// -*- C++ -*-
//===------------------------ type_traits ---------------------------------===//
//
// 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_TYPE_TRAITS
#define _LIBCPP_TYPE_TRAITS

/*
    type_traits synopsis

namespace std
{

    // helper class:
    template <class T, T v> struct integral_constant;
    typedef integral_constant<bool, true>  true_type;   // C++11
    typedef integral_constant<bool, false> false_type;  // C++11

    template <bool B>                                   // C++14
    using bool_constant = integral_constant<bool, B>;   // C++14
    typedef bool_constant<true> true_type;              // C++14
    typedef bool_constant<false> false_type;            // C++14

    // helper traits
    template <bool, class T = void> struct enable_if;
    template <bool, class T, class F> struct conditional;

    // Primary classification traits:
    template <class T> struct is_void;
    template <class T> struct is_null_pointer;  // C++14
    template <class T> struct is_integral;
    template <class T> struct is_floating_point;
    template <class T> struct is_array;
    template <class T> struct is_pointer;
    template <class T> struct is_lvalue_reference;
    template <class T> struct is_rvalue_reference;
    template <class T> struct is_member_object_pointer;
    template <class T> struct is_member_function_pointer;
    template <class T> struct is_enum;
    template <class T> struct is_union;
    template <class T> struct is_class;
    template <class T> struct is_function;

    // Secondary classification traits:
    template <class T> struct is_reference;
    template <class T> struct is_arithmetic;
    template <class T> struct is_fundamental;
    template <class T> struct is_member_pointer;
    template <class T> struct is_scoped_enum; // C++2b
    template <class T> struct is_scalar;
    template <class T> struct is_object;
    template <class T> struct is_compound;

    // Const-volatile properties and transformations:
    template <class T> struct is_const;
    template <class T> struct is_volatile;
    template <class T> struct remove_const;
    template <class T> struct remove_volatile;
    template <class T> struct remove_cv;
    template <class T> struct add_const;
    template <class T> struct add_volatile;
    template <class T> struct add_cv;

    // Reference transformations:
    template <class T> struct remove_reference;
    template <class T> struct add_lvalue_reference;
    template <class T> struct add_rvalue_reference;

    // Pointer transformations:
    template <class T> struct remove_pointer;
    template <class T> struct add_pointer;

    template<class T> struct type_identity;                     // C++20
    template<class T>
      using type_identity_t = typename type_identity<T>::type;  // C++20

    // Integral properties:
    template <class T> struct is_signed;
    template <class T> struct is_unsigned;
    template <class T> struct make_signed;
    template <class T> struct make_unsigned;

    // Array properties and transformations:
    template <class T> struct rank;
    template <class T, unsigned I = 0> struct extent;
    template <class T> struct remove_extent;
    template <class T> struct remove_all_extents;

    template <class T> struct is_bounded_array;                 // C++20
    template <class T> struct is_unbounded_array;               // C++20

    // Member introspection:
    template <class T> struct is_pod;
    template <class T> struct is_trivial;
    template <class T> struct is_trivially_copyable;
    template <class T> struct is_standard_layout;
    template <class T> struct is_literal_type;
    template <class T> struct is_empty;
    template <class T> struct is_polymorphic;
    template <class T> struct is_abstract;
    template <class T> struct is_final; // C++14
    template <class T> struct is_aggregate; // C++17

    template <class T, class... Args> struct is_constructible;
    template <class T>                struct is_default_constructible;
    template <class T>                struct is_copy_constructible;
    template <class T>                struct is_move_constructible;
    template <class T, class U>       struct is_assignable;
    template <class T>                struct is_copy_assignable;
    template <class T>                struct is_move_assignable;
    template <class T, class U>       struct is_swappable_with;       // C++17
    template <class T>                struct is_swappable;            // C++17
    template <class T>                struct is_destructible;

    template <class T, class... Args> struct is_trivially_constructible;
    template <class T>                struct is_trivially_default_constructible;
    template <class T>                struct is_trivially_copy_constructible;
    template <class T>                struct is_trivially_move_constructible;
    template <class T, class U>       struct is_trivially_assignable;
    template <class T>                struct is_trivially_copy_assignable;
    template <class T>                struct is_trivially_move_assignable;
    template <class T>                struct is_trivially_destructible;

    template <class T, class... Args> struct is_nothrow_constructible;
    template <class T>                struct is_nothrow_default_constructible;
    template <class T>                struct is_nothrow_copy_constructible;
    template <class T>                struct is_nothrow_move_constructible;
    template <class T, class U>       struct is_nothrow_assignable;
    template <class T>                struct is_nothrow_copy_assignable;
    template <class T>                struct is_nothrow_move_assignable;
    template <class T, class U>       struct is_nothrow_swappable_with; // C++17
    template <class T>                struct is_nothrow_swappable;      // C++17
    template <class T>                struct is_nothrow_destructible;

    template <class T> struct has_virtual_destructor;

    template<class T> struct has_unique_object_representations;         // C++17

    // Relationships between types:
    template <class T, class U> struct is_same;
    template <class Base, class Derived> struct is_base_of;

    template <class From, class To> struct is_convertible;
    template <typename From, typename To> struct is_nothrow_convertible;                  // C++20
    template <typename From, typename To> inline constexpr bool is_nothrow_convertible_v; // C++20

    template <class Fn, class... ArgTypes> struct is_invocable;
    template <class R, class Fn, class... ArgTypes> struct is_invocable_r;

    template <class Fn, class... ArgTypes> struct is_nothrow_invocable;
    template <class R, class Fn, class... ArgTypes> struct is_nothrow_invocable_r;

    // Alignment properties and transformations:
    template <class T> struct alignment_of;
    template <size_t Len, size_t Align = most_stringent_alignment_requirement>
        struct aligned_storage;
    template <size_t Len, class... Types> struct aligned_union;
    template <class T> struct remove_cvref; // C++20

    template <class T> struct decay;
    template <class... T> struct common_type;
    template <class T> struct underlying_type;
    template <class> class result_of; // undefined
    template <class Fn, class... ArgTypes> class result_of<Fn(ArgTypes...)>;
    template <class Fn, class... ArgTypes> struct invoke_result;  // C++17

    // const-volatile modifications:
    template <class T>
      using remove_const_t    = typename remove_const<T>::type;  // C++14
    template <class T>
      using remove_volatile_t = typename remove_volatile<T>::type;  // C++14
    template <class T>
      using remove_cv_t       = typename remove_cv<T>::type;  // C++14
    template <class T>
      using add_const_t       = typename add_const<T>::type;  // C++14
    template <class T>
      using add_volatile_t    = typename add_volatile<T>::type;  // C++14
    template <class T>
      using add_cv_t          = typename add_cv<T>::type;  // C++14

    // reference modifications:
    template <class T>
      using remove_reference_t     = typename remove_reference<T>::type;  // C++14
    template <class T>
      using add_lvalue_reference_t = typename add_lvalue_reference<T>::type;  // C++14
    template <class T>
      using add_rvalue_reference_t = typename add_rvalue_reference<T>::type;  // C++14

    // sign modifications:
    template <class T>
      using make_signed_t   = typename make_signed<T>::type;  // C++14
    template <class T>
      using make_unsigned_t = typename make_unsigned<T>::type;  // C++14

    // array modifications:
    template <class T>
      using remove_extent_t      = typename remove_extent<T>::type;  // C++14
    template <class T>
      using remove_all_extents_t = typename remove_all_extents<T>::type;  // C++14

    template <class T>
      inline constexpr bool is_bounded_array_v
        = is_bounded_array<T>::value;                                     // C++20
      inline constexpr bool is_unbounded_array_v
        = is_unbounded_array<T>::value;                                   // C++20

    // pointer modifications:
    template <class T>
      using remove_pointer_t = typename remove_pointer<T>::type;  // C++14
    template <class T>
      using add_pointer_t    = typename add_pointer<T>::type;  // C++14

    // other transformations:
    template <size_t Len, std::size_t Align=default-alignment>
      using aligned_storage_t = typename aligned_storage<Len,Align>::type;  // C++14
    template <std::size_t Len, class... Types>
      using aligned_union_t   = typename aligned_union<Len,Types...>::type;  // C++14
    template <class T>
      using remove_cvref_t    = typename remove_cvref<T>::type;  // C++20
    template <class T>
      using decay_t           = typename decay<T>::type;  // C++14
    template <bool b, class T=void>
      using enable_if_t       = typename enable_if<b,T>::type;  // C++14
    template <bool b, class T, class F>
      using conditional_t     = typename conditional<b,T,F>::type;  // C++14
    template <class... T>
      using common_type_t     = typename common_type<T...>::type;  // C++14
    template <class T>
      using underlying_type_t = typename underlying_type<T>::type;  // C++14
    template <class T>
      using result_of_t       = typename result_of<T>::type;  // C++14
    template <class Fn, class... ArgTypes>
      using invoke_result_t   = typename invoke_result<Fn, ArgTypes...>::type;  // C++17

    template <class...>
      using void_t = void;   // C++17

      // See C++14 20.10.4.1, primary type categories
      template <class T> inline constexpr bool is_void_v
        = is_void<T>::value;                                             // C++17
      template <class T> inline constexpr bool is_null_pointer_v
        = is_null_pointer<T>::value;                                     // C++17
      template <class T> inline constexpr bool is_integral_v
        = is_integral<T>::value;                                         // C++17
      template <class T> inline constexpr bool is_floating_point_v
        = is_floating_point<T>::value;                                   // C++17
      template <class T> inline constexpr bool is_array_v
        = is_array<T>::value;                                            // C++17
      template <class T> inline constexpr bool is_pointer_v
        = is_pointer<T>::value;                                          // C++17
      template <class T> inline constexpr bool is_lvalue_reference_v
        = is_lvalue_reference<T>::value;                                 // C++17
      template <class T> inline constexpr bool is_rvalue_reference_v
        = is_rvalue_reference<T>::value;                                 // C++17
      template <class T> inline constexpr bool is_member_object_pointer_v
        = is_member_object_pointer<T>::value;                            // C++17
      template <class T> inline constexpr bool is_member_function_pointer_v
        = is_member_function_pointer<T>::value;                          // C++17
      template <class T> inline constexpr bool is_enum_v
        = is_enum<T>::value;                                             // C++17
      template <class T> inline constexpr bool is_union_v
        = is_union<T>::value;                                            // C++17
      template <class T> inline constexpr bool is_class_v
        = is_class<T>::value;                                            // C++17
      template <class T> inline constexpr bool is_function_v
        = is_function<T>::value;                                         // C++17

      // See C++14 20.10.4.2, composite type categories
      template <class T> inline constexpr bool is_reference_v
        = is_reference<T>::value;                                        // C++17
      template <class T> inline constexpr bool is_arithmetic_v
        = is_arithmetic<T>::value;                                       // C++17
      template <class T> inline constexpr bool is_fundamental_v
        = is_fundamental<T>::value;                                      // C++17
      template <class T> inline constexpr bool is_object_v
        = is_object<T>::value;                                           // C++17
      template <class T> inline constexpr bool is_scalar_v
        = is_scalar<T>::value;                                           // C++17
      template <class T> inline constexpr bool is_compound_v
        = is_compound<T>::value;                                         // C++17
      template <class T> inline constexpr bool is_member_pointer_v
        = is_member_pointer<T>::value;                                   // C++17
      template <class T> inline constexpr bool is_scoped_enum_v
        = is_scoped_enum<T>::value;                                      // C++2b

      // See C++14 20.10.4.3, type properties
      template <class T> inline constexpr bool is_const_v
        = is_const<T>::value;                                            // C++17
      template <class T> inline constexpr bool is_volatile_v
        = is_volatile<T>::value;                                         // C++17
      template <class T> inline constexpr bool is_trivial_v
        = is_trivial<T>::value;                                          // C++17
      template <class T> inline constexpr bool is_trivially_copyable_v
        = is_trivially_copyable<T>::value;                               // C++17
      template <class T> inline constexpr bool is_standard_layout_v
        = is_standard_layout<T>::value;                                  // C++17
      template <class T> inline constexpr bool is_pod_v
        = is_pod<T>::value;                                              // C++17
      template <class T> inline constexpr bool is_literal_type_v
        = is_literal_type<T>::value;                                     // C++17
      template <class T> inline constexpr bool is_empty_v
        = is_empty<T>::value;                                            // C++17
      template <class T> inline constexpr bool is_polymorphic_v
        = is_polymorphic<T>::value;                                      // C++17
      template <class T> inline constexpr bool is_abstract_v
        = is_abstract<T>::value;                                         // C++17
      template <class T> inline constexpr bool is_final_v
        = is_final<T>::value;                                            // C++17
      template <class T> inline constexpr bool is_aggregate_v
        = is_aggregate<T>::value;                                        // C++17
      template <class T> inline constexpr bool is_signed_v
        = is_signed<T>::value;                                           // C++17
      template <class T> inline constexpr bool is_unsigned_v
        = is_unsigned<T>::value;                                         // C++17
      template <class T, class... Args> inline constexpr bool is_constructible_v
        = is_constructible<T, Args...>::value;                           // C++17
      template <class T> inline constexpr bool is_default_constructible_v
        = is_default_constructible<T>::value;                            // C++17
      template <class T> inline constexpr bool is_copy_constructible_v
        = is_copy_constructible<T>::value;                               // C++17
      template <class T> inline constexpr bool is_move_constructible_v
        = is_move_constructible<T>::value;                               // C++17
      template <class T, class U> inline constexpr bool is_assignable_v
        = is_assignable<T, U>::value;                                    // C++17
      template <class T> inline constexpr bool is_copy_assignable_v
        = is_copy_assignable<T>::value;                                  // C++17
      template <class T> inline constexpr bool is_move_assignable_v
        = is_move_assignable<T>::value;                                  // C++17
      template <class T, class U> inline constexpr bool is_swappable_with_v
        = is_swappable_with<T, U>::value;                                // C++17
      template <class T> inline constexpr bool is_swappable_v
        = is_swappable<T>::value;                                        // C++17
      template <class T> inline constexpr bool is_destructible_v
        = is_destructible<T>::value;                                     // C++17
      template <class T, class... Args> inline constexpr bool is_trivially_constructible_v
        = is_trivially_constructible<T, Args...>::value;                 // C++17
      template <class T> inline constexpr bool is_trivially_default_constructible_v
        = is_trivially_default_constructible<T>::value;                  // C++17
      template <class T> inline constexpr bool is_trivially_copy_constructible_v
        = is_trivially_copy_constructible<T>::value;                     // C++17
      template <class T> inline constexpr bool is_trivially_move_constructible_v
        = is_trivially_move_constructible<T>::value;                     // C++17
      template <class T, class U> inline constexpr bool is_trivially_assignable_v
        = is_trivially_assignable<T, U>::value;                          // C++17
      template <class T> inline constexpr bool is_trivially_copy_assignable_v
        = is_trivially_copy_assignable<T>::value;                        // C++17
      template <class T> inline constexpr bool is_trivially_move_assignable_v
        = is_trivially_move_assignable<T>::value;                        // C++17
      template <class T> inline constexpr bool is_trivially_destructible_v
        = is_trivially_destructible<T>::value;                           // C++17
      template <class T, class... Args> inline constexpr bool is_nothrow_constructible_v
        = is_nothrow_constructible<T, Args...>::value;                   // C++17
      template <class T> inline constexpr bool is_nothrow_default_constructible_v
        = is_nothrow_default_constructible<T>::value;                    // C++17
      template <class T> inline constexpr bool is_nothrow_copy_constructible_v
        = is_nothrow_copy_constructible<T>::value;                       // C++17
      template <class T> inline constexpr bool is_nothrow_move_constructible_v
        = is_nothrow_move_constructible<T>::value;                       // C++17
      template <class T, class U> inline constexpr bool is_nothrow_assignable_v
        = is_nothrow_assignable<T, U>::value;                            // C++17
      template <class T> inline constexpr bool is_nothrow_copy_assignable_v
        = is_nothrow_copy_assignable<T>::value;                          // C++17
      template <class T> inline constexpr bool is_nothrow_move_assignable_v
        = is_nothrow_move_assignable<T>::value;                          // C++17
      template <class T, class U> inline constexpr bool is_nothrow_swappable_with_v
        = is_nothrow_swappable_with<T, U>::value;                       // C++17
      template <class T> inline constexpr bool is_nothrow_swappable_v
        = is_nothrow_swappable<T>::value;                               // C++17
      template <class T> inline constexpr bool is_nothrow_destructible_v
        = is_nothrow_destructible<T>::value;                             // C++17
      template <class T> inline constexpr bool has_virtual_destructor_v
        = has_virtual_destructor<T>::value;                              // C++17
      template<class T> inline constexpr bool has_unique_object_representations_v // C++17
        = has_unique_object_representations<T>::value;

      // See C++14 20.10.5, type property queries
      template <class T> inline constexpr size_t alignment_of_v
        = alignment_of<T>::value;                                        // C++17
      template <class T> inline constexpr size_t rank_v
        = rank<T>::value;                                                // C++17
      template <class T, unsigned I = 0> inline constexpr size_t extent_v
        = extent<T, I>::value;                                           // C++17

      // See C++14 20.10.6, type relations
      template <class T, class U> inline constexpr bool is_same_v
        = is_same<T, U>::value;                                          // C++17
      template <class Base, class Derived> inline constexpr bool is_base_of_v
        = is_base_of<Base, Derived>::value;                              // C++17
      template <class From, class To> inline constexpr bool is_convertible_v
        = is_convertible<From, To>::value;                               // C++17
      template <class Fn, class... ArgTypes> inline constexpr bool is_invocable_v
        = is_invocable<Fn, ArgTypes...>::value;                          // C++17
      template <class R, class Fn, class... ArgTypes> inline constexpr bool is_invocable_r_v
        = is_invocable_r<R, Fn, ArgTypes...>::value;                     // C++17
      template <class Fn, class... ArgTypes> inline constexpr bool is_nothrow_invocable_v
        = is_nothrow_invocable<Fn, ArgTypes...>::value;                  // C++17
      template <class R, class Fn, class... ArgTypes> inline constexpr bool is_nothrow_invocable_r_v
        = is_nothrow_invocable_r<R, Fn, ArgTypes...>::value;             // C++17

      // [meta.logical], logical operator traits:
      template<class... B> struct conjunction;                           // C++17
      template<class... B>
        inline constexpr bool conjunction_v = conjunction<B...>::value;  // C++17
      template<class... B> struct disjunction;                           // C++17
      template<class... B>
        inline constexpr bool disjunction_v = disjunction<B...>::value;  // C++17
      template<class B> struct negation;                                 // C++17
      template<class B>
        inline constexpr bool negation_v = negation<B>::value;           // C++17

}

*/
#include <__config>
#include <cstddef>
#include <version>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _T1, class _T2> struct _LIBCPP_TEMPLATE_VIS pair;
template <class _Tp> class _LIBCPP_TEMPLATE_VIS reference_wrapper;
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS hash;

template <class _Tp, _Tp __v>
struct _LIBCPP_TEMPLATE_VIS integral_constant
{
  static _LIBCPP_CONSTEXPR const _Tp      value = __v;
  typedef _Tp               value_type;
  typedef integral_constant type;
  _LIBCPP_INLINE_VISIBILITY
  _LIBCPP_CONSTEXPR operator value_type() const _NOEXCEPT {return value;}
#if _LIBCPP_STD_VER > 11
  _LIBCPP_INLINE_VISIBILITY
  constexpr value_type operator ()() const _NOEXCEPT {return value;}
#endif
};

template <class _Tp, _Tp __v>
_LIBCPP_CONSTEXPR const _Tp integral_constant<_Tp, __v>::value;

#if _LIBCPP_STD_VER > 14
template <bool __b>
using bool_constant = integral_constant<bool, __b>;
#define _LIBCPP_BOOL_CONSTANT(__b) bool_constant<(__b)>
#else
#define _LIBCPP_BOOL_CONSTANT(__b) integral_constant<bool,(__b)>
#endif

typedef _LIBCPP_BOOL_CONSTANT(true)  true_type;
typedef _LIBCPP_BOOL_CONSTANT(false) false_type;

template <bool _Val>
using _BoolConstant _LIBCPP_NODEBUG_TYPE = integral_constant<bool, _Val>;

template <bool> struct _MetaBase;
template <>
struct _MetaBase<true> {
  template <class _Tp, class _Up>
  using _SelectImpl _LIBCPP_NODEBUG_TYPE = _Tp;
  template <template <class...> class _FirstFn, template <class...> class, class ..._Args>
  using _SelectApplyImpl _LIBCPP_NODEBUG_TYPE = _FirstFn<_Args...>;
  template <class _First, class...>
  using _FirstImpl _LIBCPP_NODEBUG_TYPE = _First;
  template <class, class _Second, class...>
  using _SecondImpl _LIBCPP_NODEBUG_TYPE = _Second;
  template <class _Tp = void>
  using _EnableIfImpl _LIBCPP_NODEBUG_TYPE = _Tp;
  template <class _Result, class _First, class ..._Rest>
  using _OrImpl _LIBCPP_NODEBUG_TYPE = typename _MetaBase<_First::value != true && sizeof...(_Rest) != 0>::template _OrImpl<_First, _Rest...>;
  template <class _Result, class _First, class ..._Rest>
  using _AndImpl _LIBCPP_NODEBUG_TYPE = typename _MetaBase<_First::value == true && sizeof...(_Rest) != 0>::template _AndImpl<_First, _Rest...>;
};

template <>
struct _MetaBase<false> {
  template <class _Tp, class _Up>
  using _SelectImpl _LIBCPP_NODEBUG_TYPE = _Up;
  template <template <class...> class, template <class...> class _SecondFn, class ..._Args>
  using _SelectApplyImpl _LIBCPP_NODEBUG_TYPE = _SecondFn<_Args...>;
  template <class _Result, class ...>
  using _OrImpl _LIBCPP_NODEBUG_TYPE = _Result;
  template <class _Result, class ...>
  using _AndImpl _LIBCPP_NODEBUG_TYPE = _Result;
};
template <bool _Cond, class _Ret = void>
using _EnableIf _LIBCPP_NODEBUG_TYPE = typename _MetaBase<_Cond>::template _EnableIfImpl<_Ret>;
template <bool _Cond, class _IfRes, class _ElseRes>
using _If _LIBCPP_NODEBUG_TYPE = typename _MetaBase<_Cond>::template _SelectImpl<_IfRes, _ElseRes>;
template <class ..._Rest>
using _Or _LIBCPP_NODEBUG_TYPE = typename _MetaBase< sizeof...(_Rest) != 0 >::template _OrImpl<false_type, _Rest...>;
template <class ..._Rest>
using _And _LIBCPP_NODEBUG_TYPE = typename _MetaBase< sizeof...(_Rest) != 0 >::template _AndImpl<true_type, _Rest...>;
template <class _Pred>
struct _Not : _BoolConstant<!_Pred::value> {};
template <class ..._Args>
using _FirstType _LIBCPP_NODEBUG_TYPE = typename _MetaBase<(sizeof...(_Args) >= 1)>::template _FirstImpl<_Args...>;
template <class ..._Args>
using _SecondType _LIBCPP_NODEBUG_TYPE = typename _MetaBase<(sizeof...(_Args) >= 2)>::template _SecondImpl<_Args...>;

template <template <class...> class _Func, class ..._Args>
struct _Lazy : _Func<_Args...> {};

// Member detector base

template <template <class...> class _Templ, class ..._Args, class = _Templ<_Args...> >
true_type __sfinae_test_impl(int);
template <template <class...> class, class ...>
false_type __sfinae_test_impl(...);

template <template <class ...> class _Templ, class ..._Args>
using _IsValidExpansion _LIBCPP_NODEBUG_TYPE = decltype(__sfinae_test_impl<_Templ, _Args...>(0));

template <class>
struct __void_t { typedef void type; };

template <class _Tp>
struct __identity { typedef _Tp type; };

template <class _Tp>
using __identity_t _LIBCPP_NODEBUG_TYPE = typename __identity<_Tp>::type;

template <class _Tp, bool>
struct _LIBCPP_TEMPLATE_VIS __dependent_type : public _Tp {};


template <bool _Bp, class _If, class _Then>
    struct _LIBCPP_TEMPLATE_VIS conditional {typedef _If type;};
template <class _If, class _Then>
    struct _LIBCPP_TEMPLATE_VIS conditional<false, _If, _Then> {typedef _Then type;};

#if _LIBCPP_STD_VER > 11
template <bool _Bp, class _If, class _Then> using conditional_t = typename conditional<_Bp, _If, _Then>::type;
#endif

template <bool, class _Tp = void> struct _LIBCPP_TEMPLATE_VIS enable_if {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS enable_if<true, _Tp> {typedef _Tp type;};

#if _LIBCPP_STD_VER > 11
template <bool _Bp, class _Tp = void> using enable_if_t = typename enable_if<_Bp, _Tp>::type;
#endif

// is_same

#if __has_keyword(__is_same)

template <class _Tp, class _Up>
struct _LIBCPP_TEMPLATE_VIS is_same : _BoolConstant<__is_same(_Tp, _Up)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, class _Up>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_same_v = __is_same(_Tp, _Up);
#endif

#else

template <class _Tp, class _Up> struct _LIBCPP_TEMPLATE_VIS is_same           : public false_type {};
template <class _Tp>            struct _LIBCPP_TEMPLATE_VIS is_same<_Tp, _Tp> : public true_type {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, class _Up>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_same_v
    = is_same<_Tp, _Up>::value;
#endif

#endif // __is_same

template <class _Tp, class _Up>
using _IsSame = _BoolConstant<
#ifdef __clang__
    __is_same(_Tp, _Up)
#else
    _VSTD::is_same<_Tp, _Up>::value
#endif
>;

template <class _Tp, class _Up>
using _IsNotSame = _BoolConstant<
#ifdef __clang__
    !__is_same(_Tp, _Up)
#else
    !_VSTD::is_same<_Tp, _Up>::value
#endif
>;


template <class _Tp>
using __test_for_primary_template = _EnableIf<
    _IsSame<_Tp, typename _Tp::__primary_template>::value
  >;
template <class _Tp>
using __is_primary_template = _IsValidExpansion<
    __test_for_primary_template, _Tp
  >;

struct __two {char __lx[2];};

// helper class:

// is_const

#if __has_keyword(__is_const)

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_const : _BoolConstant<__is_const(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_const_v = __is_const(_Tp);
#endif

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_const            : public false_type {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_const<_Tp const> : public true_type {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_const_v
    = is_const<_Tp>::value;
#endif

#endif // __has_keyword(__is_const)

// is_volatile

#if __has_keyword(__is_volatile)

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_volatile : _BoolConstant<__is_volatile(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_volatile_v = __is_volatile(_Tp);
#endif

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_volatile               : public false_type {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_volatile<_Tp volatile> : public true_type {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_volatile_v
    = is_volatile<_Tp>::value;
#endif

#endif // __has_keyword(__is_volatile)

// remove_const

#if __has_keyword(__remove_const)

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS remove_const {typedef __remove_const(_Tp) type;};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using remove_const_t = __remove_const(_Tp);
#endif

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_const            {typedef _Tp type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_const<const _Tp> {typedef _Tp type;};
#if _LIBCPP_STD_VER > 11
template <class _Tp> using remove_const_t = typename remove_const<_Tp>::type;
#endif

#endif // __has_keyword(__remove_const)

// remove_volatile

#if __has_keyword(__remove_volatile)

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS remove_volatile {typedef __remove_volatile(_Tp) type;};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using remove_volatile_t = __remove_volatile(_Tp);
#endif

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_volatile               {typedef _Tp type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_volatile<volatile _Tp> {typedef _Tp type;};
#if _LIBCPP_STD_VER > 11
template <class _Tp> using remove_volatile_t = typename remove_volatile<_Tp>::type;
#endif

#endif // __has_keyword(__remove_volatile)

// remove_cv

#if __has_keyword(__remove_cv)

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS remove_cv {typedef __remove_cv(_Tp) type;};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using remove_cv_t = __remove_cv(_Tp);
#endif

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_cv
{typedef typename remove_volatile<typename remove_const<_Tp>::type>::type type;};
#if _LIBCPP_STD_VER > 11
template <class _Tp> using remove_cv_t = typename remove_cv<_Tp>::type;
#endif

#endif // __has_keyword(__remove_cv)

// is_void

#if __has_keyword(__is_void)

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_void : _BoolConstant<__is_void(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_void_v = __is_void(_Tp);
#endif

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_void
    : public is_same<typename remove_cv<_Tp>::type, void> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_void_v
    = is_void<_Tp>::value;
#endif

#endif // __has_keyword(__is_void)

// __is_nullptr_t

template <class _Tp> struct __is_nullptr_t_impl       : public false_type {};
template <>          struct __is_nullptr_t_impl<nullptr_t> : public true_type {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS __is_nullptr_t
    : public __is_nullptr_t_impl<typename remove_cv<_Tp>::type> {};

#if _LIBCPP_STD_VER > 11
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_null_pointer
    : public __is_nullptr_t_impl<typename remove_cv<_Tp>::type> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_null_pointer_v
    = is_null_pointer<_Tp>::value;
#endif
#endif // _LIBCPP_STD_VER > 11

// is_integral

#if __has_keyword(__is_integral)

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_integral : _BoolConstant<__is_integral(_Tp)> { };

#if _LIBCPP_STD_VER > 14
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_integral_v = __is_integral(_Tp);
#endif

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_integral
    : public _BoolConstant<__libcpp_is_integral<typename remove_cv<_Tp>::type>::value> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_integral_v
    = is_integral<_Tp>::value;
#endif

#endif // __has_keyword(__is_integral)

// is_floating_point

template <class _Tp> struct __libcpp_is_floating_point              : public false_type {};
template <>          struct __libcpp_is_floating_point<float>       : public true_type {};
template <>          struct __libcpp_is_floating_point<double>      : public true_type {};
template <>          struct __libcpp_is_floating_point<long double> : public true_type {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_floating_point
    : public __libcpp_is_floating_point<typename remove_cv<_Tp>::type> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_floating_point_v
    = is_floating_point<_Tp>::value;
#endif

// is_array

#if __has_keyword(__is_array)

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_array : _BoolConstant<__is_array(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_array_v = __is_array(_Tp);
#endif

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_array
    : public false_type {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_array<_Tp[]>
    : public true_type {};
template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS is_array<_Tp[_Np]>
    : public true_type {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_array_v
    = is_array<_Tp>::value;
#endif

#endif // __has_keyword(__is_array)

// is_pointer

// Before Clang 11, __is_pointer didn't work for Objective-C types.
#if __has_keyword(__is_pointer) && !(defined(_LIBCPP_COMPILER_CLANG) && _LIBCPP_CLANG_VER < 1100)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_pointer : _BoolConstant<__is_pointer(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_pointer_v = __is_pointer(_Tp);
#endif

#else // __has_keyword(__is_pointer)

template <class _Tp> struct __libcpp_is_pointer       : public false_type {};
template <class _Tp> struct __libcpp_is_pointer<_Tp*> : public true_type {};

template <class _Tp> struct __libcpp_remove_objc_qualifiers { typedef _Tp type; };
#if defined(_LIBCPP_HAS_OBJC_ARC)
template <class _Tp> struct __libcpp_remove_objc_qualifiers<_Tp __strong> { typedef _Tp type; };
template <class _Tp> struct __libcpp_remove_objc_qualifiers<_Tp __weak> { typedef _Tp type; };
template <class _Tp> struct __libcpp_remove_objc_qualifiers<_Tp __autoreleasing> { typedef _Tp type; };
template <class _Tp> struct __libcpp_remove_objc_qualifiers<_Tp __unsafe_unretained> { typedef _Tp type; };
#endif

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_pointer
    : public __libcpp_is_pointer<typename __libcpp_remove_objc_qualifiers<typename remove_cv<_Tp>::type>::type> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_pointer_v
    = is_pointer<_Tp>::value;
#endif

#endif // __has_keyword(__is_pointer)

// is_reference

#if __has_keyword(__is_lvalue_reference) && \
    __has_keyword(__is_rvalue_reference) && \
    __has_keyword(__is_reference)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_lvalue_reference : _BoolConstant<__is_lvalue_reference(_Tp)> { };

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_rvalue_reference : _BoolConstant<__is_rvalue_reference(_Tp)> { };

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_reference : _BoolConstant<__is_reference(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_reference_v = __is_reference(_Tp);

template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_lvalue_reference_v = __is_lvalue_reference(_Tp);

template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_rvalue_reference_v = __is_rvalue_reference(_Tp);
#endif

#else // __has_keyword(__is_lvalue_reference) && etc...

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_lvalue_reference       : public false_type {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_lvalue_reference<_Tp&> : public true_type {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_rvalue_reference        : public false_type {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_rvalue_reference<_Tp&&> : public true_type {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_reference        : public false_type {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_reference<_Tp&>  : public true_type {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_reference<_Tp&&> : public true_type {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_reference_v
    = is_reference<_Tp>::value;

template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_lvalue_reference_v
    = is_lvalue_reference<_Tp>::value;

template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_rvalue_reference_v
    = is_rvalue_reference<_Tp>::value;
#endif

#endif // __has_keyword(__is_lvalue_reference) && etc...

// is_union

#if __has_feature(is_union) || defined(_LIBCPP_COMPILER_GCC)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_union
    : public integral_constant<bool, __is_union(_Tp)> {};

#else

template <class _Tp> struct __libcpp_union : public false_type {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_union
    : public __libcpp_union<typename remove_cv<_Tp>::type> {};

#endif

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_union_v
    = is_union<_Tp>::value;
#endif

// is_class

#if __has_feature(is_class) || defined(_LIBCPP_COMPILER_GCC)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_class
    : public integral_constant<bool, __is_class(_Tp)> {};

#else

namespace __is_class_imp
{
template <class _Tp> char  __test(int _Tp::*);
template <class _Tp> __two __test(...);
}

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_class
    : public integral_constant<bool, sizeof(__is_class_imp::__test<_Tp>(0)) == 1 && !is_union<_Tp>::value> {};

#endif

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_class_v
    = is_class<_Tp>::value;
#endif

// is_function

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_function
    : public _BoolConstant<
#ifdef __clang__
    __is_function(_Tp)
#else
 !(is_reference<_Tp>::value || is_const<const _Tp>::value)
#endif
    > {};


#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_function_v
    = is_function<_Tp>::value;
#endif

template <class _Tp> struct __libcpp_is_member_pointer {
  enum {
    __is_member = false,
    __is_func = false,
    __is_obj = false
  };
};
template <class _Tp, class _Up> struct __libcpp_is_member_pointer<_Tp _Up::*> {
  enum {
    __is_member = true,
    __is_func = is_function<_Tp>::value,
    __is_obj = !__is_func,
  };
};

#if __has_keyword(__is_member_function_pointer)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_member_function_pointer
    : _BoolConstant<__is_member_function_pointer(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_member_function_pointer_v
    = __is_member_function_pointer(_Tp);
#endif

#else // __has_keyword(__is_member_function_pointer)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_member_function_pointer
    : public _BoolConstant< __libcpp_is_member_pointer<typename remove_cv<_Tp>::type>::__is_func > {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_member_function_pointer_v
    = is_member_function_pointer<_Tp>::value;
#endif

#endif // __has_keyword(__is_member_function_pointer)

// is_member_pointer

#if __has_keyword(__is_member_pointer)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_member_pointer : _BoolConstant<__is_member_pointer(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_member_pointer_v = __is_member_pointer(_Tp);
#endif

#else // __has_keyword(__is_member_pointer)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_member_pointer
 : public _BoolConstant< __libcpp_is_member_pointer<typename remove_cv<_Tp>::type>::__is_member > {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_member_pointer_v
    = is_member_pointer<_Tp>::value;
#endif

#endif // __has_keyword(__is_member_pointer)

// is_member_object_pointer

#if __has_keyword(__is_member_object_pointer)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_member_object_pointer
    : _BoolConstant<__is_member_object_pointer(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_member_object_pointer_v
    = __is_member_object_pointer(_Tp);
#endif

#else // __has_keyword(__is_member_object_pointer)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_member_object_pointer
    : public _BoolConstant< __libcpp_is_member_pointer<typename remove_cv<_Tp>::type>::__is_obj >  {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_member_object_pointer_v
    = is_member_object_pointer<_Tp>::value;
#endif

#endif // __has_keyword(__is_member_object_pointer)

// is_enum

#if __has_feature(is_enum) || defined(_LIBCPP_COMPILER_GCC)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_enum
    : public integral_constant<bool, __is_enum(_Tp)> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_enum_v = __is_enum(_Tp);
#endif

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_enum
    : public integral_constant<bool, !is_void<_Tp>::value             &&
                                     !is_integral<_Tp>::value         &&
                                     !is_floating_point<_Tp>::value   &&
                                     !is_array<_Tp>::value            &&
                                     !is_pointer<_Tp>::value          &&
                                     !is_reference<_Tp>::value        &&
                                     !is_member_pointer<_Tp>::value   &&
                                     !is_union<_Tp>::value            &&
                                     !is_class<_Tp>::value            &&
                                     !is_function<_Tp>::value         > {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_enum_v
    = is_enum<_Tp>::value;
#endif

#endif // __has_feature(is_enum) || defined(_LIBCPP_COMPILER_GCC)

// is_arithmetic


template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_arithmetic
    : public integral_constant<bool, is_integral<_Tp>::value      ||
                                     is_floating_point<_Tp>::value> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_arithmetic_v
    = is_arithmetic<_Tp>::value;
#endif

// is_fundamental

// Before Clang 10, __is_fundamental didn't work for nullptr_t.
// In C++03 nullptr_t is library-provided but must still count as "fundamental."
#if __has_keyword(__is_fundamental) && !(defined(_LIBCPP_COMPILER_CLANG) && _LIBCPP_CLANG_VER < 1000) && !defined(_LIBCPP_CXX03_LANG)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_fundamental : _BoolConstant<__is_fundamental(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_fundamental_v = __is_fundamental(_Tp);
#endif

#else // __has_keyword(__is_fundamental)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_fundamental
    : public integral_constant<bool, is_void<_Tp>::value        ||
                                     __is_nullptr_t<_Tp>::value ||
                                     is_arithmetic<_Tp>::value> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_fundamental_v
    = is_fundamental<_Tp>::value;
#endif

#endif // __has_keyword(__is_fundamental)

// is_scalar

// In C++03 nullptr_t is library-provided but must still count as "scalar."
#if __has_keyword(__is_scalar) && !defined(_LIBCPP_CXX03_LANG)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_scalar : _BoolConstant<__is_scalar(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_scalar_v = __is_scalar(_Tp);
#endif

#else // __has_keyword(__is_scalar)

template <class _Tp> struct __is_block : false_type {};
#if defined(_LIBCPP_HAS_EXTENSION_BLOCKS)
template <class _Rp, class ..._Args> struct __is_block<_Rp (^)(_Args...)> : true_type {};
#endif

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_scalar
    : public integral_constant<bool, is_arithmetic<_Tp>::value     ||
                                     is_member_pointer<_Tp>::value ||
                                     is_pointer<_Tp>::value        ||
                                     __is_nullptr_t<_Tp>::value    ||
                                     __is_block<_Tp>::value        ||
                                     is_enum<_Tp>::value           > {};

template <> struct _LIBCPP_TEMPLATE_VIS is_scalar<nullptr_t> : public true_type {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_scalar_v
    = is_scalar<_Tp>::value;
#endif

#endif // __has_keyword(__is_scalar)

// is_object

#if __has_keyword(__is_object)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_object : _BoolConstant<__is_object(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_object_v = __is_object(_Tp);
#endif

#else // __has_keyword(__is_object)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_object
    : public integral_constant<bool, is_scalar<_Tp>::value ||
                                     is_array<_Tp>::value  ||
                                     is_union<_Tp>::value  ||
                                     is_class<_Tp>::value  > {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_object_v
    = is_object<_Tp>::value;
#endif

#endif // __has_keyword(__is_object)

// is_compound

// >= 11 because in C++03 nullptr isn't actually nullptr
#if __has_keyword(__is_compound) && !defined(_LIBCPP_CXX03_LANG)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_compound : _BoolConstant<__is_compound(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_compound_v = __is_compound(_Tp);
#endif

#else // __has_keyword(__is_compound)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_compound
    : public integral_constant<bool, !is_fundamental<_Tp>::value> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_compound_v
    = is_compound<_Tp>::value;
#endif

#endif // __has_keyword(__is_compound)

// __is_referenceable  [defns.referenceable]

struct __is_referenceable_impl {
    template <class _Tp> static _Tp& __test(int);
    template <class _Tp> static __two __test(...);
};

template <class _Tp>
struct __is_referenceable : integral_constant<bool,
    _IsNotSame<decltype(__is_referenceable_impl::__test<_Tp>(0)), __two>::value> {};


// add_const

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_const {
  typedef _LIBCPP_NODEBUG_TYPE const _Tp type;
};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using add_const_t = typename add_const<_Tp>::type;
#endif

// add_volatile

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_volatile {
  typedef _LIBCPP_NODEBUG_TYPE volatile _Tp type;
};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using add_volatile_t = typename add_volatile<_Tp>::type;
#endif

// add_cv
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_cv {
  typedef _LIBCPP_NODEBUG_TYPE const volatile _Tp type;
};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using add_cv_t = typename add_cv<_Tp>::type;
#endif

// remove_reference

#if __has_keyword(__remove_reference)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS remove_reference { typedef __remove_reference(_Tp) type; };

#else // __has_keyword(__remove_reference)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_reference        {typedef _LIBCPP_NODEBUG_TYPE _Tp type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_reference<_Tp&>  {typedef _LIBCPP_NODEBUG_TYPE _Tp type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_reference<_Tp&&> {typedef _LIBCPP_NODEBUG_TYPE _Tp type;};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using remove_reference_t = typename remove_reference<_Tp>::type;
#endif

#endif // __has_keyword(__remove_reference)

// add_lvalue_reference

template <class _Tp, bool = __is_referenceable<_Tp>::value> struct __add_lvalue_reference_impl            { typedef _LIBCPP_NODEBUG_TYPE _Tp  type; };
template <class _Tp                                       > struct __add_lvalue_reference_impl<_Tp, true> { typedef _LIBCPP_NODEBUG_TYPE _Tp& type; };

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_lvalue_reference
{typedef _LIBCPP_NODEBUG_TYPE typename  __add_lvalue_reference_impl<_Tp>::type type;};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using add_lvalue_reference_t = typename add_lvalue_reference<_Tp>::type;
#endif

template <class _Tp, bool = __is_referenceable<_Tp>::value> struct __add_rvalue_reference_impl            { typedef _LIBCPP_NODEBUG_TYPE  _Tp   type; };
template <class _Tp                                       > struct __add_rvalue_reference_impl<_Tp, true> { typedef _LIBCPP_NODEBUG_TYPE  _Tp&& type; };

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_rvalue_reference
{typedef _LIBCPP_NODEBUG_TYPE  typename __add_rvalue_reference_impl<_Tp>::type type;};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using add_rvalue_reference_t = typename add_rvalue_reference<_Tp>::type;
#endif

// Suppress deprecation notice for volatile-qualified return type resulting
// from volatile-qualified types _Tp.
_LIBCPP_SUPPRESS_DEPRECATED_PUSH
template <class _Tp> _Tp&& __declval(int);
template <class _Tp> _Tp   __declval(long);
_LIBCPP_SUPPRESS_DEPRECATED_POP

template <class _Tp>
decltype(_VSTD::__declval<_Tp>(0))
declval() _NOEXCEPT;

// __uncvref

template <class _Tp>
struct __uncvref  {
    typedef _LIBCPP_NODEBUG_TYPE typename remove_cv<typename remove_reference<_Tp>::type>::type type;
};

template <class _Tp>
struct __unconstref {
    typedef _LIBCPP_NODEBUG_TYPE typename remove_const<typename remove_reference<_Tp>::type>::type type;
};

#ifndef _LIBCPP_CXX03_LANG
template <class _Tp>
using __uncvref_t _LIBCPP_NODEBUG_TYPE = typename __uncvref<_Tp>::type;
#endif

// __is_same_uncvref

template <class _Tp, class _Up>
struct __is_same_uncvref : _IsSame<typename __uncvref<_Tp>::type,
                                   typename __uncvref<_Up>::type> {};

#if _LIBCPP_STD_VER > 17
// remove_cvref - same as __uncvref
template <class _Tp>
struct remove_cvref : public __uncvref<_Tp> {};

template <class _Tp> using remove_cvref_t = typename remove_cvref<_Tp>::type;
#endif


struct __any
{
    __any(...);
};

// remove_pointer

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer                      {typedef _LIBCPP_NODEBUG_TYPE _Tp type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp*>                {typedef _LIBCPP_NODEBUG_TYPE _Tp type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp* const>          {typedef _LIBCPP_NODEBUG_TYPE _Tp type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp* volatile>       {typedef _LIBCPP_NODEBUG_TYPE _Tp type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_pointer<_Tp* const volatile> {typedef _LIBCPP_NODEBUG_TYPE _Tp type;};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using remove_pointer_t = typename remove_pointer<_Tp>::type;
#endif

// add_pointer

template <class _Tp,
        bool = __is_referenceable<_Tp>::value ||
                _IsSame<typename remove_cv<_Tp>::type, void>::value>
struct __add_pointer_impl
    {typedef _LIBCPP_NODEBUG_TYPE typename remove_reference<_Tp>::type* type;};
template <class _Tp> struct __add_pointer_impl<_Tp, false>
    {typedef _LIBCPP_NODEBUG_TYPE _Tp type;};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_pointer
    {typedef _LIBCPP_NODEBUG_TYPE typename __add_pointer_impl<_Tp>::type type;};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using add_pointer_t = typename add_pointer<_Tp>::type;
#endif

// type_identity
#if _LIBCPP_STD_VER > 17
template<class _Tp> struct type_identity { typedef _Tp type; };
template<class _Tp> using type_identity_t = typename type_identity<_Tp>::type;
#endif

// is_signed

// Before Clang 10, __is_signed didn't work for floating-point types or enums.
#if __has_keyword(__is_signed) && !(defined(_LIBCPP_COMPILER_CLANG) && _LIBCPP_CLANG_VER < 1000)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_signed : _BoolConstant<__is_signed(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_signed_v = __is_signed(_Tp);
#endif

#else // __has_keyword(__is_signed)

template <class _Tp, bool = is_integral<_Tp>::value>
struct __libcpp_is_signed_impl : public _LIBCPP_BOOL_CONSTANT(_Tp(-1) < _Tp(0)) {};

template <class _Tp>
struct __libcpp_is_signed_impl<_Tp, false> : public true_type {};  // floating point

template <class _Tp, bool = is_arithmetic<_Tp>::value>
struct __libcpp_is_signed : public __libcpp_is_signed_impl<_Tp> {};

template <class _Tp> struct __libcpp_is_signed<_Tp, false> : public false_type {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_signed : public __libcpp_is_signed<_Tp> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_signed_v
    = is_signed<_Tp>::value;
#endif

#endif // __has_keyword(__is_signed)

// is_unsigned

// Before Clang 13, __is_unsigned returned true for enums with signed underlying type.
#if __has_keyword(__is_unsigned) && !(defined(_LIBCPP_COMPILER_CLANG) && _LIBCPP_CLANG_VER < 1300)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_unsigned : _BoolConstant<__is_unsigned(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_unsigned_v = __is_unsigned(_Tp);
#endif

#else // __has_keyword(__is_unsigned)

template <class _Tp, bool = is_integral<_Tp>::value>
struct __libcpp_is_unsigned_impl : public _LIBCPP_BOOL_CONSTANT(_Tp(0) < _Tp(-1)) {};

template <class _Tp>
struct __libcpp_is_unsigned_impl<_Tp, false> : public false_type {};  // floating point

template <class _Tp, bool = is_arithmetic<_Tp>::value>
struct __libcpp_is_unsigned : public __libcpp_is_unsigned_impl<_Tp> {};

template <class _Tp> struct __libcpp_is_unsigned<_Tp, false> : public false_type {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_unsigned : public __libcpp_is_unsigned<_Tp> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_unsigned_v
    = is_unsigned<_Tp>::value;
#endif

#endif // __has_keyword(__is_unsigned)

// rank

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS rank
    : public integral_constant<size_t, 0> {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS rank<_Tp[]>
    : public integral_constant<size_t, rank<_Tp>::value + 1> {};
template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS rank<_Tp[_Np]>
    : public integral_constant<size_t, rank<_Tp>::value + 1> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR size_t rank_v
    = rank<_Tp>::value;
#endif

// extent

#if __has_keyword(__array_extent)

template<class _Tp, size_t _Dim = 0>
struct _LIBCPP_TEMPLATE_VIS extent
    : integral_constant<size_t, __array_extent(_Tp, _Dim)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, unsigned _Ip = 0>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR size_t extent_v = __array_extent(_Tp, _Ip);
#endif

#else // __has_keyword(__array_extent)

template <class _Tp, unsigned _Ip = 0> struct _LIBCPP_TEMPLATE_VIS extent
    : public integral_constant<size_t, 0> {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS extent<_Tp[], 0>
    : public integral_constant<size_t, 0> {};
template <class _Tp, unsigned _Ip> struct _LIBCPP_TEMPLATE_VIS extent<_Tp[], _Ip>
    : public integral_constant<size_t, extent<_Tp, _Ip-1>::value> {};
template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS extent<_Tp[_Np], 0>
    : public integral_constant<size_t, _Np> {};
template <class _Tp, size_t _Np, unsigned _Ip> struct _LIBCPP_TEMPLATE_VIS extent<_Tp[_Np], _Ip>
    : public integral_constant<size_t, extent<_Tp, _Ip-1>::value> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, unsigned _Ip = 0>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR size_t extent_v
    = extent<_Tp, _Ip>::value;
#endif

#endif // __has_keyword(__array_extent)

// remove_extent

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_extent
    {typedef _Tp type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_extent<_Tp[]>
    {typedef _Tp type;};
template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS remove_extent<_Tp[_Np]>
    {typedef _Tp type;};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using remove_extent_t = typename remove_extent<_Tp>::type;
#endif

// remove_all_extents

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_all_extents
    {typedef _Tp type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS remove_all_extents<_Tp[]>
    {typedef typename remove_all_extents<_Tp>::type type;};
template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS remove_all_extents<_Tp[_Np]>
    {typedef typename remove_all_extents<_Tp>::type type;};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using remove_all_extents_t = typename remove_all_extents<_Tp>::type;
#endif

#if _LIBCPP_STD_VER > 17
// is_bounded_array

template <class>                 struct _LIBCPP_TEMPLATE_VIS is_bounded_array           : false_type {};
template <class _Tp, size_t _Np> struct _LIBCPP_TEMPLATE_VIS is_bounded_array<_Tp[_Np]> : true_type {};

template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR
bool is_bounded_array_v  = is_bounded_array<_Tp>::value;

// is_unbounded_array

template <class>     struct _LIBCPP_TEMPLATE_VIS is_unbounded_array        : false_type {};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_unbounded_array<_Tp[]> : true_type {};

template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR
bool is_unbounded_array_v  = is_unbounded_array<_Tp>::value;
#endif

// decay

template <class _Up, bool>
struct __decay {
    typedef _LIBCPP_NODEBUG_TYPE typename remove_cv<_Up>::type type;
};

template <class _Up>
struct __decay<_Up, true> {
public:
    typedef _LIBCPP_NODEBUG_TYPE typename conditional
                     <
                         is_array<_Up>::value,
                         typename remove_extent<_Up>::type*,
                         typename conditional
                         <
                              is_function<_Up>::value,
                              typename add_pointer<_Up>::type,
                              typename remove_cv<_Up>::type
                         >::type
                     >::type type;
};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS decay
{
private:
    typedef _LIBCPP_NODEBUG_TYPE typename remove_reference<_Tp>::type _Up;
public:
    typedef _LIBCPP_NODEBUG_TYPE typename __decay<_Up, __is_referenceable<_Up>::value>::type type;
};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using decay_t = typename decay<_Tp>::type;
#endif

// is_abstract

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_abstract
    : public integral_constant<bool, __is_abstract(_Tp)> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_abstract_v
    = is_abstract<_Tp>::value;
#endif

// is_final

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS
__libcpp_is_final : public integral_constant<bool, __is_final(_Tp)> {};

#if _LIBCPP_STD_VER > 11
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS
is_final : public integral_constant<bool, __is_final(_Tp)> {};
#endif

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_final_v
    = is_final<_Tp>::value;
#endif

// is_aggregate
#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_IS_AGGREGATE)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS
is_aggregate : public integral_constant<bool, __is_aggregate(_Tp)> {};

#if !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR constexpr bool is_aggregate_v
    = is_aggregate<_Tp>::value;
#endif

#endif // _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_IS_AGGREGATE)

// is_base_of

template <class _Bp, class _Dp>
struct _LIBCPP_TEMPLATE_VIS is_base_of
    : public integral_constant<bool, __is_base_of(_Bp, _Dp)> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Bp, class _Dp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_base_of_v
    = is_base_of<_Bp, _Dp>::value;
#endif

// __is_core_convertible

// [conv.general]/3 says "E is convertible to T" whenever "T t=E;" is well-formed.
// We can't test for that, but we can test implicit convertibility by passing it
// to a function. Notice that __is_core_convertible<void,void> is false,
// and __is_core_convertible<immovable-type,immovable-type> is true in C++17 and later.

template <class _Tp, class _Up, class = void>
struct __is_core_convertible : public false_type {};

template <class _Tp, class _Up>
struct __is_core_convertible<_Tp, _Up, decltype(
    static_cast<void(*)(_Up)>(0) ( static_cast<_Tp(*)()>(0)() )
)> : public true_type {};

// is_convertible

#if __has_feature(is_convertible_to) && !defined(_LIBCPP_USE_IS_CONVERTIBLE_FALLBACK)

template <class _T1, class _T2> struct _LIBCPP_TEMPLATE_VIS is_convertible
    : public integral_constant<bool, __is_convertible_to(_T1, _T2)> {};

#else  // __has_feature(is_convertible_to)

namespace __is_convertible_imp
{
template <class _Tp> void  __test_convert(_Tp);

template <class _From, class _To, class = void>
struct __is_convertible_test : public false_type {};

template <class _From, class _To>
struct __is_convertible_test<_From, _To,
    decltype(_VSTD::__is_convertible_imp::__test_convert<_To>(_VSTD::declval<_From>()))> : public true_type
{};

template <class _Tp, bool _IsArray =    is_array<_Tp>::value,
                     bool _IsFunction = is_function<_Tp>::value,
                     bool _IsVoid =     is_void<_Tp>::value>
                     struct __is_array_function_or_void                          {enum {value = 0};};
template <class _Tp> struct __is_array_function_or_void<_Tp, true, false, false> {enum {value = 1};};
template <class _Tp> struct __is_array_function_or_void<_Tp, false, true, false> {enum {value = 2};};
template <class _Tp> struct __is_array_function_or_void<_Tp, false, false, true> {enum {value = 3};};
}

template <class _Tp,
    unsigned = __is_convertible_imp::__is_array_function_or_void<typename remove_reference<_Tp>::type>::value>
struct __is_convertible_check
{
    static const size_t __v = 0;
};

template <class _Tp>
struct __is_convertible_check<_Tp, 0>
{
    static const size_t __v = sizeof(_Tp);
};

template <class _T1, class _T2,
    unsigned _T1_is_array_function_or_void = __is_convertible_imp::__is_array_function_or_void<_T1>::value,
    unsigned _T2_is_array_function_or_void = __is_convertible_imp::__is_array_function_or_void<_T2>::value>
struct __is_convertible
    : public integral_constant<bool,
        __is_convertible_imp::__is_convertible_test<_T1, _T2>::value
    >
{};

template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 0, 1> : public false_type {};
template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 1, 1> : public false_type {};
template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 2, 1> : public false_type {};
template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 3, 1> : public false_type {};

template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 0, 2> : public false_type {};
template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 1, 2> : public false_type {};
template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 2, 2> : public false_type {};
template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 3, 2> : public false_type {};

template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 0, 3> : public false_type {};
template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 1, 3> : public false_type {};
template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 2, 3> : public false_type {};
template <class _T1, class _T2> struct __is_convertible<_T1, _T2, 3, 3> : public true_type {};

template <class _T1, class _T2> struct _LIBCPP_TEMPLATE_VIS is_convertible
    : public __is_convertible<_T1, _T2>
{
    static const size_t __complete_check1 = __is_convertible_check<_T1>::__v;
    static const size_t __complete_check2 = __is_convertible_check<_T2>::__v;
};

#endif  // __has_feature(is_convertible_to)

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _From, class _To>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_convertible_v
    = is_convertible<_From, _To>::value;
#endif

// is_nothrow_convertible

#if _LIBCPP_STD_VER > 17

template <typename _Tp>
static void __test_noexcept(_Tp) noexcept;

template<typename _Fm, typename _To>
static bool_constant<noexcept(_VSTD::__test_noexcept<_To>(declval<_Fm>()))>
__is_nothrow_convertible_test();

template <typename _Fm, typename _To>
struct __is_nothrow_convertible_helper: decltype(__is_nothrow_convertible_test<_Fm, _To>())
{ };

template <typename _Fm, typename _To>
struct is_nothrow_convertible : _Or<
    _And<is_void<_To>, is_void<_Fm>>,
    _Lazy<_And, is_convertible<_Fm, _To>, __is_nothrow_convertible_helper<_Fm, _To>>
>::type { };

template <typename _Fm, typename _To>
inline constexpr bool is_nothrow_convertible_v = is_nothrow_convertible<_Fm, _To>::value;

#endif // _LIBCPP_STD_VER > 17

// is_empty

#if __has_feature(is_empty) || defined(_LIBCPP_COMPILER_GCC)

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_empty
    : public integral_constant<bool, __is_empty(_Tp)> {};

#else  // __has_feature(is_empty)

template <class _Tp>
struct __is_empty1
    : public _Tp
{
    double __lx;
};

struct __is_empty2
{
    double __lx;
};

template <class _Tp, bool = is_class<_Tp>::value>
struct __libcpp_empty : public integral_constant<bool, sizeof(__is_empty1<_Tp>) == sizeof(__is_empty2)> {};

template <class _Tp> struct __libcpp_empty<_Tp, false> : public false_type {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_empty : public __libcpp_empty<_Tp> {};

#endif  // __has_feature(is_empty)

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_empty_v
    = is_empty<_Tp>::value;
#endif

// is_polymorphic

#if __has_feature(is_polymorphic) || defined(_LIBCPP_COMPILER_MSVC)

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_polymorphic
    : public integral_constant<bool, __is_polymorphic(_Tp)> {};

#else

template<typename _Tp> char &__is_polymorphic_impl(
    typename enable_if<sizeof((_Tp*)dynamic_cast<const volatile void*>(declval<_Tp*>())) != 0,
                       int>::type);
template<typename _Tp> __two &__is_polymorphic_impl(...);

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_polymorphic
    : public integral_constant<bool, sizeof(__is_polymorphic_impl<_Tp>(0)) == 1> {};

#endif // __has_feature(is_polymorphic)

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_polymorphic_v
    = is_polymorphic<_Tp>::value;
#endif

// has_virtual_destructor

#if __has_feature(has_virtual_destructor) || defined(_LIBCPP_COMPILER_GCC)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS has_virtual_destructor
    : public integral_constant<bool, __has_virtual_destructor(_Tp)> {};

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS has_virtual_destructor
    : public false_type {};

#endif

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool has_virtual_destructor_v
    = has_virtual_destructor<_Tp>::value;
#endif

// has_unique_object_representations

#if _LIBCPP_STD_VER > 14 && defined(_LIBCPP_HAS_UNIQUE_OBJECT_REPRESENTATIONS)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS has_unique_object_representations
    : public integral_constant<bool,
       __has_unique_object_representations(remove_cv_t<remove_all_extents_t<_Tp>>)> {};

#if !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool has_unique_object_representations_v
    = has_unique_object_representations<_Tp>::value;
#endif

#endif

// alignment_of

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS alignment_of
    : public integral_constant<size_t, _LIBCPP_ALIGNOF(_Tp)> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR size_t alignment_of_v
    = alignment_of<_Tp>::value;
#endif

// aligned_storage

template <class _Hp, class _Tp>
struct __type_list
{
    typedef _Hp _Head;
    typedef _Tp _Tail;
};

struct __nat
{
#ifndef _LIBCPP_CXX03_LANG
    __nat() = delete;
    __nat(const __nat&) = delete;
    __nat& operator=(const __nat&) = delete;
    ~__nat() = delete;
#endif
};

template <class _Tp>
struct __align_type
{
    static const size_t value = _LIBCPP_PREFERRED_ALIGNOF(_Tp);
    typedef _Tp type;
};

struct __struct_double {long double __lx;};
struct __struct_double4 {double __lx[4];};

typedef
    __type_list<__align_type<unsigned char>,
    __type_list<__align_type<unsigned short>,
    __type_list<__align_type<unsigned int>,
    __type_list<__align_type<unsigned long>,
    __type_list<__align_type<unsigned long long>,
    __type_list<__align_type<double>,
    __type_list<__align_type<long double>,
    __type_list<__align_type<__struct_double>,
    __type_list<__align_type<__struct_double4>,
    __type_list<__align_type<int*>,
    __nat
    > > > > > > > > > > __all_types;

template <size_t _Align>
struct _ALIGNAS(_Align) __fallback_overaligned {};

template <class _TL, size_t _Align> struct __find_pod;

template <class _Hp, size_t _Align>
struct __find_pod<__type_list<_Hp, __nat>, _Align>
{
    typedef typename conditional<
                             _Align == _Hp::value,
                             typename _Hp::type,
                             __fallback_overaligned<_Align>
                         >::type type;
};

template <class _Hp, class _Tp, size_t _Align>
struct __find_pod<__type_list<_Hp, _Tp>, _Align>
{
    typedef typename conditional<
                             _Align == _Hp::value,
                             typename _Hp::type,
                             typename __find_pod<_Tp, _Align>::type
                         >::type type;
};

template <class _TL, size_t _Len> struct __find_max_align;

template <class _Hp, size_t _Len>
struct __find_max_align<__type_list<_Hp, __nat>, _Len> : public integral_constant<size_t, _Hp::value> {};

template <size_t _Len, size_t _A1, size_t _A2>
struct __select_align
{
private:
    static const size_t __min = _A2 < _A1 ? _A2 : _A1;
    static const size_t __max = _A1 < _A2 ? _A2 : _A1;
public:
    static const size_t value = _Len < __max ? __min : __max;
};

template <class _Hp, class _Tp, size_t _Len>
struct __find_max_align<__type_list<_Hp, _Tp>, _Len>
    : public integral_constant<size_t, __select_align<_Len, _Hp::value, __find_max_align<_Tp, _Len>::value>::value> {};

template <size_t _Len, size_t _Align = __find_max_align<__all_types, _Len>::value>
struct _LIBCPP_TEMPLATE_VIS aligned_storage
{
    typedef typename __find_pod<__all_types, _Align>::type _Aligner;
    union type
    {
        _Aligner __align;
        unsigned char __data[(_Len + _Align - 1)/_Align * _Align];
    };
};

#if _LIBCPP_STD_VER > 11
template <size_t _Len, size_t _Align = __find_max_align<__all_types, _Len>::value>
    using aligned_storage_t = typename aligned_storage<_Len, _Align>::type;
#endif

#define _CREATE_ALIGNED_STORAGE_SPECIALIZATION(n) \
template <size_t _Len>\
struct _LIBCPP_TEMPLATE_VIS aligned_storage<_Len, n>\
{\
    struct _ALIGNAS(n) type\
    {\
        unsigned char __lx[(_Len + n - 1)/n * n];\
    };\
}

_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x1);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x2);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x4);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x8);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x10);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x20);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x40);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x80);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x100);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x200);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x400);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x800);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x1000);
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x2000);
// PE/COFF does not support alignment beyond 8192 (=0x2000)
#if !defined(_LIBCPP_OBJECT_FORMAT_COFF)
_CREATE_ALIGNED_STORAGE_SPECIALIZATION(0x4000);
#endif // !defined(_LIBCPP_OBJECT_FORMAT_COFF)

#undef _CREATE_ALIGNED_STORAGE_SPECIALIZATION


// aligned_union

template <size_t _I0, size_t ..._In>
struct __static_max;

template <size_t _I0>
struct __static_max<_I0>
{
    static const size_t value = _I0;
};

template <size_t _I0, size_t _I1, size_t ..._In>
struct __static_max<_I0, _I1, _In...>
{
    static const size_t value = _I0 >= _I1 ? __static_max<_I0, _In...>::value :
                                             __static_max<_I1, _In...>::value;
};

template <size_t _Len, class _Type0, class ..._Types>
struct aligned_union
{
    static const size_t alignment_value = __static_max<_LIBCPP_PREFERRED_ALIGNOF(_Type0),
                                                       _LIBCPP_PREFERRED_ALIGNOF(_Types)...>::value;
    static const size_t __len = __static_max<_Len, sizeof(_Type0),
                                             sizeof(_Types)...>::value;
    typedef typename aligned_storage<__len, alignment_value>::type type;
};

#if _LIBCPP_STD_VER > 11
template <size_t _Len, class ..._Types> using aligned_union_t = typename aligned_union<_Len, _Types...>::type;
#endif

template <class _Tp>
struct __numeric_type
{
   static void __test(...);
   static float __test(float);
   static double __test(char);
   static double __test(int);
   static double __test(unsigned);
   static double __test(long);
   static double __test(unsigned long);
   static double __test(long long);
   static double __test(unsigned long long);
   static double __test(double);
   static long double __test(long double);

   typedef decltype(__test(declval<_Tp>())) type;
   static const bool value = _IsNotSame<type, void>::value;
};

template <>
struct __numeric_type<void>
{
   static const bool value = true;
};

// __promote

template <class _A1, class _A2 = void, class _A3 = void,
          bool = __numeric_type<_A1>::value &&
                 __numeric_type<_A2>::value &&
                 __numeric_type<_A3>::value>
class __promote_imp
{
public:
    static const bool value = false;
};

template <class _A1, class _A2, class _A3>
class __promote_imp<_A1, _A2, _A3, true>
{
private:
    typedef typename __promote_imp<_A1>::type __type1;
    typedef typename __promote_imp<_A2>::type __type2;
    typedef typename __promote_imp<_A3>::type __type3;
public:
    typedef decltype(__type1() + __type2() + __type3()) type;
    static const bool value = true;
};

template <class _A1, class _A2>
class __promote_imp<_A1, _A2, void, true>
{
private:
    typedef typename __promote_imp<_A1>::type __type1;
    typedef typename __promote_imp<_A2>::type __type2;
public:
    typedef decltype(__type1() + __type2()) type;
    static const bool value = true;
};

template <class _A1>
class __promote_imp<_A1, void, void, true>
{
public:
    typedef typename __numeric_type<_A1>::type type;
    static const bool value = true;
};

template <class _A1, class _A2 = void, class _A3 = void>
class __promote : public __promote_imp<_A1, _A2, _A3> {};

// make_signed / make_unsigned

typedef
    __type_list<signed char,
    __type_list<signed short,
    __type_list<signed int,
    __type_list<signed long,
    __type_list<signed long long,
#ifndef _LIBCPP_HAS_NO_INT128
    __type_list<__int128_t,
#endif
    __nat
#ifndef _LIBCPP_HAS_NO_INT128
    >
#endif
    > > > > > __signed_types;

typedef
    __type_list<unsigned char,
    __type_list<unsigned short,
    __type_list<unsigned int,
    __type_list<unsigned long,
    __type_list<unsigned long long,
#ifndef _LIBCPP_HAS_NO_INT128
    __type_list<__uint128_t,
#endif
    __nat
#ifndef _LIBCPP_HAS_NO_INT128
    >
#endif
    > > > > > __unsigned_types;

template <class _TypeList, size_t _Size, bool = _Size <= sizeof(typename _TypeList::_Head)> struct __find_first;

template <class _Hp, class _Tp, size_t _Size>
struct __find_first<__type_list<_Hp, _Tp>, _Size, true>
{
    typedef _LIBCPP_NODEBUG_TYPE _Hp type;
};

template <class _Hp, class _Tp, size_t _Size>
struct __find_first<__type_list<_Hp, _Tp>, _Size, false>
{
    typedef _LIBCPP_NODEBUG_TYPE typename __find_first<_Tp, _Size>::type type;
};

template <class _Tp, class _Up, bool = is_const<typename remove_reference<_Tp>::type>::value,
                             bool = is_volatile<typename remove_reference<_Tp>::type>::value>
struct __apply_cv
{
    typedef _LIBCPP_NODEBUG_TYPE _Up type;
};

template <class _Tp, class _Up>
struct __apply_cv<_Tp, _Up, true, false>
{
    typedef _LIBCPP_NODEBUG_TYPE const _Up type;
};

template <class _Tp, class _Up>
struct __apply_cv<_Tp, _Up, false, true>
{
    typedef volatile _Up type;
};

template <class _Tp, class _Up>
struct __apply_cv<_Tp, _Up, true, true>
{
    typedef const volatile _Up type;
};

template <class _Tp, class _Up>
struct __apply_cv<_Tp&, _Up, false, false>
{
    typedef _Up& type;
};

template <class _Tp, class _Up>
struct __apply_cv<_Tp&, _Up, true, false>
{
    typedef const _Up& type;
};

template <class _Tp, class _Up>
struct __apply_cv<_Tp&, _Up, false, true>
{
    typedef volatile _Up& type;
};

template <class _Tp, class _Up>
struct __apply_cv<_Tp&, _Up, true, true>
{
    typedef const volatile _Up& type;
};

template <class _Tp, bool = is_integral<_Tp>::value || is_enum<_Tp>::value>
struct __make_signed {};

template <class _Tp>
struct __make_signed<_Tp, true>
{
    typedef typename __find_first<__signed_types, sizeof(_Tp)>::type type;
};

template <> struct __make_signed<bool,               true> {};
template <> struct __make_signed<  signed short,     true> {typedef short     type;};
template <> struct __make_signed<unsigned short,     true> {typedef short     type;};
template <> struct __make_signed<  signed int,       true> {typedef int       type;};
template <> struct __make_signed<unsigned int,       true> {typedef int       type;};
template <> struct __make_signed<  signed long,      true> {typedef long      type;};
template <> struct __make_signed<unsigned long,      true> {typedef long      type;};
template <> struct __make_signed<  signed long long, true> {typedef long long type;};
template <> struct __make_signed<unsigned long long, true> {typedef long long type;};
#ifndef _LIBCPP_HAS_NO_INT128
template <> struct __make_signed<__int128_t,         true> {typedef __int128_t type;};
template <> struct __make_signed<__uint128_t,        true> {typedef __int128_t type;};
#endif

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS make_signed
{
    typedef typename __apply_cv<_Tp, typename __make_signed<typename remove_cv<_Tp>::type>::type>::type type;
};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using make_signed_t = typename make_signed<_Tp>::type;
#endif

template <class _Tp, bool = is_integral<_Tp>::value || is_enum<_Tp>::value>
struct __make_unsigned {};

template <class _Tp>
struct __make_unsigned<_Tp, true>
{
    typedef typename __find_first<__unsigned_types, sizeof(_Tp)>::type type;
};

template <> struct __make_unsigned<bool,               true> {};
template <> struct __make_unsigned<  signed short,     true> {typedef unsigned short     type;};
template <> struct __make_unsigned<unsigned short,     true> {typedef unsigned short     type;};
template <> struct __make_unsigned<  signed int,       true> {typedef unsigned int       type;};
template <> struct __make_unsigned<unsigned int,       true> {typedef unsigned int       type;};
template <> struct __make_unsigned<  signed long,      true> {typedef unsigned long      type;};
template <> struct __make_unsigned<unsigned long,      true> {typedef unsigned long      type;};
template <> struct __make_unsigned<  signed long long, true> {typedef unsigned long long type;};
template <> struct __make_unsigned<unsigned long long, true> {typedef unsigned long long type;};
#ifndef _LIBCPP_HAS_NO_INT128
template <> struct __make_unsigned<__int128_t,         true> {typedef __uint128_t        type;};
template <> struct __make_unsigned<__uint128_t,        true> {typedef __uint128_t        type;};
#endif

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS make_unsigned
{
    typedef typename __apply_cv<_Tp, typename __make_unsigned<typename remove_cv<_Tp>::type>::type>::type type;
};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using make_unsigned_t = typename make_unsigned<_Tp>::type;
#endif

#if _LIBCPP_STD_VER > 14
template <class...> using void_t = void;
#endif

#if _LIBCPP_STD_VER > 17
// Let COND_RES(X, Y) be:
template <class _Tp, class _Up>
using __cond_type = decltype(false ? _VSTD::declval<_Tp>() : _VSTD::declval<_Up>());

template <class _Tp, class _Up, class = void>
struct __common_type3 {};

// sub-bullet 4 - "if COND_RES(CREF(D1), CREF(D2)) denotes a type..."
template <class _Tp, class _Up>
struct __common_type3<_Tp, _Up, void_t<__cond_type<const _Tp&, const _Up&>>>
{
    using type = remove_cvref_t<__cond_type<const _Tp&, const _Up&>>;
};

template <class _Tp, class _Up, class = void>
struct __common_type2_imp : __common_type3<_Tp, _Up> {};
#else
template <class _Tp, class _Up, class = void>
struct __common_type2_imp {};
#endif

// sub-bullet 3 - "if decay_t<decltype(false ? declval<D1>() : declval<D2>())> ..."
template <class _Tp, class _Up>
struct __common_type2_imp<_Tp, _Up,
                          typename __void_t<decltype(
                                            true ? _VSTD::declval<_Tp>() : _VSTD::declval<_Up>()
                                            )>::type>
{
  typedef _LIBCPP_NODEBUG_TYPE typename decay<decltype(
                         true ? _VSTD::declval<_Tp>() : _VSTD::declval<_Up>()
                         )>::type type;
};

template <class, class = void>
struct __common_type_impl {};

// Clang provides variadic templates in C++03 as an extension.
#if !defined(_LIBCPP_CXX03_LANG) || defined(__clang__)
# define _LIBCPP_OPTIONAL_PACK(...) , __VA_ARGS__
template <class... Tp>
struct __common_types;
template <class... _Tp>
struct _LIBCPP_TEMPLATE_VIS common_type;
#else
# define _LIBCPP_OPTIONAL_PACK(...)
struct __no_arg;
template <class _Tp, class _Up, class = __no_arg>
struct __common_types;
template <class _Tp = __no_arg, class _Up = __no_arg, class _Vp = __no_arg,
          class _Unused = __no_arg>
struct common_type {
  static_assert(sizeof(_Unused) == 0,
                "common_type accepts at most 3 arguments in C++03");
};
#endif // _LIBCPP_CXX03_LANG

template <class _Tp, class _Up>
struct __common_type_impl<
    __common_types<_Tp, _Up>,
    typename __void_t<typename common_type<_Tp, _Up>::type>::type>
{
  typedef typename common_type<_Tp, _Up>::type type;
};

template <class _Tp, class _Up, class _Vp _LIBCPP_OPTIONAL_PACK(class... _Rest)>
struct __common_type_impl<
    __common_types<_Tp, _Up, _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)>,
    typename __void_t<typename common_type<_Tp, _Up>::type>::type>
    : __common_type_impl<__common_types<typename common_type<_Tp, _Up>::type,
                                        _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)> > {
};

// bullet 1 - sizeof...(Tp) == 0

template <>
struct _LIBCPP_TEMPLATE_VIS common_type<> {};

// bullet 2 - sizeof...(Tp) == 1

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS common_type<_Tp>
    : public common_type<_Tp, _Tp> {};

// bullet 3 - sizeof...(Tp) == 2

// sub-bullet 1 - "If is_same_v<T1, D1> is false or ..."
template <class _Tp, class _Up>
struct _LIBCPP_TEMPLATE_VIS common_type<_Tp, _Up>
    : conditional<
        _IsSame<_Tp, typename decay<_Tp>::type>::value && _IsSame<_Up, typename decay<_Up>::type>::value,
        __common_type2_imp<_Tp, _Up>,
        common_type<typename decay<_Tp>::type, typename decay<_Up>::type>
    >::type
{};

// bullet 4 - sizeof...(Tp) > 2

template <class _Tp, class _Up, class _Vp _LIBCPP_OPTIONAL_PACK(class... _Rest)>
struct _LIBCPP_TEMPLATE_VIS
    common_type<_Tp, _Up, _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)>
    : __common_type_impl<
          __common_types<_Tp, _Up, _Vp _LIBCPP_OPTIONAL_PACK(_Rest...)> > {};

#undef _LIBCPP_OPTIONAL_PACK

#if _LIBCPP_STD_VER > 11
template <class ..._Tp> using common_type_t = typename common_type<_Tp...>::type;
#endif

#if _LIBCPP_STD_VER > 11
// Let COPYCV(FROM, TO) be an alias for type TO with the addition of FROM’s
// top-level cv-qualifiers.
template <class _From, class _To>
struct __copy_cv
{
    using type = _To;
};

template <class _From, class _To>
struct __copy_cv<const _From, _To>
{
    using type = add_const_t<_To>;
};

template <class _From, class _To>
struct __copy_cv<volatile _From, _To>
{
    using type = add_volatile_t<_To>;
};

template <class _From, class _To>
struct __copy_cv<const volatile _From, _To>
{
    using type = add_cv_t<_To>;
};

template <class _From, class _To>
using __copy_cv_t = typename __copy_cv<_From, _To>::type;

template <class _From, class _To>
struct __copy_cvref
{
    using type = __copy_cv_t<_From, _To>;
};

template <class _From, class _To>
struct __copy_cvref<_From&, _To>
{
    using type = add_lvalue_reference_t<__copy_cv_t<_From, _To>>;
};

template <class _From, class _To>
struct __copy_cvref<_From&&, _To>
{
    using type = add_rvalue_reference_t<__copy_cv_t<_From, _To>>;
};

template <class _From, class _To>
using __copy_cvref_t = typename __copy_cvref<_From, _To>::type;

#endif // _LIBCPP_STD_VER > 11

// common_reference
#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
// Let COND_RES(X, Y) be:
template <class _Xp, class _Yp>
using __cond_res =
    decltype(false ? _VSTD::declval<_Xp(&)()>()() : _VSTD::declval<_Yp(&)()>()());

// Let `XREF(A)` denote a unary alias template `T` such that `T<U>` denotes the same type as `U`
// with the addition of `A`'s cv and reference qualifiers, for a non-reference cv-unqualified type
// `U`.
// [Note: `XREF(A)` is `__xref<A>::template __apply`]
template <class _Tp>
struct __xref {
  template<class _Up>
  using __apply = __copy_cvref_t<_Tp, _Up>;
};

// Given types `A` and `B`, let `X` be `remove_­reference_­t<A>`, let `Y` be `remove_­reference_­t<B>`,
// and let `COMMON-​REF(A, B)` be:
template<class _Ap, class _Bp, class _Xp = remove_reference_t<_Ap>, class _Yp = remove_reference_t<_Bp>>
struct __common_ref;

template<class _Xp, class _Yp>
using __common_ref_t = typename __common_ref<_Xp, _Yp>::__type;

template<class _Xp, class _Yp>
using __cv_cond_res = __cond_res<__copy_cv_t<_Xp, _Yp>&, __copy_cv_t<_Yp, _Xp>&>;


//    If `A` and `B` are both lvalue reference types, `COMMON-REF(A, B)` is
//    `COND-RES(COPYCV(X, Y) &, COPYCV(​Y, X) &)` if that type exists and is a reference type.
template<class _Ap, class _Bp, class _Xp, class _Yp>
requires requires { typename __cv_cond_res<_Xp, _Yp>; } && is_reference_v<__cv_cond_res<_Xp, _Yp>>
struct __common_ref<_Ap&, _Bp&, _Xp, _Yp>
{
    using __type = __cv_cond_res<_Xp, _Yp>;
};

//    Otherwise, let `C` be `remove_­reference_­t<COMMON-REF(X&, Y&)>&&`....
template <class _Xp, class _Yp>
using __common_ref_C = remove_reference_t<__common_ref_t<_Xp&, _Yp&>>&&;


//    .... If `A` and `B` are both rvalue reference types, `C` is well-formed, and
//    `is_­convertible_­v<A, C> && is_­convertible_­v<B, C>` is `true`, then `COMMON-REF(A, B)` is `C`.
template<class _Ap, class _Bp, class _Xp, class _Yp>
requires
  requires { typename __common_ref_C<_Xp, _Yp>; } &&
  is_convertible_v<_Ap&&, __common_ref_C<_Xp, _Yp>> &&
  is_convertible_v<_Bp&&, __common_ref_C<_Xp, _Yp>>
struct __common_ref<_Ap&&, _Bp&&, _Xp, _Yp>
{
    using __type = __common_ref_C<_Xp, _Yp>;
};

//    Otherwise, let `D` be `COMMON-REF(const X&, Y&)`....
template <class _Tp, class _Up>
using __common_ref_D = __common_ref_t<const _Tp&, _Up&>;

//    ... If `A` is an rvalue reference and `B` is an lvalue reference and `D` is well-formed and
//    `is_­convertible_­v<A, D>` is `true`, then `COMMON-REF(A, B)` is `D`.
template<class _Ap, class _Bp, class _Xp, class _Yp>
requires requires { typename __common_ref_D<_Xp, _Yp>; } &&
         is_convertible_v<_Ap&&, __common_ref_D<_Xp, _Yp>>
struct __common_ref<_Ap&&, _Bp&, _Xp, _Yp>
{
    using __type = __common_ref_D<_Xp, _Yp>;
};

//    Otherwise, if `A` is an lvalue reference and `B` is an rvalue reference, then
//    `COMMON-REF(A, B)` is `COMMON-REF(B, A)`.
template<class _Ap, class _Bp, class _Xp, class _Yp>
struct __common_ref<_Ap&, _Bp&&, _Xp, _Yp> : __common_ref<_Bp&&, _Ap&> {};

//    Otherwise, `COMMON-REF(A, B)` is ill-formed.
template<class _Ap, class _Bp, class _Xp, class _Yp>
struct __common_ref {};

// Note C: For the common_reference trait applied to a parameter pack [...]

template <class...>
struct common_reference;

template <class... _Types>
using common_reference_t = typename common_reference<_Types...>::type;

// bullet 1 - sizeof...(T) == 0
template<>
struct common_reference<> {};

// bullet 2 - sizeof...(T) == 1
template <class _Tp>
struct common_reference<_Tp>
{
    using type = _Tp;
};

// bullet 3 - sizeof...(T) == 2
template <class _Tp, class _Up> struct __common_reference_sub_bullet3;
template <class _Tp, class _Up> struct __common_reference_sub_bullet2 : __common_reference_sub_bullet3<_Tp, _Up> {};
template <class _Tp, class _Up> struct __common_reference_sub_bullet1 : __common_reference_sub_bullet2<_Tp, _Up> {};

// sub-bullet 1 - If `T1` and `T2` are reference types and `COMMON-REF(T1, T2)` is well-formed, then
// the member typedef type denotes that type.
template <class _Tp, class _Up> struct common_reference<_Tp, _Up> : __common_reference_sub_bullet1<_Tp, _Up> {};

template <class _Tp, class _Up>
requires is_reference_v<_Tp> && is_reference_v<_Up> && requires { typename __common_ref_t<_Tp, _Up>; }
struct __common_reference_sub_bullet1<_Tp, _Up>
{
    using type = __common_ref_t<_Tp, _Up>;
};

// sub-bullet 2 - Otherwise, if `basic_­common_­reference<remove_­cvref_­t<T1>, remove_­cvref_­t<T2>, ​XREF(​T1), XREF(T2)>​::​type`
// is well-formed, then the member typedef type denotes that type.
template <class, class, template <class> class, template <class> class> struct basic_common_reference {};

template <class _Tp, class _Up>
using __basic_common_reference_t = typename basic_common_reference<
    remove_cvref_t<_Tp>, remove_cvref_t<_Up>,
    __xref<_Tp>::template __apply, __xref<_Up>::template __apply>::type;

template <class _Tp, class _Up>
requires requires { typename __basic_common_reference_t<_Tp, _Up>; }
struct __common_reference_sub_bullet2<_Tp, _Up>
{
    using type = __basic_common_reference_t<_Tp, _Up>;
};

// sub-bullet 3 - Otherwise, if `COND-RES(T1, T2)` is well-formed, then the member typedef type
// denotes that type.
template <class _Tp, class _Up>
requires requires { typename __cond_res<_Tp, _Up>; }
struct __common_reference_sub_bullet3<_Tp, _Up>
{
    using type = __cond_res<_Tp, _Up>;
};


// sub-bullet 4 & 5 - Otherwise, if `common_­type_­t<T1, T2>` is well-formed, then the member typedef
//                    type denotes that type.
//                  - Otherwise, there shall be no member type.
template <class _Tp, class _Up> struct __common_reference_sub_bullet3 : common_type<_Tp, _Up> {};

// bullet 4 - If there is such a type `C`, the member typedef type shall denote the same type, if
//            any, as `common_­reference_­t<C, Rest...>`.
template <class _Tp, class _Up, class _Vp, class... _Rest>
requires requires { typename common_reference_t<_Tp, _Up>; }
struct common_reference<_Tp, _Up, _Vp, _Rest...>
    : common_reference<common_reference_t<_Tp, _Up>, _Vp, _Rest...>
{};

// bullet 5 - Otherwise, there shall be no member type.
template <class...> struct common_reference {};

#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_CONCEPTS)

// is_assignable

template<typename, typename _Tp> struct __select_2nd { typedef _LIBCPP_NODEBUG_TYPE _Tp type; };

#if __has_keyword(__is_assignable)

template<class _Tp, class _Up>
struct _LIBCPP_TEMPLATE_VIS is_assignable : _BoolConstant<__is_assignable(_Tp, _Up)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, class _Arg>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_assignable_v = __is_assignable(_Tp, _Arg);
#endif

#else // __has_keyword(__is_assignable)

template <class _Tp, class _Arg>
typename __select_2nd<decltype((_VSTD::declval<_Tp>() = _VSTD::declval<_Arg>())), true_type>::type
__is_assignable_test(int);

template <class, class>
false_type __is_assignable_test(...);


template <class _Tp, class _Arg, bool = is_void<_Tp>::value || is_void<_Arg>::value>
struct __is_assignable_imp
    : public decltype((_VSTD::__is_assignable_test<_Tp, _Arg>(0))) {};

template <class _Tp, class _Arg>
struct __is_assignable_imp<_Tp, _Arg, true>
    : public false_type
{
};

template <class _Tp, class _Arg>
struct is_assignable
    : public __is_assignable_imp<_Tp, _Arg> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, class _Arg>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_assignable_v
    = is_assignable<_Tp, _Arg>::value;
#endif

#endif  // __has_keyword(__is_assignable)

// is_copy_assignable

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_copy_assignable
    : public is_assignable<typename add_lvalue_reference<_Tp>::type,
                  typename add_lvalue_reference<typename add_const<_Tp>::type>::type> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_copy_assignable_v
    = is_copy_assignable<_Tp>::value;
#endif

// is_move_assignable

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_move_assignable
    : public is_assignable<typename add_lvalue_reference<_Tp>::type,
                           typename add_rvalue_reference<_Tp>::type> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_move_assignable_v
    = is_move_assignable<_Tp>::value;
#endif

// is_destructible

#if __has_keyword(__is_destructible)

template<class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_destructible : _BoolConstant<__is_destructible(_Tp)> { };

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_destructible_v = __is_destructible(_Tp);
#endif

#else // __has_keyword(__is_destructible)

//  if it's a reference, return true
//  if it's a function, return false
//  if it's   void,     return false
//  if it's an array of unknown bound, return false
//  Otherwise, return "declval<_Up&>().~_Up()" is well-formed
//    where _Up is remove_all_extents<_Tp>::type

template <class>
struct __is_destructible_apply { typedef int type; };

template <typename _Tp>
struct __is_destructor_wellformed {
    template <typename _Tp1>
    static char  __test (
        typename __is_destructible_apply<decltype(_VSTD::declval<_Tp1&>().~_Tp1())>::type
    );

    template <typename _Tp1>
    static __two __test (...);

    static const bool value = sizeof(__test<_Tp>(12)) == sizeof(char);
};

template <class _Tp, bool>
struct __destructible_imp;

template <class _Tp>
struct __destructible_imp<_Tp, false>
   : public _VSTD::integral_constant<bool,
        __is_destructor_wellformed<typename _VSTD::remove_all_extents<_Tp>::type>::value> {};

template <class _Tp>
struct __destructible_imp<_Tp, true>
    : public _VSTD::true_type {};

template <class _Tp, bool>
struct __destructible_false;

template <class _Tp>
struct __destructible_false<_Tp, false> : public __destructible_imp<_Tp, _VSTD::is_reference<_Tp>::value> {};

template <class _Tp>
struct __destructible_false<_Tp, true> : public _VSTD::false_type {};

template <class _Tp>
struct is_destructible
    : public __destructible_false<_Tp, _VSTD::is_function<_Tp>::value> {};

template <class _Tp>
struct is_destructible<_Tp[]>
    : public _VSTD::false_type {};

template <>
struct is_destructible<void>
    : public _VSTD::false_type {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_destructible_v
    = is_destructible<_Tp>::value;
#endif

#endif // __has_keyword(__is_destructible)

// move

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
typename remove_reference<_Tp>::type&&
move(_Tp&& __t) _NOEXCEPT
{
    typedef _LIBCPP_NODEBUG_TYPE typename remove_reference<_Tp>::type _Up;
    return static_cast<_Up&&>(__t);
}

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
_Tp&&
forward(typename remove_reference<_Tp>::type& __t) _NOEXCEPT
{
    return static_cast<_Tp&&>(__t);
}

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
_Tp&&
forward(typename remove_reference<_Tp>::type&& __t) _NOEXCEPT
{
    static_assert(!is_lvalue_reference<_Tp>::value,
                  "can not forward an rvalue as an lvalue");
    return static_cast<_Tp&&>(__t);
}

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY
typename decay<_Tp>::type
__decay_copy(_Tp&& __t)
{
    return _VSTD::forward<_Tp>(__t);
}

template <class _MP, bool _IsMemberFunctionPtr, bool _IsMemberObjectPtr>
struct __member_pointer_traits_imp
{
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...), true, false>
{
    typedef _Class _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...), true, false>
{
    typedef _Class _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const, true, false>
{
    typedef _Class const _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const, true, false>
{
    typedef _Class const _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) volatile, true, false>
{
    typedef _Class volatile _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) volatile, true, false>
{
    typedef _Class volatile _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const volatile, true, false>
{
    typedef _Class const volatile _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const volatile, true, false>
{
    typedef _Class const volatile _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

#if __has_feature(cxx_reference_qualified_functions) || defined(_LIBCPP_COMPILER_GCC)

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) &, true, false>
{
    typedef _Class& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) &, true, false>
{
    typedef _Class& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const&, true, false>
{
    typedef _Class const& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const&, true, false>
{
    typedef _Class const& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) volatile&, true, false>
{
    typedef _Class volatile& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) volatile&, true, false>
{
    typedef _Class volatile& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const volatile&, true, false>
{
    typedef _Class const volatile& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const volatile&, true, false>
{
    typedef _Class const volatile& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) &&, true, false>
{
    typedef _Class&& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) &&, true, false>
{
    typedef _Class&& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const&&, true, false>
{
    typedef _Class const&& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const&&, true, false>
{
    typedef _Class const&& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) volatile&&, true, false>
{
    typedef _Class volatile&& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) volatile&&, true, false>
{
    typedef _Class volatile&& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...) const volatile&&, true, false>
{
    typedef _Class const volatile&& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param...);
};

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param..., ...) const volatile&&, true, false>
{
    typedef _Class const volatile&& _ClassType;
    typedef _Rp _ReturnType;
    typedef _Rp (_FnType) (_Param..., ...);
};

#endif  // __has_feature(cxx_reference_qualified_functions) || defined(_LIBCPP_COMPILER_GCC)


template <class _Rp, class _Class>
struct __member_pointer_traits_imp<_Rp _Class::*, false, true>
{
    typedef _Class _ClassType;
    typedef _Rp _ReturnType;
};

template <class _MP>
struct __member_pointer_traits
    : public __member_pointer_traits_imp<typename remove_cv<_MP>::type,
                    is_member_function_pointer<_MP>::value,
                    is_member_object_pointer<_MP>::value>
{
//     typedef ... _ClassType;
//     typedef ... _ReturnType;
//     typedef ... _FnType;
};


template <class _DecayedFp>
struct __member_pointer_class_type {};

template <class _Ret, class _ClassType>
struct __member_pointer_class_type<_Ret _ClassType::*> {
  typedef _ClassType type;
};

// template <class T, class... Args> struct is_constructible;

#if defined(_LIBCPP_COMPILER_GCC) && _GNUC_VER_NEW >= 10000
# define _LIBCPP_GCC_SUPPORTS_IS_CONSTRUCTIBLE
#endif

#if !defined(_LIBCPP_CXX03_LANG) && !__has_feature(is_constructible) && !defined(_LIBCPP_GCC_SUPPORTS_IS_CONSTRUCTIBLE)

template <class _Tp, class... _Args>
struct __libcpp_is_constructible;

template <class _To, class _From>
struct __is_invalid_base_to_derived_cast {
  static_assert(is_reference<_To>::value, "Wrong specialization");
  using _RawFrom = __uncvref_t<_From>;
  using _RawTo = __uncvref_t<_To>;
  static const bool value = _And<
        _IsNotSame<_RawFrom, _RawTo>,
        is_base_of<_RawFrom, _RawTo>,
        _Not<__libcpp_is_constructible<_RawTo, _From>>
  >::value;
};

template <class _To, class _From>
struct __is_invalid_lvalue_to_rvalue_cast : false_type {
  static_assert(is_reference<_To>::value, "Wrong specialization");
};

template <class _ToRef, class _FromRef>
struct __is_invalid_lvalue_to_rvalue_cast<_ToRef&&, _FromRef&> {
  using _RawFrom = __uncvref_t<_FromRef>;
  using _RawTo = __uncvref_t<_ToRef>;
  static const bool value = _And<
      _Not<is_function<_RawTo>>,
      _Or<
        _IsSame<_RawFrom, _RawTo>,
        is_base_of<_RawTo, _RawFrom>>
    >::value;
};

struct __is_constructible_helper
{
    template <class _To>
    static void __eat(_To);

    // This overload is needed to work around a Clang bug that disallows
    // static_cast<T&&>(e) for non-reference-compatible types.
    // Example: static_cast<int&&>(declval<double>());
    // NOTE: The static_cast implementation below is required to support
    //  classes with explicit conversion operators.
    template <class _To, class _From,
              class = decltype(__eat<_To>(_VSTD::declval<_From>()))>
    static true_type __test_cast(int);

    template <class _To, class _From,
              class = decltype(static_cast<_To>(_VSTD::declval<_From>()))>
    static integral_constant<bool,
        !__is_invalid_base_to_derived_cast<_To, _From>::value &&
        !__is_invalid_lvalue_to_rvalue_cast<_To, _From>::value
    > __test_cast(long);

    template <class, class>
    static false_type __test_cast(...);

    template <class _Tp, class ..._Args,
        class = decltype(_Tp(_VSTD::declval<_Args>()...))>
    static true_type __test_nary(int);
    template <class _Tp, class...>
    static false_type __test_nary(...);

    template <class _Tp, class _A0, class = decltype(::new _Tp(_VSTD::declval<_A0>()))>
    static is_destructible<_Tp> __test_unary(int);
    template <class, class>
    static false_type __test_unary(...);
};

template <class _Tp, bool = is_void<_Tp>::value>
struct __is_default_constructible
    : decltype(__is_constructible_helper::__test_nary<_Tp>(0))
{};

template <class _Tp>
struct __is_default_constructible<_Tp, true> : false_type {};

template <class _Tp>
struct __is_default_constructible<_Tp[], false> : false_type {};

template <class _Tp, size_t _Nx>
struct __is_default_constructible<_Tp[_Nx], false>
    : __is_default_constructible<typename remove_all_extents<_Tp>::type>  {};

template <class _Tp, class... _Args>
struct __libcpp_is_constructible
{
  static_assert(sizeof...(_Args) > 1, "Wrong specialization");
  typedef decltype(__is_constructible_helper::__test_nary<_Tp, _Args...>(0))
      type;
};

template <class _Tp>
struct __libcpp_is_constructible<_Tp> : __is_default_constructible<_Tp> {};

template <class _Tp, class _A0>
struct __libcpp_is_constructible<_Tp, _A0>
    : public decltype(__is_constructible_helper::__test_unary<_Tp, _A0>(0))
{};

template <class _Tp, class _A0>
struct __libcpp_is_constructible<_Tp&, _A0>
    : public decltype(__is_constructible_helper::
    __test_cast<_Tp&, _A0>(0))
{};

template <class _Tp, class _A0>
struct __libcpp_is_constructible<_Tp&&, _A0>
    : public decltype(__is_constructible_helper::
    __test_cast<_Tp&&, _A0>(0))
{};

#endif

#if __has_feature(is_constructible) || defined(_LIBCPP_GCC_SUPPORTS_IS_CONSTRUCTIBLE)
template <class _Tp, class ..._Args>
struct _LIBCPP_TEMPLATE_VIS is_constructible
    : public integral_constant<bool, __is_constructible(_Tp, _Args...)>
    {};
#else
template <class _Tp, class... _Args>
struct _LIBCPP_TEMPLATE_VIS is_constructible
    : public __libcpp_is_constructible<_Tp, _Args...>::type {};
#endif

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, class ..._Args>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_constructible_v
    = is_constructible<_Tp, _Args...>::value;
#endif

// is_default_constructible

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_default_constructible
    : public is_constructible<_Tp>
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_default_constructible_v
    = is_default_constructible<_Tp>::value;
#endif

#ifndef _LIBCPP_CXX03_LANG
// First of all, we can't implement this check in C++03 mode because the {}
// default initialization syntax isn't valid.
// Second, we implement the trait in a funny manner with two defaulted template
// arguments to workaround Clang's PR43454.
template <class _Tp>
void __test_implicit_default_constructible(_Tp);

template <class _Tp, class = void, bool = is_default_constructible<_Tp>::value>
struct __is_implicitly_default_constructible
    : false_type
{ };

template <class _Tp>
struct __is_implicitly_default_constructible<_Tp, decltype(__test_implicit_default_constructible<_Tp const&>({})), true>
    : true_type
{ };

template <class _Tp>
struct __is_implicitly_default_constructible<_Tp, decltype(__test_implicit_default_constructible<_Tp const&>({})), false>
    : false_type
{ };
#endif // !C++03

// is_copy_constructible

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_copy_constructible
    : public is_constructible<_Tp,
                  typename add_lvalue_reference<typename add_const<_Tp>::type>::type> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_copy_constructible_v
    = is_copy_constructible<_Tp>::value;
#endif

// is_move_constructible

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_move_constructible
    : public is_constructible<_Tp, typename add_rvalue_reference<_Tp>::type>
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_move_constructible_v
    = is_move_constructible<_Tp>::value;
#endif

// is_trivially_constructible

#if __has_feature(is_trivially_constructible) || _GNUC_VER >= 501

template <class _Tp, class... _Args>
struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible
    : integral_constant<bool, __is_trivially_constructible(_Tp, _Args...)>
{
};

#else  // !__has_feature(is_trivially_constructible)

template <class _Tp, class... _Args>
struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible
    : false_type
{
};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible<_Tp>
#if __has_feature(has_trivial_constructor) || defined(_LIBCPP_COMPILER_GCC)
    : integral_constant<bool, __has_trivial_constructor(_Tp)>
#else
    : integral_constant<bool, is_scalar<_Tp>::value>
#endif
{
};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible<_Tp, _Tp&&>
    : integral_constant<bool, is_scalar<_Tp>::value>
{
};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible<_Tp, const _Tp&>
    : integral_constant<bool, is_scalar<_Tp>::value>
{
};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_trivially_constructible<_Tp, _Tp&>
    : integral_constant<bool, is_scalar<_Tp>::value>
{
};

#endif  // !__has_feature(is_trivially_constructible)


#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, class... _Args>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivially_constructible_v
    = is_trivially_constructible<_Tp, _Args...>::value;
#endif

// is_trivially_default_constructible

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_default_constructible
    : public is_trivially_constructible<_Tp>
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivially_default_constructible_v
    = is_trivially_default_constructible<_Tp>::value;
#endif

// is_trivially_copy_constructible

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_copy_constructible
    : public is_trivially_constructible<_Tp, typename add_lvalue_reference<const _Tp>::type>
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivially_copy_constructible_v
    = is_trivially_copy_constructible<_Tp>::value;
#endif

// is_trivially_move_constructible

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_move_constructible
    : public is_trivially_constructible<_Tp, typename add_rvalue_reference<_Tp>::type>
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivially_move_constructible_v
    = is_trivially_move_constructible<_Tp>::value;
#endif

// is_trivially_assignable

#if __has_feature(is_trivially_assignable) || _GNUC_VER >= 501

template <class _Tp, class _Arg>
struct is_trivially_assignable
    : integral_constant<bool, __is_trivially_assignable(_Tp, _Arg)>
{
};

#else  // !__has_feature(is_trivially_assignable)

template <class _Tp, class _Arg>
struct is_trivially_assignable
    : public false_type {};

template <class _Tp>
struct is_trivially_assignable<_Tp&, _Tp>
    : integral_constant<bool, is_scalar<_Tp>::value> {};

template <class _Tp>
struct is_trivially_assignable<_Tp&, _Tp&>
    : integral_constant<bool, is_scalar<_Tp>::value> {};

template <class _Tp>
struct is_trivially_assignable<_Tp&, const _Tp&>
    : integral_constant<bool, is_scalar<_Tp>::value> {};

template <class _Tp>
struct is_trivially_assignable<_Tp&, _Tp&&>
    : integral_constant<bool, is_scalar<_Tp>::value> {};

#endif  // !__has_feature(is_trivially_assignable)

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, class _Arg>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivially_assignable_v
    = is_trivially_assignable<_Tp, _Arg>::value;
#endif

// is_trivially_copy_assignable

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_copy_assignable
    : public is_trivially_assignable<typename add_lvalue_reference<_Tp>::type,
                  typename add_lvalue_reference<typename add_const<_Tp>::type>::type> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivially_copy_assignable_v
    = is_trivially_copy_assignable<_Tp>::value;
#endif

// is_trivially_move_assignable

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_move_assignable
    : public is_trivially_assignable<typename add_lvalue_reference<_Tp>::type,
                                     typename add_rvalue_reference<_Tp>::type>
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivially_move_assignable_v
    = is_trivially_move_assignable<_Tp>::value;
#endif

// is_trivially_destructible

#if __has_keyword(__is_trivially_destructible)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_destructible
    : public integral_constant<bool, __is_trivially_destructible(_Tp)> {};

#elif __has_feature(has_trivial_destructor) || defined(_LIBCPP_COMPILER_GCC)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_destructible
    : public integral_constant<bool, is_destructible<_Tp>::value && __has_trivial_destructor(_Tp)> {};

#else

template <class _Tp> struct __libcpp_trivial_destructor
    : public integral_constant<bool, is_scalar<_Tp>::value ||
                                     is_reference<_Tp>::value> {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_destructible
    : public __libcpp_trivial_destructor<typename remove_all_extents<_Tp>::type> {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_destructible<_Tp[]>
    : public false_type {};

#endif

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivially_destructible_v
    = is_trivially_destructible<_Tp>::value;
#endif

// is_nothrow_constructible

#if __has_keyword(__is_nothrow_constructible)

template <class _Tp, class... _Args>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_constructible
    : public integral_constant<bool, __is_nothrow_constructible(_Tp, _Args...)> {};

#else

template <bool, bool, class _Tp, class... _Args> struct __libcpp_is_nothrow_constructible;

template <class _Tp, class... _Args>
struct __libcpp_is_nothrow_constructible</*is constructible*/true, /*is reference*/false, _Tp, _Args...>
    : public integral_constant<bool, noexcept(_Tp(declval<_Args>()...))>
{
};

template <class _Tp>
void __implicit_conversion_to(_Tp) noexcept { }

template <class _Tp, class _Arg>
struct __libcpp_is_nothrow_constructible</*is constructible*/true, /*is reference*/true, _Tp, _Arg>
    : public integral_constant<bool, noexcept(_VSTD::__implicit_conversion_to<_Tp>(declval<_Arg>()))>
{
};

template <class _Tp, bool _IsReference, class... _Args>
struct __libcpp_is_nothrow_constructible</*is constructible*/false, _IsReference, _Tp, _Args...>
    : public false_type
{
};

template <class _Tp, class... _Args>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_constructible
    : __libcpp_is_nothrow_constructible<is_constructible<_Tp, _Args...>::value, is_reference<_Tp>::value, _Tp, _Args...>
{
};

template <class _Tp, size_t _Ns>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_constructible<_Tp[_Ns]>
    : __libcpp_is_nothrow_constructible<is_constructible<_Tp>::value, is_reference<_Tp>::value, _Tp>
{
};

#endif  // _LIBCPP_HAS_NO_NOEXCEPT


#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, class ..._Args>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_nothrow_constructible_v
    = is_nothrow_constructible<_Tp, _Args...>::value;
#endif

// is_nothrow_default_constructible

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_default_constructible
    : public is_nothrow_constructible<_Tp>
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_nothrow_default_constructible_v
    = is_nothrow_default_constructible<_Tp>::value;
#endif

// is_nothrow_copy_constructible

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_copy_constructible
    : public is_nothrow_constructible<_Tp,
                  typename add_lvalue_reference<typename add_const<_Tp>::type>::type> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_nothrow_copy_constructible_v
    = is_nothrow_copy_constructible<_Tp>::value;
#endif

// is_nothrow_move_constructible

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_move_constructible
    : public is_nothrow_constructible<_Tp, typename add_rvalue_reference<_Tp>::type>
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_nothrow_move_constructible_v
    = is_nothrow_move_constructible<_Tp>::value;
#endif

// is_nothrow_assignable

#if __has_keyword(__is_nothrow_assignable)

template <class _Tp, class _Arg>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_assignable
    : public integral_constant<bool, __is_nothrow_assignable(_Tp, _Arg)> {};

#else

template <bool, class _Tp, class _Arg> struct __libcpp_is_nothrow_assignable;

template <class _Tp, class _Arg>
struct __libcpp_is_nothrow_assignable<false, _Tp, _Arg>
    : public false_type
{
};

template <class _Tp, class _Arg>
struct __libcpp_is_nothrow_assignable<true, _Tp, _Arg>
    : public integral_constant<bool, noexcept(_VSTD::declval<_Tp>() = _VSTD::declval<_Arg>()) >
{
};

template <class _Tp, class _Arg>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_assignable
    : public __libcpp_is_nothrow_assignable<is_assignable<_Tp, _Arg>::value, _Tp, _Arg>
{
};

#endif  // _LIBCPP_HAS_NO_NOEXCEPT

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp, class _Arg>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_nothrow_assignable_v
    = is_nothrow_assignable<_Tp, _Arg>::value;
#endif

// is_nothrow_copy_assignable

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_copy_assignable
    : public is_nothrow_assignable<typename add_lvalue_reference<_Tp>::type,
                  typename add_lvalue_reference<typename add_const<_Tp>::type>::type> {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_nothrow_copy_assignable_v
    = is_nothrow_copy_assignable<_Tp>::value;
#endif

// is_nothrow_move_assignable

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_move_assignable
    : public is_nothrow_assignable<typename add_lvalue_reference<_Tp>::type,
                                     typename add_rvalue_reference<_Tp>::type>
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_nothrow_move_assignable_v
    = is_nothrow_move_assignable<_Tp>::value;
#endif

// is_nothrow_destructible

#if !defined(_LIBCPP_CXX03_LANG)

template <bool, class _Tp> struct __libcpp_is_nothrow_destructible;

template <class _Tp>
struct __libcpp_is_nothrow_destructible<false, _Tp>
    : public false_type
{
};

template <class _Tp>
struct __libcpp_is_nothrow_destructible<true, _Tp>
    : public integral_constant<bool, noexcept(_VSTD::declval<_Tp>().~_Tp()) >
{
};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible
    : public __libcpp_is_nothrow_destructible<is_destructible<_Tp>::value, _Tp>
{
};

template <class _Tp, size_t _Ns>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible<_Tp[_Ns]>
    : public is_nothrow_destructible<_Tp>
{
};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible<_Tp&>
    : public true_type
{
};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible<_Tp&&>
    : public true_type
{
};

#else

template <class _Tp> struct __libcpp_nothrow_destructor
    : public integral_constant<bool, is_scalar<_Tp>::value ||
                                     is_reference<_Tp>::value> {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible
    : public __libcpp_nothrow_destructor<typename remove_all_extents<_Tp>::type> {};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_destructible<_Tp[]>
    : public false_type {};

#endif

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_nothrow_destructible_v
    = is_nothrow_destructible<_Tp>::value;
#endif

// is_pod

#if __has_feature(is_pod) || defined(_LIBCPP_COMPILER_GCC)

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_pod
    : public integral_constant<bool, __is_pod(_Tp)> {};

#else

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_pod
    : public integral_constant<bool, is_trivially_default_constructible<_Tp>::value   &&
                                     is_trivially_copy_constructible<_Tp>::value      &&
                                     is_trivially_copy_assignable<_Tp>::value    &&
                                     is_trivially_destructible<_Tp>::value> {};

#endif

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_pod_v
    = is_pod<_Tp>::value;
#endif

// is_literal_type;

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_literal_type
    : public integral_constant<bool, __is_literal_type(_Tp)>
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_literal_type_v
    = is_literal_type<_Tp>::value;
#endif

// is_standard_layout;

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_standard_layout
#if __has_feature(is_standard_layout) || defined(_LIBCPP_COMPILER_GCC)
    : public integral_constant<bool, __is_standard_layout(_Tp)>
#else
    : integral_constant<bool, is_scalar<typename remove_all_extents<_Tp>::type>::value>
#endif
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_standard_layout_v
    = is_standard_layout<_Tp>::value;
#endif

// is_trivially_copyable;

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivially_copyable
#if __has_feature(is_trivially_copyable)
    : public integral_constant<bool, __is_trivially_copyable(_Tp)>
#elif _GNUC_VER >= 501
    : public integral_constant<bool, !is_volatile<_Tp>::value && __is_trivially_copyable(_Tp)>
#else
    : integral_constant<bool, is_scalar<typename remove_all_extents<_Tp>::type>::value>
#endif
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivially_copyable_v
    = is_trivially_copyable<_Tp>::value;
#endif

// is_trivial;

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_trivial
#if __has_feature(is_trivial) || defined(_LIBCPP_COMPILER_GCC)
    : public integral_constant<bool, __is_trivial(_Tp)>
#else
    : integral_constant<bool, is_trivially_copyable<_Tp>::value &&
                                 is_trivially_default_constructible<_Tp>::value>
#endif
    {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_trivial_v
    = is_trivial<_Tp>::value;
#endif

template <class _Tp> struct __is_reference_wrapper_impl : public false_type {};
template <class _Tp> struct __is_reference_wrapper_impl<reference_wrapper<_Tp> > : public true_type {};
template <class _Tp> struct __is_reference_wrapper
    : public __is_reference_wrapper_impl<typename remove_cv<_Tp>::type> {};

#ifndef _LIBCPP_CXX03_LANG

template <class _Fp, class _A0,
         class _DecayFp = typename decay<_Fp>::type,
         class _DecayA0 = typename decay<_A0>::type,
         class _ClassT = typename __member_pointer_class_type<_DecayFp>::type>
using __enable_if_bullet1 = typename enable_if
    <
        is_member_function_pointer<_DecayFp>::value
        && is_base_of<_ClassT, _DecayA0>::value
    >::type;

template <class _Fp, class _A0,
         class _DecayFp = typename decay<_Fp>::type,
         class _DecayA0 = typename decay<_A0>::type>
using __enable_if_bullet2 = typename enable_if
    <
        is_member_function_pointer<_DecayFp>::value
        && __is_reference_wrapper<_DecayA0>::value
    >::type;

template <class _Fp, class _A0,
         class _DecayFp = typename decay<_Fp>::type,
         class _DecayA0 = typename decay<_A0>::type,
         class _ClassT = typename __member_pointer_class_type<_DecayFp>::type>
using __enable_if_bullet3 = typename enable_if
    <
        is_member_function_pointer<_DecayFp>::value
        && !is_base_of<_ClassT, _DecayA0>::value
        && !__is_reference_wrapper<_DecayA0>::value
    >::type;

template <class _Fp, class _A0,
         class _DecayFp = typename decay<_Fp>::type,
         class _DecayA0 = typename decay<_A0>::type,
         class _ClassT = typename __member_pointer_class_type<_DecayFp>::type>
using __enable_if_bullet4 = typename enable_if
    <
        is_member_object_pointer<_DecayFp>::value
        && is_base_of<_ClassT, _DecayA0>::value
    >::type;

template <class _Fp, class _A0,
         class _DecayFp = typename decay<_Fp>::type,
         class _DecayA0 = typename decay<_A0>::type>
using __enable_if_bullet5 = typename enable_if
    <
        is_member_object_pointer<_DecayFp>::value
        && __is_reference_wrapper<_DecayA0>::value
    >::type;

template <class _Fp, class _A0,
         class _DecayFp = typename decay<_Fp>::type,
         class _DecayA0 = typename decay<_A0>::type,
         class _ClassT = typename __member_pointer_class_type<_DecayFp>::type>
using __enable_if_bullet6 = typename enable_if
    <
        is_member_object_pointer<_DecayFp>::value
        && !is_base_of<_ClassT, _DecayA0>::value
        && !__is_reference_wrapper<_DecayA0>::value
    >::type;

// __invoke forward declarations

// fall back - none of the bullets

#define _LIBCPP_INVOKE_RETURN(...) \
    noexcept(noexcept(__VA_ARGS__)) -> decltype(__VA_ARGS__) \
    { return __VA_ARGS__; }

template <class ..._Args>
auto __invoke(__any, _Args&& ...__args) -> __nat;

template <class ..._Args>
auto __invoke_constexpr(__any, _Args&& ...__args) -> __nat;

// bullets 1, 2 and 3

template <class _Fp, class _A0, class ..._Args,
          class = __enable_if_bullet1<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR_AFTER_CXX17 auto
__invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
_LIBCPP_INVOKE_RETURN((_VSTD::forward<_A0>(__a0).*__f)(_VSTD::forward<_Args>(__args)...))

template <class _Fp, class _A0, class ..._Args,
          class = __enable_if_bullet1<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR auto
__invoke_constexpr(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
_LIBCPP_INVOKE_RETURN((_VSTD::forward<_A0>(__a0).*__f)(_VSTD::forward<_Args>(__args)...))

template <class _Fp, class _A0, class ..._Args,
          class = __enable_if_bullet2<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR_AFTER_CXX17 auto
__invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
_LIBCPP_INVOKE_RETURN((__a0.get().*__f)(_VSTD::forward<_Args>(__args)...))

template <class _Fp, class _A0, class ..._Args,
          class = __enable_if_bullet2<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR auto
__invoke_constexpr(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
_LIBCPP_INVOKE_RETURN((__a0.get().*__f)(_VSTD::forward<_Args>(__args)...))

template <class _Fp, class _A0, class ..._Args,
          class = __enable_if_bullet3<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR_AFTER_CXX17 auto
__invoke(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
_LIBCPP_INVOKE_RETURN(((*_VSTD::forward<_A0>(__a0)).*__f)(_VSTD::forward<_Args>(__args)...))

template <class _Fp, class _A0, class ..._Args,
          class = __enable_if_bullet3<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR auto
__invoke_constexpr(_Fp&& __f, _A0&& __a0, _Args&& ...__args)
_LIBCPP_INVOKE_RETURN(((*_VSTD::forward<_A0>(__a0)).*__f)(_VSTD::forward<_Args>(__args)...))

// bullets 4, 5 and 6

template <class _Fp, class _A0,
          class = __enable_if_bullet4<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR_AFTER_CXX17 auto
__invoke(_Fp&& __f, _A0&& __a0)
_LIBCPP_INVOKE_RETURN(_VSTD::forward<_A0>(__a0).*__f)

template <class _Fp, class _A0,
          class = __enable_if_bullet4<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR auto
__invoke_constexpr(_Fp&& __f, _A0&& __a0)
_LIBCPP_INVOKE_RETURN(_VSTD::forward<_A0>(__a0).*__f)

template <class _Fp, class _A0,
          class = __enable_if_bullet5<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR_AFTER_CXX17 auto
__invoke(_Fp&& __f, _A0&& __a0)
_LIBCPP_INVOKE_RETURN(__a0.get().*__f)

template <class _Fp, class _A0,
          class = __enable_if_bullet5<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR auto
__invoke_constexpr(_Fp&& __f, _A0&& __a0)
_LIBCPP_INVOKE_RETURN(__a0.get().*__f)

template <class _Fp, class _A0,
          class = __enable_if_bullet6<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR_AFTER_CXX17 auto
__invoke(_Fp&& __f, _A0&& __a0)
_LIBCPP_INVOKE_RETURN((*_VSTD::forward<_A0>(__a0)).*__f)

template <class _Fp, class _A0,
          class = __enable_if_bullet6<_Fp, _A0>>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR auto
__invoke_constexpr(_Fp&& __f, _A0&& __a0)
_LIBCPP_INVOKE_RETURN((*_VSTD::forward<_A0>(__a0)).*__f)

// bullet 7

template <class _Fp, class ..._Args>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR_AFTER_CXX17 auto
__invoke(_Fp&& __f, _Args&& ...__args)
_LIBCPP_INVOKE_RETURN(_VSTD::forward<_Fp>(__f)(_VSTD::forward<_Args>(__args)...))

template <class _Fp, class ..._Args>
inline _LIBCPP_INLINE_VISIBILITY
_LIBCPP_CONSTEXPR auto
__invoke_constexpr(_Fp&& __f, _Args&& ...__args)
_LIBCPP_INVOKE_RETURN(_VSTD::forward<_Fp>(__f)(_VSTD::forward<_Args>(__args)...))

#undef _LIBCPP_INVOKE_RETURN

// __invokable
template <class _Ret, class _Fp, class ..._Args>
struct __invokable_r
{
  template <class _XFp, class ..._XArgs>
  static auto __try_call(int) -> decltype(
    _VSTD::__invoke(_VSTD::declval<_XFp>(), _VSTD::declval<_XArgs>()...));
  template <class _XFp, class ..._XArgs>
  static __nat __try_call(...);

  // FIXME: Check that _Ret, _Fp, and _Args... are all complete types, cv void,
  // or incomplete array types as required by the standard.
  using _Result = decltype(__try_call<_Fp, _Args...>(0));

  using type =
  typename conditional<
      _IsNotSame<_Result, __nat>::value,
      typename conditional<
          is_void<_Ret>::value,
          true_type,
          is_convertible<_Result, _Ret>
      >::type,
      false_type
  >::type;
  static const bool value = type::value;
};
template <class _Fp, class ..._Args>
using __invokable = __invokable_r<void, _Fp, _Args...>;

template <bool _IsInvokable, bool _IsCVVoid, class _Ret, class _Fp, class ..._Args>
struct __nothrow_invokable_r_imp {
  static const bool value = false;
};

template <class _Ret, class _Fp, class ..._Args>
struct __nothrow_invokable_r_imp<true, false, _Ret, _Fp, _Args...>
{
    typedef __nothrow_invokable_r_imp _ThisT;

    template <class _Tp>
    static void __test_noexcept(_Tp) noexcept;

    static const bool value = noexcept(_ThisT::__test_noexcept<_Ret>(
        _VSTD::__invoke(_VSTD::declval<_Fp>(), _VSTD::declval<_Args>()...)));
};

template <class _Ret, class _Fp, class ..._Args>
struct __nothrow_invokable_r_imp<true, true, _Ret, _Fp, _Args...>
{
    static const bool value = noexcept(
        _VSTD::__invoke(_VSTD::declval<_Fp>(), _VSTD::declval<_Args>()...));
};

template <class _Ret, class _Fp, class ..._Args>
using __nothrow_invokable_r =
    __nothrow_invokable_r_imp<
            __invokable_r<_Ret, _Fp, _Args...>::value,
            is_void<_Ret>::value,
            _Ret, _Fp, _Args...
    >;

template <class _Fp, class ..._Args>
using __nothrow_invokable =
    __nothrow_invokable_r_imp<
            __invokable<_Fp, _Args...>::value,
            true, void, _Fp, _Args...
    >;

template <class _Fp, class ..._Args>
struct __invoke_of
    : public enable_if<
        __invokable<_Fp, _Args...>::value,
        typename __invokable_r<void, _Fp, _Args...>::_Result>
{
};

#endif // _LIBCPP_CXX03_LANG

// result_of

template <class _Callable> class result_of;

#ifndef _LIBCPP_CXX03_LANG

template <class _Fp, class ..._Args>
class _LIBCPP_TEMPLATE_VIS result_of<_Fp(_Args...)>
    : public __invoke_of<_Fp, _Args...>
{
};

#else // C++03

template <class _Fn, bool, bool>
class __result_of
{
};

template <class _Fn, class ..._Args>
class __result_of<_Fn(_Args...), true, false>
{
public:
    typedef decltype(declval<_Fn>()(declval<_Args>()...)) type;
};

template <class _MP, class _Tp, bool _IsMemberFunctionPtr>
struct __result_of_mp;

// member function pointer

template <class _MP, class _Tp>
struct __result_of_mp<_MP, _Tp, true>
{
    using type = typename __member_pointer_traits<_MP>::_ReturnType;
};

// member data pointer

template <class _MP, class _Tp, bool>
struct __result_of_mdp;

template <class _Rp, class _Class, class _Tp>
struct __result_of_mdp<_Rp _Class::*, _Tp, false>
{
    using type = typename __apply_cv<decltype(*_VSTD::declval<_Tp>()), _Rp>::type&;
};

template <class _Rp, class _Class, class _Tp>
struct __result_of_mdp<_Rp _Class::*, _Tp, true>
{
    using type = typename __apply_cv<_Tp, _Rp>::type&;
};

template <class _Rp, class _Class, class _Tp>
struct __result_of_mp<_Rp _Class::*, _Tp, false>
    : public __result_of_mdp<_Rp _Class::*, _Tp,
            is_base_of<_Class, typename remove_reference<_Tp>::type>::value>
{
};

template <class _Fn, class _Tp>
class __result_of<_Fn(_Tp), false, true>  // _Fn must be member pointer
    : public __result_of_mp<typename remove_reference<_Fn>::type,
                            _Tp,
                            is_member_function_pointer<typename remove_reference<_Fn>::type>::value>
{
};

template <class _Fn, class _Tp, class ..._Args>
class __result_of<_Fn(_Tp, _Args...), false, true>  // _Fn must be member pointer
    : public __result_of_mp<typename remove_reference<_Fn>::type,
                            _Tp,
                            is_member_function_pointer<typename remove_reference<_Fn>::type>::value>
{
};

template <class _Fn, class ..._Args>
class _LIBCPP_TEMPLATE_VIS result_of<_Fn(_Args...)>
    : public __result_of<_Fn(_Args...),
                         is_class<typename remove_reference<_Fn>::type>::value ||
                         is_function<typename remove_pointer<typename remove_reference<_Fn>::type>::type>::value,
                         is_member_pointer<typename remove_reference<_Fn>::type>::value
                        >
{
};

#endif  // C++03

#if _LIBCPP_STD_VER > 11
template <class _Tp> using result_of_t = typename result_of<_Tp>::type;
#endif

#if _LIBCPP_STD_VER > 14

// invoke_result

template <class _Fn, class... _Args>
struct _LIBCPP_TEMPLATE_VIS invoke_result
    : __invoke_of<_Fn, _Args...>
{
};

template <class _Fn, class... _Args>
using invoke_result_t = typename invoke_result<_Fn, _Args...>::type;

// is_invocable

template <class _Fn, class ..._Args>
struct _LIBCPP_TEMPLATE_VIS is_invocable
    : integral_constant<bool, __invokable<_Fn, _Args...>::value> {};

template <class _Ret, class _Fn, class ..._Args>
struct _LIBCPP_TEMPLATE_VIS is_invocable_r
    : integral_constant<bool, __invokable_r<_Ret, _Fn, _Args...>::value> {};

template <class _Fn, class ..._Args>
_LIBCPP_INLINE_VAR constexpr bool is_invocable_v
    = is_invocable<_Fn, _Args...>::value;

template <class _Ret, class _Fn, class ..._Args>
_LIBCPP_INLINE_VAR constexpr bool is_invocable_r_v
    = is_invocable_r<_Ret, _Fn, _Args...>::value;

// is_nothrow_invocable

template <class _Fn, class ..._Args>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_invocable
    : integral_constant<bool, __nothrow_invokable<_Fn, _Args...>::value> {};

template <class _Ret, class _Fn, class ..._Args>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_invocable_r
    : integral_constant<bool, __nothrow_invokable_r<_Ret, _Fn, _Args...>::value> {};

template <class _Fn, class ..._Args>
_LIBCPP_INLINE_VAR constexpr bool is_nothrow_invocable_v
    = is_nothrow_invocable<_Fn, _Args...>::value;

template <class _Ret, class _Fn, class ..._Args>
_LIBCPP_INLINE_VAR constexpr bool is_nothrow_invocable_r_v
    = is_nothrow_invocable_r<_Ret, _Fn, _Args...>::value;

#endif // _LIBCPP_STD_VER > 14

template <class _Tp> struct __is_swappable;
template <class _Tp> struct __is_nothrow_swappable;

// swap, swap_ranges

template <class _ForwardIterator1, class _ForwardIterator2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
_ForwardIterator2
swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2);

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY
#ifndef _LIBCPP_CXX03_LANG
typename enable_if
<
    is_move_constructible<_Tp>::value &&
    is_move_assignable<_Tp>::value
>::type
#else
void
#endif
_LIBCPP_CONSTEXPR_AFTER_CXX17
swap(_Tp& __x, _Tp& __y) _NOEXCEPT_(is_nothrow_move_constructible<_Tp>::value &&
                                    is_nothrow_move_assignable<_Tp>::value)
{
    _Tp __t(_VSTD::move(__x));
    __x = _VSTD::move(__y);
    __y = _VSTD::move(__t);
}

template<class _Tp, size_t _Np>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
typename enable_if<
    __is_swappable<_Tp>::value
>::type
swap(_Tp (&__a)[_Np], _Tp (&__b)[_Np]) _NOEXCEPT_(__is_nothrow_swappable<_Tp>::value)
{
    _VSTD::swap_ranges(__a, __a + _Np, __b);
}

template <class _ForwardIterator1, class _ForwardIterator2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
_ForwardIterator2
swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2)
{
    for(; __first1 != __last1; ++__first1, (void) ++__first2)
        swap(*__first1, *__first2);
    return __first2;
}

// iter_swap

template <class _ForwardIterator1, class _ForwardIterator2>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
void
iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
    //                                  _NOEXCEPT_(_NOEXCEPT_(swap(*__a, *__b)))
               _NOEXCEPT_(_NOEXCEPT_(swap(*_VSTD::declval<_ForwardIterator1>(),
                                          *_VSTD::declval<_ForwardIterator2>())))
{
    swap(*__a, *__b);
}

// __swappable

namespace __detail
{
// ALL generic swap overloads MUST already have a declaration available at this point.

template <class _Tp, class _Up = _Tp,
          bool _NotVoid = !is_void<_Tp>::value && !is_void<_Up>::value>
struct __swappable_with
{
    template <class _LHS, class _RHS>
    static decltype(swap(_VSTD::declval<_LHS>(), _VSTD::declval<_RHS>()))
    __test_swap(int);
    template <class, class>
    static __nat __test_swap(long);

    // Extra parens are needed for the C++03 definition of decltype.
    typedef decltype((__test_swap<_Tp, _Up>(0))) __swap1;
    typedef decltype((__test_swap<_Up, _Tp>(0))) __swap2;

    static const bool value = _IsNotSame<__swap1, __nat>::value
                           && _IsNotSame<__swap2, __nat>::value;
};

template <class _Tp, class _Up>
struct __swappable_with<_Tp, _Up,  false> : false_type {};

template <class _Tp, class _Up = _Tp, bool _Swappable = __swappable_with<_Tp, _Up>::value>
struct __nothrow_swappable_with {
  static const bool value =
#ifndef _LIBCPP_HAS_NO_NOEXCEPT
      noexcept(swap(_VSTD::declval<_Tp>(), _VSTD::declval<_Up>()))
  &&  noexcept(swap(_VSTD::declval<_Up>(), _VSTD::declval<_Tp>()));
#else
      false;
#endif
};

template <class _Tp, class _Up>
struct __nothrow_swappable_with<_Tp, _Up, false> : false_type {};

}  // __detail

template <class _Tp>
struct __is_swappable
    : public integral_constant<bool, __detail::__swappable_with<_Tp&>::value>
{
};

template <class _Tp>
struct __is_nothrow_swappable
    : public integral_constant<bool, __detail::__nothrow_swappable_with<_Tp&>::value>
{
};

#if _LIBCPP_STD_VER > 14

template <class _Tp, class _Up>
struct _LIBCPP_TEMPLATE_VIS is_swappable_with
    : public integral_constant<bool, __detail::__swappable_with<_Tp, _Up>::value>
{
};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_swappable
    : public conditional<
        __is_referenceable<_Tp>::value,
        is_swappable_with<
            typename add_lvalue_reference<_Tp>::type,
            typename add_lvalue_reference<_Tp>::type>,
        false_type
    >::type
{
};

template <class _Tp, class _Up>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_swappable_with
    : public integral_constant<bool, __detail::__nothrow_swappable_with<_Tp, _Up>::value>
{
};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_nothrow_swappable
    : public conditional<
        __is_referenceable<_Tp>::value,
        is_nothrow_swappable_with<
            typename add_lvalue_reference<_Tp>::type,
            typename add_lvalue_reference<_Tp>::type>,
        false_type
    >::type
{
};

template <class _Tp, class _Up>
_LIBCPP_INLINE_VAR constexpr bool is_swappable_with_v
    = is_swappable_with<_Tp, _Up>::value;

template <class _Tp>
_LIBCPP_INLINE_VAR constexpr bool is_swappable_v
    = is_swappable<_Tp>::value;

template <class _Tp, class _Up>
_LIBCPP_INLINE_VAR constexpr bool is_nothrow_swappable_with_v
    = is_nothrow_swappable_with<_Tp, _Up>::value;

template <class _Tp>
_LIBCPP_INLINE_VAR constexpr bool is_nothrow_swappable_v
    = is_nothrow_swappable<_Tp>::value;

#endif // _LIBCPP_STD_VER > 14

template <class _Tp, bool = is_enum<_Tp>::value> struct __underlying_type_impl;

template <class _Tp>
struct __underlying_type_impl<_Tp, false> {};

template <class _Tp>
struct __underlying_type_impl<_Tp, true>
{
    typedef __underlying_type(_Tp) type;
};

template <class _Tp>
struct underlying_type : __underlying_type_impl<_Tp, is_enum<_Tp>::value> {};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using underlying_type_t = typename underlying_type<_Tp>::type;
#endif

template <class _Tp, bool = is_enum<_Tp>::value>
struct __sfinae_underlying_type
{
    typedef typename underlying_type<_Tp>::type type;
    typedef decltype(((type)1) + 0) __promoted_type;
};

template <class _Tp>
struct __sfinae_underlying_type<_Tp, false> {};

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
int __convert_to_integral(int __val) { return __val; }

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
unsigned __convert_to_integral(unsigned __val) { return __val; }

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
long __convert_to_integral(long __val) { return __val; }

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
unsigned long __convert_to_integral(unsigned long __val) { return __val; }

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
long long __convert_to_integral(long long __val) { return __val; }

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
unsigned long long __convert_to_integral(unsigned long long __val) {return __val; }

template<typename _Fp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
typename enable_if<is_floating_point<_Fp>::value, long long>::type
 __convert_to_integral(_Fp __val) { return __val; }

#ifndef _LIBCPP_HAS_NO_INT128
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
__int128_t __convert_to_integral(__int128_t __val) { return __val; }

inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
__uint128_t __convert_to_integral(__uint128_t __val) { return __val; }
#endif

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
typename __sfinae_underlying_type<_Tp>::__promoted_type
__convert_to_integral(_Tp __val) { return __val; }

#ifndef _LIBCPP_CXX03_LANG

template <class _Tp>
struct __has_operator_addressof_member_imp
{
    template <class _Up>
        static auto __test(int)
            -> typename __select_2nd<decltype(_VSTD::declval<_Up>().operator&()), true_type>::type;
    template <class>
        static auto __test(long) -> false_type;

    static const bool value = decltype(__test<_Tp>(0))::value;
};

template <class _Tp>
struct __has_operator_addressof_free_imp
{
    template <class _Up>
        static auto __test(int)
            -> typename __select_2nd<decltype(operator&(_VSTD::declval<_Up>())), true_type>::type;
    template <class>
        static auto __test(long) -> false_type;

    static const bool value = decltype(__test<_Tp>(0))::value;
};

template <class _Tp>
struct __has_operator_addressof
    : public integral_constant<bool, __has_operator_addressof_member_imp<_Tp>::value
                                  || __has_operator_addressof_free_imp<_Tp>::value>
{};

#endif  // _LIBCPP_CXX03_LANG

// is_scoped_enum [meta.unary.prop]

#if _LIBCPP_STD_VER > 20
template <class _Tp, bool = is_enum_v<_Tp> >
struct __is_scoped_enum_helper : false_type {};

template <class _Tp>
struct __is_scoped_enum_helper<_Tp, true>
    : public bool_constant<!is_convertible_v<_Tp, underlying_type_t<_Tp> > > {};

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS is_scoped_enum
    : public __is_scoped_enum_helper<_Tp> {};

template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_scoped_enum_v =
    is_scoped_enum<_Tp>::value;
#endif

#if _LIBCPP_STD_VER > 14

template <class... _Args>
struct conjunction : _And<_Args...> {};
template<class... _Args>
_LIBCPP_INLINE_VAR constexpr bool conjunction_v
    = conjunction<_Args...>::value;

template <class... _Args>
struct disjunction : _Or<_Args...> {};
template<class... _Args>
_LIBCPP_INLINE_VAR constexpr bool disjunction_v
    = disjunction<_Args...>::value;

template <class _Tp>
struct negation : _Not<_Tp> {};
template<class _Tp>
_LIBCPP_INLINE_VAR constexpr bool negation_v
    = negation<_Tp>::value;
#endif  // _LIBCPP_STD_VER > 14

// These traits are used in __tree and __hash_table
struct __extract_key_fail_tag {};
struct __extract_key_self_tag {};
struct __extract_key_first_tag {};

template <class _ValTy, class _Key,
          class _RawValTy = typename __unconstref<_ValTy>::type>
struct __can_extract_key
    : conditional<_IsSame<_RawValTy, _Key>::value, __extract_key_self_tag,
                  __extract_key_fail_tag>::type {};

template <class _Pair, class _Key, class _First, class _Second>
struct __can_extract_key<_Pair, _Key, pair<_First, _Second> >
    : conditional<_IsSame<typename remove_const<_First>::type, _Key>::value,
                  __extract_key_first_tag, __extract_key_fail_tag>::type {};

// __can_extract_map_key uses true_type/false_type instead of the tags.
// It returns true if _Key != _ContainerValueTy (the container is a map not a set)
// and _ValTy == _Key.
template <class _ValTy, class _Key, class _ContainerValueTy,
          class _RawValTy = typename __unconstref<_ValTy>::type>
struct __can_extract_map_key
    : integral_constant<bool, _IsSame<_RawValTy, _Key>::value> {};

// This specialization returns __extract_key_fail_tag for non-map containers
// because _Key == _ContainerValueTy
template <class _ValTy, class _Key, class _RawValTy>
struct __can_extract_map_key<_ValTy, _Key, _Key, _RawValTy>
    : false_type {};

#ifndef _LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED
#if _LIBCPP_STD_VER > 17
_LIBCPP_INLINE_VISIBILITY
inline constexpr bool is_constant_evaluated() noexcept {
  return __builtin_is_constant_evaluated();
}
#endif

inline _LIBCPP_CONSTEXPR
bool __libcpp_is_constant_evaluated() _NOEXCEPT { return __builtin_is_constant_evaluated(); }
#else
inline _LIBCPP_CONSTEXPR
bool __libcpp_is_constant_evaluated() _NOEXCEPT { return false; }
#endif

template <class _CharT>
using _IsCharLikeType = _And<is_standard_layout<_CharT>, is_trivial<_CharT> >;

_LIBCPP_END_NAMESPACE_STD

#if _LIBCPP_STD_VER > 14
// std::byte
namespace std  // purposefully not versioned
{


}
#endif

#endif  // _LIBCPP_TYPE_TRAITS