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

   1 // Move, forward and identity for C++11 + swap -*- C++ -*-
   2
   3 // Copyright (C) 2007-2020 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 #endif
  37
  38 namespace std _GLIBCXX_VISIBILITY(default)
  39 {
  40 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  41
  42   // Used, in C++03 mode too, by allocators, etc.
  43   /**
  44    *  @brief Same as C++11 std::addressof
  45    *  @ingroup utilities
  46    */
  47   template<typename _Tp>
  48     inline _GLIBCXX_CONSTEXPR _Tp*
  49     __addressof(_Tp& __r) _GLIBCXX_NOEXCEPT
  50     { return __builtin_addressof(__r); }
  51
  52 #if __cplusplus >= 201103L
  53
  54 _GLIBCXX_END_NAMESPACE_VERSION
  55 } // namespace
  56
  57 #include <type_traits> // Brings in std::declval too.
  58
  59 namespace std _GLIBCXX_VISIBILITY(default)
  60 {
  61 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  62
  63   /**
  64    *  @addtogroup utilities
  65    *  @{
  66    */
  67
  68   /**
  69    *  @brief  Forward an lvalue.
  70    *  @return The parameter cast to the specified type.
  71    *
  72    *  This function is used to implement "perfect forwarding".
  73    */
  74   template<typename _Tp>
  75     constexpr _Tp&&
  76     forward(typename std::remove_reference<_Tp>::type& __t) noexcept
  77     { return static_cast<_Tp&&>(__t); }
  78
  79   /**
  80    *  @brief  Forward an rvalue.
  81    *  @return The parameter cast to the specified type.
  82    *
  83    *  This function is used to implement "perfect forwarding".
  84    */
  85   template<typename _Tp>
  86     constexpr _Tp&&
  87     forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
  88     {
  89       static_assert(!std::is_lvalue_reference<_Tp>::value, "template argument"
  90                     " substituting _Tp is an lvalue reference type");
  91       return static_cast<_Tp&&>(__t);
  92     }
  93
  94   /**
  95    *  @brief  Convert a value to an rvalue.
  96    *  @param  __t  A thing of arbitrary type.
  97    *  @return The parameter cast to an rvalue-reference to allow moving it.
  98   */
  99   template<typename _Tp>
 100     constexpr typename std::remove_reference<_Tp>::type&&
 101     move(_Tp&& __t) noexcept
 102     { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
 103
 104
 105   template<typename _Tp>
 106     struct __move_if_noexcept_cond
 107     : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
 108                     is_copy_constructible<_Tp>>::type { };
 109
 110   /**
 111    *  @brief  Conditionally convert a value to an rvalue.
 112    *  @param  __x  A thing of arbitrary type.
 113    *  @return The parameter, possibly cast to an rvalue-reference.
 114    *
 115    *  Same as std::move unless the type's move constructor could throw and the
 116    *  type is copyable, in which case an lvalue-reference is returned instead.
 117    */
 118   template<typename _Tp>
 119     constexpr typename
 120     conditional<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>::type
 121     move_if_noexcept(_Tp& __x) noexcept
 122     { return std::move(__x); }
 123
 124   // declval, from type_traits.
 125
 126 #if __cplusplus > 201402L
 127   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 128   // 2296. std::addressof should be constexpr
 129 # define __cpp_lib_addressof_constexpr 201603
 130 #endif
 131   /**
 132    *  @brief Returns the actual address of the object or function
 133    *         referenced by r, even in the presence of an overloaded
 134    *         operator&.
 135    *  @param  __r  Reference to an object or function.
 136    *  @return   The actual address.
 137   */
 138   template<typename _Tp>
 139     inline _GLIBCXX17_CONSTEXPR _Tp*
 140     addressof(_Tp& __r) noexcept
 141     { return std::__addressof(__r); }
 142
 143   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 144   // 2598. addressof works on temporaries
 145   template<typename _Tp>
 146     const _Tp* addressof(const _Tp&&) = delete;
 147
 148   // C++11 version of std::exchange for internal use.
 149   template <typename _Tp, typename _Up = _Tp>
 150     _GLIBCXX20_CONSTEXPR
 151     inline _Tp
 152     __exchange(_Tp& __obj, _Up&& __new_val)
 153     {
 154       _Tp __old_val = std::move(__obj);
 155       __obj = std::forward<_Up>(__new_val);
 156       return __old_val;
 157     }
 158
 159   /// @} group utilities
 160
 161 #define _GLIBCXX_FWDREF(_Tp) _Tp&&
 162 #define _GLIBCXX_MOVE(__val) std::move(__val)
 163 #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
 164 #else
 165 #define _GLIBCXX_FWDREF(_Tp) const _Tp&
 166 #define _GLIBCXX_MOVE(__val) (__val)
 167 #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
 168 #endif
 169
 170   /**
 171    *  @addtogroup utilities
 172    *  @{
 173    */
 174
 175   /**
 176    *  @brief Swaps two values.
 177    *  @param  __a  A thing of arbitrary type.
 178    *  @param  __b  Another thing of arbitrary type.
 179    *  @return   Nothing.
 180   */
 181   template<typename _Tp>
 182     _GLIBCXX20_CONSTEXPR
 183     inline
 184 #if __cplusplus >= 201103L
 185     typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
 186                               is_move_constructible<_Tp>,
 187                               is_move_assignable<_Tp>>::value>::type
 188 #else
 189     void
 190 #endif
 191     swap(_Tp& __a, _Tp& __b)
 192     _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
 193                                 is_nothrow_move_assignable<_Tp>>::value)
 194     {
 195 #if __cplusplus < 201103L
 196       // concept requirements
 197       __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
 198 #endif
 199       _Tp __tmp = _GLIBCXX_MOVE(__a);
 200       __a = _GLIBCXX_MOVE(__b);
 201       __b = _GLIBCXX_MOVE(__tmp);
 202     }
 203
 204   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 205   // DR 809. std::swap should be overloaded for array types.
 206   /// Swap the contents of two arrays.
 207   template<typename _Tp, size_t _Nm>
 208     _GLIBCXX20_CONSTEXPR
 209     inline
 210 #if __cplusplus >= 201103L
 211     typename enable_if<__is_swappable<_Tp>::value>::type
 212 #else
 213     void
 214 #endif
 215     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
 216     _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
 217     {
 218       for (size_t __n = 0; __n < _Nm; ++__n)
 219         swap(__a[__n], __b[__n]);
 220     }
 221
 222   /// @} group utilities
 223 _GLIBCXX_END_NAMESPACE_VERSION
 224 } // namespace
 225
 226 #endif /* _MOVE_H */