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      1 // -*- C++ -*-
      2 //===--------------------------- tuple ------------------------------------===//
      3 //
      4 //                     The LLVM Compiler Infrastructure
      5 //
      6 // This file is distributed under the University of Illinois Open Source
      7 // License. See LICENSE.TXT for details.
      8 //
      9 //===----------------------------------------------------------------------===//
     10 
     11 #ifndef _LIBCPP_TUPLE
     12 #define _LIBCPP_TUPLE
     13 
     14 /*
     15     tuple synopsis
     16 
     17 namespace std
     18 {
     19 
     20 template <class... T>
     21 class tuple {
     22 public:
     23     constexpr tuple();
     24     explicit tuple(const T&...);  // constexpr in C++14
     25     template <class... U>
     26         explicit tuple(U&&...);  // constexpr in C++14
     27     tuple(const tuple&) = default;
     28     tuple(tuple&&) = default;
     29     template <class... U>
     30         tuple(const tuple<U...>&);  // constexpr in C++14
     31     template <class... U>
     32         tuple(tuple<U...>&&);  // constexpr in C++14
     33     template <class U1, class U2>
     34         tuple(const pair<U1, U2>&); // iff sizeof...(T) == 2 // constexpr in C++14
     35     template <class U1, class U2>
     36         tuple(pair<U1, U2>&&); // iff sizeof...(T) == 2  // constexpr in C++14
     37 
     38     // allocator-extended constructors
     39     template <class Alloc>
     40         tuple(allocator_arg_t, const Alloc& a);
     41     template <class Alloc>
     42         tuple(allocator_arg_t, const Alloc& a, const T&...);
     43     template <class Alloc, class... U>
     44         tuple(allocator_arg_t, const Alloc& a, U&&...);
     45     template <class Alloc>
     46         tuple(allocator_arg_t, const Alloc& a, const tuple&);
     47     template <class Alloc>
     48         tuple(allocator_arg_t, const Alloc& a, tuple&&);
     49     template <class Alloc, class... U>
     50         tuple(allocator_arg_t, const Alloc& a, const tuple<U...>&);
     51     template <class Alloc, class... U>
     52         tuple(allocator_arg_t, const Alloc& a, tuple<U...>&&);
     53     template <class Alloc, class U1, class U2>
     54         tuple(allocator_arg_t, const Alloc& a, const pair<U1, U2>&);
     55     template <class Alloc, class U1, class U2>
     56         tuple(allocator_arg_t, const Alloc& a, pair<U1, U2>&&);
     57 
     58     tuple& operator=(const tuple&);
     59     tuple&
     60         operator=(tuple&&) noexcept(AND(is_nothrow_move_assignable<T>::value ...));
     61     template <class... U>
     62         tuple& operator=(const tuple<U...>&);
     63     template <class... U>
     64         tuple& operator=(tuple<U...>&&);
     65     template <class U1, class U2>
     66         tuple& operator=(const pair<U1, U2>&); // iff sizeof...(T) == 2
     67     template <class U1, class U2>
     68         tuple& operator=(pair<U1, U2>&&); //iffsizeof...(T) == 2
     69 
     70     void swap(tuple&) noexcept(AND(swap(declval<T&>(), declval<T&>())...));
     71 };
     72 
     73 const unspecified ignore;
     74 
     75 template <class... T> tuple<V...>  make_tuple(T&&...); // constexpr in C++14
     76 template <class... T> tuple<ATypes...> forward_as_tuple(T&&...) noexcept; // constexpr in C++14
     77 template <class... T> tuple<T&...> tie(T&...) noexcept; // constexpr in C++14
     78 template <class... Tuples> tuple<CTypes...> tuple_cat(Tuples&&... tpls); // constexpr in C++14
     79 
     80 // [tuple.apply], calling a function with a tuple of arguments:
     81 template <class F, class Tuple>
     82   constexpr decltype(auto) apply(F&& f, Tuple&& t); // C++17
     83 template <class T, class Tuple>
     84   constexpr T make_from_tuple(Tuple&& t); // C++17
     85 
     86 // 20.4.1.4, tuple helper classes:
     87 template <class T> class tuple_size; // undefined
     88 template <class... T> class tuple_size<tuple<T...>>;
     89 template <class T>
     90  constexpr size_t tuple_size_v = tuple_size<T>::value; // C++17
     91 template <size_t I, class T> class tuple_element; // undefined
     92 template <size_t I, class... T> class tuple_element<I, tuple<T...>>;
     93 template <size_t I, class T>
     94   using tuple_element_t = typename tuple_element <I, T>::type; // C++14
     95 
     96 // 20.4.1.5, element access:
     97 template <size_t I, class... T>
     98     typename tuple_element<I, tuple<T...>>::type&
     99     get(tuple<T...>&) noexcept; // constexpr in C++14
    100 template <size_t I, class... T>
    101     const typename tuple_element<I, tuple<T...>>::type&
    102     get(const tuple<T...>&) noexcept; // constexpr in C++14
    103 template <size_t I, class... T>
    104     typename tuple_element<I, tuple<T...>>::type&&
    105     get(tuple<T...>&&) noexcept; // constexpr in C++14
    106 template <size_t I, class... T>
    107     const typename tuple_element<I, tuple<T...>>::type&&
    108     get(const tuple<T...>&&) noexcept; // constexpr in C++14
    109 
    110 template <class T1, class... T>
    111     constexpr T1& get(tuple<T...>&) noexcept;  // C++14
    112 template <class T1, class... T>
    113     constexpr const T1& get(const tuple<T...>&) noexcept;   // C++14
    114 template <class T1, class... T>
    115     constexpr T1&& get(tuple<T...>&&) noexcept;   // C++14
    116 template <class T1, class... T>
    117     constexpr const T1&& get(const tuple<T...>&&) noexcept;   // C++14
    118 
    119 // 20.4.1.6, relational operators:
    120 template<class... T, class... U> bool operator==(const tuple<T...>&, const tuple<U...>&); // constexpr in C++14
    121 template<class... T, class... U> bool operator<(const tuple<T...>&, const tuple<U...>&);  // constexpr in C++14
    122 template<class... T, class... U> bool operator!=(const tuple<T...>&, const tuple<U...>&); // constexpr in C++14
    123 template<class... T, class... U> bool operator>(const tuple<T...>&, const tuple<U...>&);  // constexpr in C++14
    124 template<class... T, class... U> bool operator<=(const tuple<T...>&, const tuple<U...>&); // constexpr in C++14
    125 template<class... T, class... U> bool operator>=(const tuple<T...>&, const tuple<U...>&); // constexpr in C++14
    126 
    127 template <class... Types, class Alloc>
    128   struct uses_allocator<tuple<Types...>, Alloc>;
    129 
    130 template <class... Types>
    131   void
    132   swap(tuple<Types...>& x, tuple<Types...>& y) noexcept(noexcept(x.swap(y)));
    133 
    134 }  // std
    135 
    136 */
    137 
    138 #include <__config>
    139 #include <__tuple>
    140 #include <cstddef>
    141 #include <type_traits>
    142 #include <__functional_base>
    143 #include <utility>
    144 
    145 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
    146 #pragma GCC system_header
    147 #endif
    148 
    149 _LIBCPP_BEGIN_NAMESPACE_STD
    150 
    151 #ifndef _LIBCPP_CXX03_LANG
    152 
    153 
    154 // __tuple_leaf
    155 
    156 template <size_t _Ip, class _Hp,
    157           bool=is_empty<_Hp>::value && !__libcpp_is_final<_Hp>::value
    158          >
    159 class __tuple_leaf;
    160 
    161 template <size_t _Ip, class _Hp, bool _Ep>
    162 inline _LIBCPP_INLINE_VISIBILITY
    163 void swap(__tuple_leaf<_Ip, _Hp, _Ep>& __x, __tuple_leaf<_Ip, _Hp, _Ep>& __y)
    164     _NOEXCEPT_(__is_nothrow_swappable<_Hp>::value)
    165 {
    166     swap(__x.get(), __y.get());
    167 }
    168 
    169 template <size_t _Ip, class _Hp, bool>
    170 class __tuple_leaf
    171 {
    172     _Hp __value_;
    173 
    174     template <class _Tp>
    175     static constexpr bool __can_bind_reference() {
    176         using _RawTp = typename remove_reference<_Tp>::type;
    177         using _RawHp = typename remove_reference<_Hp>::type;
    178         using _CheckLValueArg = integral_constant<bool,
    179             is_lvalue_reference<_Tp>::value
    180         ||  is_same<_RawTp, reference_wrapper<_RawHp>>::value
    181         ||  is_same<_RawTp, reference_wrapper<typename remove_const<_RawHp>::type>>::value
    182         >;
    183         return  !is_reference<_Hp>::value
    184             || (is_lvalue_reference<_Hp>::value && _CheckLValueArg::value)
    185             || (is_rvalue_reference<_Hp>::value && !is_lvalue_reference<_Tp>::value);
    186     }
    187 
    188     __tuple_leaf& operator=(const __tuple_leaf&);
    189 public:
    190     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR __tuple_leaf()
    191              _NOEXCEPT_(is_nothrow_default_constructible<_Hp>::value) : __value_()
    192        {static_assert(!is_reference<_Hp>::value,
    193               "Attempted to default construct a reference element in a tuple");}
    194 
    195     template <class _Alloc>
    196         _LIBCPP_INLINE_VISIBILITY
    197         __tuple_leaf(integral_constant<int, 0>, const _Alloc&)
    198             : __value_()
    199         {static_assert(!is_reference<_Hp>::value,
    200               "Attempted to default construct a reference element in a tuple");}
    201 
    202     template <class _Alloc>
    203         _LIBCPP_INLINE_VISIBILITY
    204         __tuple_leaf(integral_constant<int, 1>, const _Alloc& __a)
    205             : __value_(allocator_arg_t(), __a)
    206         {static_assert(!is_reference<_Hp>::value,
    207               "Attempted to default construct a reference element in a tuple");}
    208 
    209     template <class _Alloc>
    210         _LIBCPP_INLINE_VISIBILITY
    211         __tuple_leaf(integral_constant<int, 2>, const _Alloc& __a)
    212             : __value_(__a)
    213         {static_assert(!is_reference<_Hp>::value,
    214               "Attempted to default construct a reference element in a tuple");}
    215 
    216     template <class _Tp,
    217               class = typename enable_if<
    218                   __lazy_and<
    219                       __lazy_not<is_same<typename decay<_Tp>::type, __tuple_leaf>>
    220                     , is_constructible<_Hp, _Tp>
    221                     >::value
    222                 >::type
    223             >
    224         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    225         explicit __tuple_leaf(_Tp&& __t) _NOEXCEPT_((is_nothrow_constructible<_Hp, _Tp>::value))
    226             : __value_(_VSTD::forward<_Tp>(__t))
    227         {static_assert(__can_bind_reference<_Tp>(),
    228        "Attempted to construct a reference element in a tuple with an rvalue");}
    229 
    230     template <class _Tp, class _Alloc>
    231         _LIBCPP_INLINE_VISIBILITY
    232         explicit __tuple_leaf(integral_constant<int, 0>, const _Alloc&, _Tp&& __t)
    233             : __value_(_VSTD::forward<_Tp>(__t))
    234         {static_assert(__can_bind_reference<_Tp>(),
    235        "Attempted to construct a reference element in a tuple with an rvalue");}
    236 
    237     template <class _Tp, class _Alloc>
    238         _LIBCPP_INLINE_VISIBILITY
    239         explicit __tuple_leaf(integral_constant<int, 1>, const _Alloc& __a, _Tp&& __t)
    240             : __value_(allocator_arg_t(), __a, _VSTD::forward<_Tp>(__t))
    241         {static_assert(!is_reference<_Hp>::value,
    242             "Attempted to uses-allocator construct a reference element in a tuple");}
    243 
    244     template <class _Tp, class _Alloc>
    245         _LIBCPP_INLINE_VISIBILITY
    246         explicit __tuple_leaf(integral_constant<int, 2>, const _Alloc& __a, _Tp&& __t)
    247             : __value_(_VSTD::forward<_Tp>(__t), __a)
    248         {static_assert(!is_reference<_Hp>::value,
    249            "Attempted to uses-allocator construct a reference element in a tuple");}
    250 
    251     __tuple_leaf(const __tuple_leaf& __t) = default;
    252     __tuple_leaf(__tuple_leaf&& __t) = default;
    253 
    254     template <class _Tp>
    255         _LIBCPP_INLINE_VISIBILITY
    256         __tuple_leaf&
    257         operator=(_Tp&& __t) _NOEXCEPT_((is_nothrow_assignable<_Hp&, _Tp>::value))
    258         {
    259             __value_ = _VSTD::forward<_Tp>(__t);
    260             return *this;
    261         }
    262 
    263     _LIBCPP_INLINE_VISIBILITY
    264     int swap(__tuple_leaf& __t) _NOEXCEPT_(__is_nothrow_swappable<__tuple_leaf>::value)
    265     {
    266         _VSTD::swap(*this, __t);
    267         return 0;
    268     }
    269 
    270     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11       _Hp& get()       _NOEXCEPT {return __value_;}
    271     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 const _Hp& get() const _NOEXCEPT {return __value_;}
    272 };
    273 
    274 template <size_t _Ip, class _Hp>
    275 class __tuple_leaf<_Ip, _Hp, true>
    276     : private _Hp
    277 {
    278 
    279     __tuple_leaf& operator=(const __tuple_leaf&);
    280 public:
    281     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR __tuple_leaf()
    282              _NOEXCEPT_(is_nothrow_default_constructible<_Hp>::value) {}
    283 
    284     template <class _Alloc>
    285         _LIBCPP_INLINE_VISIBILITY
    286         __tuple_leaf(integral_constant<int, 0>, const _Alloc&) {}
    287 
    288     template <class _Alloc>
    289         _LIBCPP_INLINE_VISIBILITY
    290         __tuple_leaf(integral_constant<int, 1>, const _Alloc& __a)
    291             : _Hp(allocator_arg_t(), __a) {}
    292 
    293     template <class _Alloc>
    294         _LIBCPP_INLINE_VISIBILITY
    295         __tuple_leaf(integral_constant<int, 2>, const _Alloc& __a)
    296             : _Hp(__a) {}
    297 
    298     template <class _Tp,
    299               class = typename enable_if<
    300                   __lazy_and<
    301                         __lazy_not<is_same<typename decay<_Tp>::type, __tuple_leaf>>
    302                       , is_constructible<_Hp, _Tp>
    303                     >::value
    304                 >::type
    305             >
    306         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    307         explicit __tuple_leaf(_Tp&& __t) _NOEXCEPT_((is_nothrow_constructible<_Hp, _Tp>::value))
    308             : _Hp(_VSTD::forward<_Tp>(__t)) {}
    309 
    310     template <class _Tp, class _Alloc>
    311         _LIBCPP_INLINE_VISIBILITY
    312         explicit __tuple_leaf(integral_constant<int, 0>, const _Alloc&, _Tp&& __t)
    313             : _Hp(_VSTD::forward<_Tp>(__t)) {}
    314 
    315     template <class _Tp, class _Alloc>
    316         _LIBCPP_INLINE_VISIBILITY
    317         explicit __tuple_leaf(integral_constant<int, 1>, const _Alloc& __a, _Tp&& __t)
    318             : _Hp(allocator_arg_t(), __a, _VSTD::forward<_Tp>(__t)) {}
    319 
    320     template <class _Tp, class _Alloc>
    321         _LIBCPP_INLINE_VISIBILITY
    322         explicit __tuple_leaf(integral_constant<int, 2>, const _Alloc& __a, _Tp&& __t)
    323             : _Hp(_VSTD::forward<_Tp>(__t), __a) {}
    324 
    325     __tuple_leaf(__tuple_leaf const &) = default;
    326     __tuple_leaf(__tuple_leaf &&) = default;
    327 
    328     template <class _Tp>
    329         _LIBCPP_INLINE_VISIBILITY
    330         __tuple_leaf&
    331         operator=(_Tp&& __t) _NOEXCEPT_((is_nothrow_assignable<_Hp&, _Tp>::value))
    332         {
    333             _Hp::operator=(_VSTD::forward<_Tp>(__t));
    334             return *this;
    335         }
    336 
    337     _LIBCPP_INLINE_VISIBILITY
    338     int
    339     swap(__tuple_leaf& __t) _NOEXCEPT_(__is_nothrow_swappable<__tuple_leaf>::value)
    340     {
    341         _VSTD::swap(*this, __t);
    342         return 0;
    343     }
    344 
    345     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11       _Hp& get()       _NOEXCEPT {return static_cast<_Hp&>(*this);}
    346     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 const _Hp& get() const _NOEXCEPT {return static_cast<const _Hp&>(*this);}
    347 };
    348 
    349 template <class ..._Tp>
    350 _LIBCPP_INLINE_VISIBILITY
    351 void __swallow(_Tp&&...) _NOEXCEPT {}
    352 
    353 template <class ..._Tp>
    354 struct __lazy_all : __all<_Tp::value...> {};
    355 
    356 template <class _Tp>
    357 struct __all_default_constructible;
    358 
    359 template <class ..._Tp>
    360 struct __all_default_constructible<__tuple_types<_Tp...>>
    361     : __all<is_default_constructible<_Tp>::value...>
    362 { };
    363 
    364 // __tuple_impl
    365 
    366 template<class _Indx, class ..._Tp> struct __tuple_impl;
    367 
    368 template<size_t ..._Indx, class ..._Tp>
    369 struct _LIBCPP_DECLSPEC_EMPTY_BASES __tuple_impl<__tuple_indices<_Indx...>, _Tp...>
    370     : public __tuple_leaf<_Indx, _Tp>...
    371 {
    372     _LIBCPP_INLINE_VISIBILITY
    373     _LIBCPP_CONSTEXPR __tuple_impl()
    374         _NOEXCEPT_(__all<is_nothrow_default_constructible<_Tp>::value...>::value) {}
    375 
    376     template <size_t ..._Uf, class ..._Tf,
    377               size_t ..._Ul, class ..._Tl, class ..._Up>
    378         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    379         explicit
    380         __tuple_impl(__tuple_indices<_Uf...>, __tuple_types<_Tf...>,
    381                      __tuple_indices<_Ul...>, __tuple_types<_Tl...>,
    382                      _Up&&... __u)
    383                      _NOEXCEPT_((__all<is_nothrow_constructible<_Tf, _Up>::value...>::value &&
    384                                  __all<is_nothrow_default_constructible<_Tl>::value...>::value)) :
    385             __tuple_leaf<_Uf, _Tf>(_VSTD::forward<_Up>(__u))...,
    386             __tuple_leaf<_Ul, _Tl>()...
    387             {}
    388 
    389     template <class _Alloc, size_t ..._Uf, class ..._Tf,
    390               size_t ..._Ul, class ..._Tl, class ..._Up>
    391         _LIBCPP_INLINE_VISIBILITY
    392         explicit
    393         __tuple_impl(allocator_arg_t, const _Alloc& __a,
    394                      __tuple_indices<_Uf...>, __tuple_types<_Tf...>,
    395                      __tuple_indices<_Ul...>, __tuple_types<_Tl...>,
    396                      _Up&&... __u) :
    397             __tuple_leaf<_Uf, _Tf>(__uses_alloc_ctor<_Tf, _Alloc, _Up>(), __a,
    398             _VSTD::forward<_Up>(__u))...,
    399             __tuple_leaf<_Ul, _Tl>(__uses_alloc_ctor<_Tl, _Alloc>(), __a)...
    400             {}
    401 
    402     template <class _Tuple,
    403               class = typename enable_if
    404                       <
    405                          __tuple_constructible<_Tuple, tuple<_Tp...> >::value
    406                       >::type
    407              >
    408         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    409         __tuple_impl(_Tuple&& __t) _NOEXCEPT_((__all<is_nothrow_constructible<_Tp, typename tuple_element<_Indx,
    410                                        typename __make_tuple_types<_Tuple>::type>::type>::value...>::value))
    411             : __tuple_leaf<_Indx, _Tp>(_VSTD::forward<typename tuple_element<_Indx,
    412                                        typename __make_tuple_types<_Tuple>::type>::type>(_VSTD::get<_Indx>(__t)))...
    413             {}
    414 
    415     template <class _Alloc, class _Tuple,
    416               class = typename enable_if
    417                       <
    418                          __tuple_constructible<_Tuple, tuple<_Tp...> >::value
    419                       >::type
    420              >
    421         _LIBCPP_INLINE_VISIBILITY
    422         __tuple_impl(allocator_arg_t, const _Alloc& __a, _Tuple&& __t)
    423             : __tuple_leaf<_Indx, _Tp>(__uses_alloc_ctor<_Tp, _Alloc, typename tuple_element<_Indx,
    424                                        typename __make_tuple_types<_Tuple>::type>::type>(), __a,
    425                                        _VSTD::forward<typename tuple_element<_Indx,
    426                                        typename __make_tuple_types<_Tuple>::type>::type>(_VSTD::get<_Indx>(__t)))...
    427             {}
    428 
    429     template <class _Tuple>
    430         _LIBCPP_INLINE_VISIBILITY
    431         typename enable_if
    432         <
    433             __tuple_assignable<_Tuple, tuple<_Tp...> >::value,
    434             __tuple_impl&
    435         >::type
    436         operator=(_Tuple&& __t) _NOEXCEPT_((__all<is_nothrow_assignable<_Tp&, typename tuple_element<_Indx,
    437                                        typename __make_tuple_types<_Tuple>::type>::type>::value...>::value))
    438         {
    439             __swallow(__tuple_leaf<_Indx, _Tp>::operator=(_VSTD::forward<typename tuple_element<_Indx,
    440                                        typename __make_tuple_types<_Tuple>::type>::type>(_VSTD::get<_Indx>(__t)))...);
    441             return *this;
    442         }
    443 
    444     __tuple_impl(const __tuple_impl&) = default;
    445     __tuple_impl(__tuple_impl&&) = default;
    446 
    447     _LIBCPP_INLINE_VISIBILITY
    448     __tuple_impl&
    449     operator=(const __tuple_impl& __t) _NOEXCEPT_((__all<is_nothrow_copy_assignable<_Tp>::value...>::value))
    450     {
    451         __swallow(__tuple_leaf<_Indx, _Tp>::operator=(static_cast<const __tuple_leaf<_Indx, _Tp>&>(__t).get())...);
    452         return *this;
    453     }
    454 
    455     _LIBCPP_INLINE_VISIBILITY
    456     __tuple_impl&
    457     operator=(__tuple_impl&& __t) _NOEXCEPT_((__all<is_nothrow_move_assignable<_Tp>::value...>::value))
    458     {
    459         __swallow(__tuple_leaf<_Indx, _Tp>::operator=(_VSTD::forward<_Tp>(static_cast<__tuple_leaf<_Indx, _Tp>&>(__t).get()))...);
    460         return *this;
    461     }
    462 
    463     _LIBCPP_INLINE_VISIBILITY
    464     void swap(__tuple_impl& __t)
    465         _NOEXCEPT_(__all<__is_nothrow_swappable<_Tp>::value...>::value)
    466     {
    467         __swallow(__tuple_leaf<_Indx, _Tp>::swap(static_cast<__tuple_leaf<_Indx, _Tp>&>(__t))...);
    468     }
    469 };
    470 
    471 
    472 
    473 template <class ..._Tp>
    474 class _LIBCPP_TEMPLATE_VIS tuple
    475 {
    476     typedef __tuple_impl<typename __make_tuple_indices<sizeof...(_Tp)>::type, _Tp...> _BaseT;
    477 
    478     _BaseT __base_;
    479 
    480 #if defined(_LIBCPP_ENABLE_TUPLE_IMPLICIT_REDUCED_ARITY_EXTENSION)
    481     static constexpr bool _EnableImplicitReducedArityExtension = true;
    482 #else
    483     static constexpr bool _EnableImplicitReducedArityExtension = false;
    484 #endif
    485 
    486     template <class ..._Args>
    487     struct _PackExpandsToThisTuple : false_type {};
    488 
    489     template <class _Arg>
    490     struct _PackExpandsToThisTuple<_Arg>
    491         : is_same<typename __uncvref<_Arg>::type, tuple> {};
    492 
    493     template <bool _MaybeEnable, class _Dummy = void>
    494     struct _CheckArgsConstructor : __check_tuple_constructor_fail {};
    495 
    496     template <class _Dummy>
    497     struct _CheckArgsConstructor<true, _Dummy>
    498     {
    499         template <class ..._Args>
    500         static constexpr bool __enable_default() {
    501             return __all<is_default_constructible<_Args>::value...>::value;
    502         }
    503 
    504         template <class ..._Args>
    505         static constexpr bool __enable_explicit() {
    506             return
    507                 __tuple_constructible<
    508                     tuple<_Args...>,
    509                     typename __make_tuple_types<tuple,
    510                              sizeof...(_Args) < sizeof...(_Tp) ?
    511                                  sizeof...(_Args) :
    512                                  sizeof...(_Tp)>::type
    513                 >::value &&
    514                 !__tuple_convertible<
    515                     tuple<_Args...>,
    516                     typename __make_tuple_types<tuple,
    517                              sizeof...(_Args) < sizeof...(_Tp) ?
    518                                  sizeof...(_Args) :
    519                                  sizeof...(_Tp)>::type
    520                 >::value &&
    521                 __all_default_constructible<
    522                     typename __make_tuple_types<tuple, sizeof...(_Tp),
    523                              sizeof...(_Args) < sizeof...(_Tp) ?
    524                                  sizeof...(_Args) :
    525                                  sizeof...(_Tp)>::type
    526                 >::value;
    527         }
    528 
    529         template <class ..._Args>
    530         static constexpr bool __enable_implicit() {
    531             return
    532                 __tuple_convertible<
    533                     tuple<_Args...>,
    534                     typename __make_tuple_types<tuple,
    535                              sizeof...(_Args) < sizeof...(_Tp) ?
    536                                  sizeof...(_Args) :
    537                                  sizeof...(_Tp)>::type
    538                 >::value &&
    539                 __all_default_constructible<
    540                     typename __make_tuple_types<tuple, sizeof...(_Tp),
    541                              sizeof...(_Args) < sizeof...(_Tp) ?
    542                                  sizeof...(_Args) :
    543                                  sizeof...(_Tp)>::type
    544                 >::value;
    545         }
    546     };
    547 
    548     template <bool _MaybeEnable,
    549               bool = sizeof...(_Tp) == 1,
    550               class _Dummy = void>
    551     struct _CheckTupleLikeConstructor : __check_tuple_constructor_fail {};
    552 
    553     template <class _Dummy>
    554     struct _CheckTupleLikeConstructor<true, false, _Dummy>
    555     {
    556         template <class _Tuple>
    557         static constexpr bool __enable_implicit() {
    558             return __tuple_convertible<_Tuple, tuple>::value;
    559         }
    560 
    561         template <class _Tuple>
    562         static constexpr bool __enable_explicit() {
    563             return __tuple_constructible<_Tuple, tuple>::value
    564                && !__tuple_convertible<_Tuple, tuple>::value;
    565         }
    566     };
    567 
    568     template <class _Dummy>
    569     struct _CheckTupleLikeConstructor<true, true, _Dummy>
    570     {
    571         // This trait is used to disable the tuple-like constructor when
    572         // the UTypes... constructor should be selected instead.
    573         // See LWG issue #2549.
    574         template <class _Tuple>
    575         using _PreferTupleLikeConstructor = __lazy_or<
    576             // Don't attempt the two checks below if the tuple we are given
    577             // has the same type as this tuple.
    578             is_same<typename __uncvref<_Tuple>::type, tuple>,
    579             __lazy_and<
    580                 __lazy_not<is_constructible<_Tp..., _Tuple>>,
    581                 __lazy_not<is_convertible<_Tuple, _Tp...>>
    582             >
    583         >;
    584 
    585         template <class _Tuple>
    586         static constexpr bool __enable_implicit() {
    587             return __lazy_and<
    588                 __tuple_convertible<_Tuple, tuple>,
    589                 _PreferTupleLikeConstructor<_Tuple>
    590             >::value;
    591         }
    592 
    593         template <class _Tuple>
    594         static constexpr bool __enable_explicit() {
    595             return __lazy_and<
    596                 __tuple_constructible<_Tuple, tuple>,
    597                 _PreferTupleLikeConstructor<_Tuple>,
    598                 __lazy_not<__tuple_convertible<_Tuple, tuple>>
    599             >::value;
    600         }
    601     };
    602 
    603     template <size_t _Jp, class ..._Up> friend _LIBCPP_CONSTEXPR_AFTER_CXX11
    604         typename tuple_element<_Jp, tuple<_Up...> >::type& get(tuple<_Up...>&) _NOEXCEPT;
    605     template <size_t _Jp, class ..._Up> friend _LIBCPP_CONSTEXPR_AFTER_CXX11
    606         const typename tuple_element<_Jp, tuple<_Up...> >::type& get(const tuple<_Up...>&) _NOEXCEPT;
    607     template <size_t _Jp, class ..._Up> friend _LIBCPP_CONSTEXPR_AFTER_CXX11
    608         typename tuple_element<_Jp, tuple<_Up...> >::type&& get(tuple<_Up...>&&) _NOEXCEPT;
    609     template <size_t _Jp, class ..._Up> friend _LIBCPP_CONSTEXPR_AFTER_CXX11
    610         const typename tuple_element<_Jp, tuple<_Up...> >::type&& get(const tuple<_Up...>&&) _NOEXCEPT;
    611 public:
    612 
    613     template <bool _Dummy = true, class = typename enable_if<
    614         _CheckArgsConstructor<_Dummy>::template __enable_default<_Tp...>()
    615     >::type>
    616     _LIBCPP_INLINE_VISIBILITY
    617     _LIBCPP_CONSTEXPR tuple()
    618         _NOEXCEPT_(__all<is_nothrow_default_constructible<_Tp>::value...>::value) {}
    619 
    620     tuple(tuple const&) = default;
    621     tuple(tuple&&) = default;
    622 
    623     template <class _AllocArgT, class _Alloc, bool _Dummy = true, class = typename enable_if<
    624         __lazy_and<
    625             is_same<allocator_arg_t, _AllocArgT>,
    626             __lazy_all<__dependent_type<is_default_constructible<_Tp>, _Dummy>...>
    627        >::value
    628     >::type>
    629     _LIBCPP_INLINE_VISIBILITY
    630     tuple(_AllocArgT, _Alloc const& __a)
    631       : __base_(allocator_arg_t(), __a,
    632                     __tuple_indices<>(), __tuple_types<>(),
    633                     typename __make_tuple_indices<sizeof...(_Tp), 0>::type(),
    634                     __tuple_types<_Tp...>()) {}
    635 
    636     template <bool _Dummy = true,
    637               typename enable_if
    638                       <
    639                          _CheckArgsConstructor<
    640                             _Dummy
    641                          >::template __enable_implicit<_Tp const&...>(),
    642                          bool
    643                       >::type = false
    644         >
    645     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    646     tuple(const _Tp& ... __t) _NOEXCEPT_((__all<is_nothrow_copy_constructible<_Tp>::value...>::value))
    647         : __base_(typename __make_tuple_indices<sizeof...(_Tp)>::type(),
    648                 typename __make_tuple_types<tuple, sizeof...(_Tp)>::type(),
    649                 typename __make_tuple_indices<0>::type(),
    650                 typename __make_tuple_types<tuple, 0>::type(),
    651                 __t...
    652                ) {}
    653 
    654     template <bool _Dummy = true,
    655               typename enable_if
    656                       <
    657                          _CheckArgsConstructor<
    658                             _Dummy
    659                          >::template __enable_explicit<_Tp const&...>(),
    660                          bool
    661                       >::type = false
    662         >
    663     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    664     explicit tuple(const _Tp& ... __t) _NOEXCEPT_((__all<is_nothrow_copy_constructible<_Tp>::value...>::value))
    665         : __base_(typename __make_tuple_indices<sizeof...(_Tp)>::type(),
    666                 typename __make_tuple_types<tuple, sizeof...(_Tp)>::type(),
    667                 typename __make_tuple_indices<0>::type(),
    668                 typename __make_tuple_types<tuple, 0>::type(),
    669                 __t...
    670                ) {}
    671 
    672     template <class _Alloc, bool _Dummy = true,
    673               typename enable_if
    674                       <
    675                          _CheckArgsConstructor<
    676                             _Dummy
    677                          >::template __enable_implicit<_Tp const&...>(),
    678                          bool
    679                       >::type = false
    680         >
    681       _LIBCPP_INLINE_VISIBILITY
    682       tuple(allocator_arg_t, const _Alloc& __a, const _Tp& ... __t)
    683         : __base_(allocator_arg_t(), __a,
    684                 typename __make_tuple_indices<sizeof...(_Tp)>::type(),
    685                 typename __make_tuple_types<tuple, sizeof...(_Tp)>::type(),
    686                 typename __make_tuple_indices<0>::type(),
    687                 typename __make_tuple_types<tuple, 0>::type(),
    688                 __t...
    689                ) {}
    690 
    691     template <class _Alloc, bool _Dummy = true,
    692               typename enable_if
    693                       <
    694                          _CheckArgsConstructor<
    695                             _Dummy
    696                          >::template __enable_explicit<_Tp const&...>(),
    697                          bool
    698                       >::type = false
    699         >
    700       _LIBCPP_INLINE_VISIBILITY
    701       explicit
    702       tuple(allocator_arg_t, const _Alloc& __a, const _Tp& ... __t)
    703         : __base_(allocator_arg_t(), __a,
    704                 typename __make_tuple_indices<sizeof...(_Tp)>::type(),
    705                 typename __make_tuple_types<tuple, sizeof...(_Tp)>::type(),
    706                 typename __make_tuple_indices<0>::type(),
    707                 typename __make_tuple_types<tuple, 0>::type(),
    708                 __t...
    709                ) {}
    710 
    711     template <class ..._Up,
    712               bool _PackIsTuple = _PackExpandsToThisTuple<_Up...>::value,
    713               typename enable_if
    714                       <
    715                          _CheckArgsConstructor<
    716                              sizeof...(_Up) == sizeof...(_Tp)
    717                              && !_PackIsTuple
    718                          >::template __enable_implicit<_Up...>() ||
    719                         _CheckArgsConstructor<
    720                             _EnableImplicitReducedArityExtension
    721                             && sizeof...(_Up) < sizeof...(_Tp)
    722                             && !_PackIsTuple
    723                          >::template __enable_implicit<_Up...>(),
    724                          bool
    725                       >::type = false
    726              >
    727         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    728         tuple(_Up&&... __u)
    729             _NOEXCEPT_((
    730                 is_nothrow_constructible<_BaseT,
    731                     typename __make_tuple_indices<sizeof...(_Up)>::type,
    732                     typename __make_tuple_types<tuple, sizeof...(_Up)>::type,
    733                     typename __make_tuple_indices<sizeof...(_Tp), sizeof...(_Up)>::type,
    734                     typename __make_tuple_types<tuple, sizeof...(_Tp), sizeof...(_Up)>::type,
    735                     _Up...
    736                 >::value
    737             ))
    738             : __base_(typename __make_tuple_indices<sizeof...(_Up)>::type(),
    739                     typename __make_tuple_types<tuple, sizeof...(_Up)>::type(),
    740                     typename __make_tuple_indices<sizeof...(_Tp), sizeof...(_Up)>::type(),
    741                     typename __make_tuple_types<tuple, sizeof...(_Tp), sizeof...(_Up)>::type(),
    742                     _VSTD::forward<_Up>(__u)...) {}
    743 
    744     template <class ..._Up,
    745               typename enable_if
    746                       <
    747                          _CheckArgsConstructor<
    748                              sizeof...(_Up) <= sizeof...(_Tp)
    749                              && !_PackExpandsToThisTuple<_Up...>::value
    750                          >::template __enable_explicit<_Up...>() ||
    751                          _CheckArgsConstructor<
    752                             !_EnableImplicitReducedArityExtension
    753                             && sizeof...(_Up) < sizeof...(_Tp)
    754                             && !_PackExpandsToThisTuple<_Up...>::value
    755                          >::template __enable_implicit<_Up...>(),
    756                          bool
    757                       >::type = false
    758              >
    759         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    760         explicit
    761         tuple(_Up&&... __u)
    762             _NOEXCEPT_((
    763                 is_nothrow_constructible<_BaseT,
    764                     typename __make_tuple_indices<sizeof...(_Up)>::type,
    765                     typename __make_tuple_types<tuple, sizeof...(_Up)>::type,
    766                     typename __make_tuple_indices<sizeof...(_Tp), sizeof...(_Up)>::type,
    767                     typename __make_tuple_types<tuple, sizeof...(_Tp), sizeof...(_Up)>::type,
    768                     _Up...
    769                 >::value
    770             ))
    771             : __base_(typename __make_tuple_indices<sizeof...(_Up)>::type(),
    772                     typename __make_tuple_types<tuple, sizeof...(_Up)>::type(),
    773                     typename __make_tuple_indices<sizeof...(_Tp), sizeof...(_Up)>::type(),
    774                     typename __make_tuple_types<tuple, sizeof...(_Tp), sizeof...(_Up)>::type(),
    775                     _VSTD::forward<_Up>(__u)...) {}
    776 
    777     template <class _Alloc, class ..._Up,
    778               typename enable_if
    779                       <
    780                          _CheckArgsConstructor<
    781                              sizeof...(_Up) == sizeof...(_Tp) &&
    782                              !_PackExpandsToThisTuple<_Up...>::value
    783                          >::template __enable_implicit<_Up...>(),
    784                          bool
    785                       >::type = false
    786              >
    787         _LIBCPP_INLINE_VISIBILITY
    788         tuple(allocator_arg_t, const _Alloc& __a, _Up&&... __u)
    789             : __base_(allocator_arg_t(), __a,
    790                     typename __make_tuple_indices<sizeof...(_Up)>::type(),
    791                     typename __make_tuple_types<tuple, sizeof...(_Up)>::type(),
    792                     typename __make_tuple_indices<sizeof...(_Tp), sizeof...(_Up)>::type(),
    793                     typename __make_tuple_types<tuple, sizeof...(_Tp), sizeof...(_Up)>::type(),
    794                     _VSTD::forward<_Up>(__u)...) {}
    795 
    796     template <class _Alloc, class ..._Up,
    797               typename enable_if
    798                       <
    799                          _CheckArgsConstructor<
    800                              sizeof...(_Up) == sizeof...(_Tp) &&
    801                              !_PackExpandsToThisTuple<_Up...>::value
    802                          >::template __enable_explicit<_Up...>(),
    803                          bool
    804                       >::type = false
    805              >
    806         _LIBCPP_INLINE_VISIBILITY
    807         explicit
    808         tuple(allocator_arg_t, const _Alloc& __a, _Up&&... __u)
    809             : __base_(allocator_arg_t(), __a,
    810                     typename __make_tuple_indices<sizeof...(_Up)>::type(),
    811                     typename __make_tuple_types<tuple, sizeof...(_Up)>::type(),
    812                     typename __make_tuple_indices<sizeof...(_Tp), sizeof...(_Up)>::type(),
    813                     typename __make_tuple_types<tuple, sizeof...(_Tp), sizeof...(_Up)>::type(),
    814                     _VSTD::forward<_Up>(__u)...) {}
    815 
    816     template <class _Tuple,
    817               typename enable_if
    818                       <
    819                          _CheckTupleLikeConstructor<
    820                              __tuple_like_with_size<_Tuple, sizeof...(_Tp)>::value
    821                              && !_PackExpandsToThisTuple<_Tuple>::value
    822                          >::template __enable_implicit<_Tuple>(),
    823                          bool
    824                       >::type = false
    825              >
    826         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    827         tuple(_Tuple&& __t) _NOEXCEPT_((is_nothrow_constructible<_BaseT, _Tuple>::value))
    828             : __base_(_VSTD::forward<_Tuple>(__t)) {}
    829 
    830     template <class _Tuple,
    831               typename enable_if
    832                       <
    833                          _CheckTupleLikeConstructor<
    834                              __tuple_like_with_size<_Tuple, sizeof...(_Tp)>::value
    835                              && !_PackExpandsToThisTuple<_Tuple>::value
    836                          >::template __enable_explicit<_Tuple>(),
    837                          bool
    838                       >::type = false
    839              >
    840         _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    841         explicit
    842         tuple(_Tuple&& __t) _NOEXCEPT_((is_nothrow_constructible<_BaseT, _Tuple>::value))
    843             : __base_(_VSTD::forward<_Tuple>(__t)) {}
    844 
    845     template <class _Alloc, class _Tuple,
    846               typename enable_if
    847                       <
    848                          _CheckTupleLikeConstructor<
    849                              __tuple_like_with_size<_Tuple, sizeof...(_Tp)>::value
    850                          >::template __enable_implicit<_Tuple>(),
    851                          bool
    852                       >::type = false
    853              >
    854         _LIBCPP_INLINE_VISIBILITY
    855         tuple(allocator_arg_t, const _Alloc& __a, _Tuple&& __t)
    856             : __base_(allocator_arg_t(), __a, _VSTD::forward<_Tuple>(__t)) {}
    857 
    858     template <class _Alloc, class _Tuple,
    859               typename enable_if
    860                       <
    861                          _CheckTupleLikeConstructor<
    862                              __tuple_like_with_size<_Tuple, sizeof...(_Tp)>::value
    863                          >::template __enable_explicit<_Tuple>(),
    864                          bool
    865                       >::type = false
    866              >
    867         _LIBCPP_INLINE_VISIBILITY
    868         explicit
    869         tuple(allocator_arg_t, const _Alloc& __a, _Tuple&& __t)
    870             : __base_(allocator_arg_t(), __a, _VSTD::forward<_Tuple>(__t)) {}
    871 
    872     using _CanCopyAssign = __all<is_copy_assignable<_Tp>::value...>;
    873     using _CanMoveAssign = __all<is_move_assignable<_Tp>::value...>;
    874 
    875     _LIBCPP_INLINE_VISIBILITY
    876     tuple& operator=(typename conditional<_CanCopyAssign::value, tuple, __nat>::type const& __t)
    877         _NOEXCEPT_((__all<is_nothrow_copy_assignable<_Tp>::value...>::value))
    878     {
    879         __base_.operator=(__t.__base_);
    880         return *this;
    881     }
    882 
    883     _LIBCPP_INLINE_VISIBILITY
    884     tuple& operator=(typename conditional<_CanMoveAssign::value, tuple, __nat>::type&& __t)
    885         _NOEXCEPT_((__all<is_nothrow_move_assignable<_Tp>::value...>::value))
    886     {
    887         __base_.operator=(static_cast<_BaseT&&>(__t.__base_));
    888         return *this;
    889     }
    890 
    891     template <class _Tuple,
    892               class = typename enable_if
    893                       <
    894                          __tuple_assignable<_Tuple, tuple>::value
    895                       >::type
    896              >
    897         _LIBCPP_INLINE_VISIBILITY
    898         tuple&
    899         operator=(_Tuple&& __t) _NOEXCEPT_((is_nothrow_assignable<_BaseT&, _Tuple>::value))
    900         {
    901             __base_.operator=(_VSTD::forward<_Tuple>(__t));
    902             return *this;
    903         }
    904 
    905     _LIBCPP_INLINE_VISIBILITY
    906     void swap(tuple& __t) _NOEXCEPT_(__all<__is_nothrow_swappable<_Tp>::value...>::value)
    907         {__base_.swap(__t.__base_);}
    908 };
    909 
    910 template <>
    911 class _LIBCPP_TEMPLATE_VIS tuple<>
    912 {
    913 public:
    914     _LIBCPP_INLINE_VISIBILITY
    915     _LIBCPP_CONSTEXPR tuple() _NOEXCEPT {}
    916     template <class _Alloc>
    917     _LIBCPP_INLINE_VISIBILITY
    918         tuple(allocator_arg_t, const _Alloc&) _NOEXCEPT {}
    919     template <class _Alloc>
    920     _LIBCPP_INLINE_VISIBILITY
    921         tuple(allocator_arg_t, const _Alloc&, const tuple&) _NOEXCEPT {}
    922     template <class _Up>
    923     _LIBCPP_INLINE_VISIBILITY
    924         tuple(array<_Up, 0>) _NOEXCEPT {}
    925     template <class _Alloc, class _Up>
    926     _LIBCPP_INLINE_VISIBILITY
    927         tuple(allocator_arg_t, const _Alloc&, array<_Up, 0>) _NOEXCEPT {}
    928     _LIBCPP_INLINE_VISIBILITY
    929     void swap(tuple&) _NOEXCEPT {}
    930 };
    931 
    932 #ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
    933 // NOTE: These are not yet standardized, but are required to simulate the
    934 // implicit deduction guide that should be generated had libc++ declared the
    935 // tuple-like constructors "correctly"
    936 template <class _Alloc, class ..._Args>
    937 tuple(allocator_arg_t, const _Alloc&, tuple<_Args...> const&) -> tuple<_Args...>;
    938 template <class _Alloc, class ..._Args>
    939 tuple(allocator_arg_t, const _Alloc&, tuple<_Args...>&&) -> tuple<_Args...>;
    940 #endif
    941 
    942 template <class ..._Tp>
    943 inline _LIBCPP_INLINE_VISIBILITY
    944 typename enable_if
    945 <
    946     __all<__is_swappable<_Tp>::value...>::value,
    947     void
    948 >::type
    949 swap(tuple<_Tp...>& __t, tuple<_Tp...>& __u)
    950                  _NOEXCEPT_(__all<__is_nothrow_swappable<_Tp>::value...>::value)
    951     {__t.swap(__u);}
    952 
    953 // get
    954 
    955 template <size_t _Ip, class ..._Tp>
    956 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    957 typename tuple_element<_Ip, tuple<_Tp...> >::type&
    958 get(tuple<_Tp...>& __t) _NOEXCEPT
    959 {
    960     typedef typename tuple_element<_Ip, tuple<_Tp...> >::type type;
    961     return static_cast<__tuple_leaf<_Ip, type>&>(__t.__base_).get();
    962 }
    963 
    964 template <size_t _Ip, class ..._Tp>
    965 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    966 const typename tuple_element<_Ip, tuple<_Tp...> >::type&
    967 get(const tuple<_Tp...>& __t) _NOEXCEPT
    968 {
    969     typedef typename tuple_element<_Ip, tuple<_Tp...> >::type type;
    970     return static_cast<const __tuple_leaf<_Ip, type>&>(__t.__base_).get();
    971 }
    972 
    973 template <size_t _Ip, class ..._Tp>
    974 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    975 typename tuple_element<_Ip, tuple<_Tp...> >::type&&
    976 get(tuple<_Tp...>&& __t) _NOEXCEPT
    977 {
    978     typedef typename tuple_element<_Ip, tuple<_Tp...> >::type type;
    979     return static_cast<type&&>(
    980              static_cast<__tuple_leaf<_Ip, type>&&>(__t.__base_).get());
    981 }
    982 
    983 template <size_t _Ip, class ..._Tp>
    984 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
    985 const typename tuple_element<_Ip, tuple<_Tp...> >::type&&
    986 get(const tuple<_Tp...>&& __t) _NOEXCEPT
    987 {
    988     typedef typename tuple_element<_Ip, tuple<_Tp...> >::type type;
    989     return static_cast<const type&&>(
    990              static_cast<const __tuple_leaf<_Ip, type>&&>(__t.__base_).get());
    991 }
    992 
    993 #if _LIBCPP_STD_VER > 11
    994 
    995 namespace __find_detail {
    996 
    997 static constexpr size_t __not_found = -1;
    998 static constexpr size_t __ambiguous = __not_found - 1;
    999 
   1000 inline _LIBCPP_INLINE_VISIBILITY
   1001 constexpr size_t __find_idx_return(size_t __curr_i, size_t __res, bool __matches) {
   1002     return !__matches ? __res :
   1003         (__res == __not_found ? __curr_i : __ambiguous);
   1004 }
   1005 
   1006 template <size_t _Nx>
   1007 inline _LIBCPP_INLINE_VISIBILITY
   1008 constexpr size_t __find_idx(size_t __i, const bool (&__matches)[_Nx]) {
   1009   return __i == _Nx ? __not_found :
   1010       __find_idx_return(__i, __find_idx(__i + 1, __matches), __matches[__i]);
   1011 }
   1012 
   1013 template <class _T1, class ..._Args>
   1014 struct __find_exactly_one_checked {
   1015   static constexpr bool __matches[] = {is_same<_T1, _Args>::value...};
   1016     static constexpr size_t value = __find_detail::__find_idx(0, __matches);
   1017     static_assert (value != __not_found, "type not found in type list" );
   1018     static_assert(value != __ambiguous,"type occurs more than once in type list");
   1019 };
   1020 
   1021 template <class _T1>
   1022 struct __find_exactly_one_checked<_T1> {
   1023     static_assert(!is_same<_T1, _T1>::value, "type not in empty type list");
   1024 };
   1025 
   1026 } // namespace __find_detail;
   1027 
   1028 template <typename _T1, typename... _Args>
   1029 struct __find_exactly_one_t
   1030     : public __find_detail::__find_exactly_one_checked<_T1, _Args...> {
   1031 };
   1032 
   1033 template <class _T1, class... _Args>
   1034 inline _LIBCPP_INLINE_VISIBILITY
   1035 constexpr _T1& get(tuple<_Args...>& __tup) noexcept
   1036 {
   1037     return _VSTD::get<__find_exactly_one_t<_T1, _Args...>::value>(__tup);
   1038 }
   1039 
   1040 template <class _T1, class... _Args>
   1041 inline _LIBCPP_INLINE_VISIBILITY
   1042 constexpr _T1 const& get(tuple<_Args...> const& __tup) noexcept
   1043 {
   1044     return _VSTD::get<__find_exactly_one_t<_T1, _Args...>::value>(__tup);
   1045 }
   1046 
   1047 template <class _T1, class... _Args>
   1048 inline _LIBCPP_INLINE_VISIBILITY
   1049 constexpr _T1&& get(tuple<_Args...>&& __tup) noexcept
   1050 {
   1051     return _VSTD::get<__find_exactly_one_t<_T1, _Args...>::value>(_VSTD::move(__tup));
   1052 }
   1053 
   1054 template <class _T1, class... _Args>
   1055 inline _LIBCPP_INLINE_VISIBILITY
   1056 constexpr _T1 const&& get(tuple<_Args...> const&& __tup) noexcept
   1057 {
   1058     return _VSTD::get<__find_exactly_one_t<_T1, _Args...>::value>(_VSTD::move(__tup));
   1059 }
   1060 
   1061 #endif
   1062 
   1063 // tie
   1064 
   1065 template <class ..._Tp>
   1066 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1067 tuple<_Tp&...>
   1068 tie(_Tp&... __t) _NOEXCEPT
   1069 {
   1070     return tuple<_Tp&...>(__t...);
   1071 }
   1072 
   1073 template <class _Up>
   1074 struct __ignore_t
   1075 {
   1076     template <class _Tp>
   1077     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1078     const __ignore_t& operator=(_Tp&&) const {return *this;}
   1079 };
   1080 
   1081 namespace {
   1082   constexpr __ignore_t<unsigned char> ignore = __ignore_t<unsigned char>();
   1083 }
   1084 
   1085 template <class _Tp>
   1086 struct __make_tuple_return_impl
   1087 {
   1088     typedef _Tp type;
   1089 };
   1090 
   1091 template <class _Tp>
   1092 struct __make_tuple_return_impl<reference_wrapper<_Tp> >
   1093 {
   1094     typedef _Tp& type;
   1095 };
   1096 
   1097 template <class _Tp>
   1098 struct __make_tuple_return
   1099 {
   1100     typedef typename __make_tuple_return_impl<typename decay<_Tp>::type>::type type;
   1101 };
   1102 
   1103 template <class... _Tp>
   1104 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1105 tuple<typename __make_tuple_return<_Tp>::type...>
   1106 make_tuple(_Tp&&... __t)
   1107 {
   1108     return tuple<typename __make_tuple_return<_Tp>::type...>(_VSTD::forward<_Tp>(__t)...);
   1109 }
   1110 
   1111 template <class... _Tp>
   1112 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1113 tuple<_Tp&&...>
   1114 forward_as_tuple(_Tp&&... __t) _NOEXCEPT
   1115 {
   1116     return tuple<_Tp&&...>(_VSTD::forward<_Tp>(__t)...);
   1117 }
   1118 
   1119 template <size_t _Ip>
   1120 struct __tuple_equal
   1121 {
   1122     template <class _Tp, class _Up>
   1123     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1124     bool operator()(const _Tp& __x, const _Up& __y)
   1125     {
   1126         return __tuple_equal<_Ip - 1>()(__x, __y) && _VSTD::get<_Ip-1>(__x) == _VSTD::get<_Ip-1>(__y);
   1127     }
   1128 };
   1129 
   1130 template <>
   1131 struct __tuple_equal<0>
   1132 {
   1133     template <class _Tp, class _Up>
   1134     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1135     bool operator()(const _Tp&, const _Up&)
   1136     {
   1137         return true;
   1138     }
   1139 };
   1140 
   1141 template <class ..._Tp, class ..._Up>
   1142 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1143 bool
   1144 operator==(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
   1145 {
   1146     return __tuple_equal<sizeof...(_Tp)>()(__x, __y);
   1147 }
   1148 
   1149 template <class ..._Tp, class ..._Up>
   1150 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1151 bool
   1152 operator!=(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
   1153 {
   1154     return !(__x == __y);
   1155 }
   1156 
   1157 template <size_t _Ip>
   1158 struct __tuple_less
   1159 {
   1160     template <class _Tp, class _Up>
   1161     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1162     bool operator()(const _Tp& __x, const _Up& __y)
   1163     {
   1164         const size_t __idx = tuple_size<_Tp>::value - _Ip;
   1165         if (_VSTD::get<__idx>(__x) < _VSTD::get<__idx>(__y))
   1166             return true;
   1167         if (_VSTD::get<__idx>(__y) < _VSTD::get<__idx>(__x))
   1168             return false;
   1169         return __tuple_less<_Ip-1>()(__x, __y);
   1170     }
   1171 };
   1172 
   1173 template <>
   1174 struct __tuple_less<0>
   1175 {
   1176     template <class _Tp, class _Up>
   1177     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1178     bool operator()(const _Tp&, const _Up&)
   1179     {
   1180         return false;
   1181     }
   1182 };
   1183 
   1184 template <class ..._Tp, class ..._Up>
   1185 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1186 bool
   1187 operator<(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
   1188 {
   1189     return __tuple_less<sizeof...(_Tp)>()(__x, __y);
   1190 }
   1191 
   1192 template <class ..._Tp, class ..._Up>
   1193 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1194 bool
   1195 operator>(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
   1196 {
   1197     return __y < __x;
   1198 }
   1199 
   1200 template <class ..._Tp, class ..._Up>
   1201 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1202 bool
   1203 operator>=(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
   1204 {
   1205     return !(__x < __y);
   1206 }
   1207 
   1208 template <class ..._Tp, class ..._Up>
   1209 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1210 bool
   1211 operator<=(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
   1212 {
   1213     return !(__y < __x);
   1214 }
   1215 
   1216 // tuple_cat
   1217 
   1218 template <class _Tp, class _Up> struct __tuple_cat_type;
   1219 
   1220 template <class ..._Ttypes, class ..._Utypes>
   1221 struct __tuple_cat_type<tuple<_Ttypes...>, __tuple_types<_Utypes...> >
   1222 {
   1223     typedef tuple<_Ttypes..., _Utypes...> type;
   1224 };
   1225 
   1226 template <class _ResultTuple, bool _Is_Tuple0TupleLike, class ..._Tuples>
   1227 struct __tuple_cat_return_1
   1228 {
   1229 };
   1230 
   1231 template <class ..._Types, class _Tuple0>
   1232 struct __tuple_cat_return_1<tuple<_Types...>, true, _Tuple0>
   1233 {
   1234     typedef typename __tuple_cat_type<tuple<_Types...>,
   1235             typename __make_tuple_types<typename remove_reference<_Tuple0>::type>::type>::type
   1236                                                                            type;
   1237 };
   1238 
   1239 template <class ..._Types, class _Tuple0, class _Tuple1, class ..._Tuples>
   1240 struct __tuple_cat_return_1<tuple<_Types...>, true, _Tuple0, _Tuple1, _Tuples...>
   1241     : public __tuple_cat_return_1<
   1242                  typename __tuple_cat_type<
   1243                      tuple<_Types...>,
   1244                      typename __make_tuple_types<typename remove_reference<_Tuple0>::type>::type
   1245                  >::type,
   1246                  __tuple_like<typename remove_reference<_Tuple1>::type>::value,
   1247                  _Tuple1, _Tuples...>
   1248 {
   1249 };
   1250 
   1251 template <class ..._Tuples> struct __tuple_cat_return;
   1252 
   1253 template <class _Tuple0, class ..._Tuples>
   1254 struct __tuple_cat_return<_Tuple0, _Tuples...>
   1255     : public __tuple_cat_return_1<tuple<>,
   1256          __tuple_like<typename remove_reference<_Tuple0>::type>::value, _Tuple0,
   1257                                                                      _Tuples...>
   1258 {
   1259 };
   1260 
   1261 template <>
   1262 struct __tuple_cat_return<>
   1263 {
   1264     typedef tuple<> type;
   1265 };
   1266 
   1267 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1268 tuple<>
   1269 tuple_cat()
   1270 {
   1271     return tuple<>();
   1272 }
   1273 
   1274 template <class _Rp, class _Indices, class _Tuple0, class ..._Tuples>
   1275 struct __tuple_cat_return_ref_imp;
   1276 
   1277 template <class ..._Types, size_t ..._I0, class _Tuple0>
   1278 struct __tuple_cat_return_ref_imp<tuple<_Types...>, __tuple_indices<_I0...>, _Tuple0>
   1279 {
   1280     typedef typename remove_reference<_Tuple0>::type _T0;
   1281     typedef tuple<_Types..., typename __apply_cv<_Tuple0,
   1282                           typename tuple_element<_I0, _T0>::type>::type&&...> type;
   1283 };
   1284 
   1285 template <class ..._Types, size_t ..._I0, class _Tuple0, class _Tuple1, class ..._Tuples>
   1286 struct __tuple_cat_return_ref_imp<tuple<_Types...>, __tuple_indices<_I0...>,
   1287                                   _Tuple0, _Tuple1, _Tuples...>
   1288     : public __tuple_cat_return_ref_imp<
   1289          tuple<_Types..., typename __apply_cv<_Tuple0,
   1290                typename tuple_element<_I0,
   1291                   typename remove_reference<_Tuple0>::type>::type>::type&&...>,
   1292          typename __make_tuple_indices<tuple_size<typename
   1293                                  remove_reference<_Tuple1>::type>::value>::type,
   1294          _Tuple1, _Tuples...>
   1295 {
   1296 };
   1297 
   1298 template <class _Tuple0, class ..._Tuples>
   1299 struct __tuple_cat_return_ref
   1300     : public __tuple_cat_return_ref_imp<tuple<>,
   1301                typename __make_tuple_indices<
   1302                         tuple_size<typename remove_reference<_Tuple0>::type>::value
   1303                >::type, _Tuple0, _Tuples...>
   1304 {
   1305 };
   1306 
   1307 template <class _Types, class _I0, class _J0>
   1308 struct __tuple_cat;
   1309 
   1310 template <class ..._Types, size_t ..._I0, size_t ..._J0>
   1311 struct __tuple_cat<tuple<_Types...>, __tuple_indices<_I0...>, __tuple_indices<_J0...> >
   1312 {
   1313     template <class _Tuple0>
   1314     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1315     typename __tuple_cat_return_ref<tuple<_Types...>&&, _Tuple0&&>::type
   1316     operator()(tuple<_Types...> __t, _Tuple0&& __t0)
   1317     {
   1318         return forward_as_tuple(_VSTD::forward<_Types>(_VSTD::get<_I0>(__t))...,
   1319                                       _VSTD::get<_J0>(_VSTD::forward<_Tuple0>(__t0))...);
   1320     }
   1321 
   1322     template <class _Tuple0, class _Tuple1, class ..._Tuples>
   1323     _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1324     typename __tuple_cat_return_ref<tuple<_Types...>&&, _Tuple0&&, _Tuple1&&, _Tuples&&...>::type
   1325     operator()(tuple<_Types...> __t, _Tuple0&& __t0, _Tuple1&& __t1, _Tuples&& ...__tpls)
   1326     {
   1327         typedef typename remove_reference<_Tuple0>::type _T0;
   1328         typedef typename remove_reference<_Tuple1>::type _T1;
   1329         return __tuple_cat<
   1330            tuple<_Types..., typename __apply_cv<_Tuple0, typename tuple_element<_J0, _T0>::type>::type&&...>,
   1331            typename __make_tuple_indices<sizeof ...(_Types) + tuple_size<_T0>::value>::type,
   1332            typename __make_tuple_indices<tuple_size<_T1>::value>::type>()
   1333                            (forward_as_tuple(
   1334                               _VSTD::forward<_Types>(_VSTD::get<_I0>(__t))...,
   1335                               _VSTD::get<_J0>(_VSTD::forward<_Tuple0>(__t0))...
   1336                             ),
   1337                             _VSTD::forward<_Tuple1>(__t1),
   1338                             _VSTD::forward<_Tuples>(__tpls)...);
   1339     }
   1340 };
   1341 
   1342 template <class _Tuple0, class... _Tuples>
   1343 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
   1344 typename __tuple_cat_return<_Tuple0, _Tuples...>::type
   1345 tuple_cat(_Tuple0&& __t0, _Tuples&&... __tpls)
   1346 {
   1347     typedef typename remove_reference<_Tuple0>::type _T0;
   1348     return __tuple_cat<tuple<>, __tuple_indices<>,
   1349                   typename __make_tuple_indices<tuple_size<_T0>::value>::type>()
   1350                   (tuple<>(), _VSTD::forward<_Tuple0>(__t0),
   1351                                             _VSTD::forward<_Tuples>(__tpls)...);
   1352 }
   1353 
   1354 template <class ..._Tp, class _Alloc>
   1355 struct _LIBCPP_TEMPLATE_VIS uses_allocator<tuple<_Tp...>, _Alloc>
   1356     : true_type {};
   1357 
   1358 template <class _T1, class _T2>
   1359 template <class... _Args1, class... _Args2, size_t ..._I1, size_t ..._I2>
   1360 inline _LIBCPP_INLINE_VISIBILITY
   1361 pair<_T1, _T2>::pair(piecewise_construct_t,
   1362                      tuple<_Args1...>& __first_args, tuple<_Args2...>& __second_args,
   1363                      __tuple_indices<_I1...>, __tuple_indices<_I2...>)
   1364     :  first(_VSTD::forward<_Args1>(_VSTD::get<_I1>( __first_args))...),
   1365       second(_VSTD::forward<_Args2>(_VSTD::get<_I2>(__second_args))...)
   1366 {
   1367 }
   1368 
   1369 #if _LIBCPP_STD_VER > 14
   1370 template <class _Tp>
   1371 constexpr size_t tuple_size_v = tuple_size<_Tp>::value;
   1372 
   1373 #define _LIBCPP_NOEXCEPT_RETURN(...) noexcept(noexcept(__VA_ARGS__)) { return __VA_ARGS__; }
   1374 
   1375 template <class _Fn, class _Tuple, size_t ..._Id>
   1376 inline _LIBCPP_INLINE_VISIBILITY
   1377 constexpr decltype(auto) __apply_tuple_impl(_Fn && __f, _Tuple && __t,
   1378                                             __tuple_indices<_Id...>)
   1379 _LIBCPP_NOEXCEPT_RETURN(
   1380     _VSTD::__invoke_constexpr(
   1381         _VSTD::forward<_Fn>(__f),
   1382         _VSTD::get<_Id>(_VSTD::forward<_Tuple>(__t))...)
   1383 )
   1384 
   1385 template <class _Fn, class _Tuple>
   1386 inline _LIBCPP_INLINE_VISIBILITY
   1387 constexpr decltype(auto) apply(_Fn && __f, _Tuple && __t)
   1388 _LIBCPP_NOEXCEPT_RETURN(
   1389     _VSTD::__apply_tuple_impl(
   1390         _VSTD::forward<_Fn>(__f), _VSTD::forward<_Tuple>(__t),
   1391         typename __make_tuple_indices<tuple_size_v<decay_t<_Tuple>>>::type{})
   1392 )
   1393 
   1394 template <class _Tp, class _Tuple, size_t... _Idx>
   1395 inline _LIBCPP_INLINE_VISIBILITY
   1396 constexpr _Tp __make_from_tuple_impl(_Tuple&& __t, __tuple_indices<_Idx...>)
   1397 _LIBCPP_NOEXCEPT_RETURN(
   1398     _Tp(_VSTD::get<_Idx>(_VSTD::forward<_Tuple>(__t))...)
   1399 )
   1400 
   1401 template <class _Tp, class _Tuple>
   1402 inline _LIBCPP_INLINE_VISIBILITY
   1403 constexpr _Tp make_from_tuple(_Tuple&& __t)
   1404 _LIBCPP_NOEXCEPT_RETURN(
   1405     _VSTD::__make_from_tuple_impl<_Tp>(_VSTD::forward<_Tuple>(__t),
   1406         typename __make_tuple_indices<tuple_size_v<decay_t<_Tuple>>>::type{})
   1407 )
   1408 
   1409 #undef _LIBCPP_NOEXCEPT_RETURN
   1410 
   1411 #endif // _LIBCPP_STD_VER > 14
   1412 
   1413 #endif // !defined(_LIBCPP_CXX03_LANG)
   1414 
   1415 _LIBCPP_END_NAMESPACE_STD
   1416 
   1417 #endif  // _LIBCPP_TUPLE
   1418