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generate.hpp
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1 // Range v3 library
3 //
4 // Copyright Eric Niebler 2014-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_GENERATE_HPP
15 #define RANGES_V3_VIEW_GENERATE_HPP
16 
17 #include <type_traits>
18 #include <utility>
19 
20 #include <meta/meta.hpp>
21 
22 #include <range/v3/range_fwd.hpp>
23 
31 #include <range/v3/utility/static_const.hpp>
32 #include <range/v3/view/facade.hpp>
33 
34 #include <range/v3/detail/prologue.hpp>
35 
36 namespace ranges
37 {
40  template<typename G>
41  struct generate_view : view_facade<generate_view<G>, infinite>
42  {
43  private:
44  friend range_access;
45  using result_t = invoke_result_t<G &>;
46  semiregular_box_t<G> gen_;
47  detail::non_propagating_cache<result_t> val_;
48  struct cursor
49  {
50  private:
52 
53  public:
54  cursor() = default;
55  explicit cursor(generate_view * view)
56  : view_(view)
57  {}
58  result_t && read() const
59  {
60  if(!view_->val_)
61  view_->val_.emplace(view_->gen_());
62  return static_cast<result_t &&>(static_cast<result_t &>(*view_->val_));
63  }
64  void next()
65  {
66  if(view_->val_)
67  view_->val_.reset();
68  else
69  static_cast<void>(view_->gen_());
70  }
71  };
72  cursor begin_cursor()
73  {
74  return cursor{this};
75  }
76  unreachable_sentinel_t end_cursor() const
77  {
78  return {};
79  }
80 
81  public:
82  generate_view() = default;
83  explicit generate_view(G g)
84  : gen_(std::move(g))
85  {}
86  result_t & cached()
87  {
88  return *val_;
89  }
90  };
91 
92  namespace views
93  {
94  struct generate_fn
95  {
96  template(typename G)(
97  requires invocable<G &> AND copy_constructible<G> AND
98  std::is_object<detail::decay_t<invoke_result_t<G &>>>::value AND
99  constructible_from<detail::decay_t<invoke_result_t<G &>>,
100  invoke_result_t<G &>> AND
101  assignable_from<detail::decay_t<invoke_result_t<G &>> &,
102  invoke_result_t<G &>>)
103  generate_view<G> operator()(G g) const
104  {
105  return generate_view<G>{std::move(g)};
106  }
107  };
108 
112  } // namespace views
114 } // namespace ranges
115 
116 #include <range/v3/detail/epilogue.hpp>
117 #include <range/v3/detail/satisfy_boost_range.hpp>
118 RANGES_SATISFY_BOOST_RANGE(::ranges::generate_view)
119 
120 #endif
CPP_concept view_
\concept view_
Definition: concepts.hpp:252
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
Tiny meta-programming library.
Definition: generate.hpp:42
Definition: unreachable_sentinel.hpp:27
A utility for constructing a view from a (derived) type that implements begin and end cursors.
Definition: facade.hpp:66
Definition: generate.hpp:95