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

   1 // Move, forward and identity for C++11 + swap -*- C++ -*-
   2
   3 // Copyright (C) 2007-2025 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     __attribute__((__always_inline__))
  51     inline _GLIBCXX_CONSTEXPR _Tp*
  52     __addressof(_Tp& __r) _GLIBCXX_NOEXCEPT
  53     { return __builtin_addressof(__r); }
  54
  55 #if __cplusplus >= 201103L
  56
  57   /**
  58    *  @addtogroup utilities
  59    *  @{
  60    */
  61
  62   /**
  63    *  @brief  Forward an lvalue.
  64    *  @return The parameter cast to the specified type.
  65    *
  66    *  This function is used to implement "perfect forwarding".
  67    *  @since C++11
  68    */
  69   template<typename _Tp>
  70     [[__nodiscard__,__gnu__::__always_inline__]]
  71     constexpr _Tp&&
  72     forward(typename std::remove_reference<_Tp>::type& __t) noexcept
  73     { return static_cast<_Tp&&>(__t); }
  74
  75   /**
  76    *  @brief  Forward an rvalue.
  77    *  @return The parameter cast to the specified type.
  78    *
  79    *  This function is used to implement "perfect forwarding".
  80    *  @since C++11
  81    */
  82   template<typename _Tp>
  83     [[__nodiscard__,__gnu__::__always_inline__]]
  84     constexpr _Tp&&
  85     forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
  86     {
  87       static_assert(!std::is_lvalue_reference<_Tp>::value,
  88           "std::forward must not be used to convert an rvalue to an lvalue");
  89       return static_cast<_Tp&&>(__t);
  90     }
  91
  92 #if __glibcxx_forward_like // C++ >= 23
  93   template<typename _Tp, typename _Up>
  94   struct __like_impl; // _Tp must be a reference and _Up an lvalue reference
  95
  96   template<typename _Tp, typename _Up>
  97   struct __like_impl<_Tp&, _Up&>
  98   { using type = _Up&; };
  99
 100   template<typename _Tp, typename _Up>
 101   struct __like_impl<const _Tp&, _Up&>
 102   { using type = const _Up&; };
 103
 104   template<typename _Tp, typename _Up>
 105   struct __like_impl<_Tp&&, _Up&>
 106   { using type = _Up&&; };
 107
 108   template<typename _Tp, typename _Up>
 109   struct __like_impl<const _Tp&&, _Up&>
 110   { using type = const _Up&&; };
 111
 112   template<typename _Tp, typename _Up>
 113     using __like_t = typename __like_impl<_Tp&&, _Up&>::type;
 114
 115   /** @brief Forward with the cv-qualifiers and value category of another type.
 116    *  @tparam _Tp An lvalue reference or rvalue reference.
 117    *  @tparam _Up An lvalue reference type deduced from the function argument.
 118    *  @param __x An lvalue.
 119    *  @return `__x` converted to match the qualifiers of `_Tp`.
 120    *  @since C++23
 121    */
 122   template<typename _Tp, typename _Up>
 123   [[nodiscard,__gnu__::__always_inline__]]
 124   constexpr __like_t<_Tp, _Up>
 125   forward_like(_Up&& __x) noexcept
 126   { return static_cast<__like_t<_Tp, _Up>>(__x); }
 127 #endif
 128
 129   /**
 130    *  @brief  Convert a value to an rvalue.
 131    *  @param  __t  A thing of arbitrary type.
 132    *  @return The parameter cast to an rvalue-reference to allow moving it.
 133    *  @since C++11
 134   */
 135   template<typename _Tp>
 136     [[__nodiscard__,__gnu__::__always_inline__]]
 137     constexpr typename std::remove_reference<_Tp>::type&&
 138     move(_Tp&& __t) noexcept
 139     { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
 140
 141
 142   template<typename _Tp>
 143     struct __move_if_noexcept_cond
 144     : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
 145                     is_copy_constructible<_Tp>>::type { };
 146
 147   /**
 148    *  @brief  Conditionally convert a value to an rvalue.
 149    *  @param  __x  A thing of arbitrary type.
 150    *  @return The parameter, possibly cast to an rvalue-reference.
 151    *
 152    *  Same as std::move unless the type's move constructor could throw and the
 153    *  type is copyable, in which case an lvalue-reference is returned instead.
 154    *  @since C++11
 155    */
 156   template<typename _Tp>
 157     [[__nodiscard__,__gnu__::__always_inline__]]
 158     constexpr
 159     __conditional_t<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>
 160     move_if_noexcept(_Tp& __x) noexcept
 161     { return std::move(__x); }
 162
 163   // declval, from type_traits.
 164
 165   /**
 166    *  @brief Returns the actual address of the object or function
 167    *         referenced by r, even in the presence of an overloaded
 168    *         operator&.
 169    *  @param  __r  Reference to an object or function.
 170    *  @return   The actual address.
 171    *  @since C++11
 172   */
 173   template<typename _Tp>
 174     [[__nodiscard__,__gnu__::__always_inline__]]
 175     inline _GLIBCXX17_CONSTEXPR _Tp*
 176     addressof(_Tp& __r) noexcept
 177     { return __builtin_addressof(__r); }
 178
 179   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 180   // 2598. addressof works on temporaries
 181   template<typename _Tp>
 182     const _Tp* addressof(const _Tp&&) = delete;
 183
 184   // C++11 version of std::exchange for internal use.
 185   template <typename _Tp, typename _Up = _Tp>
 186     _GLIBCXX20_CONSTEXPR
 187     inline _Tp
 188     __exchange(_Tp& __obj, _Up&& __new_val)
 189     {
 190       _Tp __old_val = std::move(__obj);
 191       __obj = std::forward<_Up>(__new_val);
 192       return __old_val;
 193     }
 194
 195   /// @} group utilities
 196
 197 #define _GLIBCXX_FWDREF(_Tp) _Tp&&
 198 #define _GLIBCXX_MOVE(__val) std::move(__val)
 199 #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
 200 #else
 201 #define _GLIBCXX_FWDREF(_Tp) const _Tp&
 202 #define _GLIBCXX_MOVE(__val) (__val)
 203 #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
 204 #endif
 205
 206   /**
 207    *  @addtogroup utilities
 208    *  @{
 209    */
 210
 211   /**
 212    *  @brief Swaps two values.
 213    *  @param  __a  A thing of arbitrary type.
 214    *  @param  __b  Another thing of arbitrary type.
 215    *  @return   Nothing.
 216   */
 217   template<typename _Tp>
 218     _GLIBCXX20_CONSTEXPR
 219     inline
 220 #if __cplusplus >= 201103L
 221     typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
 222                               is_move_constructible<_Tp>,
 223                               is_move_assignable<_Tp>>::value>::type
 224 #else
 225     void
 226 #endif
 227     swap(_Tp& __a, _Tp& __b)
 228     _GLIBCXX_NOEXCEPT_IF(__and_<is_nothrow_move_constructible<_Tp>,
 229                                 is_nothrow_move_assignable<_Tp>>::value)
 230     {
 231 #if __cplusplus < 201103L
 232       // concept requirements
 233       __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
 234 #endif
 235       _Tp __tmp = _GLIBCXX_MOVE(__a);
 236       __a = _GLIBCXX_MOVE(__b);
 237       __b = _GLIBCXX_MOVE(__tmp);
 238     }
 239
 240   // _GLIBCXX_RESOLVE_LIB_DEFECTS
 241   // DR 809. std::swap should be overloaded for array types.
 242   /// Swap the contents of two arrays.
 243   template<typename _Tp, size_t _Nm>
 244     _GLIBCXX20_CONSTEXPR
 245     inline
 246 #if __cplusplus >= 201103L
 247     typename enable_if<__is_swappable<_Tp>::value>::type
 248 #else
 249     void
 250 #endif
 251     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
 252     _GLIBCXX_NOEXCEPT_IF(__is_nothrow_swappable<_Tp>::value)
 253     {
 254       for (size_t __n = 0; __n < _Nm; ++__n)
 255         swap(__a[__n], __b[__n]);
 256     }
 257
 258   /// @} group utilities
 259 _GLIBCXX_END_NAMESPACE_VERSION
 260 } // namespace
 261
 262 #endif /* _MOVE_H */