text: // -*- C++ -*-
  //===----------------------------------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef _LIBCPP___TUPLE
  #define _LIBCPP___TUPLE
  
  #include <__config>
  #include <cstddef>
  #include <type_traits>
  
  #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  #pragma GCC system_header
  #endif
  
  
  _LIBCPP_BEGIN_NAMESPACE_STD
  
  template <class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_size;
  
  #if !defined(_LIBCPP_CXX03_LANG)
  template <class _Tp, class...>
  using __enable_if_tuple_size_imp = _Tp;
  
  template <class _Tp>
  struct _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
      const _Tp,
      typename enable_if<!is_volatile<_Tp>::value>::type,
      integral_constant<size_t, sizeof(tuple_size<_Tp>)>>>
      : public integral_constant<size_t, tuple_size<_Tp>::value> {};
  
  template <class _Tp>
  struct _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
      volatile _Tp,
      typename enable_if<!is_const<_Tp>::value>::type,
      integral_constant<size_t, sizeof(tuple_size<_Tp>)>>>
      : public integral_constant<size_t, tuple_size<_Tp>::value> {};
  
  template <class _Tp>
  struct _LIBCPP_TEMPLATE_VIS tuple_size<__enable_if_tuple_size_imp<
      const volatile _Tp,
      integral_constant<size_t, sizeof(tuple_size<_Tp>)>>>
      : public integral_constant<size_t, tuple_size<_Tp>::value> {};
  
  #else
  template <class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_size<const _Tp> : public tuple_size<_Tp> {};
  template <class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_size<volatile _Tp> : public tuple_size<_Tp> {};
  template <class _Tp> struct _LIBCPP_TEMPLATE_VIS tuple_size<const volatile _Tp> : public tuple_size<_Tp> {};
  #endif
  
  template <size_t _Ip, class _Tp> class _LIBCPP_TEMPLATE_VIS tuple_element;
  
  template <size_t _Ip, class _Tp>
  class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, const _Tp>
  {
  public:
      typedef typename add_const<typename tuple_element<_Ip, _Tp>::type>::type type;
  };
  
  template <size_t _Ip, class _Tp>
  class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, volatile _Tp>
  {
  public:
      typedef typename add_volatile<typename tuple_element<_Ip, _Tp>::type>::type type;
  };
  
  template <size_t _Ip, class _Tp>
  class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, const volatile _Tp>
  {
  public:
      typedef typename add_cv<typename tuple_element<_Ip, _Tp>::type>::type type;
  };
  
  template <class _Tp> struct __tuple_like : false_type {};
  
  template <class _Tp> struct __tuple_like<const _Tp> : public __tuple_like<_Tp> {};
  template <class _Tp> struct __tuple_like<volatile _Tp> : public __tuple_like<_Tp> {};
  template <class _Tp> struct __tuple_like<const volatile _Tp> : public __tuple_like<_Tp> {};
  
  // tuple specializations
  
  #ifndef _LIBCPP_CXX03_LANG
  
  template <size_t...> struct __tuple_indices {};
  
  template <class _IdxType, _IdxType... _Values>
  struct __integer_sequence {
    template <template <class _OIdxType, _OIdxType...> class _ToIndexSeq, class _ToIndexType>
    using __convert = _ToIndexSeq<_ToIndexType, _Values...>;
  
    template <size_t _Sp>
    using __to_tuple_indices = __tuple_indices<(_Values + _Sp)...>;
  };
  
  #if !__has_builtin(__make_integer_seq) || defined(_LIBCPP_TESTING_FALLBACK_MAKE_INTEGER_SEQUENCE)
  namespace __detail {
  
  template<typename _Tp, size_t ..._Extra> struct __repeat;
  template<typename _Tp, _Tp ..._Np, size_t ..._Extra> struct __repeat<__integer_sequence<_Tp, _Np...>, _Extra...> {
    typedef __integer_sequence<_Tp,
                             _Np...,
                             sizeof...(_Np) + _Np...,
                             2 * sizeof...(_Np) + _Np...,
                             3 * sizeof...(_Np) + _Np...,
                             4 * sizeof...(_Np) + _Np...,
                             5 * sizeof...(_Np) + _Np...,
                             6 * sizeof...(_Np) + _Np...,
                             7 * sizeof...(_Np) + _Np...,
                             _Extra...> type;
  };
  
  template<size_t _Np> struct __parity;
  template<size_t _Np> struct __make : __parity<_Np % 8>::template __pmake<_Np> {};
  
  template<> struct __make<0> { typedef __integer_sequence<size_t> type; };
  template<> struct __make<1> { typedef __integer_sequence<size_t, 0> type; };
  template<> struct __make<2> { typedef __integer_sequence<size_t, 0, 1> type; };
  template<> struct __make<3> { typedef __integer_sequence<size_t, 0, 1, 2> type; };
  template<> struct __make<4> { typedef __integer_sequence<size_t, 0, 1, 2, 3> type; };
  template<> struct __make<5> { typedef __integer_sequence<size_t, 0, 1, 2, 3, 4> type; };
  template<> struct __make<6> { typedef __integer_sequence<size_t, 0, 1, 2, 3, 4, 5> type; };
  template<> struct __make<7> { typedef __integer_sequence<size_t, 0, 1, 2, 3, 4, 5, 6> type; };
  
  template<> struct __parity<0> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type> {}; };
  template<> struct __parity<1> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 1> {}; };
  template<> struct __parity<2> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 2, _Np - 1> {}; };
  template<> struct __parity<3> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 3, _Np - 2, _Np - 1> {}; };
  template<> struct __parity<4> { template<size_t _Np> struct __pmake : __repeat<typename __make<_Np / 8>::type, _Np - 4, _Np - 3, _Np - 2, _Np - 1> {}; };
  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> {}; };
  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> {}; };
  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> {}; };
  
  } // namespace detail
  
  #endif  // !__has_builtin(__make_integer_seq) || defined(_LIBCPP_TESTING_FALLBACK_MAKE_INTEGER_SEQUENCE)
  
  #if __has_builtin(__make_integer_seq)
  template <size_t _Ep, size_t _Sp>
  using __make_indices_imp =
      typename __make_integer_seq<__integer_sequence, size_t, _Ep - _Sp>::template
      __to_tuple_indices<_Sp>;
  #else
  template <size_t _Ep, size_t _Sp>
  using __make_indices_imp =
      typename __detail::__make<_Ep - _Sp>::type::template __to_tuple_indices<_Sp>;
  
  #endif
  
  template <size_t _Ep, size_t _Sp = 0>
  struct __make_tuple_indices
  {
      static_assert(_Sp <= _Ep, "__make_tuple_indices input error");
      typedef __make_indices_imp<_Ep, _Sp> type;
  };
  
  
  template <class ..._Tp> class _LIBCPP_TEMPLATE_VIS tuple;
  
  template <class... _Tp> struct __tuple_like<tuple<_Tp...> > : true_type {};
  
  template <class ..._Tp>
  struct _LIBCPP_TEMPLATE_VIS tuple_size<tuple<_Tp...> >
      : public integral_constant<size_t, sizeof...(_Tp)>
  {
  };
  
  template <size_t _Ip, class ..._Tp>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  typename tuple_element<_Ip, tuple<_Tp...> >::type&
  get(tuple<_Tp...>&) _NOEXCEPT;
  
  template <size_t _Ip, class ..._Tp>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  const typename tuple_element<_Ip, tuple<_Tp...> >::type&
  get(const tuple<_Tp...>&) _NOEXCEPT;
  
  template <size_t _Ip, class ..._Tp>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  typename tuple_element<_Ip, tuple<_Tp...> >::type&&
  get(tuple<_Tp...>&&) _NOEXCEPT;
  
  template <size_t _Ip, class ..._Tp>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  const typename tuple_element<_Ip, tuple<_Tp...> >::type&&
  get(const tuple<_Tp...>&&) _NOEXCEPT;
  
  #endif // !defined(_LIBCPP_CXX03_LANG)
  
  // pair specializations
  
  template <class _T1, class _T2> struct __tuple_like<pair<_T1, _T2> > : true_type {};
  
  template <size_t _Ip, class _T1, class _T2>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  typename tuple_element<_Ip, pair<_T1, _T2> >::type&
  get(pair<_T1, _T2>&) _NOEXCEPT;
  
  template <size_t _Ip, class _T1, class _T2>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  const typename tuple_element<_Ip, pair<_T1, _T2> >::type&
  get(const pair<_T1, _T2>&) _NOEXCEPT;
  
  #ifndef _LIBCPP_CXX03_LANG
  template <size_t _Ip, class _T1, class _T2>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  typename tuple_element<_Ip, pair<_T1, _T2> >::type&&
  get(pair<_T1, _T2>&&) _NOEXCEPT;
  
  template <size_t _Ip, class _T1, class _T2>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  const typename tuple_element<_Ip, pair<_T1, _T2> >::type&&
  get(const pair<_T1, _T2>&&) _NOEXCEPT;
  #endif
  
  // array specializations
  
  template <class _Tp, size_t _Size> struct _LIBCPP_TEMPLATE_VIS array;
  
  template <class _Tp, size_t _Size> struct __tuple_like<array<_Tp, _Size> > : true_type {};
  
  template <size_t _Ip, class _Tp, size_t _Size>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  _Tp&
  get(array<_Tp, _Size>&) _NOEXCEPT;
  
  template <size_t _Ip, class _Tp, size_t _Size>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  const _Tp&
  get(const array<_Tp, _Size>&) _NOEXCEPT;
  
  #ifndef _LIBCPP_CXX03_LANG
  template <size_t _Ip, class _Tp, size_t _Size>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  _Tp&&
  get(array<_Tp, _Size>&&) _NOEXCEPT;
  
  template <size_t _Ip, class _Tp, size_t _Size>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
  const _Tp&&
  get(const array<_Tp, _Size>&&) _NOEXCEPT;
  #endif
  
  #ifndef _LIBCPP_CXX03_LANG
  
  // __tuple_types
  
  template <class ..._Tp> struct __tuple_types {};
  
  #if !__has_builtin(__type_pack_element)
  
  namespace __indexer_detail {
  
  template <size_t _Idx, class _Tp>
  struct __indexed { using type = _Tp; };
  
  template <class _Types, class _Indexes> struct __indexer;
  
  template <class ..._Types, size_t ..._Idx>
  struct __indexer<__tuple_types<_Types...>, __tuple_indices<_Idx...>>
      : __indexed<_Idx, _Types>...
  {};
  
  template <size_t _Idx, class _Tp>
  __indexed<_Idx, _Tp> __at_index(__indexed<_Idx, _Tp> const&);
  
  } // namespace __indexer_detail
  
  template <size_t _Idx, class ..._Types>
  using __type_pack_element = typename decltype(
      __indexer_detail::__at_index<_Idx>(
          __indexer_detail::__indexer<
              __tuple_types<_Types...>,
              typename __make_tuple_indices<sizeof...(_Types)>::type
          >{})
    )::type;
  #endif
  
  template <size_t _Ip, class ..._Types>
  class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, __tuple_types<_Types...>>
  {
  public:
      static_assert(_Ip < sizeof...(_Types), "tuple_element index out of range");
      typedef __type_pack_element<_Ip, _Types...> type;
  };
  
  
  template <class ..._Tp>
  struct _LIBCPP_TEMPLATE_VIS tuple_size<__tuple_types<_Tp...> >
      : public integral_constant<size_t, sizeof...(_Tp)>
  {
  };
  
  template <class... _Tp> struct __tuple_like<__tuple_types<_Tp...> > : true_type {};
  
  template <bool _ApplyLV, bool _ApplyConst, bool _ApplyVolatile>
  struct __apply_cv_mf;
  template <>
  struct __apply_cv_mf<false, false, false> {
    template <class _Tp> using __apply = _Tp;
  };
  template <>
  struct __apply_cv_mf<false, true, false> {
    template <class _Tp> using __apply = const _Tp;
  };
  template <>
  struct __apply_cv_mf<false, false, true> {
    template <class _Tp> using __apply = volatile _Tp;
  };
  template <>
  struct __apply_cv_mf<false, true, true> {
    template <class _Tp> using __apply = const volatile _Tp;
  };
  template <>
  struct __apply_cv_mf<true, false, false> {
    template <class _Tp> using __apply = _Tp&;
  };
  template <>
  struct __apply_cv_mf<true, true, false> {
    template <class _Tp> using __apply = const _Tp&;
  };
  template <>
  struct __apply_cv_mf<true, false, true> {
    template <class _Tp> using __apply = volatile _Tp&;
  };
  template <>
  struct __apply_cv_mf<true, true, true> {
    template <class _Tp> using __apply = const volatile _Tp&;
  };
  template <class _Tp, class _RawTp = typename remove_reference<_Tp>::type>
  using __apply_cv_t = __apply_cv_mf<
      is_lvalue_reference<_Tp>::value,
      is_const<_RawTp>::value,
      is_volatile<_RawTp>::value>;
  
  // __make_tuple_types
  
  // __make_tuple_types<_Tuple<_Types...>, _Ep, _Sp>::type is a
  // __tuple_types<_Types...> using only those _Types in the range [_Sp, _Ep).
  // _Sp defaults to 0 and _Ep defaults to tuple_size<_Tuple>.  If _Tuple is a
  // lvalue_reference type, then __tuple_types<_Types&...> is the result.
  
  template <class _TupleTypes, class _TupleIndices>
  struct __make_tuple_types_flat;
  
  template <template <class...> class _Tuple, class ..._Types, size_t ..._Idx>
  struct __make_tuple_types_flat<_Tuple<_Types...>, __tuple_indices<_Idx...>> {
    // Specialization for pair, tuple, and __tuple_types
    template <class _Tp, class _ApplyFn = __apply_cv_t<_Tp>>
    using __apply_quals = __tuple_types<
        typename _ApplyFn::template __apply<__type_pack_element<_Idx, _Types...>>...
      >;
  };
  
  template <class _Vt, size_t _Np, size_t ..._Idx>
  struct __make_tuple_types_flat<array<_Vt, _Np>, __tuple_indices<_Idx...>> {
    template <size_t>
    using __value_type = _Vt;
    template <class _Tp, class _ApplyFn = __apply_cv_t<_Tp>>
    using __apply_quals = __tuple_types<
        typename _ApplyFn::template __apply<__value_type<_Idx>>...
      >;
  };
  
  template <class _Tp, size_t _Ep = tuple_size<typename remove_reference<_Tp>::type>::value,
            size_t _Sp = 0,
            bool _SameSize = (_Ep == tuple_size<typename remove_reference<_Tp>::type>::value)>
  struct __make_tuple_types
  {
      static_assert(_Sp <= _Ep, "__make_tuple_types input error");
      using _RawTp = typename remove_cv<typename remove_reference<_Tp>::type>::type;
      using _Maker = __make_tuple_types_flat<_RawTp, typename __make_tuple_indices<_Ep, _Sp>::type>;
      using type = typename _Maker::template __apply_quals<_Tp>;
  };
  
  template <class ..._Types, size_t _Ep>
  struct __make_tuple_types<tuple<_Types...>, _Ep, 0, true> {
    typedef __tuple_types<_Types...> type;
  };
  
  template <class ..._Types, size_t _Ep>
  struct __make_tuple_types<__tuple_types<_Types...>, _Ep, 0, true> {
    typedef __tuple_types<_Types...> type;
  };
  
  template <bool ..._Preds>
  struct __all_dummy;
  
  template <bool ..._Pred>
  using __all = is_same<__all_dummy<_Pred...>, __all_dummy<((void)_Pred, true)...>>;
  
  struct __tuple_sfinae_base {
    template <template <class, class...> class _Trait,
              class ..._LArgs, class ..._RArgs>
    static auto __do_test(__tuple_types<_LArgs...>, __tuple_types<_RArgs...>)
      -> __all<typename enable_if<_Trait<_LArgs, _RArgs>::value, bool>::type{true}...>;
    template <template <class...> class>
    static auto __do_test(...) -> false_type;
  
    template <class _FromArgs, class _ToArgs>
    using __constructible = decltype(__do_test<is_constructible>(_ToArgs{}, _FromArgs{}));
    template <class _FromArgs, class _ToArgs>
    using __convertible = decltype(__do_test<is_convertible>(_FromArgs{}, _ToArgs{}));
    template <class _FromArgs, class _ToArgs>
    using __assignable = decltype(__do_test<is_assignable>(_ToArgs{}, _FromArgs{}));
  };
  
  // __tuple_convertible
  
  template <class _Tp, class _Up, bool = __tuple_like<typename remove_reference<_Tp>::type>::value,
                                  bool = __tuple_like<_Up>::value>
  struct __tuple_convertible
      : public false_type {};
  
  template <class _Tp, class _Up>
  struct __tuple_convertible<_Tp, _Up, true, true>
      : public __tuple_sfinae_base::__convertible<
        typename __make_tuple_types<_Tp>::type
      , typename __make_tuple_types<_Up>::type
      >
  {};
  
  // __tuple_constructible
  
  template <class _Tp, class _Up, bool = __tuple_like<typename remove_reference<_Tp>::type>::value,
                                  bool = __tuple_like<_Up>::value>
  struct __tuple_constructible
      : public false_type {};
  
  template <class _Tp, class _Up>
  struct __tuple_constructible<_Tp, _Up, true, true>
      : public __tuple_sfinae_base::__constructible<
        typename __make_tuple_types<_Tp>::type
      , typename __make_tuple_types<_Up>::type
      >
  {};
  
  // __tuple_assignable
  
  template <class _Tp, class _Up, bool = __tuple_like<typename remove_reference<_Tp>::type>::value,
                                  bool = __tuple_like<_Up>::value>
  struct __tuple_assignable
      : public false_type {};
  
  template <class _Tp, class _Up>
  struct __tuple_assignable<_Tp, _Up, true, true>
      : public __tuple_sfinae_base::__assignable<
        typename __make_tuple_types<_Tp>::type
      , typename __make_tuple_types<_Up&>::type
      >
  {};
  
  
  template <size_t _Ip, class ..._Tp>
  class _LIBCPP_TEMPLATE_VIS tuple_element<_Ip, tuple<_Tp...> >
  {
  public:
      typedef typename tuple_element<_Ip, __tuple_types<_Tp...> >::type type;
  };
  
  #if _LIBCPP_STD_VER > 11
  template <size_t _Ip, class ..._Tp>
  using tuple_element_t = typename tuple_element <_Ip, _Tp...>::type;
  #endif
  
  template <bool _IsTuple, class _SizeTrait, size_t _Expected>
  struct __tuple_like_with_size_imp : false_type {};
  
  template <class _SizeTrait, size_t _Expected>
  struct __tuple_like_with_size_imp<true, _SizeTrait, _Expected>
      : integral_constant<bool, _SizeTrait::value == _Expected> {};
  
  template <class _Tuple, size_t _ExpectedSize,
            class _RawTuple = typename __uncvref<_Tuple>::type>
  using __tuple_like_with_size = __tuple_like_with_size_imp<
                                     __tuple_like<_RawTuple>::value,
                                     tuple_size<_RawTuple>, _ExpectedSize
                                >;
  
  struct _LIBCPP_TYPE_VIS __check_tuple_constructor_fail {
      template <class ...>
      static constexpr bool __enable_default() { return false; }
      template <class ...>
      static constexpr bool __enable_explicit() { return false; }
      template <class ...>
      static constexpr bool __enable_implicit() { return false; }
      template <class ...>
      static constexpr bool __enable_assign() { return false; }
  };
  #endif // !defined(_LIBCPP_CXX03_LANG)
  
  #if _LIBCPP_STD_VER > 14
  
  template <bool _CanCopy, bool _CanMove>
  struct __sfinae_ctor_base {};
  template <>
  struct __sfinae_ctor_base<false, false> {
    __sfinae_ctor_base() = default;
    __sfinae_ctor_base(__sfinae_ctor_base const&) = delete;
    __sfinae_ctor_base(__sfinae_ctor_base &&) = delete;
    __sfinae_ctor_base& operator=(__sfinae_ctor_base const&) = default;
    __sfinae_ctor_base& operator=(__sfinae_ctor_base&&) = default;
  };
  template <>
  struct __sfinae_ctor_base<true, false> {
    __sfinae_ctor_base() = default;
    __sfinae_ctor_base(__sfinae_ctor_base const&) = default;
    __sfinae_ctor_base(__sfinae_ctor_base &&) = delete;
    __sfinae_ctor_base& operator=(__sfinae_ctor_base const&) = default;
    __sfinae_ctor_base& operator=(__sfinae_ctor_base&&) = default;
  };
  template <>
  struct __sfinae_ctor_base<false, true> {
    __sfinae_ctor_base() = default;
    __sfinae_ctor_base(__sfinae_ctor_base const&) = delete;
    __sfinae_ctor_base(__sfinae_ctor_base &&) = default;
    __sfinae_ctor_base& operator=(__sfinae_ctor_base const&) = default;
    __sfinae_ctor_base& operator=(__sfinae_ctor_base&&) = default;
  };
  
  template <bool _CanCopy, bool _CanMove>
  struct __sfinae_assign_base {};
  template <>
  struct __sfinae_assign_base<false, false> {
    __sfinae_assign_base() = default;
    __sfinae_assign_base(__sfinae_assign_base const&) = default;
    __sfinae_assign_base(__sfinae_assign_base &&) = default;
    __sfinae_assign_base& operator=(__sfinae_assign_base const&) = delete;
    __sfinae_assign_base& operator=(__sfinae_assign_base&&) = delete;
  };
  template <>
  struct __sfinae_assign_base<true, false> {
    __sfinae_assign_base() = default;
    __sfinae_assign_base(__sfinae_assign_base const&) = default;
    __sfinae_assign_base(__sfinae_assign_base &&) = default;
    __sfinae_assign_base& operator=(__sfinae_assign_base const&) = default;
    __sfinae_assign_base& operator=(__sfinae_assign_base&&) = delete;
  };
  template <>
  struct __sfinae_assign_base<false, true> {
    __sfinae_assign_base() = default;
    __sfinae_assign_base(__sfinae_assign_base const&) = default;
    __sfinae_assign_base(__sfinae_assign_base &&) = default;
    __sfinae_assign_base& operator=(__sfinae_assign_base const&) = delete;
    __sfinae_assign_base& operator=(__sfinae_assign_base&&) = default;
  };
  #endif // _LIBCPP_STD_VER > 14
  
  _LIBCPP_END_NAMESPACE_STD
  
  #endif  // _LIBCPP___TUPLE
  