libstdc++
utility.h
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1 // Utilities used throughout the library -*- C++ -*-
2 
3 // Copyright (C) 2004-2022 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file include/bits/utility.h
26  * This is an internal header file, included by other library headers.
27  * Do not attempt to use it directly. @headername{utility}
28  *
29  * This file contains the parts of `<utility>` needed by other headers,
30  * so they don't need to include the whole of `<utility>`.
31  */
32 
33 #ifndef _GLIBCXX_UTILITY_H
34 #define _GLIBCXX_UTILITY_H 1
35 
36 #pragma GCC system_header
37 
38 #if __cplusplus >= 201103L
39 
40 #include <type_traits>
41 #include <bits/move.h>
42 
43 namespace std _GLIBCXX_VISIBILITY(default)
44 {
45 _GLIBCXX_BEGIN_NAMESPACE_VERSION
46 
47  /// Finds the size of a given tuple type.
48  template<typename _Tp>
49  struct tuple_size;
50 
51  // _GLIBCXX_RESOLVE_LIB_DEFECTS
52  // 2313. tuple_size should always derive from integral_constant<size_t, N>
53  // 2770. tuple_size<const T> specialization is not SFINAE compatible
54 
55  template<typename _Tp,
56  typename _Up = typename remove_cv<_Tp>::type,
57  typename = typename enable_if<is_same<_Tp, _Up>::value>::type,
58  size_t = tuple_size<_Tp>::value>
59  using __enable_if_has_tuple_size = _Tp;
60 
61  template<typename _Tp>
62  struct tuple_size<const __enable_if_has_tuple_size<_Tp>>
63  : public tuple_size<_Tp> { };
64 
65  template<typename _Tp>
66  struct tuple_size<volatile __enable_if_has_tuple_size<_Tp>>
67  : public tuple_size<_Tp> { };
68 
69  template<typename _Tp>
70  struct tuple_size<const volatile __enable_if_has_tuple_size<_Tp>>
71  : public tuple_size<_Tp> { };
72 
73 #if __cplusplus >= 201703L
74  template<typename _Tp>
75  inline constexpr size_t tuple_size_v = tuple_size<_Tp>::value;
76 #endif
77 
78  /// Gives the type of the ith element of a given tuple type.
79  template<size_t __i, typename _Tp>
80  struct tuple_element;
81 
82  // Duplicate of C++14's tuple_element_t for internal use in C++11 mode
83  template<size_t __i, typename _Tp>
84  using __tuple_element_t = typename tuple_element<__i, _Tp>::type;
85 
86  template<size_t __i, typename _Tp>
87  struct tuple_element<__i, const _Tp>
88  {
89  typedef typename add_const<__tuple_element_t<__i, _Tp>>::type type;
90  };
91 
92  template<size_t __i, typename _Tp>
93  struct tuple_element<__i, volatile _Tp>
94  {
95  typedef typename add_volatile<__tuple_element_t<__i, _Tp>>::type type;
96  };
97 
98  template<size_t __i, typename _Tp>
99  struct tuple_element<__i, const volatile _Tp>
100  {
101  typedef typename add_cv<__tuple_element_t<__i, _Tp>>::type type;
102  };
103 
104 #if __cplusplus >= 201402L
105 
106  // Return the index of _Tp in _Types, if it occurs exactly once.
107  // Otherwise, return sizeof...(_Types).
108  template<typename _Tp, typename... _Types>
109  constexpr size_t
110  __find_uniq_type_in_pack()
111  {
112  constexpr size_t __sz = sizeof...(_Types);
113  constexpr bool __found[__sz] = { __is_same(_Tp, _Types) ... };
114  size_t __n = __sz;
115  for (size_t __i = 0; __i < __sz; ++__i)
116  {
117  if (__found[__i])
118  {
119  if (__n < __sz) // more than one _Tp found
120  return __sz;
121  __n = __i;
122  }
123  }
124  return __n;
125  }
126 
127 // The standard says this macro and alias template should be in <tuple> but we
128 // we define them here, to be available in <array>, <utility> and <ranges> too.
129 // _GLIBCXX_RESOLVE_LIB_DEFECTS
130 // 3378. tuple_size_v/tuple_element_t should be available when
131 // tuple_size/tuple_element are
132 #define __cpp_lib_tuple_element_t 201402L
133 
134  template<size_t __i, typename _Tp>
135  using tuple_element_t = typename tuple_element<__i, _Tp>::type;
136 #endif // C++14
137 
138  // Stores a tuple of indices. Used by tuple and pair, and by bind() to
139  // extract the elements in a tuple.
140  template<size_t... _Indexes> struct _Index_tuple { };
141 
142  // Builds an _Index_tuple<0, 1, 2, ..., _Num-1>.
143  template<size_t _Num>
144  struct _Build_index_tuple
145  {
146 #if __has_builtin(__make_integer_seq)
147  template<typename, size_t... _Indices>
148  using _IdxTuple = _Index_tuple<_Indices...>;
149 
150  // Clang defines __make_integer_seq for this purpose.
151  using __type = __make_integer_seq<_IdxTuple, size_t, _Num>;
152 #else
153  // For GCC and other compilers, use __integer_pack instead.
154  using __type = _Index_tuple<__integer_pack(_Num)...>;
155 #endif
156  };
157 
158 #if __cplusplus >= 201402L
159 
160 #define __cpp_lib_integer_sequence 201304L
161 
162  /// Class template integer_sequence
163  template<typename _Tp, _Tp... _Idx>
165  {
166  typedef _Tp value_type;
167  static constexpr size_t size() noexcept { return sizeof...(_Idx); }
168  };
169 
170  /// Alias template make_integer_sequence
171  template<typename _Tp, _Tp _Num>
173 #if __has_builtin(__make_integer_seq)
174  = __make_integer_seq<integer_sequence, _Tp, _Num>;
175 #else
176  = integer_sequence<_Tp, __integer_pack(_Num)...>;
177 #endif
178 
179  /// Alias template index_sequence
180  template<size_t... _Idx>
181  using index_sequence = integer_sequence<size_t, _Idx...>;
182 
183  /// Alias template make_index_sequence
184  template<size_t _Num>
186 
187  /// Alias template index_sequence_for
188  template<typename... _Types>
189  using index_sequence_for = make_index_sequence<sizeof...(_Types)>;
190 
191 #if __cplusplus >= 201703L
192 
193  //
194  struct in_place_t {
195  explicit in_place_t() = default;
196  };
197 
198  inline constexpr in_place_t in_place{};
199 
200  template<typename _Tp> struct in_place_type_t
201  {
202  explicit in_place_type_t() = default;
203  };
204 
205  template<typename _Tp>
206  inline constexpr in_place_type_t<_Tp> in_place_type{};
207 
208  template<size_t _Idx> struct in_place_index_t
209  {
210  explicit in_place_index_t() = default;
211  };
212 
213  template<size_t _Idx>
214  inline constexpr in_place_index_t<_Idx> in_place_index{};
215 
216  template<typename>
217  inline constexpr bool __is_in_place_type_v = false;
218 
219  template<typename _Tp>
220  inline constexpr bool __is_in_place_type_v<in_place_type_t<_Tp>> = true;
221 
222  template<typename _Tp>
223  using __is_in_place_type = bool_constant<__is_in_place_type_v<_Tp>>;
224 
225 #endif // C++17
226 #endif // C++14
227 
228  template<size_t _Np, typename... _Types>
229  struct _Nth_type
230  { };
231 
232  template<typename _Tp0, typename... _Rest>
233  struct _Nth_type<0, _Tp0, _Rest...>
234  { using type = _Tp0; };
235 
236  template<typename _Tp0, typename _Tp1, typename... _Rest>
237  struct _Nth_type<1, _Tp0, _Tp1, _Rest...>
238  { using type = _Tp1; };
239 
240  template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
241  struct _Nth_type<2, _Tp0, _Tp1, _Tp2, _Rest...>
242  { using type = _Tp2; };
243 
244  template<size_t _Np, typename _Tp0, typename _Tp1, typename _Tp2,
245  typename... _Rest>
246 #if __cpp_concepts
247  requires (_Np >= 3)
248 #endif
249  struct _Nth_type<_Np, _Tp0, _Tp1, _Tp2, _Rest...>
250  : _Nth_type<_Np - 3, _Rest...>
251  { };
252 
253 #if ! __cpp_concepts // Need additional specializations to avoid ambiguities.
254  template<typename _Tp0, typename _Tp1, typename... _Rest>
255  struct _Nth_type<0, _Tp0, _Tp1, _Rest...>
256  { using type = _Tp0; };
257 
258  template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
259  struct _Nth_type<0, _Tp0, _Tp1, _Tp2, _Rest...>
260  { using type = _Tp0; };
261 
262  template<typename _Tp0, typename _Tp1, typename _Tp2, typename... _Rest>
263  struct _Nth_type<1, _Tp0, _Tp1, _Tp2, _Rest...>
264  { using type = _Tp1; };
265 #endif
266 
267 _GLIBCXX_END_NAMESPACE_VERSION
268 } // namespace
269 
270 #endif // C++11
271 #endif /* _GLIBCXX_UTILITY_H */
Define a member typedef type only if a boolean constant is true.
Definition: type_traits:2228
Class template integer_sequence.
Definition: utility.h:164
remove_cv
Definition: type_traits:231
Gives the type of the ith element of a given tuple type.
Definition: utility.h:80
Finds the size of a given tuple type.
Definition: utility.h:49
make_integer_sequence< size_t, _Num > make_index_sequence
Alias template make_index_sequence.
Definition: utility.h:185
make_index_sequence< sizeof...(_Types)> index_sequence_for
Alias template index_sequence_for.
Definition: utility.h:189
add_const
Definition: type_traits:1579
add_volatile
Definition: type_traits:1584
__make_integer_seq< integer_sequence, _Tp, _Num > make_integer_sequence
Alias template make_integer_sequence.
Definition: utility.h:174