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      1 // -*- C++ -*-
      2 //===-------------------------- utility -----------------------------------===//
      3 //
      4 //                     The LLVM Compiler Infrastructure
      5 //
      6 // This file is dual licensed under the MIT and the University of Illinois Open
      7 // Source Licenses. See LICENSE.TXT for details.
      8 //
      9 //===----------------------------------------------------------------------===//
     10 
     11 #ifndef _LIBCPP_UTILITY
     12 #define _LIBCPP_UTILITY
     13 
     14 /*
     15     utility synopsis
     16 
     17 namespace std
     18 {
     19 
     20 template <class T>
     21     void
     22     swap(T& a, T& b);
     23 
     24 namespace rel_ops
     25 {
     26     template<class T> bool operator!=(const T&, const T&);
     27     template<class T> bool operator> (const T&, const T&);
     28     template<class T> bool operator<=(const T&, const T&);
     29     template<class T> bool operator>=(const T&, const T&);
     30 }
     31 
     32 template<class T>
     33 void
     34 swap(T& a, T& b) noexcept(is_nothrow_move_constructible<T>::value &&
     35                           is_nothrow_move_assignable<T>::value);
     36 
     37 template <class T, size_t N>
     38 void
     39 swap(T (&a)[N], T (&b)[N]) noexcept(noexcept(swap(*a, *b)));
     40 
     41 template <class T> T&& forward(typename remove_reference<T>::type& t) noexcept;  // constexpr in C++14
     42 template <class T> T&& forward(typename remove_reference<T>::type&& t) noexcept; // constexpr in C++14
     43 
     44 template <class T> typename remove_reference<T>::type&& move(T&&) noexcept;      // constexpr in C++14
     45 
     46 template <class T>
     47     typename conditional
     48     <
     49         !is_nothrow_move_constructible<T>::value && is_copy_constructible<T>::value,
     50         const T&,
     51         T&&
     52     >::type
     53     move_if_noexcept(T& x) noexcept; // constexpr in C++14
     54 
     55 template <class T> typename add_rvalue_reference<T>::type declval() noexcept;
     56 
     57 template <class T1, class T2>
     58 struct pair
     59 {
     60     typedef T1 first_type;
     61     typedef T2 second_type;
     62 
     63     T1 first;
     64     T2 second;
     65 
     66     pair(const pair&) = default;
     67     pair(pair&&) = default;
     68     constexpr pair();
     69     pair(const T1& x, const T2& y);                          // constexpr in C++14
     70     template <class U, class V> pair(U&& x, V&& y);          // constexpr in C++14
     71     template <class U, class V> pair(const pair<U, V>& p);   // constexpr in C++14
     72     template <class U, class V> pair(pair<U, V>&& p);        // constexpr in C++14
     73     template <class... Args1, class... Args2>
     74         pair(piecewise_construct_t, tuple<Args1...> first_args,
     75              tuple<Args2...> second_args);
     76 
     77     template <class U, class V> pair& operator=(const pair<U, V>& p);
     78     pair& operator=(pair&& p) noexcept(is_nothrow_move_assignable<T1>::value &&
     79                                        is_nothrow_move_assignable<T2>::value);
     80     template <class U, class V> pair& operator=(pair<U, V>&& p);
     81 
     82     void swap(pair& p) noexcept(noexcept(swap(first, p.first)) &&
     83                                 noexcept(swap(second, p.second)));
     84 };
     85 
     86 template <class T1, class T2> bool operator==(const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
     87 template <class T1, class T2> bool operator!=(const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
     88 template <class T1, class T2> bool operator< (const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
     89 template <class T1, class T2> bool operator> (const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
     90 template <class T1, class T2> bool operator>=(const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
     91 template <class T1, class T2> bool operator<=(const pair<T1,T2>&, const pair<T1,T2>&); // constexpr in C++14
     92 
     93 template <class T1, class T2> pair<V1, V2> make_pair(T1&&, T2&&);   // constexpr in C++14
     94 template <class T1, class T2>
     95 void
     96 swap(pair<T1, T2>& x, pair<T1, T2>& y) noexcept(noexcept(x.swap(y)));
     97 
     98 struct piecewise_construct_t { };
     99 constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
    100 
    101 template <class T> class tuple_size;
    102 template <size_t I, class T> class tuple_element;
    103 
    104 template <class T1, class T2> struct tuple_size<pair<T1, T2> >;
    105 template <class T1, class T2> struct tuple_element<0, pair<T1, T2> >;
    106 template <class T1, class T2> struct tuple_element<1, pair<T1, T2> >;
    107 
    108 template<size_t I, class T1, class T2>
    109     typename tuple_element<I, pair<T1, T2> >::type&
    110     get(pair<T1, T2>&) noexcept; // constexpr in C++14
    111 
    112 template<size_t I, class T1, class T2>
    113     const typename const tuple_element<I, pair<T1, T2> >::type&
    114     get(const pair<T1, T2>&) noexcept; // constexpr in C++14
    115 
    116 template<size_t I, class T1, class T2>
    117     typename tuple_element<I, pair<T1, T2> >::type&&
    118     get(pair<T1, T2>&&) noexcept; // constexpr in C++14
    119 
    120 template<class T1, class T2>
    121     constexpr T1& get(pair<T1, T2>&) noexcept; // C++14
    122 
    123 template<size_t I, class T1, class T2>
    124     constexpr T1 const& get(pair<T1, T2> const &) noexcept; // C++14
    125 
    126 template<size_t I, class T1, class T2>
    127     constexpr T1&& get(pair<T1, T2>&&) noexcept; // C++14
    128 
    129 // C++14
    130 
    131 template<class T, T... I>
    132 struct integer_sequence
    133 {
    134     typedef T value_type;
    135 
    136     static constexpr size_t size() noexcept;
    137 };
    138 
    139 template<size_t... I>
    140   using index_sequence = integer_sequence<size_t, I...>;
    141 
    142 template<class T, T N>
    143   using make_integer_sequence = integer_sequence<T, 0, 1, ..., N-1>;
    144 template<size_t N>
    145   using make_index_sequence = make_integer_sequence<size_t, N>;
    146 
    147 template<class... T>
    148   using index_sequence_for = make_index_sequence<sizeof...(T)>;
    149 
    150 template<class T, class U=T> 
    151     T exchange(T& obj, U&& new_value);
    152 }  // std
    153 
    154 */
    155 
    156 #include <__config>
    157 #include <__tuple>
    158 #include <type_traits>
    159 
    160 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
    161 #pragma GCC system_header
    162 #endif
    163 
    164 _LIBCPP_BEGIN_NAMESPACE_STD
    165 
    166 namespace rel_ops
    167 {
    168 
    169 template<class _Tp>
    170 inline _LIBCPP_INLINE_VISIBILITY
    171 bool
    172 operator!=(const _Tp& __x, const _Tp& __y)
    173 {
    174     return !(__x == __y);
    175 }
    176 
    177 template<class _Tp>
    178 inline _LIBCPP_INLINE_VISIBILITY
    179 bool
    180 operator> (const _Tp& __x, const _Tp& __y)
    181 {
    182     return __y < __x;
    183 }
    184 
    185 template<class _Tp>
    186 inline _LIBCPP_INLINE_VISIBILITY
    187 bool
    188 operator<=(const _Tp& __x, const _Tp& __y)
    189 {
    190     return !(__y < __x);
    191 }
    192 
    193 template<class _Tp>
    194 inline _LIBCPP_INLINE_VISIBILITY
    195 bool
    196 operator>=(const _Tp& __x, const _Tp& __y)
    197 {
    198     return !(__x < __y);
    199 }
    200 
    201 }  // rel_ops
    202 
    203 // swap_ranges
    204 
    205 // forward
    206 template<class _Tp, size_t _Np>
    207 inline _LIBCPP_INLINE_VISIBILITY
    208 void swap(_Tp (&__a)[_Np], _Tp (&__b)[_Np]) _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value);
    209 
    210 template <class _ForwardIterator1, class _ForwardIterator2>
    211 inline _LIBCPP_INLINE_VISIBILITY
    212 _ForwardIterator2
    213 swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2)
    214 {
    215     for(; __first1 != __last1; ++__first1, (void) ++__first2)
    216         swap(*__first1, *__first2);
    217     return __first2;
    218 }
    219 
    220 template<class _Tp, size_t _Np>
    221 inline _LIBCPP_INLINE_VISIBILITY
    222 void
    223 swap(_Tp (&__a)[_Np], _Tp (&__b)[_Np]) _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value)
    224 {
    225     _VSTD::swap_ranges(__a, __a + _Np, __b);
    226 }
    227 
    228 template <class _Tp>
    229 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    230 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    231 typename conditional
    232 <
    233     !is_nothrow_move_constructible<_Tp>::value && is_copy_constructible<_Tp>::value,
    234     const _Tp&,
    235     _Tp&&
    236 >::type
    237 #else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    238 const _Tp&
    239 #endif
    240 move_if_noexcept(_Tp& __x) _NOEXCEPT
    241 {
    242     return _VSTD::move(__x);
    243 }
    244 
    245 struct _LIBCPP_TYPE_VIS_ONLY piecewise_construct_t { };
    246 #if defined(_LIBCPP_HAS_NO_CONSTEXPR) || defined(_LIBCPP_BUILDING_UTILITY)
    247 extern const piecewise_construct_t piecewise_construct;// = piecewise_construct_t();
    248 #else
    249 constexpr piecewise_construct_t piecewise_construct = piecewise_construct_t();
    250 #endif
    251 
    252 template <class _T1, class _T2>
    253 struct _LIBCPP_TYPE_VIS_ONLY pair
    254 {
    255     typedef _T1 first_type;
    256     typedef _T2 second_type;
    257 
    258     _T1 first;
    259     _T2 second;
    260 
    261     // pair(const pair&) = default;
    262     // pair(pair&&) = default;
    263 
    264     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR pair() : first(), second() {}
    265 
    266     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    267     pair(const _T1& __x, const _T2& __y)
    268         : first(__x), second(__y) {}
    269 
    270     template<class _U1, class _U2>
    271         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    272         pair(const pair<_U1, _U2>& __p
    273 #ifndef _LIBCPP_HAS_NO_ADVANCED_SFINAE
    274                  ,typename enable_if<is_convertible<const _U1&, _T1>::value &&
    275                                     is_convertible<const _U2&, _T2>::value>::type* = 0
    276 #endif
    277                                       )
    278             : first(__p.first), second(__p.second) {}
    279 
    280 #if !defined(_LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS) && _LIBCPP_TRIVIAL_PAIR_COPY_CTOR
    281     _LIBCPP_INLINE_VISIBILITY
    282     pair(const pair& __p) = default;
    283 #elif !defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES) || !_LIBCPP_TRIVIAL_PAIR_COPY_CTOR
    284     _LIBCPP_INLINE_VISIBILITY
    285     pair(const pair& __p)
    286         _NOEXCEPT_(is_nothrow_copy_constructible<first_type>::value &&
    287                    is_nothrow_copy_constructible<second_type>::value)
    288         : first(__p.first),
    289           second(__p.second)
    290     {
    291     }
    292 #endif
    293 
    294     _LIBCPP_INLINE_VISIBILITY
    295     pair& operator=(const pair& __p)
    296         _NOEXCEPT_(is_nothrow_copy_assignable<first_type>::value &&
    297                    is_nothrow_copy_assignable<second_type>::value)
    298     {
    299         first = __p.first;
    300         second = __p.second;
    301         return *this;
    302     }
    303 
    304 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    305 
    306     template <class _U1, class _U2,
    307               class = typename enable_if<is_convertible<_U1, first_type>::value &&
    308                                          is_convertible<_U2, second_type>::value>::type>
    309         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    310         pair(_U1&& __u1, _U2&& __u2)
    311             : first(_VSTD::forward<_U1>(__u1)),
    312               second(_VSTD::forward<_U2>(__u2))
    313             {}
    314 
    315     template<class _U1, class _U2>
    316         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    317         pair(pair<_U1, _U2>&& __p,
    318                  typename enable_if<is_convertible<_U1, _T1>::value &&
    319                                     is_convertible<_U2, _T2>::value>::type* = 0)
    320             : first(_VSTD::forward<_U1>(__p.first)),
    321               second(_VSTD::forward<_U2>(__p.second)) {}
    322 
    323 #ifndef _LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS
    324     _LIBCPP_INLINE_VISIBILITY
    325     pair(pair&& __p) = default;
    326 #else
    327     _LIBCPP_INLINE_VISIBILITY
    328     pair(pair&& __p) _NOEXCEPT_(is_nothrow_move_constructible<first_type>::value &&
    329                                 is_nothrow_move_constructible<second_type>::value)
    330         : first(_VSTD::forward<first_type>(__p.first)),
    331           second(_VSTD::forward<second_type>(__p.second))
    332     {
    333     }
    334 #endif
    335 
    336     _LIBCPP_INLINE_VISIBILITY
    337     pair&
    338     operator=(pair&& __p) _NOEXCEPT_(is_nothrow_move_assignable<first_type>::value &&
    339                                      is_nothrow_move_assignable<second_type>::value)
    340     {
    341         first = _VSTD::forward<first_type>(__p.first);
    342         second = _VSTD::forward<second_type>(__p.second);
    343         return *this;
    344     }
    345 
    346 #ifndef _LIBCPP_HAS_NO_VARIADICS
    347 
    348     template<class _Tuple,
    349              class = typename enable_if<__tuple_convertible<_Tuple, pair>::value>::type>
    350         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    351         pair(_Tuple&& __p)
    352             : first(_VSTD::forward<typename tuple_element<0,
    353                                   typename __make_tuple_types<_Tuple>::type>::type>(_VSTD::get<0>(__p))),
    354               second(_VSTD::forward<typename tuple_element<1,
    355                                    typename __make_tuple_types<_Tuple>::type>::type>(_VSTD::get<1>(__p)))
    356             {}
    357 
    358 
    359 
    360     template <class... _Args1, class... _Args2>
    361         _LIBCPP_INLINE_VISIBILITY
    362         pair(piecewise_construct_t __pc, tuple<_Args1...> __first_args,
    363                                     tuple<_Args2...> __second_args)
    364             : pair(__pc, __first_args, __second_args,
    365                    typename __make_tuple_indices<sizeof...(_Args1)>::type(),
    366                    typename __make_tuple_indices<sizeof...(_Args2) >::type())
    367             {}
    368 
    369     template <class _Tuple,
    370               class = typename enable_if<__tuple_assignable<_Tuple, pair>::value>::type>
    371         _LIBCPP_INLINE_VISIBILITY
    372         pair&
    373         operator=(_Tuple&& __p)
    374         {
    375             typedef typename __make_tuple_types<_Tuple>::type _TupleRef;
    376             typedef typename tuple_element<0, _TupleRef>::type _U0;
    377             typedef typename tuple_element<1, _TupleRef>::type _U1;
    378             first  = _VSTD::forward<_U0>(_VSTD::get<0>(__p));
    379             second = _VSTD::forward<_U1>(_VSTD::get<1>(__p));
    380             return *this;
    381         }
    382 
    383 #endif  // _LIBCPP_HAS_NO_VARIADICS
    384 
    385 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    386     _LIBCPP_INLINE_VISIBILITY
    387     void
    388     swap(pair& __p) _NOEXCEPT_(__is_nothrow_swappable<first_type>::value &&
    389                                __is_nothrow_swappable<second_type>::value)
    390     {
    391         _VSTD::iter_swap(&first, &__p.first);
    392         _VSTD::iter_swap(&second, &__p.second);
    393     }
    394 private:
    395 
    396 #ifndef _LIBCPP_HAS_NO_VARIADICS
    397     template <class... _Args1, class... _Args2, size_t... _I1, size_t... _I2>
    398         _LIBCPP_INLINE_VISIBILITY
    399         pair(piecewise_construct_t,
    400              tuple<_Args1...>& __first_args, tuple<_Args2...>& __second_args,
    401              __tuple_indices<_I1...>, __tuple_indices<_I2...>);
    402 #endif  // _LIBCPP_HAS_NO_VARIADICS
    403 };
    404 
    405 template <class _T1, class _T2>
    406 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    407 bool
    408 operator==(const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
    409 {
    410     return __x.first == __y.first && __x.second == __y.second;
    411 }
    412 
    413 template <class _T1, class _T2>
    414 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    415 bool
    416 operator!=(const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
    417 {
    418     return !(__x == __y);
    419 }
    420 
    421 template <class _T1, class _T2>
    422 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    423 bool
    424 operator< (const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
    425 {
    426     return __x.first < __y.first || (!(__y.first < __x.first) && __x.second < __y.second);
    427 }
    428 
    429 template <class _T1, class _T2>
    430 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    431 bool
    432 operator> (const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
    433 {
    434     return __y < __x;
    435 }
    436 
    437 template <class _T1, class _T2>
    438 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    439 bool
    440 operator>=(const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
    441 {
    442     return !(__x < __y);
    443 }
    444 
    445 template <class _T1, class _T2>
    446 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    447 bool
    448 operator<=(const pair<_T1,_T2>& __x, const pair<_T1,_T2>& __y)
    449 {
    450     return !(__y < __x);
    451 }
    452 
    453 template <class _T1, class _T2>
    454 inline _LIBCPP_INLINE_VISIBILITY
    455 typename enable_if
    456 <
    457     __is_swappable<_T1>::value &&
    458     __is_swappable<_T2>::value,
    459     void
    460 >::type
    461 swap(pair<_T1, _T2>& __x, pair<_T1, _T2>& __y)
    462                      _NOEXCEPT_((__is_nothrow_swappable<_T1>::value &&
    463                                  __is_nothrow_swappable<_T2>::value))
    464 {
    465     __x.swap(__y);
    466 }
    467 
    468 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    469 
    470 template <class _Tp> class _LIBCPP_TYPE_VIS_ONLY reference_wrapper;
    471 
    472 template <class _Tp>
    473 struct __make_pair_return_impl
    474 {
    475     typedef _Tp type;
    476 };
    477 
    478 template <class _Tp>
    479 struct __make_pair_return_impl<reference_wrapper<_Tp>>
    480 {
    481     typedef _Tp& type;
    482 };
    483 
    484 template <class _Tp>
    485 struct __make_pair_return
    486 {
    487     typedef typename __make_pair_return_impl<typename decay<_Tp>::type>::type type;
    488 };
    489 
    490 template <class _T1, class _T2>
    491 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    492 pair<typename __make_pair_return<_T1>::type, typename __make_pair_return<_T2>::type>
    493 make_pair(_T1&& __t1, _T2&& __t2)
    494 {
    495     return pair<typename __make_pair_return<_T1>::type, typename __make_pair_return<_T2>::type>
    496                (_VSTD::forward<_T1>(__t1), _VSTD::forward<_T2>(__t2));
    497 }
    498 
    499 #else  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    500 
    501 template <class _T1, class _T2>
    502 inline _LIBCPP_INLINE_VISIBILITY
    503 pair<_T1,_T2>
    504 make_pair(_T1 __x, _T2 __y)
    505 {
    506     return pair<_T1, _T2>(__x, __y);
    507 }
    508 
    509 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    510 
    511 template <class _T1, class _T2>
    512   class _LIBCPP_TYPE_VIS_ONLY tuple_size<pair<_T1, _T2> >
    513     : public integral_constant<size_t, 2> {};
    514 
    515 template <class _T1, class _T2>
    516 class _LIBCPP_TYPE_VIS_ONLY tuple_element<0, pair<_T1, _T2> >
    517 {
    518 public:
    519     typedef _T1 type;
    520 };
    521 
    522 template <class _T1, class _T2>
    523 class _LIBCPP_TYPE_VIS_ONLY tuple_element<1, pair<_T1, _T2> >
    524 {
    525 public:
    526     typedef _T2 type;
    527 };
    528 
    529 template <size_t _Ip> struct __get_pair;
    530 
    531 template <>
    532 struct __get_pair<0>
    533 {
    534     template <class _T1, class _T2>
    535     static
    536     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    537     _T1&
    538     get(pair<_T1, _T2>& __p) _NOEXCEPT {return __p.first;}
    539 
    540     template <class _T1, class _T2>
    541     static
    542     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    543     const _T1&
    544     get(const pair<_T1, _T2>& __p) _NOEXCEPT {return __p.first;}
    545 
    546 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    547 
    548     template <class _T1, class _T2>
    549     static
    550     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    551     _T1&&
    552     get(pair<_T1, _T2>&& __p) _NOEXCEPT {return _VSTD::forward<_T1>(__p.first);}
    553 
    554 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    555 };
    556 
    557 template <>
    558 struct __get_pair<1>
    559 {
    560     template <class _T1, class _T2>
    561     static
    562     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    563     _T2&
    564     get(pair<_T1, _T2>& __p) _NOEXCEPT {return __p.second;}
    565 
    566     template <class _T1, class _T2>
    567     static
    568     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    569     const _T2&
    570     get(const pair<_T1, _T2>& __p) _NOEXCEPT {return __p.second;}
    571 
    572 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    573 
    574     template <class _T1, class _T2>
    575     static
    576     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    577     _T2&&
    578     get(pair<_T1, _T2>&& __p) _NOEXCEPT {return _VSTD::forward<_T2>(__p.second);}
    579 
    580 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    581 };
    582 
    583 template <size_t _Ip, class _T1, class _T2>
    584 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    585 typename tuple_element<_Ip, pair<_T1, _T2> >::type&
    586 get(pair<_T1, _T2>& __p) _NOEXCEPT
    587 {
    588     return __get_pair<_Ip>::get(__p);
    589 }
    590 
    591 template <size_t _Ip, class _T1, class _T2>
    592 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    593 const typename tuple_element<_Ip, pair<_T1, _T2> >::type&
    594 get(const pair<_T1, _T2>& __p) _NOEXCEPT
    595 {
    596     return __get_pair<_Ip>::get(__p);
    597 }
    598 
    599 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
    600 
    601 template <size_t _Ip, class _T1, class _T2>
    602 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    603 typename tuple_element<_Ip, pair<_T1, _T2> >::type&&
    604 get(pair<_T1, _T2>&& __p) _NOEXCEPT
    605 {
    606     return __get_pair<_Ip>::get(_VSTD::move(__p));
    607 }
    608 
    609 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
    610 
    611 #if _LIBCPP_STD_VER > 11
    612 template <class _T1, class _T2>
    613 inline _LIBCPP_INLINE_VISIBILITY
    614 constexpr _T1 & get(pair<_T1, _T2>& __p) _NOEXCEPT
    615 {
    616     return __get_pair<0>::get(__p);
    617 }
    618 
    619 template <class _T1, class _T2>
    620 inline _LIBCPP_INLINE_VISIBILITY
    621 constexpr _T1 const & get(pair<_T1, _T2> const& __p) _NOEXCEPT
    622 {
    623     return __get_pair<0>::get(__p);
    624 }
    625 
    626 template <class _T1, class _T2>
    627 inline _LIBCPP_INLINE_VISIBILITY
    628 constexpr _T1 && get(pair<_T1, _T2>&& __p) _NOEXCEPT
    629 {
    630     return __get_pair<0>::get(_VSTD::move(__p));
    631 }
    632 
    633 template <class _T1, class _T2>
    634 inline _LIBCPP_INLINE_VISIBILITY
    635 constexpr _T1 & get(pair<_T2, _T1>& __p) _NOEXCEPT
    636 {
    637     return __get_pair<1>::get(__p);
    638 }
    639 
    640 template <class _T1, class _T2>
    641 inline _LIBCPP_INLINE_VISIBILITY
    642 constexpr _T1 const & get(pair<_T2, _T1> const& __p) _NOEXCEPT
    643 {
    644     return __get_pair<1>::get(__p);
    645 }
    646 
    647 template <class _T1, class _T2>
    648 inline _LIBCPP_INLINE_VISIBILITY
    649 constexpr _T1 && get(pair<_T2, _T1>&& __p) _NOEXCEPT
    650 {
    651     return __get_pair<1>::get(_VSTD::move(__p));
    652 }
    653 
    654 #endif
    655 
    656 #if _LIBCPP_STD_VER > 11
    657 
    658 template<class _Tp, _Tp... _Ip>
    659 struct _LIBCPP_TYPE_VIS_ONLY integer_sequence
    660 {
    661     typedef _Tp value_type;
    662     static_assert( is_integral<_Tp>::value,
    663                   "std::integer_sequence can only be instantiated with an integral type" );
    664     static
    665     _LIBCPP_INLINE_VISIBILITY
    666     constexpr
    667     size_t
    668     size() noexcept { return sizeof...(_Ip); }
    669 };
    670 
    671 template<size_t... _Ip>
    672     using index_sequence = integer_sequence<size_t, _Ip...>;
    673 
    674 namespace __detail {
    675 
    676 template<typename _Tp, size_t ..._Extra> struct __repeat;
    677 template<typename _Tp, _Tp ..._Np, size_t ..._Extra> struct __repeat<integer_sequence<_Tp, _Np...>, _Extra...> {
    678   typedef integer_sequence<_Tp,
    679                            _Np...,
    680                            sizeof...(_Np) + _Np...,
    681                            2 * sizeof...(_Np) + _Np...,
    682                            3 * sizeof...(_Np) + _Np...,
    683                            4 * sizeof...(_Np) + _Np...,
    684                            5 * sizeof...(_Np) + _Np...,
    685                            6 * sizeof...(_Np) + _Np...,
    686                            7 * sizeof...(_Np) + _Np...,
    687                            _Extra...> type;
    688 };
    689 
    690 template<size_t _Np> struct __parity;
    691 template<size_t _Np> struct __make : __parity<_Np % 8>::template __pmake<_Np> {};
    692 
    693 template<> struct __make<0> { typedef integer_sequence<size_t> type; };
    694 template<> struct __make<1> { typedef integer_sequence<size_t, 0> type; };
    695 template<> struct __make<2> { typedef integer_sequence<size_t, 0, 1> type; };
    696 template<> struct __make<3> { typedef integer_sequence<size_t, 0, 1, 2> type; };
    697 template<> struct __make<4> { typedef integer_sequence<size_t, 0, 1, 2, 3> type; };
    698 template<> struct __make<5> { typedef integer_sequence<size_t, 0, 1, 2, 3, 4> type; };
    699 template<> struct __make<6> { typedef integer_sequence<size_t, 0, 1, 2, 3, 4, 5> type; };
    700 template<> struct __make<7> { typedef integer_sequence<size_t, 0, 1, 2, 3, 4, 5, 6> type; };
    701 
    702 template<> struct __parity<0> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type> {}; };
    703 template<> struct __parity<1> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 1> {}; };
    704 template<> struct __parity<2> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 2, _Np - 1> {}; };
    705 template<> struct __parity<3> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 3, _Np - 2, _Np - 1> {}; };
    706 template<> struct __parity<4> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 4, _Np - 3, _Np - 2, _Np - 1> {}; };
    707 template<> struct __parity<5> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 5, _Np - 4, _Np - 3, _Np - 2, _Np - 1> {}; };
    708 template<> struct __parity<6> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 6, _Np - 5, _Np - 4, _Np - 3, _Np - 2, _Np - 1> {}; };
    709 template<> struct __parity<7> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 7, _Np - 6, _Np - 5, _Np - 4, _Np - 3, _Np - 2, _Np - 1> {}; };
    710 
    711 template<typename _Tp, typename _Up> struct __convert {
    712   template<typename> struct __result;
    713   template<_Tp ..._Np> struct __result<integer_sequence<_Tp, _Np...> > { typedef integer_sequence<_Up, _Np...> type; };
    714 };
    715 template<typename _Tp> struct __convert<_Tp, _Tp> { template<typename _Up> struct __result { typedef _Up type; }; };
    716 
    717 }
    718 
    719 template<typename _Tp, _Tp _Np> using __make_integer_sequence_unchecked =
    720   typename __detail::__convert<size_t, _Tp>::template __result<typename __detail::__make<_Np>::type>::type;
    721 
    722 template <class _Tp, _Tp _Ep>
    723 struct __make_integer_sequence
    724 {
    725     static_assert(is_integral<_Tp>::value,
    726                   "std::make_integer_sequence can only be instantiated with an integral type" );
    727     static_assert(0 <= _Ep, "std::make_integer_sequence input shall not be negative");
    728     typedef __make_integer_sequence_unchecked<_Tp, _Ep> type;
    729 };
    730 
    731 template<class _Tp, _Tp _Np>
    732     using make_integer_sequence = typename __make_integer_sequence<_Tp, _Np>::type;
    733 
    734 template<size_t _Np>
    735     using make_index_sequence = make_integer_sequence<size_t, _Np>;
    736 
    737 template<class... _Tp>
    738     using index_sequence_for = make_index_sequence<sizeof...(_Tp)>;
    739   
    740 #endif  // _LIBCPP_STD_VER > 11
    741 
    742 #if _LIBCPP_STD_VER > 11
    743 template<class _T1, class _T2 = _T1>
    744 inline _LIBCPP_INLINE_VISIBILITY
    745 _T1 exchange(_T1& __obj, _T2 && __new_value)
    746 {
    747     _T1 __old_value = _VSTD::move(__obj);
    748     __obj = _VSTD::forward<_T2>(__new_value);
    749     return __old_value;
    750 }    
    751 #endif  // _LIBCPP_STD_VER > 11
    752 
    753 _LIBCPP_END_NAMESPACE_STD
    754 
    755 #endif  // _LIBCPP_UTILITY
    756