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

   1 // Move, forward and identity for C++11 + swap -*- C++ -*-
   2
   3 // Copyright (C) 2007-2024 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 bits/move.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
  30 #ifndef _MOVE_H
  31 #define _MOVE_H 1
  32
  33 #include <bits/c++config.h>
  34 #if __cplusplus < 201103L
  35 # include <bits/concept_check.h>
  36 #else
  37 # include <type_traits> // Brings in std::declval too.
  38 #endif
  39
  40 namespace std _GLIBCXX_VISIBILITY(default)
  41 {
  42 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  43
  44   // Used, in C++03 mode too, by allocators, etc.
  45   /**
  46    *  @brief Same as C++11 std::addressof
  47    *  @ingroup utilities
  48    */
  49   template<typename _Tp>
  50     inline _GLIBCXX_CONSTEXPR _Tp*
  51     __addressof(_Tp& __r) _GLIBCXX_NOEXCEPT
  52     { return __builtin_addressof(__r); }
  53
  54 #if __cplusplus >= 201103L
  55
  56   /**
  57    *  @addtogroup utilities
  58    *  @{
  59    */
  60
  61   /**
  62    *  @brief  Forward an lvalue.
  63    *  @return The parameter cast to the specified type.
  64    *
  65    *  This function is used to implement "perfect forwarding".
  66    */
  67   template<typename _Tp>
  68     _GLIBCXX_NODISCARD
  69     constexpr _Tp&&
  70     forward(typename std::remove_reference<_Tp>::type& __t) noexcept
  71     { return static_cast<_Tp&&>(__t); }
  72
  73   /**
  74    *  @brief  Forward an rvalue.
  75    *  @return The parameter cast to the specified type.
  76    *
  77    *  This function is used to implement "perfect forwarding".
  78    */
  79   template<typename _Tp>
  80     _GLIBCXX_NODISCARD
  81     constexpr _Tp&&
  82     forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
  83     {
  84       static_assert(!std::is_lvalue_reference<_Tp>::value,
  85           "std::forward must not be used to convert an rvalue to an lvalue");
  86       return static_cast<_Tp&&>(__t);
  87     }
  88
  89 #if __glibcxx_forward_like // C++ >= 23
  90   template<typename _Tp, typename _Up>
  91   struct __like_impl; // _Tp must be a reference and _Up an lvalue reference
  92
  93   template<typename _Tp, typename _Up>
  94   struct __like_impl<_Tp&, _Up&>
  95   { using type = _Up&; };
  96
  97   template<typename _Tp, typename _Up>
  98   struct __like_impl<const _Tp&, _Up&>
  99   { using type = const _Up&; };
 100
 101   template<typename _Tp, typename _Up>
 102   struct __like_impl<_Tp&&, _Up&>
 103   { using type = _Up&&; };
 104
 105   template<typename _Tp, typename _Up>
 106   struct __like_impl<const _Tp&&, _Up&>
 107   { using type = const _Up&&; };
 108
 109   template<typename _Tp, typename _Up>
 110     using __like_t = typename __like_impl<_Tp&&, _Up&>::type;
 111
 112   template<typename _Tp, typename _Up>
 113   [[nodiscard]]
 114   constexpr __like_t<_Tp, _Up>
 115   forward_like(_Up&& __x) noexcept
 116   { return static_cast<__like_t<_Tp, _Up>>(__x); }
 117 #endif
 118
 119   /**
 120    *  @brief  Convert a value to an rvalue.
 121    *  @param  __t  A thing of arbitrary type.
 122    *  @return The parameter cast to an rvalue-reference to allow moving it.
 123   */
 124   template<typename _Tp>
 125     _GLIBCXX_NODISCARD
 126     constexpr typename std::remove_reference<_Tp>::type&&
 127     move(_Tp&& __t) noexcept
 128     { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
 129
 130
 131   template<typename _Tp>
 132     struct __move_if_noexcept_cond
 133     : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
 134                     is_copy_constructible<_Tp>>::type { };
 135
 136   /**
 137    *  @brief  Conditionally convert a value to an rvalue.
 138    *  @param  __x  A thing of arbitrary type.
 139    *  @return The parameter, possibly cast to an rvalue-reference.
 140    *
 141    *  Same as std::move unless the type's move constructor could throw and the
 142    *  type is copyable, in which case an lvalue-reference is returned instead.
 143    */
 144   template<typename _Tp>
 145     _GLIBCXX_NODISCARD
 146     constexpr
 147     __conditional_t<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>
 148     move_if_noexcept(_Tp& __x) noexcept
 149     { return std::move(__x); }
 150
 151   // declval, from type_traits.
 152
 153   /**
 154    *  @brief Returns the actual address of the object or function
 155    *         referenced by r, even in the presence of an overloaded
 156    *         operator&.
 157    *  @param  __r  Reference to an object or function.
 158    *  @return   The actual address.
 159   */
 160   template<typename _Tp>
 161     _GLIBCXX_NODISCARD
 162     inline _GLIBCXX17_CONSTEXPR _Tp*
 163     addressof(_Tp& __r) noexcept
 164     { return std::__addressof(__r); }
 165
 166   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 167   // 2598. addressof works on temporaries
 168   template<typename _Tp>
 169     const _Tp* addressof(const _Tp&&) = delete;
 170
 171   // C++11 version of std::exchange for internal use.
 172   template <typename _Tp, typename _Up = _Tp>
 173     _GLIBCXX20_CONSTEXPR
 174     inline _Tp
 175     __exchange(_Tp& __obj, _Up&& __new_val)
 176     {
 177       _Tp __old_val = std::move(__obj);
 178       __obj = std::forward<_Up>(__new_val);
 179       return __old_val;
 180     }
 181
 182   /// @} group utilities
 183
 184 #define _GLIBCXX_FWDREF(_Tp) _Tp&&
 185 #define _GLIBCXX_MOVE(__val) std::move(__val)
 186 #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
 187 #else
 188 #define _GLIBCXX_FWDREF(_Tp) const _Tp&
 189 #define _GLIBCXX_MOVE(__val) (__val)
 190 #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
 191 #endif
 192
 193   /**
 194    *  @addtogroup utilities
 195    *  @{
 196    */
 197
 198   /**
 199    *  @brief Swaps two values.
 200    *  @param  __a  A thing of arbitrary type.
 201    *  @param  __b  Another thing of arbitrary type.
 202    *  @return   Nothing.
 203   */
 204   template<typename _Tp>
 205     _GLIBCXX20_CONSTEXPR
 206     inline
 207 #if __cplusplus >= 201103L
 208     typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
 209                               is_move_constructible<_Tp>,
 210                               is_move_assignable<_Tp>>::value>::type
 211 #else
 212     void
 213 #endif
 214     swap(_Tp& __a, _Tp& __b)
 215     _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
 216                                 is_nothrow_move_assignable<_Tp>>::value)
 217     {
 218 #if __cplusplus < 201103L
 219       // concept requirements
 220       __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
 221 #endif
 222       _Tp __tmp = _GLIBCXX_MOVE(__a);
 223       __a = _GLIBCXX_MOVE(__b);
 224       __b = _GLIBCXX_MOVE(__tmp);
 225     }
 226
 227   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 228   // DR 809. std::swap should be overloaded for array types.
 229   /// Swap the contents of two arrays.
 230   template<typename _Tp, size_t _Nm>
 231     _GLIBCXX20_CONSTEXPR
 232     inline
 233 #if __cplusplus >= 201103L
 234     typename enable_if<__is_swappable<_Tp>::value>::type
 235 #else
 236     void
 237 #endif
 238     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
 239     _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
 240     {
 241       for (size_t __n = 0; __n < _Nm; ++__n)
 242         swap(__a[__n], __b[__n]);
 243     }
 244
 245   /// @} group utilities
 246 _GLIBCXX_END_NAMESPACE_VERSION
 247 } // namespace
 248
 249 #endif /* _MOVE_H */