libstdc++-v3/include/bits/utility.h

   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>
 164     struct integer_sequence
 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>
 172     using make_integer_sequence
 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>
 185     using make_index_sequence = make_integer_sequence<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 */