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

   1 // Move, forward and identity for C++11 + swap -*- C++ -*-
   2
   3 // Copyright (C) 2007-2023 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   [[nodiscard]]
  92   constexpr decltype(auto)
  93   forward_like(_Up&& __x) noexcept
  94   {
  95     constexpr bool __as_rval = is_rvalue_reference_v<_Tp&&>;
  96
  97     if constexpr (is_const_v<remove_reference_t<_Tp>>)
  98       {
  99         using _Up2 = remove_reference_t<_Up>;
 100         if constexpr (__as_rval)
 101           return static_cast<const _Up2&&>(__x);
 102         else
 103           return static_cast<const _Up2&>(__x);
 104       }
 105     else
 106       {
 107         if constexpr (__as_rval)
 108           return static_cast<remove_reference_t<_Up>&&>(__x);
 109         else
 110           return static_cast<_Up&>(__x);
 111       }
 112   }
 113 #endif
 114
 115   /**
 116    *  @brief  Convert a value to an rvalue.
 117    *  @param  __t  A thing of arbitrary type.
 118    *  @return The parameter cast to an rvalue-reference to allow moving it.
 119   */
 120   template<typename _Tp>
 121     _GLIBCXX_NODISCARD
 122     constexpr typename std::remove_reference<_Tp>::type&&
 123     move(_Tp&& __t) noexcept
 124     { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
 125
 126
 127   template<typename _Tp>
 128     struct __move_if_noexcept_cond
 129     : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
 130                     is_copy_constructible<_Tp>>::type { };
 131
 132   /**
 133    *  @brief  Conditionally convert a value to an rvalue.
 134    *  @param  __x  A thing of arbitrary type.
 135    *  @return The parameter, possibly cast to an rvalue-reference.
 136    *
 137    *  Same as std::move unless the type's move constructor could throw and the
 138    *  type is copyable, in which case an lvalue-reference is returned instead.
 139    */
 140   template<typename _Tp>
 141     _GLIBCXX_NODISCARD
 142     constexpr
 143     __conditional_t<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>
 144     move_if_noexcept(_Tp& __x) noexcept
 145     { return std::move(__x); }
 146
 147   // declval, from type_traits.
 148
 149   /**
 150    *  @brief Returns the actual address of the object or function
 151    *         referenced by r, even in the presence of an overloaded
 152    *         operator&.
 153    *  @param  __r  Reference to an object or function.
 154    *  @return   The actual address.
 155   */
 156   template<typename _Tp>
 157     _GLIBCXX_NODISCARD
 158     inline _GLIBCXX17_CONSTEXPR _Tp*
 159     addressof(_Tp& __r) noexcept
 160     { return std::__addressof(__r); }
 161
 162   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 163   // 2598. addressof works on temporaries
 164   template<typename _Tp>
 165     const _Tp* addressof(const _Tp&&) = delete;
 166
 167   // C++11 version of std::exchange for internal use.
 168   template <typename _Tp, typename _Up = _Tp>
 169     _GLIBCXX20_CONSTEXPR
 170     inline _Tp
 171     __exchange(_Tp& __obj, _Up&& __new_val)
 172     {
 173       _Tp __old_val = std::move(__obj);
 174       __obj = std::forward<_Up>(__new_val);
 175       return __old_val;
 176     }
 177
 178   /// @} group utilities
 179
 180 #define _GLIBCXX_FWDREF(_Tp) _Tp&&
 181 #define _GLIBCXX_MOVE(__val) std::move(__val)
 182 #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
 183 #else
 184 #define _GLIBCXX_FWDREF(_Tp) const _Tp&
 185 #define _GLIBCXX_MOVE(__val) (__val)
 186 #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
 187 #endif
 188
 189   /**
 190    *  @addtogroup utilities
 191    *  @{
 192    */
 193
 194   /**
 195    *  @brief Swaps two values.
 196    *  @param  __a  A thing of arbitrary type.
 197    *  @param  __b  Another thing of arbitrary type.
 198    *  @return   Nothing.
 199   */
 200   template<typename _Tp>
 201     _GLIBCXX20_CONSTEXPR
 202     inline
 203 #if __cplusplus >= 201103L
 204     typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
 205                               is_move_constructible<_Tp>,
 206                               is_move_assignable<_Tp>>::value>::type
 207 #else
 208     void
 209 #endif
 210     swap(_Tp& __a, _Tp& __b)
 211     _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
 212                                 is_nothrow_move_assignable<_Tp>>::value)
 213     {
 214 #if __cplusplus < 201103L
 215       // concept requirements
 216       __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
 217 #endif
 218       _Tp __tmp = _GLIBCXX_MOVE(__a);
 219       __a = _GLIBCXX_MOVE(__b);
 220       __b = _GLIBCXX_MOVE(__tmp);
 221     }
 222
 223   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 224   // DR 809. std::swap should be overloaded for array types.
 225   /// Swap the contents of two arrays.
 226   template<typename _Tp, size_t _Nm>
 227     _GLIBCXX20_CONSTEXPR
 228     inline
 229 #if __cplusplus >= 201103L
 230     typename enable_if<__is_swappable<_Tp>::value>::type
 231 #else
 232     void
 233 #endif
 234     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
 235     _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
 236     {
 237       for (size_t __n = 0; __n < _Nm; ++__n)
 238         swap(__a[__n], __b[__n]);
 239     }
 240
 241   /// @} group utilities
 242 _GLIBCXX_END_NAMESPACE_VERSION
 243 } // namespace
 244
 245 #endif /* _MOVE_H */