
184  } // namespace views
185 
186  namespace cpp20
187  {
188  namespace views
189  {
190  using ranges::views::drop;
191  }
192  template(typename Rng)(
193  requires view_<Rng>)
194  using drop_view = ranges::drop_view<Rng>;
195  } // namespace cpp20
197 } // namespace ranges
198 
199 #include <range/v3/detail/epilogue.hpp>
200 #include <range/v3/detail/satisfy_boost_range.hpp>
201 RANGES_SATISFY_BOOST_RANGE(::ranges::drop_view)
202 
203 #endif
CPP_concept random_access_range
\concept random_access_range
Definition: concepts.hpp:140
CPP_concept range
\concept range
Definition: concepts.hpp:69
decltype(begin(declval(Rng &))) iterator_t
Definition: access.hpp:698
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
drop_c< L, N::type::value > drop
Return a new meta::list by removing the first N elements from L.
Definition: meta.hpp:2037
Tiny meta-programming library.
Definition: drop.hpp:49
Definition: concepts.hpp:271
Definition: concepts.hpp:277
Definition: subrange.hpp:196
Definition: interface.hpp:129
Definition: drop.hpp:143
Definition: drop.hpp:170