libstdc++
move.h
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00001 // Move, forward and identity for C++11 + swap -*- C++ -*-
00002 
00003 // Copyright (C) 2007-2017 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the
00007 // terms of the GNU General Public License as published by the
00008 // Free Software Foundation; either version 3, or (at your option)
00009 // any later version.
00010 
00011 // This library is distributed in the hope that it will be useful,
00012 // but WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00014 // GNU General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /** @file bits/move.h
00026  *  This is an internal header file, included by other library headers.
00027  *  Do not attempt to use it directly. @headername{utility}
00028  */
00029 
00030 #ifndef _MOVE_H
00031 #define _MOVE_H 1
00032 
00033 #include <bits/c++config.h>
00034 #include <bits/concept_check.h>
00035 
00036 namespace std _GLIBCXX_VISIBILITY(default)
00037 {
00038 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00039 
00040   // Used, in C++03 mode too, by allocators, etc.
00041   /**
00042    *  @brief Same as C++11 std::addressof
00043    *  @ingroup utilities
00044    */
00045   template<typename _Tp>
00046     inline _GLIBCXX_CONSTEXPR _Tp*
00047     __addressof(_Tp& __r) _GLIBCXX_NOEXCEPT
00048     { return __builtin_addressof(__r); }
00049 
00050 _GLIBCXX_END_NAMESPACE_VERSION
00051 } // namespace
00052 
00053 #if __cplusplus >= 201103L
00054 #include <type_traits> // Brings in std::declval too.
00055 
00056 namespace std _GLIBCXX_VISIBILITY(default)
00057 {
00058 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00059 
00060   /**
00061    *  @addtogroup utilities
00062    *  @{
00063    */
00064 
00065   /**
00066    *  @brief  Forward an lvalue.
00067    *  @return The parameter cast to the specified type.
00068    *
00069    *  This function is used to implement "perfect forwarding".
00070    */
00071   template<typename _Tp>
00072     constexpr _Tp&&
00073     forward(typename std::remove_reference<_Tp>::type& __t) noexcept
00074     { return static_cast<_Tp&&>(__t); }
00075 
00076   /**
00077    *  @brief  Forward an rvalue.
00078    *  @return The parameter cast to the specified type.
00079    *
00080    *  This function is used to implement "perfect forwarding".
00081    */
00082   template<typename _Tp>
00083     constexpr _Tp&&
00084     forward(typename std::remove_reference<_Tp>::type&& __t) noexcept
00085     {
00086       static_assert(!std::is_lvalue_reference<_Tp>::value, "template argument"
00087                     " substituting _Tp is an lvalue reference type");
00088       return static_cast<_Tp&&>(__t);
00089     }
00090 
00091   /**
00092    *  @brief  Convert a value to an rvalue.
00093    *  @param  __t  A thing of arbitrary type.
00094    *  @return The parameter cast to an rvalue-reference to allow moving it.
00095   */
00096   template<typename _Tp>
00097     constexpr typename std::remove_reference<_Tp>::type&&
00098     move(_Tp&& __t) noexcept
00099     { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
00100 
00101 
00102   template<typename _Tp>
00103     struct __move_if_noexcept_cond
00104     : public __and_<__not_<is_nothrow_move_constructible<_Tp>>,
00105                     is_copy_constructible<_Tp>>::type { };
00106 
00107   /**
00108    *  @brief  Conditionally convert a value to an rvalue.
00109    *  @param  __x  A thing of arbitrary type.
00110    *  @return The parameter, possibly cast to an rvalue-reference.
00111    *
00112    *  Same as std::move unless the type's move constructor could throw and the
00113    *  type is copyable, in which case an lvalue-reference is returned instead.
00114    */
00115   template<typename _Tp>
00116     constexpr typename
00117     conditional<__move_if_noexcept_cond<_Tp>::value, const _Tp&, _Tp&&>::type
00118     move_if_noexcept(_Tp& __x) noexcept
00119     { return std::move(__x); }
00120 
00121   // declval, from type_traits.
00122 
00123 #if __cplusplus > 201402L
00124   // _GLIBCXX_RESOLVE_LIB_DEFECTS
00125   // 2296. std::addressof should be constexpr
00126 # define __cpp_lib_addressof_constexpr 201603
00127 #endif
00128   /**
00129    *  @brief Returns the actual address of the object or function
00130    *         referenced by r, even in the presence of an overloaded
00131    *         operator&.
00132    *  @param  __r  Reference to an object or function.
00133    *  @return   The actual address.
00134   */
00135   template<typename _Tp>
00136     inline _GLIBCXX17_CONSTEXPR _Tp*
00137     addressof(_Tp& __r) noexcept
00138     { return std::__addressof(__r); }
00139 
00140   // _GLIBCXX_RESOLVE_LIB_DEFECTS
00141   // 2598. addressof works on temporaries
00142   template<typename _Tp>
00143     const _Tp* addressof(const _Tp&&) = delete;
00144 
00145   // C++11 version of std::exchange for internal use.
00146   template <typename _Tp, typename _Up = _Tp>
00147     inline _Tp
00148     __exchange(_Tp& __obj, _Up&& __new_val)
00149     {
00150       _Tp __old_val = std::move(__obj);
00151       __obj = std::forward<_Up>(__new_val);
00152       return __old_val;
00153     }
00154 
00155   /// @} group utilities
00156 _GLIBCXX_END_NAMESPACE_VERSION
00157 } // namespace
00158 
00159 #define _GLIBCXX_MOVE(__val) std::move(__val)
00160 #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
00161 #else
00162 #define _GLIBCXX_MOVE(__val) (__val)
00163 #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
00164 #endif
00165 
00166 namespace std _GLIBCXX_VISIBILITY(default)
00167 {
00168 _GLIBCXX_BEGIN_NAMESPACE_VERSION
00169 
00170   /**
00171    *  @addtogroup utilities
00172    *  @{
00173    */
00174 
00175   /**
00176    *  @brief Swaps two values.
00177    *  @param  __a  A thing of arbitrary type.
00178    *  @param  __b  Another thing of arbitrary type.
00179    *  @return   Nothing.
00180   */
00181   template<typename _Tp>
00182     inline
00183 #if __cplusplus >= 201103L
00184     typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
00185                               is_move_constructible<_Tp>,
00186                               is_move_assignable<_Tp>>::value>::type
00187     swap(_Tp& __a, _Tp& __b)
00188     noexcept(__and_<is_nothrow_move_constructible<_Tp>,
00189                     is_nothrow_move_assignable<_Tp>>::value)
00190 #else
00191     void
00192     swap(_Tp& __a, _Tp& __b)
00193 #endif
00194     {
00195       // concept requirements
00196       __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
00197 
00198       _Tp __tmp = _GLIBCXX_MOVE(__a);
00199       __a = _GLIBCXX_MOVE(__b);
00200       __b = _GLIBCXX_MOVE(__tmp);
00201     }
00202 
00203   // _GLIBCXX_RESOLVE_LIB_DEFECTS
00204   // DR 809. std::swap should be overloaded for array types.
00205   /// Swap the contents of two arrays.
00206   template<typename _Tp, size_t _Nm>
00207     inline
00208 #if __cplusplus >= 201103L
00209     typename enable_if<__is_swappable<_Tp>::value>::type
00210     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
00211     noexcept(__is_nothrow_swappable<_Tp>::value)
00212 #else
00213     void
00214     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
00215 #endif
00216     {
00217       for (size_t __n = 0; __n < _Nm; ++__n)
00218         swap(__a[__n], __b[__n]);
00219     }
00220 
00221   /// @} group utilities
00222 _GLIBCXX_END_NAMESPACE_VERSION
00223 } // namespace
00224 
00225 #endif /* _MOVE_H */