include/functional

// -*- C++ -*-
//===------------------------ functional ----------------------------------===//
//
// 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_FUNCTIONAL
#define _LIBCPP_FUNCTIONAL

/*
    functional synopsis

namespace std
{

template <class Arg, class Result>
struct unary_function
{
    typedef Arg    argument_type;
    typedef Result result_type;
};

template <class Arg1, class Arg2, class Result>
struct binary_function
{
    typedef Arg1   first_argument_type;
    typedef Arg2   second_argument_type;
    typedef Result result_type;
};

template <class T>
class reference_wrapper
    : public unary_function<T1, R> // if wrapping a unary functor
    : public binary_function<T1, T2, R> // if wraping a binary functor
{
public:
    // types
    typedef T type;
    typedef see below result_type; // Not always defined

    // construct/copy/destroy
    template<class U>
      reference_wrapper(U&&);
    reference_wrapper(const reference_wrapper<T>& x) noexcept;

    // assignment
    reference_wrapper& operator=(const reference_wrapper<T>& x) noexcept;

    // access
    operator T& () const noexcept;
    T& get() const noexcept;

    // invoke
    template <class... ArgTypes>
      typename result_of<T&(ArgTypes&&...)>::type
          operator() (ArgTypes&&...) const;
};

template <class T>
  reference_wrapper(T&) -> reference_wrapper<T>;

template <class T> reference_wrapper<T> ref(T& t) noexcept;
template <class T> void ref(const T&& t) = delete;
template <class T> reference_wrapper<T> ref(reference_wrapper<T>t) noexcept;

template <class T> reference_wrapper<const T> cref(const T& t) noexcept;
template <class T> void cref(const T&& t) = delete;
template <class T> reference_wrapper<const T> cref(reference_wrapper<T> t) noexcept;

template <class T> struct unwrap_reference;                                       // since C++20
template <class T> struct unwrap_ref_decay : unwrap_reference<decay_t<T>> { };    // since C++20
template <class T> using unwrap_reference_t = typename unwrap_reference<T>::type; // since C++20
template <class T> using unwrap_ref_decay_t = typename unwrap_ref_decay<T>::type; // since C++20

template <class T> // <class T=void> in C++14
struct plus : binary_function<T, T, T>
{
    T operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct minus : binary_function<T, T, T>
{
    T operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct multiplies : binary_function<T, T, T>
{
    T operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct divides : binary_function<T, T, T>
{
    T operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct modulus : binary_function<T, T, T>
{
    T operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct negate : unary_function<T, T>
{
    T operator()(const T& x) const;
};

template <class T> // <class T=void> in C++14
struct equal_to : binary_function<T, T, bool>
{
    bool operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct not_equal_to : binary_function<T, T, bool>
{
    bool operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct greater : binary_function<T, T, bool>
{
    bool operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct less : binary_function<T, T, bool>
{
    bool operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct greater_equal : binary_function<T, T, bool>
{
    bool operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct less_equal : binary_function<T, T, bool>
{
    bool operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct logical_and : binary_function<T, T, bool>
{
    bool operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct logical_or : binary_function<T, T, bool>
{
    bool operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct logical_not : unary_function<T, bool>
{
    bool operator()(const T& x) const;
};

template <class T> // <class T=void> in C++14
struct bit_and : binary_function<T, T, T>
{
    T operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct bit_or : binary_function<T, T, T>
{
    T operator()(const T& x, const T& y) const;
};

template <class T> // <class T=void> in C++14
struct bit_xor : binary_function<T, T, T>
{
    T operator()(const T& x, const T& y) const;
};

template <class T=void> // C++14
struct bit_not : unary_function<T, T>
{
    T operator()(const T& x) const;
};

struct identity; // C++20

template <class Predicate>
class unary_negate // deprecated in C++17
    : public unary_function<typename Predicate::argument_type, bool>
{
public:
    explicit unary_negate(const Predicate& pred);
    bool operator()(const typename Predicate::argument_type& x) const;
};

template <class Predicate> // deprecated in C++17
unary_negate<Predicate> not1(const Predicate& pred);

template <class Predicate>
class binary_negate // deprecated in C++17
    : public binary_function<typename Predicate::first_argument_type,
                             typename Predicate::second_argument_type,
                             bool>
{
public:
    explicit binary_negate(const Predicate& pred);
    bool operator()(const typename Predicate::first_argument_type& x,
                    const typename Predicate::second_argument_type& y) const;
};

template <class Predicate> // deprecated in C++17
binary_negate<Predicate> not2(const Predicate& pred);

template <class F>
constexpr unspecified not_fn(F&& f); // C++17, constexpr in C++20

template<class T> struct is_bind_expression;
template<class T> struct is_placeholder;

    // See C++14 20.9.9, Function object binders
template <class T> inline constexpr bool is_bind_expression_v
  = is_bind_expression<T>::value; // C++17
template <class T> inline constexpr int is_placeholder_v
  = is_placeholder<T>::value; // C++17


template<class Fn, class... BoundArgs>
  constexpr unspecified bind(Fn&&, BoundArgs&&...);  // constexpr in C++20
template<class R, class Fn, class... BoundArgs>
  constexpr unspecified bind(Fn&&, BoundArgs&&...);  // constexpr in C++20

template<class F, class... Args>
 constexpr // constexpr in C++20
 invoke_result_t<F, Args...> invoke(F&& f, Args&&... args) // C++17
    noexcept(is_nothrow_invocable_v<F, Args...>);

namespace placeholders {
  // M is the implementation-defined number of placeholders
  extern unspecified _1;
  extern unspecified _2;
  .
  .
  .
  extern unspecified _Mp;
}

template <class Operation>
class binder1st     // deprecated in C++11, removed in C++17
    : public unary_function<typename Operation::second_argument_type,
                            typename Operation::result_type>
{
protected:
    Operation                               op;
    typename Operation::first_argument_type value;
public:
    binder1st(const Operation& x, const typename Operation::first_argument_type y);
    typename Operation::result_type operator()(      typename Operation::second_argument_type& x) const;
    typename Operation::result_type operator()(const typename Operation::second_argument_type& x) const;
};

template <class Operation, class T>
binder1st<Operation> bind1st(const Operation& op, const T& x);  // deprecated in C++11, removed in C++17

template <class Operation>
class binder2nd     // deprecated in C++11, removed in C++17
    : public unary_function<typename Operation::first_argument_type,
                            typename Operation::result_type>
{
protected:
    Operation                                op;
    typename Operation::second_argument_type value;
public:
    binder2nd(const Operation& x, const typename Operation::second_argument_type y);
    typename Operation::result_type operator()(      typename Operation::first_argument_type& x) const;
    typename Operation::result_type operator()(const typename Operation::first_argument_type& x) const;
};

template <class Operation, class T>
binder2nd<Operation> bind2nd(const Operation& op, const T& x);  // deprecated in C++11, removed in C++17

template <class Arg, class Result>      // deprecated in C++11, removed in C++17
class pointer_to_unary_function : public unary_function<Arg, Result>
{
public:
    explicit pointer_to_unary_function(Result (*f)(Arg));
    Result operator()(Arg x) const;
};

template <class Arg, class Result>
pointer_to_unary_function<Arg,Result> ptr_fun(Result (*f)(Arg));      // deprecated in C++11, removed in C++17

template <class Arg1, class Arg2, class Result>      // deprecated in C++11, removed in C++17
class pointer_to_binary_function : public binary_function<Arg1, Arg2, Result>
{
public:
    explicit pointer_to_binary_function(Result (*f)(Arg1, Arg2));
    Result operator()(Arg1 x, Arg2 y) const;
};

template <class Arg1, class Arg2, class Result>
pointer_to_binary_function<Arg1,Arg2,Result> ptr_fun(Result (*f)(Arg1,Arg2));      // deprecated in C++11, removed in C++17

template<class S, class T>      // deprecated in C++11, removed in C++17
class mem_fun_t : public unary_function<T*, S>
{
public:
    explicit mem_fun_t(S (T::*p)());
    S operator()(T* p) const;
};

template<class S, class T, class A>
class mem_fun1_t : public binary_function<T*, A, S>      // deprecated in C++11, removed in C++17
{
public:
    explicit mem_fun1_t(S (T::*p)(A));
    S operator()(T* p, A x) const;
};

template<class S, class T>          mem_fun_t<S,T>    mem_fun(S (T::*f)());      // deprecated in C++11, removed in C++17
template<class S, class T, class A> mem_fun1_t<S,T,A> mem_fun(S (T::*f)(A));     // deprecated in C++11, removed in C++17

template<class S, class T>
class mem_fun_ref_t : public unary_function<T, S>      // deprecated in C++11, removed in C++17
{
public:
    explicit mem_fun_ref_t(S (T::*p)());
    S operator()(T& p) const;
};

template<class S, class T, class A>
class mem_fun1_ref_t : public binary_function<T, A, S>      // deprecated in C++11, removed in C++17
{
public:
    explicit mem_fun1_ref_t(S (T::*p)(A));
    S operator()(T& p, A x) const;
};

template<class S, class T>          mem_fun_ref_t<S,T>    mem_fun_ref(S (T::*f)());      // deprecated in C++11, removed in C++17
template<class S, class T, class A> mem_fun1_ref_t<S,T,A> mem_fun_ref(S (T::*f)(A));     // deprecated in C++11, removed in C++17

template <class S, class T>
class const_mem_fun_t : public unary_function<const T*, S>      // deprecated in C++11, removed in C++17
{
public:
    explicit const_mem_fun_t(S (T::*p)() const);
    S operator()(const T* p) const;
};

template <class S, class T, class A>
class const_mem_fun1_t : public binary_function<const T*, A, S>      // deprecated in C++11, removed in C++17
{
public:
    explicit const_mem_fun1_t(S (T::*p)(A) const);
    S operator()(const T* p, A x) const;
};

template <class S, class T>          const_mem_fun_t<S,T>    mem_fun(S (T::*f)() const);      // deprecated in C++11, removed in C++17
template <class S, class T, class A> const_mem_fun1_t<S,T,A> mem_fun(S (T::*f)(A) const);     // deprecated in C++11, removed in C++17

template <class S, class T>
class const_mem_fun_ref_t : public unary_function<T, S>      // deprecated in C++11, removed in C++17
{
public:
    explicit const_mem_fun_ref_t(S (T::*p)() const);
    S operator()(const T& p) const;
};

template <class S, class T, class A>
class const_mem_fun1_ref_t : public binary_function<T, A, S>      // deprecated in C++11, removed in C++17
{
public:
    explicit const_mem_fun1_ref_t(S (T::*p)(A) const);
    S operator()(const T& p, A x) const;
};

template <class S, class T>          const_mem_fun_ref_t<S,T>    mem_fun_ref(S (T::*f)() const);   // deprecated in C++11, removed in C++17
template <class S, class T, class A> const_mem_fun1_ref_t<S,T,A> mem_fun_ref(S (T::*f)(A) const);  // deprecated in C++11, removed in C++17

template<class R, class T>
constexpr unspecified mem_fn(R T::*); // constexpr in C++20

class bad_function_call
    : public exception
{
};

template<class> class function; // undefined

template<class R, class... ArgTypes>
class function<R(ArgTypes...)>
  : public unary_function<T1, R>      // iff sizeof...(ArgTypes) == 1 and
                                      // ArgTypes contains T1
  : public binary_function<T1, T2, R> // iff sizeof...(ArgTypes) == 2 and
                                      // ArgTypes contains T1 and T2
{
public:
    typedef R result_type;

    // construct/copy/destroy:
    function() noexcept;
    function(nullptr_t) noexcept;
    function(const function&);
    function(function&&) noexcept;
    template<class F>
      function(F);
    template<Allocator Alloc>
      function(allocator_arg_t, const Alloc&) noexcept;            // removed in C++17
    template<Allocator Alloc>
      function(allocator_arg_t, const Alloc&, nullptr_t) noexcept; // removed in C++17
    template<Allocator Alloc>
      function(allocator_arg_t, const Alloc&, const function&);    // removed in C++17
    template<Allocator Alloc>
      function(allocator_arg_t, const Alloc&, function&&);         // removed in C++17
    template<class F, Allocator Alloc>
      function(allocator_arg_t, const Alloc&, F);                  // removed in C++17

    function& operator=(const function&);
    function& operator=(function&&) noexcept;
    function& operator=(nullptr_t) noexcept;
    template<class F>
      function& operator=(F&&);
    template<class F>
      function& operator=(reference_wrapper<F>) noexcept;

    ~function();

    // function modifiers:
    void swap(function&) noexcept;
    template<class F, class Alloc>
      void assign(F&&, const Alloc&);                 // Removed in C++17

    // function capacity:
    explicit operator bool() const noexcept;

    // function invocation:
    R operator()(ArgTypes...) const;

    // function target access:
    const std::type_info& target_type() const noexcept;
    template <typename T>       T* target() noexcept;
    template <typename T> const T* target() const noexcept;
};

// Deduction guides
template<class R, class ...Args>
function(R(*)(Args...)) -> function<R(Args...)>; // since C++17

template<class F>
function(F) -> function<see-below>; // since C++17

// Null pointer comparisons:
template <class R, class ... ArgTypes>
  bool operator==(const function<R(ArgTypes...)>&, nullptr_t) noexcept;

template <class R, class ... ArgTypes>
  bool operator==(nullptr_t, const function<R(ArgTypes...)>&) noexcept;

template <class R, class ... ArgTypes>
  bool operator!=(const function<R(ArgTypes...)>&, nullptr_t) noexcept;

template <class  R, class ... ArgTypes>
  bool operator!=(nullptr_t, const function<R(ArgTypes...)>&) noexcept;

// specialized algorithms:
template <class  R, class ... ArgTypes>
  void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&) noexcept;

template <class T> struct hash;

template <> struct hash<bool>;
template <> struct hash<char>;
template <> struct hash<signed char>;
template <> struct hash<unsigned char>;
template <> struct hash<char8_t>; // since C++20
template <> struct hash<char16_t>;
template <> struct hash<char32_t>;
template <> struct hash<wchar_t>;
template <> struct hash<short>;
template <> struct hash<unsigned short>;
template <> struct hash<int>;
template <> struct hash<unsigned int>;
template <> struct hash<long>;
template <> struct hash<long long>;
template <> struct hash<unsigned long>;
template <> struct hash<unsigned long long>;

template <> struct hash<float>;
template <> struct hash<double>;
template <> struct hash<long double>;

template<class T> struct hash<T*>;
template <> struct hash<nullptr_t>;  // C++17

}  // std

POLICY:  For non-variadic implementations, the number of arguments is limited
         to 3.  It is hoped that the need for non-variadic implementations
         will be minimal.

*/

#include <__config>
#include <concepts>
#include <type_traits>
#include <typeinfo>
#include <exception>
#include <memory>
#include <tuple>
#include <utility>
#include <version>

#include <__functional_base>

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

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS plus : binary_function<_Tp, _Tp, _Tp>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
        {return __x + __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS plus<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) + _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) + _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) + _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS minus : binary_function<_Tp, _Tp, _Tp>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
        {return __x - __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS minus<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) - _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) - _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) - _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS multiplies : binary_function<_Tp, _Tp, _Tp>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
        {return __x * __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS multiplies<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) * _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) * _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) * _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS divides : binary_function<_Tp, _Tp, _Tp>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
        {return __x / __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS divides<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) / _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) / _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) / _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS modulus : binary_function<_Tp, _Tp, _Tp>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
        {return __x % __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS modulus<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) % _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) % _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) % _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS negate : unary_function<_Tp, _Tp>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    _Tp operator()(const _Tp& __x) const
        {return -__x;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS negate<void>
{
    template <class _Tp>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_Tp&& __x) const
    _NOEXCEPT_(noexcept(- _VSTD::forward<_Tp>(__x)))
    -> decltype        (- _VSTD::forward<_Tp>(__x))
        { return        - _VSTD::forward<_Tp>(__x); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS equal_to : binary_function<_Tp, _Tp, bool>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp& __x, const _Tp& __y) const
        {return __x == __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS equal_to<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) == _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) == _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) == _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS not_equal_to : binary_function<_Tp, _Tp, bool>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp& __x, const _Tp& __y) const
        {return __x != __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS not_equal_to<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) != _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) != _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) != _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS greater : binary_function<_Tp, _Tp, bool>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp& __x, const _Tp& __y) const
        {return __x > __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS greater<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) > _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) > _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) > _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


// less in <__functional_base>

#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS greater_equal : binary_function<_Tp, _Tp, bool>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp& __x, const _Tp& __y) const
        {return __x >= __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS greater_equal<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) >= _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) >= _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) >= _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS less_equal : binary_function<_Tp, _Tp, bool>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp& __x, const _Tp& __y) const
        {return __x <= __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS less_equal<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) <= _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) <= _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) <= _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS logical_and : binary_function<_Tp, _Tp, bool>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp& __x, const _Tp& __y) const
        {return __x && __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS logical_and<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) && _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) && _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) && _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS logical_or : binary_function<_Tp, _Tp, bool>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp& __x, const _Tp& __y) const
        {return __x || __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS logical_or<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) || _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) || _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) || _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS logical_not : unary_function<_Tp, bool>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp& __x) const
        {return !__x;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS logical_not<void>
{
    template <class _Tp>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_Tp&& __x) const
    _NOEXCEPT_(noexcept(!_VSTD::forward<_Tp>(__x)))
    -> decltype        (!_VSTD::forward<_Tp>(__x))
        { return        !_VSTD::forward<_Tp>(__x); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS bit_and : binary_function<_Tp, _Tp, _Tp>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
        {return __x & __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS bit_and<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) & _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) & _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) & _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS bit_or : binary_function<_Tp, _Tp, _Tp>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
        {return __x | __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS bit_or<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) | _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) | _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) | _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
#else
template <class _Tp>
#endif
struct _LIBCPP_TEMPLATE_VIS bit_xor : binary_function<_Tp, _Tp, _Tp>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    _Tp operator()(const _Tp& __x, const _Tp& __y) const
        {return __x ^ __y;}
};

#if _LIBCPP_STD_VER > 11
template <>
struct _LIBCPP_TEMPLATE_VIS bit_xor<void>
{
    template <class _T1, class _T2>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_T1&& __t, _T2&& __u) const
    _NOEXCEPT_(noexcept(_VSTD::forward<_T1>(__t) ^ _VSTD::forward<_T2>(__u)))
    -> decltype        (_VSTD::forward<_T1>(__t) ^ _VSTD::forward<_T2>(__u))
        { return        _VSTD::forward<_T1>(__t) ^ _VSTD::forward<_T2>(__u); }
    typedef void is_transparent;
};
#endif


#if _LIBCPP_STD_VER > 11
template <class _Tp = void>
struct _LIBCPP_TEMPLATE_VIS bit_not : unary_function<_Tp, _Tp>
{
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    _Tp operator()(const _Tp& __x) const
        {return ~__x;}
};

template <>
struct _LIBCPP_TEMPLATE_VIS bit_not<void>
{
    template <class _Tp>
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    auto operator()(_Tp&& __x) const
    _NOEXCEPT_(noexcept(~_VSTD::forward<_Tp>(__x)))
    -> decltype        (~_VSTD::forward<_Tp>(__x))
        { return        ~_VSTD::forward<_Tp>(__x); }
    typedef void is_transparent;
};
#endif

template <class _Predicate>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX17 unary_negate
    : public unary_function<typename _Predicate::argument_type, bool>
{
    _Predicate __pred_;
public:
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    explicit unary_negate(const _Predicate& __pred)
        : __pred_(__pred) {}
    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    bool operator()(const typename _Predicate::argument_type& __x) const
        {return !__pred_(__x);}
};

template <class _Predicate>
_LIBCPP_DEPRECATED_IN_CXX17 inline _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
unary_negate<_Predicate>
not1(const _Predicate& __pred) {return unary_negate<_Predicate>(__pred);}

template <class _Predicate>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX17 binary_negate
    : public binary_function<typename _Predicate::first_argument_type,
                             typename _Predicate::second_argument_type,
                             bool>
{
    _Predicate __pred_;
public:
    _LIBCPP_INLINE_VISIBILITY explicit _LIBCPP_CONSTEXPR_AFTER_CXX11
    binary_negate(const _Predicate& __pred) : __pred_(__pred) {}

    _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
    bool operator()(const typename _Predicate::first_argument_type& __x,
                    const typename _Predicate::second_argument_type& __y) const
        {return !__pred_(__x, __y);}
};

template <class _Predicate>
_LIBCPP_DEPRECATED_IN_CXX17 inline _LIBCPP_CONSTEXPR_AFTER_CXX11 _LIBCPP_INLINE_VISIBILITY
binary_negate<_Predicate>
not2(const _Predicate& __pred) {return binary_negate<_Predicate>(__pred);}

#if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_BINDERS)
template <class __Operation>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 binder1st
    : public unary_function<typename __Operation::second_argument_type,
                            typename __Operation::result_type>
{
protected:
    __Operation                               op;
    typename __Operation::first_argument_type value;
public:
    _LIBCPP_INLINE_VISIBILITY binder1st(const __Operation& __x,
                               const typename __Operation::first_argument_type __y)
        : op(__x), value(__y) {}
    _LIBCPP_INLINE_VISIBILITY typename __Operation::result_type operator()
        (typename __Operation::second_argument_type& __x) const
            {return op(value, __x);}
    _LIBCPP_INLINE_VISIBILITY typename __Operation::result_type operator()
        (const typename __Operation::second_argument_type& __x) const
            {return op(value, __x);}
};

template <class __Operation, class _Tp>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
binder1st<__Operation>
bind1st(const __Operation& __op, const _Tp& __x)
    {return binder1st<__Operation>(__op, __x);}

template <class __Operation>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 binder2nd
    : public unary_function<typename __Operation::first_argument_type,
                            typename __Operation::result_type>
{
protected:
    __Operation                                op;
    typename __Operation::second_argument_type value;
public:
    _LIBCPP_INLINE_VISIBILITY
    binder2nd(const __Operation& __x, const typename __Operation::second_argument_type __y)
        : op(__x), value(__y) {}
    _LIBCPP_INLINE_VISIBILITY typename __Operation::result_type operator()
        (      typename __Operation::first_argument_type& __x) const
            {return op(__x, value);}
    _LIBCPP_INLINE_VISIBILITY typename __Operation::result_type operator()
        (const typename __Operation::first_argument_type& __x) const
            {return op(__x, value);}
};

template <class __Operation, class _Tp>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
binder2nd<__Operation>
bind2nd(const __Operation& __op, const _Tp& __x)
    {return binder2nd<__Operation>(__op, __x);}

template <class _Arg, class _Result>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 pointer_to_unary_function
    : public unary_function<_Arg, _Result>
{
    _Result (*__f_)(_Arg);
public:
    _LIBCPP_INLINE_VISIBILITY explicit pointer_to_unary_function(_Result (*__f)(_Arg))
        : __f_(__f) {}
    _LIBCPP_INLINE_VISIBILITY _Result operator()(_Arg __x) const
        {return __f_(__x);}
};

template <class _Arg, class _Result>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
pointer_to_unary_function<_Arg,_Result>
ptr_fun(_Result (*__f)(_Arg))
    {return pointer_to_unary_function<_Arg,_Result>(__f);}

template <class _Arg1, class _Arg2, class _Result>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 pointer_to_binary_function
    : public binary_function<_Arg1, _Arg2, _Result>
{
    _Result (*__f_)(_Arg1, _Arg2);
public:
    _LIBCPP_INLINE_VISIBILITY explicit pointer_to_binary_function(_Result (*__f)(_Arg1, _Arg2))
        : __f_(__f) {}
    _LIBCPP_INLINE_VISIBILITY _Result operator()(_Arg1 __x, _Arg2 __y) const
        {return __f_(__x, __y);}
};

template <class _Arg1, class _Arg2, class _Result>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
pointer_to_binary_function<_Arg1,_Arg2,_Result>
ptr_fun(_Result (*__f)(_Arg1,_Arg2))
    {return pointer_to_binary_function<_Arg1,_Arg2,_Result>(__f);}

template<class _Sp, class _Tp>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 mem_fun_t
    : public unary_function<_Tp*, _Sp>
{
    _Sp (_Tp::*__p_)();
public:
    _LIBCPP_INLINE_VISIBILITY explicit mem_fun_t(_Sp (_Tp::*__p)())
        : __p_(__p) {}
    _LIBCPP_INLINE_VISIBILITY _Sp operator()(_Tp* __p) const
        {return (__p->*__p_)();}
};

template<class _Sp, class _Tp, class _Ap>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 mem_fun1_t
    : public binary_function<_Tp*, _Ap, _Sp>
{
    _Sp (_Tp::*__p_)(_Ap);
public:
    _LIBCPP_INLINE_VISIBILITY explicit mem_fun1_t(_Sp (_Tp::*__p)(_Ap))
        : __p_(__p) {}
    _LIBCPP_INLINE_VISIBILITY _Sp operator()(_Tp* __p, _Ap __x) const
        {return (__p->*__p_)(__x);}
};

template<class _Sp, class _Tp>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
mem_fun_t<_Sp,_Tp>
mem_fun(_Sp (_Tp::*__f)())
    {return mem_fun_t<_Sp,_Tp>(__f);}

template<class _Sp, class _Tp, class _Ap>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
mem_fun1_t<_Sp,_Tp,_Ap>
mem_fun(_Sp (_Tp::*__f)(_Ap))
    {return mem_fun1_t<_Sp,_Tp,_Ap>(__f);}

template<class _Sp, class _Tp>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 mem_fun_ref_t
    : public unary_function<_Tp, _Sp>
{
    _Sp (_Tp::*__p_)();
public:
    _LIBCPP_INLINE_VISIBILITY explicit mem_fun_ref_t(_Sp (_Tp::*__p)())
        : __p_(__p) {}
    _LIBCPP_INLINE_VISIBILITY _Sp operator()(_Tp& __p) const
        {return (__p.*__p_)();}
};

template<class _Sp, class _Tp, class _Ap>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 mem_fun1_ref_t
    : public binary_function<_Tp, _Ap, _Sp>
{
    _Sp (_Tp::*__p_)(_Ap);
public:
    _LIBCPP_INLINE_VISIBILITY explicit mem_fun1_ref_t(_Sp (_Tp::*__p)(_Ap))
        : __p_(__p) {}
    _LIBCPP_INLINE_VISIBILITY _Sp operator()(_Tp& __p, _Ap __x) const
        {return (__p.*__p_)(__x);}
};

template<class _Sp, class _Tp>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
mem_fun_ref_t<_Sp,_Tp>
mem_fun_ref(_Sp (_Tp::*__f)())
    {return mem_fun_ref_t<_Sp,_Tp>(__f);}

template<class _Sp, class _Tp, class _Ap>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
mem_fun1_ref_t<_Sp,_Tp,_Ap>
mem_fun_ref(_Sp (_Tp::*__f)(_Ap))
    {return mem_fun1_ref_t<_Sp,_Tp,_Ap>(__f);}

template <class _Sp, class _Tp>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 const_mem_fun_t
    : public unary_function<const _Tp*, _Sp>
{
    _Sp (_Tp::*__p_)() const;
public:
    _LIBCPP_INLINE_VISIBILITY explicit const_mem_fun_t(_Sp (_Tp::*__p)() const)
        : __p_(__p) {}
    _LIBCPP_INLINE_VISIBILITY _Sp operator()(const _Tp* __p) const
        {return (__p->*__p_)();}
};

template <class _Sp, class _Tp, class _Ap>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 const_mem_fun1_t
    : public binary_function<const _Tp*, _Ap, _Sp>
{
    _Sp (_Tp::*__p_)(_Ap) const;
public:
    _LIBCPP_INLINE_VISIBILITY explicit const_mem_fun1_t(_Sp (_Tp::*__p)(_Ap) const)
        : __p_(__p) {}
    _LIBCPP_INLINE_VISIBILITY _Sp operator()(const _Tp* __p, _Ap __x) const
        {return (__p->*__p_)(__x);}
};

template <class _Sp, class _Tp>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
const_mem_fun_t<_Sp,_Tp>
mem_fun(_Sp (_Tp::*__f)() const)
    {return const_mem_fun_t<_Sp,_Tp>(__f);}

template <class _Sp, class _Tp, class _Ap>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
const_mem_fun1_t<_Sp,_Tp,_Ap>
mem_fun(_Sp (_Tp::*__f)(_Ap) const)
    {return const_mem_fun1_t<_Sp,_Tp,_Ap>(__f);}

template <class _Sp, class _Tp>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 const_mem_fun_ref_t
    : public unary_function<_Tp, _Sp>
{
    _Sp (_Tp::*__p_)() const;
public:
    _LIBCPP_INLINE_VISIBILITY explicit const_mem_fun_ref_t(_Sp (_Tp::*__p)() const)
        : __p_(__p) {}
    _LIBCPP_INLINE_VISIBILITY _Sp operator()(const _Tp& __p) const
        {return (__p.*__p_)();}
};

template <class _Sp, class _Tp, class _Ap>
class _LIBCPP_TEMPLATE_VIS _LIBCPP_DEPRECATED_IN_CXX11 const_mem_fun1_ref_t
    : public binary_function<_Tp, _Ap, _Sp>
{
    _Sp (_Tp::*__p_)(_Ap) const;
public:
    _LIBCPP_INLINE_VISIBILITY explicit const_mem_fun1_ref_t(_Sp (_Tp::*__p)(_Ap) const)
        : __p_(__p) {}
    _LIBCPP_INLINE_VISIBILITY _Sp operator()(const _Tp& __p, _Ap __x) const
        {return (__p.*__p_)(__x);}
};

template <class _Sp, class _Tp>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
const_mem_fun_ref_t<_Sp,_Tp>
mem_fun_ref(_Sp (_Tp::*__f)() const)
    {return const_mem_fun_ref_t<_Sp,_Tp>(__f);}

template <class _Sp, class _Tp, class _Ap>
_LIBCPP_DEPRECATED_IN_CXX11 inline _LIBCPP_INLINE_VISIBILITY
const_mem_fun1_ref_t<_Sp,_Tp,_Ap>
mem_fun_ref(_Sp (_Tp::*__f)(_Ap) const)
    {return const_mem_fun1_ref_t<_Sp,_Tp,_Ap>(__f);}
#endif

////////////////////////////////////////////////////////////////////////////////
//                                MEMFUN
//==============================================================================

template <class _Tp>
class __mem_fn
    : public __weak_result_type<_Tp>
{
public:
    // types
    typedef _Tp type;
private:
    type __f_;

public:
    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
    __mem_fn(type __f) _NOEXCEPT : __f_(__f) {}

#ifndef _LIBCPP_CXX03_LANG
    // invoke
    template <class... _ArgTypes>
    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
    typename __invoke_return<type, _ArgTypes...>::type
    operator() (_ArgTypes&&... __args) const {
        return _VSTD::__invoke(__f_, _VSTD::forward<_ArgTypes>(__args)...);
    }
#else

    template <class _A0>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return0<type, _A0>::type
    operator() (_A0& __a0) const {
        return _VSTD::__invoke(__f_, __a0);
    }

    template <class _A0>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return0<type, _A0 const>::type
    operator() (_A0 const& __a0) const {
        return _VSTD::__invoke(__f_, __a0);
    }

    template <class _A0, class _A1>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return1<type, _A0, _A1>::type
    operator() (_A0& __a0, _A1& __a1) const {
        return _VSTD::__invoke(__f_, __a0, __a1);
    }

    template <class _A0, class _A1>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return1<type, _A0 const, _A1>::type
    operator() (_A0 const& __a0, _A1& __a1) const {
        return _VSTD::__invoke(__f_, __a0, __a1);
    }

    template <class _A0, class _A1>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return1<type, _A0, _A1 const>::type
    operator() (_A0& __a0, _A1 const& __a1) const {
        return _VSTD::__invoke(__f_, __a0, __a1);
    }

    template <class _A0, class _A1>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return1<type, _A0 const, _A1 const>::type
    operator() (_A0 const& __a0, _A1 const& __a1) const {
        return _VSTD::__invoke(__f_, __a0, __a1);
    }

    template <class _A0, class _A1, class _A2>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return2<type, _A0, _A1, _A2>::type
    operator() (_A0& __a0, _A1& __a1, _A2& __a2) const {
        return _VSTD::__invoke(__f_, __a0, __a1, __a2);
    }

    template <class _A0, class _A1, class _A2>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return2<type, _A0 const, _A1, _A2>::type
    operator() (_A0 const& __a0, _A1& __a1, _A2& __a2) const {
        return _VSTD::__invoke(__f_, __a0, __a1, __a2);
    }

    template <class _A0, class _A1, class _A2>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return2<type, _A0, _A1 const, _A2>::type
    operator() (_A0& __a0, _A1 const& __a1, _A2& __a2) const {
        return _VSTD::__invoke(__f_, __a0, __a1, __a2);
    }

    template <class _A0, class _A1, class _A2>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return2<type, _A0, _A1, _A2 const>::type
    operator() (_A0& __a0, _A1& __a1, _A2 const& __a2) const {
        return _VSTD::__invoke(__f_, __a0, __a1, __a2);
    }

    template <class _A0, class _A1, class _A2>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return2<type, _A0 const, _A1 const, _A2>::type
    operator() (_A0 const& __a0, _A1 const& __a1, _A2& __a2) const {
        return _VSTD::__invoke(__f_, __a0, __a1, __a2);
    }

    template <class _A0, class _A1, class _A2>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return2<type, _A0 const, _A1, _A2 const>::type
    operator() (_A0 const& __a0, _A1& __a1, _A2 const& __a2) const {
        return _VSTD::__invoke(__f_, __a0, __a1, __a2);
    }

    template <class _A0, class _A1, class _A2>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return2<type, _A0, _A1 const, _A2 const>::type
    operator() (_A0& __a0, _A1 const& __a1, _A2 const& __a2) const {
        return _VSTD::__invoke(__f_, __a0, __a1, __a2);
    }

    template <class _A0, class _A1, class _A2>
    _LIBCPP_INLINE_VISIBILITY
    typename __invoke_return2<type, _A0 const, _A1 const, _A2 const>::type
    operator() (_A0 const& __a0, _A1 const& __a1, _A2 const& __a2) const {
        return _VSTD::__invoke(__f_, __a0, __a1, __a2);
    }
#endif
};

template<class _Rp, class _Tp>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
__mem_fn<_Rp _Tp::*>
mem_fn(_Rp _Tp::* __pm) _NOEXCEPT
{
    return __mem_fn<_Rp _Tp::*>(__pm);
}

////////////////////////////////////////////////////////////////////////////////
//                                FUNCTION
//==============================================================================

// bad_function_call

class _LIBCPP_EXCEPTION_ABI bad_function_call
    : public exception
{
#ifdef _LIBCPP_ABI_BAD_FUNCTION_CALL_KEY_FUNCTION
public:
    virtual ~bad_function_call() _NOEXCEPT;

    virtual const char* what() const _NOEXCEPT;
#endif
};

_LIBCPP_NORETURN inline _LIBCPP_INLINE_VISIBILITY
void __throw_bad_function_call()
{
#ifndef _LIBCPP_NO_EXCEPTIONS
    throw bad_function_call();
#else
    _VSTD::abort();
#endif
}

#if defined(_LIBCPP_CXX03_LANG) && !defined(_LIBCPP_DISABLE_DEPRECATION_WARNINGS) && __has_attribute(deprecated)
#   define _LIBCPP_DEPRECATED_CXX03_FUNCTION \
        __attribute__((deprecated("Using std::function in C++03 is not supported anymore. Please upgrade to C++11 or later, or use a different type")))
#else
#   define _LIBCPP_DEPRECATED_CXX03_FUNCTION /* nothing */
#endif

template<class _Fp> class _LIBCPP_DEPRECATED_CXX03_FUNCTION _LIBCPP_TEMPLATE_VIS function; // undefined

namespace __function
{

template<class _Rp>
struct __maybe_derive_from_unary_function
{
};

template<class _Rp, class _A1>
struct __maybe_derive_from_unary_function<_Rp(_A1)>
    : public unary_function<_A1, _Rp>
{
};

template<class _Rp>
struct __maybe_derive_from_binary_function
{
};

template<class _Rp, class _A1, class _A2>
struct __maybe_derive_from_binary_function<_Rp(_A1, _A2)>
    : public binary_function<_A1, _A2, _Rp>
{
};

template <class _Fp>
_LIBCPP_INLINE_VISIBILITY
bool __not_null(_Fp const&) { return true; }

template <class _Fp>
_LIBCPP_INLINE_VISIBILITY
bool __not_null(_Fp* __ptr) { return __ptr; }

template <class _Ret, class _Class>
_LIBCPP_INLINE_VISIBILITY
bool __not_null(_Ret _Class::*__ptr) { return __ptr; }

template <class _Fp>
_LIBCPP_INLINE_VISIBILITY
bool __not_null(function<_Fp> const& __f) { return !!__f; }

#ifdef _LIBCPP_HAS_EXTENSION_BLOCKS
template <class _Rp, class ..._Args>
_LIBCPP_INLINE_VISIBILITY
bool __not_null(_Rp (^__p)(_Args...)) { return __p; }
#endif

} // namespace __function

#ifndef _LIBCPP_CXX03_LANG

namespace __function {

// __alloc_func holds a functor and an allocator.

template <class _Fp, class _Ap, class _FB> class __alloc_func;
template <class _Fp, class _FB>
class __default_alloc_func;

template <class _Fp, class _Ap, class _Rp, class... _ArgTypes>
class __alloc_func<_Fp, _Ap, _Rp(_ArgTypes...)>
{
    __compressed_pair<_Fp, _Ap> __f_;

  public:
    typedef _LIBCPP_NODEBUG_TYPE _Fp _Target;
    typedef _LIBCPP_NODEBUG_TYPE _Ap _Alloc;

    _LIBCPP_INLINE_VISIBILITY
    const _Target& __target() const { return __f_.first(); }

    // WIN32 APIs may define __allocator, so use __get_allocator instead.
    _LIBCPP_INLINE_VISIBILITY
    const _Alloc& __get_allocator() const { return __f_.second(); }

    _LIBCPP_INLINE_VISIBILITY
    explicit __alloc_func(_Target&& __f)
        : __f_(piecewise_construct, _VSTD::forward_as_tuple(_VSTD::move(__f)),
               _VSTD::forward_as_tuple())
    {
    }

    _LIBCPP_INLINE_VISIBILITY
    explicit __alloc_func(const _Target& __f, const _Alloc& __a)
        : __f_(piecewise_construct, _VSTD::forward_as_tuple(__f),
               _VSTD::forward_as_tuple(__a))
    {
    }

    _LIBCPP_INLINE_VISIBILITY
    explicit __alloc_func(const _Target& __f, _Alloc&& __a)
        : __f_(piecewise_construct, _VSTD::forward_as_tuple(__f),
               _VSTD::forward_as_tuple(_VSTD::move(__a)))
    {
    }

    _LIBCPP_INLINE_VISIBILITY
    explicit __alloc_func(_Target&& __f, _Alloc&& __a)
        : __f_(piecewise_construct, _VSTD::forward_as_tuple(_VSTD::move(__f)),
               _VSTD::forward_as_tuple(_VSTD::move(__a)))
    {
    }

    _LIBCPP_INLINE_VISIBILITY
    _Rp operator()(_ArgTypes&&... __arg)
    {
        typedef __invoke_void_return_wrapper<_Rp> _Invoker;
        return _Invoker::__call(__f_.first(),
                                _VSTD::forward<_ArgTypes>(__arg)...);
    }

    _LIBCPP_INLINE_VISIBILITY
    __alloc_func* __clone() const
    {
        typedef allocator_traits<_Alloc> __alloc_traits;
        typedef
            typename __rebind_alloc_helper<__alloc_traits, __alloc_func>::type
                _AA;
        _AA __a(__f_.second());
        typedef __allocator_destructor<_AA> _Dp;
        unique_ptr<__alloc_func, _Dp> __hold(__a.allocate(1), _Dp(__a, 1));
        ::new ((void*)__hold.get()) __alloc_func(__f_.first(), _Alloc(__a));
        return __hold.release();
    }

    _LIBCPP_INLINE_VISIBILITY
    void destroy() _NOEXCEPT { __f_.~__compressed_pair<_Target, _Alloc>(); }

    static void __destroy_and_delete(__alloc_func* __f) {
      typedef allocator_traits<_Alloc> __alloc_traits;
      typedef typename __rebind_alloc_helper<__alloc_traits, __alloc_func>::type
          _FunAlloc;
      _FunAlloc __a(__f->__get_allocator());
      __f->destroy();
      __a.deallocate(__f, 1);
    }
};

template <class _Fp, class _Rp, class... _ArgTypes>
class __default_alloc_func<_Fp, _Rp(_ArgTypes...)> {
  _Fp __f_;

public:
  typedef _LIBCPP_NODEBUG_TYPE _Fp _Target;

  _LIBCPP_INLINE_VISIBILITY
  const _Target& __target() const { return __f_; }

  _LIBCPP_INLINE_VISIBILITY
  explicit __default_alloc_func(_Target&& __f) : __f_(_VSTD::move(__f)) {}

  _LIBCPP_INLINE_VISIBILITY
  explicit __default_alloc_func(const _Target& __f) : __f_(__f) {}

  _LIBCPP_INLINE_VISIBILITY
  _Rp operator()(_ArgTypes&&... __arg) {
    typedef __invoke_void_return_wrapper<_Rp> _Invoker;
    return _Invoker::__call(__f_, _VSTD::forward<_ArgTypes>(__arg)...);
  }

  _LIBCPP_INLINE_VISIBILITY
  __default_alloc_func* __clone() const {
      __builtin_new_allocator::__holder_t __hold =
        __builtin_new_allocator::__allocate_type<__default_alloc_func>(1);
    __default_alloc_func* __res =
        ::new ((void*)__hold.get()) __default_alloc_func(__f_);
    (void)__hold.release();
    return __res;
  }

  _LIBCPP_INLINE_VISIBILITY
  void destroy() _NOEXCEPT { __f_.~_Target(); }

  static void __destroy_and_delete(__default_alloc_func* __f) {
    __f->destroy();
      __builtin_new_allocator::__deallocate_type<__default_alloc_func>(__f, 1);
  }
};

// __base provides an abstract interface for copyable functors.

template<class _Fp> class _LIBCPP_TEMPLATE_VIS __base;

template<class _Rp, class ..._ArgTypes>
class __base<_Rp(_ArgTypes...)>
{
    __base(const __base&);
    __base& operator=(const __base&);
public:
    _LIBCPP_INLINE_VISIBILITY __base() {}
    _LIBCPP_INLINE_VISIBILITY virtual ~__base() {}
    virtual __base* __clone() const = 0;
    virtual void __clone(__base*) const = 0;
    virtual void destroy() _NOEXCEPT = 0;
    virtual void destroy_deallocate() _NOEXCEPT = 0;
    virtual _Rp operator()(_ArgTypes&& ...) = 0;
#ifndef _LIBCPP_NO_RTTI
    virtual const void* target(const type_info&) const _NOEXCEPT = 0;
    virtual const std::type_info& target_type() const _NOEXCEPT = 0;
#endif // _LIBCPP_NO_RTTI
};

// __func implements __base for a given functor type.

template<class _FD, class _Alloc, class _FB> class __func;

template<class _Fp, class _Alloc, class _Rp, class ..._ArgTypes>
class __func<_Fp, _Alloc, _Rp(_ArgTypes...)>
    : public  __base<_Rp(_ArgTypes...)>
{
    __alloc_func<_Fp, _Alloc, _Rp(_ArgTypes...)> __f_;
public:
    _LIBCPP_INLINE_VISIBILITY
    explicit __func(_Fp&& __f)
        : __f_(_VSTD::move(__f)) {}

    _LIBCPP_INLINE_VISIBILITY
    explicit __func(const _Fp& __f, const _Alloc& __a)
        : __f_(__f, __a) {}

    _LIBCPP_INLINE_VISIBILITY
    explicit __func(const _Fp& __f, _Alloc&& __a)
        : __f_(__f, _VSTD::move(__a)) {}

    _LIBCPP_INLINE_VISIBILITY
    explicit __func(_Fp&& __f, _Alloc&& __a)
        : __f_(_VSTD::move(__f), _VSTD::move(__a)) {}

    virtual __base<_Rp(_ArgTypes...)>* __clone() const;
    virtual void __clone(__base<_Rp(_ArgTypes...)>*) const;
    virtual void destroy() _NOEXCEPT;
    virtual void destroy_deallocate() _NOEXCEPT;
    virtual _Rp operator()(_ArgTypes&&... __arg);
#ifndef _LIBCPP_NO_RTTI
    virtual const void* target(const type_info&) const _NOEXCEPT;
    virtual const std::type_info& target_type() const _NOEXCEPT;
#endif // _LIBCPP_NO_RTTI
};

template<class _Fp, class _Alloc, class _Rp, class ..._ArgTypes>
__base<_Rp(_ArgTypes...)>*
__func<_Fp, _Alloc, _Rp(_ArgTypes...)>::__clone() const
{
    typedef allocator_traits<_Alloc> __alloc_traits;
    typedef typename __rebind_alloc_helper<__alloc_traits, __func>::type _Ap;
    _Ap __a(__f_.__get_allocator());
    typedef __allocator_destructor<_Ap> _Dp;
    unique_ptr<__func, _Dp> __hold(__a.allocate(1), _Dp(__a, 1));
    ::new ((void*)__hold.get()) __func(__f_.__target(), _Alloc(__a));
    return __hold.release();
}

template<class _Fp, class _Alloc, class _Rp, class ..._ArgTypes>
void
__func<_Fp, _Alloc, _Rp(_ArgTypes...)>::__clone(__base<_Rp(_ArgTypes...)>* __p) const
{
    ::new ((void*)__p) __func(__f_.__target(), __f_.__get_allocator());
}

template<class _Fp, class _Alloc, class _Rp, class ..._ArgTypes>
void
__func<_Fp, _Alloc, _Rp(_ArgTypes...)>::destroy() _NOEXCEPT
{
    __f_.destroy();
}

template<class _Fp, class _Alloc, class _Rp, class ..._ArgTypes>
void
__func<_Fp, _Alloc, _Rp(_ArgTypes...)>::destroy_deallocate() _NOEXCEPT
{
    typedef allocator_traits<_Alloc> __alloc_traits;
    typedef typename __rebind_alloc_helper<__alloc_traits, __func>::type _Ap;
    _Ap __a(__f_.__get_allocator());
    __f_.destroy();
    __a.deallocate(this, 1);
}

template<class _Fp, class _Alloc, class _Rp, class ..._ArgTypes>
_Rp
__func<_Fp, _Alloc, _Rp(_ArgTypes...)>::operator()(_ArgTypes&& ... __arg)
{
    return __f_(_VSTD::forward<_ArgTypes>(__arg)...);
}

#ifndef _LIBCPP_NO_RTTI

template<class _Fp, class _Alloc, class _Rp, class ..._ArgTypes>
const void*
__func<_Fp, _Alloc, _Rp(_ArgTypes...)>::target(const type_info& __ti) const _NOEXCEPT
{
    if (__ti == typeid(_Fp))
        return &__f_.__target();
    return nullptr;
}

template<class _Fp, class _Alloc, class _Rp, class ..._ArgTypes>
const std::type_info&
__func<_Fp, _Alloc, _Rp(_ArgTypes...)>::target_type() const _NOEXCEPT
{
    return typeid(_Fp);
}

#endif // _LIBCPP_NO_RTTI

// __value_func creates a value-type from a __func.

template <class _Fp> class __value_func;

template <class _Rp, class... _ArgTypes> class __value_func<_Rp(_ArgTypes...)>
{
    typename aligned_storage<3 * sizeof(void*)>::type __buf_;

    typedef __base<_Rp(_ArgTypes...)> __func;
    __func* __f_;

    _LIBCPP_NO_CFI static __func* __as_base(void* p)
    {
        return reinterpret_cast<__func*>(p);
    }

  public:
    _LIBCPP_INLINE_VISIBILITY
    __value_func() _NOEXCEPT : __f_(nullptr) {}

    template <class _Fp, class _Alloc>
    _LIBCPP_INLINE_VISIBILITY __value_func(_Fp&& __f, const _Alloc& __a)
        : __f_(nullptr)
    {
        typedef allocator_traits<_Alloc> __alloc_traits;
        typedef __function::__func<_Fp, _Alloc, _Rp(_ArgTypes...)> _Fun;
        typedef typename __rebind_alloc_helper<__alloc_traits, _Fun>::type
            _FunAlloc;

        if (__function::__not_null(__f))
        {
            _FunAlloc __af(__a);
            if (sizeof(_Fun) <= sizeof(__buf_) &&
                is_nothrow_copy_constructible<_Fp>::value &&
                is_nothrow_copy_constructible<_FunAlloc>::value)
            {
                __f_ =
                    ::new ((void*)&__buf_) _Fun(_VSTD::move(__f), _Alloc(__af));
            }
            else
            {
                typedef __allocator_destructor<_FunAlloc> _Dp;
                unique_ptr<__func, _Dp> __hold(__af.allocate(1), _Dp(__af, 1));
                ::new ((void*)__hold.get()) _Fun(_VSTD::move(__f), _Alloc(__a));
                __f_ = __hold.release();
            }
        }
    }

    template <class _Fp,
        class = typename enable_if<!is_same<typename decay<_Fp>::type, __value_func>::value>::type>
    _LIBCPP_INLINE_VISIBILITY explicit __value_func(_Fp&& __f)
        : __value_func(_VSTD::forward<_Fp>(__f), allocator<_Fp>()) {}

    _LIBCPP_INLINE_VISIBILITY
    __value_func(const __value_func& __f)
    {
        if (__f.__f_ == nullptr)
            __f_ = nullptr;
        else if ((void*)__f.__f_ == &__f.__buf_)
        {
            __f_ = __as_base(&__buf_);
            __f.__f_->__clone(__f_);
        }
        else
            __f_ = __f.__f_->__clone();
    }

    _LIBCPP_INLINE_VISIBILITY
    __value_func(__value_func&& __f) _NOEXCEPT
    {
        if (__f.__f_ == nullptr)
            __f_ = nullptr;
        else if ((void*)__f.__f_ == &__f.__buf_)
        {
            __f_ = __as_base(&__buf_);
            __f.__f_->__clone(__f_);
        }
        else
        {
            __f_ = __f.__f_;
            __f.__f_ = nullptr;
        }
    }

    _LIBCPP_INLINE_VISIBILITY
    ~__value_func()
    {
        if ((void*)__f_ == &__buf_)
            __f_->destroy();
        else if (__f_)
            __f_->destroy_deallocate();
    }

    _LIBCPP_INLINE_VISIBILITY
    __value_func& operator=(__value_func&& __f)
    {
        *this = nullptr;
        if (__f.__f_ == nullptr)
            __f_ = nullptr;
        else if ((void*)__f.__f_ == &__f.__buf_)
        {
            __f_ = __as_base(&__buf_);
            __f.__f_->__clone(__f_);
        }
        else
        {
            __f_ = __f.__f_;
            __f.__f_ = nullptr;
        }
        return *this;
    }

    _LIBCPP_INLINE_VISIBILITY
    __value_func& operator=(nullptr_t)
    {
        __func* __f = __f_;
        __f_ = nullptr;
        if ((void*)__f == &__buf_)
            __f->destroy();
        else if (__f)
            __f->destroy_deallocate();
        return *this;
    }

    _LIBCPP_INLINE_VISIBILITY
    _Rp operator()(_ArgTypes&&... __args) const
    {
        if (__f_ == nullptr)
            __throw_bad_function_call();
        return (*__f_)(_VSTD::forward<_ArgTypes>(__args)...);
    }

    _LIBCPP_INLINE_VISIBILITY
    void swap(__value_func& __f) _NOEXCEPT
    {
        if (&__f == this)
            return;
        if ((void*)__f_ == &__buf_ && (void*)__f.__f_ == &__f.__buf_)
        {
            typename aligned_storage<sizeof(__buf_)>::type __tempbuf;
            __func* __t = __as_base(&__tempbuf);
            __f_->__clone(__t);
            __f_->destroy();
            __f_ = nullptr;
            __f.__f_->__clone(__as_base(&__buf_));
            __f.__f_->destroy();
            __f.__f_ = nullptr;
            __f_ = __as_base(&__buf_);
            __t->__clone(__as_base(&__f.__buf_));
            __t->destroy();
            __f.__f_ = __as_base(&__f.__buf_);
        }
        else if ((void*)__f_ == &__buf_)
        {
            __f_->__clone(__as_base(&__f.__buf_));
            __f_->destroy();
            __f_ = __f.__f_;
            __f.__f_ = __as_base(&__f.__buf_);
        }
        else if ((void*)__f.__f_ == &__f.__buf_)
        {
            __f.__f_->__clone(__as_base(&__buf_));
            __f.__f_->destroy();
            __f.__f_ = __f_;
            __f_ = __as_base(&__buf_);
        }
        else
            _VSTD::swap(__f_, __f.__f_);
    }

    _LIBCPP_INLINE_VISIBILITY
    _LIBCPP_EXPLICIT operator bool() const _NOEXCEPT { return __f_ != nullptr; }

#ifndef _LIBCPP_NO_RTTI
    _LIBCPP_INLINE_VISIBILITY
    const std::type_info& target_type() const _NOEXCEPT
    {
        if (__f_ == nullptr)
            return typeid(void);
        return __f_->target_type();
    }

    template <typename _Tp>
    _LIBCPP_INLINE_VISIBILITY const _Tp* target() const _NOEXCEPT
    {
        if (__f_ == nullptr)
            return nullptr;
        return (const _Tp*)__f_->target(typeid(_Tp));
    }
#endif // _LIBCPP_NO_RTTI
};

// Storage for a functor object, to be used with __policy to manage copy and
// destruction.
union __policy_storage
{
    mutable char __small[sizeof(void*) * 2];
    void* __large;
};

// True if _Fun can safely be held in __policy_storage.__small.
template <typename _Fun>
struct __use_small_storage
    : public integral_constant<
          bool, sizeof(_Fun) <= sizeof(__policy_storage) &&
                    _LIBCPP_ALIGNOF(_Fun) <= _LIBCPP_ALIGNOF(__policy_storage) &&
                    is_trivially_copy_constructible<_Fun>::value &&
                    is_trivially_destructible<_Fun>::value> {};

// Policy contains information about how to copy, destroy, and move the
// underlying functor. You can think of it as a vtable of sorts.
struct __policy
{
    // Used to copy or destroy __large values. null for trivial objects.
    void* (*const __clone)(const void*);
    void (*const __destroy)(void*);

    // True if this is the null policy (no value).
    const bool __is_null;

    // The target type. May be null if RTTI is disabled.
    const std::type_info* const __type_info;

    // Returns a pointer to a static policy object suitable for the functor
    // type.
    template <typename _Fun>
    _LIBCPP_INLINE_VISIBILITY static const __policy* __create()
    {
        return __choose_policy<_Fun>(__use_small_storage<_Fun>());
    }

    _LIBCPP_INLINE_VISIBILITY
    static const __policy* __create_empty()
    {
        static const _LIBCPP_CONSTEXPR __policy __policy_ = {nullptr, nullptr,
                                                             true,
#ifndef _LIBCPP_NO_RTTI
                                                             &typeid(void)
#else
                                                             nullptr
#endif
        };
        return &__policy_;
    }

  private:
    template <typename _Fun> static void* __large_clone(const void* __s)
    {
        const _Fun* __f = static_cast<const _Fun*>(__s);
        return __f->__clone();
    }

    template <typename _Fun>
    static void __large_destroy(void* __s) {
      _Fun::__destroy_and_delete(static_cast<_Fun*>(__s));
    }

    template <typename _Fun>
    _LIBCPP_INLINE_VISIBILITY static const __policy*
    __choose_policy(/* is_small = */ false_type) {
      static const _LIBCPP_CONSTEXPR __policy __policy_ = {
          &__large_clone<_Fun>, &__large_destroy<_Fun>, false,
#ifndef _LIBCPP_NO_RTTI
          &typeid(typename _Fun::_Target)
#else
          nullptr
#endif
      };
        return &__policy_;
    }

    template <typename _Fun>
    _LIBCPP_INLINE_VISIBILITY static const __policy*
        __choose_policy(/* is_small = */ true_type)
    {
        static const _LIBCPP_CONSTEXPR __policy __policy_ = {
            nullptr, nullptr, false,
#ifndef _LIBCPP_NO_RTTI
            &typeid(typename _Fun::_Target)
#else
            nullptr
#endif
        };
        return &__policy_;
    }
};

// Used to choose between perfect forwarding or pass-by-value. Pass-by-value is
// faster for types that can be passed in registers.
template <typename _Tp>
using __fast_forward =
    typename conditional<is_scalar<_Tp>::value, _Tp, _Tp&&>::type;

// __policy_invoker calls an instance of __alloc_func held in __policy_storage.

template <class _Fp> struct __policy_invoker;

template <class _Rp, class... _ArgTypes>
struct __policy_invoker<_Rp(_ArgTypes...)>
{
    typedef _Rp (*__Call)(const __policy_storage*,
                          __fast_forward<_ArgTypes>...);

    __Call __call_;

    // Creates an invoker that throws bad_function_call.
    _LIBCPP_INLINE_VISIBILITY
    __policy_invoker() : __call_(&__call_empty) {}

    // Creates an invoker that calls the given instance of __func.
    template <typename _Fun>
    _LIBCPP_INLINE_VISIBILITY static __policy_invoker __create()
    {
        return __policy_invoker(&__call_impl<_Fun>);
    }

  private:
    _LIBCPP_INLINE_VISIBILITY
    explicit __policy_invoker(__Call __c) : __call_(__c) {}

    static _Rp __call_empty(const __policy_storage*,
                            __fast_forward<_ArgTypes>...)
    {
        __throw_bad_function_call();
    }

    template <typename _Fun>
    static _Rp __call_impl(const __policy_storage* __buf,
                           __fast_forward<_ArgTypes>... __args)
    {
        _Fun* __f = reinterpret_cast<_Fun*>(__use_small_storage<_Fun>::value
                                                ? &__buf->__small
                                                : __buf->__large);
        return (*__f)(_VSTD::forward<_ArgTypes>(__args)...);
    }
};

// __policy_func uses a __policy and __policy_invoker to create a type-erased,
// copyable functor.

template <class _Fp> class __policy_func;

template <class _Rp, class... _ArgTypes> class __policy_func<_Rp(_ArgTypes...)>
{
    // Inline storage for small objects.
    __policy_storage __buf_;

    // Calls the value stored in __buf_. This could technically be part of
    // policy, but storing it here eliminates a level of indirection inside
    // operator().
    typedef __function::__policy_invoker<_Rp(_ArgTypes...)> __invoker;
    __invoker __invoker_;

    // The policy that describes how to move / copy / destroy __buf_. Never
    // null, even if the function is empty.
    const __policy* __policy_;

  public:
    _LIBCPP_INLINE_VISIBILITY
    __policy_func() : __policy_(__policy::__create_empty()) {}

    template <class _Fp, class _Alloc>
    _LIBCPP_INLINE_VISIBILITY __policy_func(_Fp&& __f, const _Alloc& __a)
        : __policy_(__policy::__create_empty())
    {
        typedef __alloc_func<_Fp, _Alloc, _Rp(_ArgTypes...)> _Fun;
        typedef allocator_traits<_Alloc> __alloc_traits;
        typedef typename __rebind_alloc_helper<__alloc_traits, _Fun>::type
            _FunAlloc;

        if (__function::__not_null(__f))
        {
            __invoker_ = __invoker::template __create<_Fun>();
            __policy_ = __policy::__create<_Fun>();

            _FunAlloc __af(__a);
            if (__use_small_storage<_Fun>())
            {
                ::new ((void*)&__buf_.__small)
                    _Fun(_VSTD::move(__f), _Alloc(__af));
            }
            else
            {
                typedef __allocator_destructor<_FunAlloc> _Dp;
                unique_ptr<_Fun, _Dp> __hold(__af.allocate(1), _Dp(__af, 1));
                ::new ((void*)__hold.get())
                    _Fun(_VSTD::move(__f), _Alloc(__af));
                __buf_.__large = __hold.release();
            }
        }
    }

    template <class _Fp, class = typename enable_if<!is_same<typename decay<_Fp>::type, __policy_func>::value>::type>
    _LIBCPP_INLINE_VISIBILITY explicit __policy_func(_Fp&& __f)
        : __policy_(__policy::__create_empty()) {
      typedef __default_alloc_func<_Fp, _Rp(_ArgTypes...)> _Fun;

      if (__function::__not_null(__f)) {
        __invoker_ = __invoker::template __create<_Fun>();
        __policy_ = __policy::__create<_Fun>();
        if (__use_small_storage<_Fun>()) {
          ::new ((void*)&__buf_.__small) _Fun(_VSTD::move(__f));
        } else {
          __builtin_new_allocator::__holder_t __hold =
              __builtin_new_allocator::__allocate_type<_Fun>(1);
          __buf_.__large = ::new ((void*)__hold.get()) _Fun(_VSTD::move(__f));
          (void)__hold.release();
        }
      }
    }

    _LIBCPP_INLINE_VISIBILITY
    __policy_func(const __policy_func& __f)
        : __buf_(__f.__buf_), __invoker_(__f.__invoker_),
          __policy_(__f.__policy_)
    {
        if (__policy_->__clone)
            __buf_.__large = __policy_->__clone(__f.__buf_.__large);
    }

    _LIBCPP_INLINE_VISIBILITY
    __policy_func(__policy_func&& __f)
        : __buf_(__f.__buf_), __invoker_(__f.__invoker_),
          __policy_(__f.__policy_)
    {
        if (__policy_->__destroy)
        {
            __f.__policy_ = __policy::__create_empty();
            __f.__invoker_ = __invoker();
        }
    }

    _LIBCPP_INLINE_VISIBILITY
    ~__policy_func()
    {
        if (__policy_->__destroy)
            __policy_->__destroy(__buf_.__large);
    }

    _LIBCPP_INLINE_VISIBILITY
    __policy_func& operator=(__policy_func&& __f)
    {
        *this = nullptr;
        __buf_ = __f.__buf_;
        __invoker_ = __f.__invoker_;
        __policy_ = __f.__policy_;
        __f.__policy_ = __policy::__create_empty();
        __f.__invoker_ = __invoker();
        return *this;
    }

    _LIBCPP_INLINE_VISIBILITY
    __policy_func& operator=(nullptr_t)
    {
        const __policy* __p = __policy_;
        __policy_ = __policy::__create_empty();
        __invoker_ = __invoker();
        if (__p->__destroy)
            __p->__destroy(__buf_.__large);
        return *this;
    }

    _LIBCPP_INLINE_VISIBILITY
    _Rp operator()(_ArgTypes&&... __args) const
    {
        return __invoker_.__call_(_VSTD::addressof(__buf_),
                                  _VSTD::forward<_ArgTypes>(__args)...);
    }

    _LIBCPP_INLINE_VISIBILITY
    void swap(__policy_func& __f)
    {
        _VSTD::swap(__invoker_, __f.__invoker_);
        _VSTD::swap(__policy_, __f.__policy_);
        _VSTD::swap(__buf_, __f.__buf_);
    }

    _LIBCPP_INLINE_VISIBILITY
    explicit operator bool() const _NOEXCEPT
    {
        return !__policy_->__is_null;
    }

#ifndef _LIBCPP_NO_RTTI
    _LIBCPP_INLINE_VISIBILITY
    const std::type_info& target_type() const _NOEXCEPT
    {
        return *__policy_->__type_info;
    }

    template <typename _Tp>
    _LIBCPP_INLINE_VISIBILITY const _Tp* target() const _NOEXCEPT
    {
        if (__policy_->__is_null || typeid(_Tp) != *__policy_->__type_info)
            return nullptr;
        if (__policy_->__clone) // Out of line storage.
            return reinterpret_cast<const _Tp*>(__buf_.__large);
        else
            return reinterpret_cast<const _Tp*>(&__buf_.__small);
    }
#endif // _LIBCPP_NO_RTTI
};

#if defined(_LIBCPP_HAS_BLOCKS_RUNTIME) && !defined(_LIBCPP_HAS_OBJC_ARC)

extern "C" void *_Block_copy(const void *);
extern "C" void _Block_release(const void *);

template<class _Rp1, class ..._ArgTypes1, class _Alloc, class _Rp, class ..._ArgTypes>
class __func<_Rp1(^)(_ArgTypes1...), _Alloc, _Rp(_ArgTypes...)>
    : public  __base<_Rp(_ArgTypes...)>
{
    typedef _Rp1(^__block_type)(_ArgTypes1...);
    __block_type __f_;

public:
    _LIBCPP_INLINE_VISIBILITY
    explicit __func(__block_type const& __f)
        : __f_(reinterpret_cast<__block_type>(__f ? _Block_copy(__f) : nullptr))
    { }

    // [TODO] add && to save on a retain

    _LIBCPP_INLINE_VISIBILITY
    explicit __func(__block_type __f, const _Alloc& /* unused */)
        : __f_(reinterpret_cast<__block_type>(__f ? _Block_copy(__f) : nullptr))
    { }

    virtual __base<_Rp(_ArgTypes...)>* __clone() const {
        _LIBCPP_ASSERT(false,
            "Block pointers are just pointers, so they should always fit into "
            "std::function's small buffer optimization. This function should "
            "never be invoked.");
        return nullptr;
    }

    virtual void __clone(__base<_Rp(_ArgTypes...)>* __p) const {
        ::new ((void*)__p) __func(__f_);
    }

    virtual void destroy() _NOEXCEPT {
        if (__f_)
            _Block_release(__f_);
        __f_ = 0;
    }

    virtual void destroy_deallocate() _NOEXCEPT {
        _LIBCPP_ASSERT(false,
            "Block pointers are just pointers, so they should always fit into "
            "std::function's small buffer optimization. This function should "
            "never be invoked.");
    }

    virtual _Rp operator()(_ArgTypes&& ... __arg) {
        return _VSTD::__invoke(__f_, _VSTD::forward<_ArgTypes>(__arg)...);
    }

#ifndef _LIBCPP_NO_RTTI
    virtual const void* target(type_info const& __ti) const _NOEXCEPT {
        if (__ti == typeid(__func::__block_type))
            return &__f_;
        return (const void*)nullptr;
    }

    virtual const std::type_info& target_type() const _NOEXCEPT {
        return typeid(__func::__block_type);
    }
#endif // _LIBCPP_NO_RTTI
};

#endif // _LIBCPP_HAS_EXTENSION_BLOCKS && !_LIBCPP_HAS_OBJC_ARC

}  // __function

template<class _Rp, class ..._ArgTypes>
class _LIBCPP_TEMPLATE_VIS function<_Rp(_ArgTypes...)>
    : public __function::__maybe_derive_from_unary_function<_Rp(_ArgTypes...)>,
      public __function::__maybe_derive_from_binary_function<_Rp(_ArgTypes...)>
{
#ifndef _LIBCPP_ABI_OPTIMIZED_FUNCTION
    typedef __function::__value_func<_Rp(_ArgTypes...)> __func;
#else
    typedef __function::__policy_func<_Rp(_ArgTypes...)> __func;
#endif

    __func __f_;

    template <class _Fp, bool = _And<
        _IsNotSame<__uncvref_t<_Fp>, function>,
        __invokable<_Fp, _ArgTypes...>
    >::value>
    struct __callable;
    template <class _Fp>
        struct __callable<_Fp, true>
        {
            static const bool value = is_void<_Rp>::value ||
                __is_core_convertible<typename __invoke_of<_Fp, _ArgTypes...>::type,
                                      _Rp>::value;
        };
    template <class _Fp>
        struct __callable<_Fp, false>
        {
            static const bool value = false;
        };

  template <class _Fp>
  using _EnableIfLValueCallable = typename enable_if<__callable<_Fp&>::value>::type;
public:
    typedef _Rp result_type;

    // construct/copy/destroy:
    _LIBCPP_INLINE_VISIBILITY
    function() _NOEXCEPT { }
    _LIBCPP_INLINE_VISIBILITY
    function(nullptr_t) _NOEXCEPT {}
    function(const function&);
    function(function&&) _NOEXCEPT;
    template<class _Fp, class = _EnableIfLValueCallable<_Fp>>
    function(_Fp);

#if _LIBCPP_STD_VER <= 14
    template<class _Alloc>
      _LIBCPP_INLINE_VISIBILITY
      function(allocator_arg_t, const _Alloc&) _NOEXCEPT {}
    template<class _Alloc>
      _LIBCPP_INLINE_VISIBILITY
      function(allocator_arg_t, const _Alloc&, nullptr_t) _NOEXCEPT {}
    template<class _Alloc>
      function(allocator_arg_t, const _Alloc&, const function&);
    template<class _Alloc>
      function(allocator_arg_t, const _Alloc&, function&&);
    template<class _Fp, class _Alloc, class = _EnableIfLValueCallable<_Fp>>
      function(allocator_arg_t, const _Alloc& __a, _Fp __f);
#endif

    function& operator=(const function&);
    function& operator=(function&&) _NOEXCEPT;
    function& operator=(nullptr_t) _NOEXCEPT;
    template<class _Fp, class = _EnableIfLValueCallable<typename decay<_Fp>::type>>
    function& operator=(_Fp&&);

    ~function();

    // function modifiers:
    void swap(function&) _NOEXCEPT;

#if _LIBCPP_STD_VER <= 14
    template<class _Fp, class _Alloc>
      _LIBCPP_INLINE_VISIBILITY
      void assign(_Fp&& __f, const _Alloc& __a)
        {function(allocator_arg, __a, _VSTD::forward<_Fp>(__f)).swap(*this);}
#endif

    // function capacity:
    _LIBCPP_INLINE_VISIBILITY
    _LIBCPP_EXPLICIT operator bool() const _NOEXCEPT {
      return static_cast<bool>(__f_);
    }

    // deleted overloads close possible hole in the type system
    template<class _R2, class... _ArgTypes2>
      bool operator==(const function<_R2(_ArgTypes2...)>&) const = delete;
    template<class _R2, class... _ArgTypes2>
      bool operator!=(const function<_R2(_ArgTypes2...)>&) const = delete;
public:
    // function invocation:
    _Rp operator()(_ArgTypes...) const;

#ifndef _LIBCPP_NO_RTTI
    // function target access:
    const std::type_info& target_type() const _NOEXCEPT;
    template <typename _Tp> _Tp* target() _NOEXCEPT;
    template <typename _Tp> const _Tp* target() const _NOEXCEPT;
#endif // _LIBCPP_NO_RTTI
};

#ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
template<class _Rp, class ..._Ap>
function(_Rp(*)(_Ap...)) -> function<_Rp(_Ap...)>;

template<class _Fp>
struct __strip_signature;

template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...)> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) const> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) volatile> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) const volatile> { using type = _Rp(_Ap...); };

template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) &> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) const &> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) volatile &> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) const volatile &> { using type = _Rp(_Ap...); };

template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) noexcept> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) const noexcept> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) volatile noexcept> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) const volatile noexcept> { using type = _Rp(_Ap...); };

template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) & noexcept> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) const & noexcept> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) volatile & noexcept> { using type = _Rp(_Ap...); };
template<class _Rp, class _Gp, class ..._Ap>
struct __strip_signature<_Rp (_Gp::*) (_Ap...) const volatile & noexcept> { using type = _Rp(_Ap...); };

template<class _Fp, class _Stripped = typename __strip_signature<decltype(&_Fp::operator())>::type>
function(_Fp) -> function<_Stripped>;
#endif // !_LIBCPP_HAS_NO_DEDUCTION_GUIDES

template<class _Rp, class ..._ArgTypes>
function<_Rp(_ArgTypes...)>::function(const function& __f) : __f_(__f.__f_) {}

#if _LIBCPP_STD_VER <= 14
template<class _Rp, class ..._ArgTypes>
template <class _Alloc>
function<_Rp(_ArgTypes...)>::function(allocator_arg_t, const _Alloc&,
                                     const function& __f) : __f_(__f.__f_) {}
#endif

template <class _Rp, class... _ArgTypes>
function<_Rp(_ArgTypes...)>::function(function&& __f) _NOEXCEPT
    : __f_(_VSTD::move(__f.__f_)) {}

#if _LIBCPP_STD_VER <= 14
template<class _Rp, class ..._ArgTypes>
template <class _Alloc>
function<_Rp(_ArgTypes...)>::function(allocator_arg_t, const _Alloc&,
                                      function&& __f)
    : __f_(_VSTD::move(__f.__f_)) {}
#endif

template <class _Rp, class... _ArgTypes>
template <class _Fp, class>
function<_Rp(_ArgTypes...)>::function(_Fp __f) : __f_(_VSTD::move(__f)) {}

#if _LIBCPP_STD_VER <= 14
template <class _Rp, class... _ArgTypes>
template <class _Fp, class _Alloc, class>
function<_Rp(_ArgTypes...)>::function(allocator_arg_t, const _Alloc& __a,
                                      _Fp __f)
    : __f_(_VSTD::move(__f), __a) {}
#endif

template<class _Rp, class ..._ArgTypes>
function<_Rp(_ArgTypes...)>&
function<_Rp(_ArgTypes...)>::operator=(const function& __f)
{
    function(__f).swap(*this);
    return *this;
}

template<class _Rp, class ..._ArgTypes>
function<_Rp(_ArgTypes...)>&
function<_Rp(_ArgTypes...)>::operator=(function&& __f) _NOEXCEPT
{
    __f_ = _VSTD::move(__f.__f_);
    return *this;
}

template<class _Rp, class ..._ArgTypes>
function<_Rp(_ArgTypes...)>&
function<_Rp(_ArgTypes...)>::operator=(nullptr_t) _NOEXCEPT
{
    __f_ = nullptr;
    return *this;
}

template<class _Rp, class ..._ArgTypes>
template <class _Fp, class>
function<_Rp(_ArgTypes...)>&
function<_Rp(_ArgTypes...)>::operator=(_Fp&& __f)
{
    function(_VSTD::forward<_Fp>(__f)).swap(*this);
    return *this;
}

template<class _Rp, class ..._ArgTypes>
function<_Rp(_ArgTypes...)>::~function() {}

template<class _Rp, class ..._ArgTypes>
void
function<_Rp(_ArgTypes...)>::swap(function& __f) _NOEXCEPT
{
    __f_.swap(__f.__f_);
}

template<class _Rp, class ..._ArgTypes>
_Rp
function<_Rp(_ArgTypes...)>::operator()(_ArgTypes... __arg) const
{
    return __f_(_VSTD::forward<_ArgTypes>(__arg)...);
}

#ifndef _LIBCPP_NO_RTTI

template<class _Rp, class ..._ArgTypes>
const std::type_info&
function<_Rp(_ArgTypes...)>::target_type() const _NOEXCEPT
{
    return __f_.target_type();
}

template<class _Rp, class ..._ArgTypes>
template <typename _Tp>
_Tp*
function<_Rp(_ArgTypes...)>::target() _NOEXCEPT
{
    return (_Tp*)(__f_.template target<_Tp>());
}

template<class _Rp, class ..._ArgTypes>
template <typename _Tp>
const _Tp*
function<_Rp(_ArgTypes...)>::target() const _NOEXCEPT
{
    return __f_.template target<_Tp>();
}

#endif // _LIBCPP_NO_RTTI

template <class _Rp, class... _ArgTypes>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator==(const function<_Rp(_ArgTypes...)>& __f, nullptr_t) _NOEXCEPT {return !__f;}

template <class _Rp, class... _ArgTypes>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator==(nullptr_t, const function<_Rp(_ArgTypes...)>& __f) _NOEXCEPT {return !__f;}

template <class _Rp, class... _ArgTypes>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator!=(const function<_Rp(_ArgTypes...)>& __f, nullptr_t) _NOEXCEPT {return (bool)__f;}

template <class _Rp, class... _ArgTypes>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator!=(nullptr_t, const function<_Rp(_ArgTypes...)>& __f) _NOEXCEPT {return (bool)__f;}

template <class _Rp, class... _ArgTypes>
inline _LIBCPP_INLINE_VISIBILITY
void
swap(function<_Rp(_ArgTypes...)>& __x, function<_Rp(_ArgTypes...)>& __y) _NOEXCEPT
{return __x.swap(__y);}

#else // _LIBCPP_CXX03_LANG

#include <__functional_03>

#endif

////////////////////////////////////////////////////////////////////////////////
//                                  BIND
//==============================================================================

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

#if _LIBCPP_STD_VER > 14
template <class _Tp>
_LIBCPP_INLINE_VAR constexpr size_t is_bind_expression_v = is_bind_expression<_Tp>::value;
#endif

template<class _Tp> struct __is_placeholder : public integral_constant<int, 0> {};
template<class _Tp> struct _LIBCPP_TEMPLATE_VIS is_placeholder
    : public __is_placeholder<typename remove_cv<_Tp>::type> {};

#if _LIBCPP_STD_VER > 14
template <class _Tp>
_LIBCPP_INLINE_VAR constexpr size_t is_placeholder_v = is_placeholder<_Tp>::value;
#endif

namespace placeholders
{

template <int _Np> struct __ph {};

#if defined(_LIBCPP_CXX03_LANG) || defined(_LIBCPP_BUILDING_LIBRARY)
_LIBCPP_FUNC_VIS extern const __ph<1>   _1;
_LIBCPP_FUNC_VIS extern const __ph<2>   _2;
_LIBCPP_FUNC_VIS extern const __ph<3>   _3;
_LIBCPP_FUNC_VIS extern const __ph<4>   _4;
_LIBCPP_FUNC_VIS extern const __ph<5>   _5;
_LIBCPP_FUNC_VIS extern const __ph<6>   _6;
_LIBCPP_FUNC_VIS extern const __ph<7>   _7;
_LIBCPP_FUNC_VIS extern const __ph<8>   _8;
_LIBCPP_FUNC_VIS extern const __ph<9>   _9;
_LIBCPP_FUNC_VIS extern const __ph<10> _10;
#else
/* _LIBCPP_INLINE_VAR */ constexpr __ph<1>   _1{};
/* _LIBCPP_INLINE_VAR */ constexpr __ph<2>   _2{};
/* _LIBCPP_INLINE_VAR */ constexpr __ph<3>   _3{};
/* _LIBCPP_INLINE_VAR */ constexpr __ph<4>   _4{};
/* _LIBCPP_INLINE_VAR */ constexpr __ph<5>   _5{};
/* _LIBCPP_INLINE_VAR */ constexpr __ph<6>   _6{};
/* _LIBCPP_INLINE_VAR */ constexpr __ph<7>   _7{};
/* _LIBCPP_INLINE_VAR */ constexpr __ph<8>   _8{};
/* _LIBCPP_INLINE_VAR */ constexpr __ph<9>   _9{};
/* _LIBCPP_INLINE_VAR */ constexpr __ph<10> _10{};
#endif // defined(_LIBCPP_CXX03_LANG) || defined(_LIBCPP_BUILDING_LIBRARY)

}  // placeholders

template<int _Np>
struct __is_placeholder<placeholders::__ph<_Np> >
    : public integral_constant<int, _Np> {};


#ifndef _LIBCPP_CXX03_LANG

template <class _Tp, class _Uj>
inline _LIBCPP_INLINE_VISIBILITY
_Tp&
__mu(reference_wrapper<_Tp> __t, _Uj&)
{
    return __t.get();
}

template <class _Ti, class ..._Uj, size_t ..._Indx>
inline _LIBCPP_INLINE_VISIBILITY
typename __invoke_of<_Ti&, _Uj...>::type
__mu_expand(_Ti& __ti, tuple<_Uj...>& __uj, __tuple_indices<_Indx...>)
{
    return __ti(_VSTD::forward<_Uj>(_VSTD::get<_Indx>(__uj))...);
}

template <class _Ti, class ..._Uj>
inline _LIBCPP_INLINE_VISIBILITY
typename _EnableIf
<
    is_bind_expression<_Ti>::value,
    __invoke_of<_Ti&, _Uj...>
>::type
__mu(_Ti& __ti, tuple<_Uj...>& __uj)
{
    typedef typename __make_tuple_indices<sizeof...(_Uj)>::type __indices;
    return _VSTD::__mu_expand(__ti, __uj, __indices());
}

template <bool IsPh, class _Ti, class _Uj>
struct __mu_return2 {};

template <class _Ti, class _Uj>
struct __mu_return2<true, _Ti, _Uj>
{
    typedef typename tuple_element<is_placeholder<_Ti>::value - 1, _Uj>::type type;
};

template <class _Ti, class _Uj>
inline _LIBCPP_INLINE_VISIBILITY
typename enable_if
<
    0 < is_placeholder<_Ti>::value,
    typename __mu_return2<0 < is_placeholder<_Ti>::value, _Ti, _Uj>::type
>::type
__mu(_Ti&, _Uj& __uj)
{
    const size_t _Indx = is_placeholder<_Ti>::value - 1;
    return _VSTD::forward<typename tuple_element<_Indx, _Uj>::type>(_VSTD::get<_Indx>(__uj));
}

template <class _Ti, class _Uj>
inline _LIBCPP_INLINE_VISIBILITY
typename enable_if
<
    !is_bind_expression<_Ti>::value &&
    is_placeholder<_Ti>::value == 0 &&
    !__is_reference_wrapper<_Ti>::value,
    _Ti&
>::type
__mu(_Ti& __ti, _Uj&)
{
    return __ti;
}

template <class _Ti, bool IsReferenceWrapper, bool IsBindEx, bool IsPh,
          class _TupleUj>
struct __mu_return_impl;

template <bool _Invokable, class _Ti, class ..._Uj>
struct __mu_return_invokable  // false
{
    typedef __nat type;
};

template <class _Ti, class ..._Uj>
struct __mu_return_invokable<true, _Ti, _Uj...>
{
    typedef typename __invoke_of<_Ti&, _Uj...>::type type;
};

template <class _Ti, class ..._Uj>
struct __mu_return_impl<_Ti, false, true, false, tuple<_Uj...> >
    : public __mu_return_invokable<__invokable<_Ti&, _Uj...>::value, _Ti, _Uj...>
{
};

template <class _Ti, class _TupleUj>
struct __mu_return_impl<_Ti, false, false, true, _TupleUj>
{
    typedef typename tuple_element<is_placeholder<_Ti>::value - 1,
                                   _TupleUj>::type&& type;
};

template <class _Ti, class _TupleUj>
struct __mu_return_impl<_Ti, true, false, false, _TupleUj>
{
    typedef typename _Ti::type& type;
};

template <class _Ti, class _TupleUj>
struct __mu_return_impl<_Ti, false, false, false, _TupleUj>
{
    typedef _Ti& type;
};

template <class _Ti, class _TupleUj>
struct __mu_return
    : public __mu_return_impl<_Ti,
                              __is_reference_wrapper<_Ti>::value,
                              is_bind_expression<_Ti>::value,
                              0 < is_placeholder<_Ti>::value &&
                              is_placeholder<_Ti>::value <= tuple_size<_TupleUj>::value,
                              _TupleUj>
{
};

template <class _Fp, class _BoundArgs, class _TupleUj>
struct __is_valid_bind_return
{
    static const bool value = false;
};

template <class _Fp, class ..._BoundArgs, class _TupleUj>
struct __is_valid_bind_return<_Fp, tuple<_BoundArgs...>, _TupleUj>
{
    static const bool value = __invokable<_Fp,
                    typename __mu_return<_BoundArgs, _TupleUj>::type...>::value;
};

template <class _Fp, class ..._BoundArgs, class _TupleUj>
struct __is_valid_bind_return<_Fp, const tuple<_BoundArgs...>, _TupleUj>
{
    static const bool value = __invokable<_Fp,
                    typename __mu_return<const _BoundArgs, _TupleUj>::type...>::value;
};

template <class _Fp, class _BoundArgs, class _TupleUj,
          bool = __is_valid_bind_return<_Fp, _BoundArgs, _TupleUj>::value>
struct __bind_return;

template <class _Fp, class ..._BoundArgs, class _TupleUj>
struct __bind_return<_Fp, tuple<_BoundArgs...>, _TupleUj, true>
{
    typedef typename __invoke_of
    <
        _Fp&,
        typename __mu_return
        <
            _BoundArgs,
            _TupleUj
        >::type...
    >::type type;
};

template <class _Fp, class ..._BoundArgs, class _TupleUj>
struct __bind_return<_Fp, const tuple<_BoundArgs...>, _TupleUj, true>
{
    typedef typename __invoke_of
    <
        _Fp&,
        typename __mu_return
        <
            const _BoundArgs,
            _TupleUj
        >::type...
    >::type type;
};

template <class _Fp, class _BoundArgs, size_t ..._Indx, class _Args>
inline _LIBCPP_INLINE_VISIBILITY
typename __bind_return<_Fp, _BoundArgs, _Args>::type
__apply_functor(_Fp& __f, _BoundArgs& __bound_args, __tuple_indices<_Indx...>,
                _Args&& __args)
{
    return _VSTD::__invoke(__f, _VSTD::__mu(_VSTD::get<_Indx>(__bound_args), __args)...);
}

template<class _Fp, class ..._BoundArgs>
class __bind
    : public __weak_result_type<typename decay<_Fp>::type>
{
protected:
    typedef typename decay<_Fp>::type _Fd;
    typedef tuple<typename decay<_BoundArgs>::type...> _Td;
private:
    _Fd __f_;
    _Td __bound_args_;

    typedef typename __make_tuple_indices<sizeof...(_BoundArgs)>::type __indices;
public:
    template <class _Gp, class ..._BA,
              class = typename enable_if
                               <
                                  is_constructible<_Fd, _Gp>::value &&
                                  !is_same<typename remove_reference<_Gp>::type,
                                           __bind>::value
                               >::type>
      _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
      explicit __bind(_Gp&& __f, _BA&& ...__bound_args)
        : __f_(_VSTD::forward<_Gp>(__f)),
          __bound_args_(_VSTD::forward<_BA>(__bound_args)...) {}

    template <class ..._Args>
        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
        typename __bind_return<_Fd, _Td, tuple<_Args&&...> >::type
        operator()(_Args&& ...__args)
        {
            return _VSTD::__apply_functor(__f_, __bound_args_, __indices(),
                                  tuple<_Args&&...>(_VSTD::forward<_Args>(__args)...));
        }

    template <class ..._Args>
        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
        typename __bind_return<const _Fd, const _Td, tuple<_Args&&...> >::type
        operator()(_Args&& ...__args) const
        {
            return _VSTD::__apply_functor(__f_, __bound_args_, __indices(),
                                   tuple<_Args&&...>(_VSTD::forward<_Args>(__args)...));
        }
};

template<class _Fp, class ..._BoundArgs>
struct __is_bind_expression<__bind<_Fp, _BoundArgs...> > : public true_type {};

template<class _Rp, class _Fp, class ..._BoundArgs>
class __bind_r
    : public __bind<_Fp, _BoundArgs...>
{
    typedef __bind<_Fp, _BoundArgs...> base;
    typedef typename base::_Fd _Fd;
    typedef typename base::_Td _Td;
public:
    typedef _Rp result_type;


    template <class _Gp, class ..._BA,
              class = typename enable_if
                               <
                                  is_constructible<_Fd, _Gp>::value &&
                                  !is_same<typename remove_reference<_Gp>::type,
                                           __bind_r>::value
                               >::type>
      _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
      explicit __bind_r(_Gp&& __f, _BA&& ...__bound_args)
        : base(_VSTD::forward<_Gp>(__f),
               _VSTD::forward<_BA>(__bound_args)...) {}

    template <class ..._Args>
        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
        typename enable_if
        <
            is_convertible<typename __bind_return<_Fd, _Td, tuple<_Args&&...> >::type,
                           result_type>::value || is_void<_Rp>::value,
            result_type
        >::type
        operator()(_Args&& ...__args)
        {
            typedef __invoke_void_return_wrapper<_Rp> _Invoker;
            return _Invoker::__call(static_cast<base&>(*this), _VSTD::forward<_Args>(__args)...);
        }

    template <class ..._Args>
        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
        typename enable_if
        <
            is_convertible<typename __bind_return<const _Fd, const _Td, tuple<_Args&&...> >::type,
                           result_type>::value || is_void<_Rp>::value,
            result_type
        >::type
        operator()(_Args&& ...__args) const
        {
            typedef __invoke_void_return_wrapper<_Rp> _Invoker;
            return _Invoker::__call(static_cast<base const&>(*this), _VSTD::forward<_Args>(__args)...);
        }
};

template<class _Rp, class _Fp, class ..._BoundArgs>
struct __is_bind_expression<__bind_r<_Rp, _Fp, _BoundArgs...> > : public true_type {};

template<class _Fp, class ..._BoundArgs>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
__bind<_Fp, _BoundArgs...>
bind(_Fp&& __f, _BoundArgs&&... __bound_args)
{
    typedef __bind<_Fp, _BoundArgs...> type;
    return type(_VSTD::forward<_Fp>(__f), _VSTD::forward<_BoundArgs>(__bound_args)...);
}

template<class _Rp, class _Fp, class ..._BoundArgs>
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
__bind_r<_Rp, _Fp, _BoundArgs...>
bind(_Fp&& __f, _BoundArgs&&... __bound_args)
{
    typedef __bind_r<_Rp, _Fp, _BoundArgs...> type;
    return type(_VSTD::forward<_Fp>(__f), _VSTD::forward<_BoundArgs>(__bound_args)...);
}

#endif // _LIBCPP_CXX03_LANG

#if _LIBCPP_STD_VER > 14

template<class _Op, class _Tuple,
         class _Idxs = typename __make_tuple_indices<tuple_size<_Tuple>::value>::type>
struct __perfect_forward_impl;

template<class _Op, class... _Bound, size_t... _Idxs>
struct __perfect_forward_impl<_Op, __tuple_types<_Bound...>, __tuple_indices<_Idxs...>>
{
    tuple<_Bound...> __bound_;

    template<class... _Args>
    _LIBCPP_INLINE_VISIBILITY constexpr auto operator()(_Args&&... __args) &
    noexcept(noexcept(_Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...)))
    -> decltype(      _Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...))
    {return           _Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...);}

    template<class... _Args>
    _LIBCPP_INLINE_VISIBILITY constexpr auto operator()(_Args&&... __args) const&
    noexcept(noexcept(_Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...)))
    -> decltype(      _Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...))
    {return           _Op::__call(_VSTD::get<_Idxs>(__bound_)..., _VSTD::forward<_Args>(__args)...);}

    template<class... _Args>
    _LIBCPP_INLINE_VISIBILITY constexpr auto operator()(_Args&&... __args) &&
    noexcept(noexcept(_Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
                                  _VSTD::forward<_Args>(__args)...)))
    -> decltype(      _Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
                                  _VSTD::forward<_Args>(__args)...))
    {return           _Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
                                  _VSTD::forward<_Args>(__args)...);}

    template<class... _Args>
    _LIBCPP_INLINE_VISIBILITY constexpr auto operator()(_Args&&... __args) const&&
    noexcept(noexcept(_Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
                                  _VSTD::forward<_Args>(__args)...)))
    -> decltype(      _Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
                                  _VSTD::forward<_Args>(__args)...))
    {return           _Op::__call(_VSTD::get<_Idxs>(_VSTD::move(__bound_))...,
                                  _VSTD::forward<_Args>(__args)...);}

    template<class _Fn = typename tuple_element<0, tuple<_Bound...>>::type,
             class = _EnableIf<is_copy_constructible_v<_Fn>>>
    constexpr __perfect_forward_impl(__perfect_forward_impl const& __other)
        : __bound_(__other.__bound_) {}

    template<class _Fn = typename tuple_element<0, tuple<_Bound...>>::type,
             class = _EnableIf<is_move_constructible_v<_Fn>>>
    constexpr __perfect_forward_impl(__perfect_forward_impl && __other)
        : __bound_(_VSTD::move(__other.__bound_)) {}

    template<class... _BoundArgs>
    explicit constexpr __perfect_forward_impl(_BoundArgs&&... __bound) :
        __bound_(_VSTD::forward<_BoundArgs>(__bound)...) { }
};

template<class _Op, class... _Args>
using __perfect_forward =
    __perfect_forward_impl<_Op, __tuple_types<decay_t<_Args>...>>;

struct __not_fn_op
{
    template<class... _Args>
    static _LIBCPP_CONSTEXPR_AFTER_CXX17 auto __call(_Args&&... __args)
    noexcept(noexcept(!_VSTD::invoke(_VSTD::forward<_Args>(__args)...)))
    -> decltype(      !_VSTD::invoke(_VSTD::forward<_Args>(__args)...))
    { return          !_VSTD::invoke(_VSTD::forward<_Args>(__args)...); }
};

template<class _Fn,
         class = _EnableIf<is_constructible_v<decay_t<_Fn>, _Fn> &&
                           is_move_constructible_v<_Fn>>>
_LIBCPP_CONSTEXPR_AFTER_CXX17 auto not_fn(_Fn&& __f)
{
    return __perfect_forward<__not_fn_op, _Fn>(_VSTD::forward<_Fn>(__f));
}

#endif // _LIBCPP_STD_VER > 14

#if _LIBCPP_STD_VER > 17

struct __bind_front_op
{
    template<class... _Args>
    constexpr static auto __call(_Args&&... __args)
    noexcept(noexcept(_VSTD::invoke(_VSTD::forward<_Args>(__args)...)))
    -> decltype(      _VSTD::invoke(_VSTD::forward<_Args>(__args)...))
    { return          _VSTD::invoke(_VSTD::forward<_Args>(__args)...); }
};

template<class _Fn, class... _Args,
         class = _EnableIf<conjunction<is_constructible<decay_t<_Fn>, _Fn>,
                                       is_move_constructible<decay_t<_Fn>>,
                                       is_constructible<decay_t<_Args>, _Args>...,
                                       is_move_constructible<decay_t<_Args>>...
                                       >::value>>
constexpr auto bind_front(_Fn&& __f, _Args&&... __args)
{
    return __perfect_forward<__bind_front_op, _Fn, _Args...>(_VSTD::forward<_Fn>(__f),
                                                             _VSTD::forward<_Args>(__args)...);
}

#endif // _LIBCPP_STD_VER > 17

// struct hash<T*> in <memory>

template <class _BinaryPredicate, class _ForwardIterator1, class _ForwardIterator2>
pair<_ForwardIterator1, _ForwardIterator1> _LIBCPP_CONSTEXPR_AFTER_CXX11
__search(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
         _ForwardIterator2 __first2, _ForwardIterator2 __last2, _BinaryPredicate __pred,
         forward_iterator_tag, forward_iterator_tag)
{
    if (__first2 == __last2)
        return _VSTD::make_pair(__first1, __first1);  // Everything matches an empty sequence
    while (true)
    {
        // Find first element in sequence 1 that matchs *__first2, with a mininum of loop checks
        while (true)
        {
            if (__first1 == __last1)  // return __last1 if no element matches *__first2
                return _VSTD::make_pair(__last1, __last1);
            if (__pred(*__first1, *__first2))
                break;
            ++__first1;
        }
        // *__first1 matches *__first2, now match elements after here
        _ForwardIterator1 __m1 = __first1;
        _ForwardIterator2 __m2 = __first2;
        while (true)
        {
            if (++__m2 == __last2)  // If pattern exhausted, __first1 is the answer (works for 1 element pattern)
                return _VSTD::make_pair(__first1, __m1);
            if (++__m1 == __last1)  // Otherwise if source exhaused, pattern not found
                return _VSTD::make_pair(__last1, __last1);
            if (!__pred(*__m1, *__m2))  // if there is a mismatch, restart with a new __first1
            {
                ++__first1;
                break;
            }  // else there is a match, check next elements
        }
    }
}

template <class _BinaryPredicate, class _RandomAccessIterator1, class _RandomAccessIterator2>
_LIBCPP_CONSTEXPR_AFTER_CXX11
pair<_RandomAccessIterator1, _RandomAccessIterator1>
__search(_RandomAccessIterator1 __first1, _RandomAccessIterator1 __last1,
         _RandomAccessIterator2 __first2, _RandomAccessIterator2 __last2, _BinaryPredicate __pred,
           random_access_iterator_tag, random_access_iterator_tag)
{
    typedef typename iterator_traits<_RandomAccessIterator1>::difference_type _D1;
    typedef typename iterator_traits<_RandomAccessIterator2>::difference_type _D2;
    // Take advantage of knowing source and pattern lengths.  Stop short when source is smaller than pattern
    const _D2 __len2 = __last2 - __first2;
    if (__len2 == 0)
        return _VSTD::make_pair(__first1, __first1);
    const _D1 __len1 = __last1 - __first1;
    if (__len1 < __len2)
        return _VSTD::make_pair(__last1, __last1);
    const _RandomAccessIterator1 __s = __last1 - (__len2 - 1);  // Start of pattern match can't go beyond here

    while (true)
    {
        while (true)
        {
            if (__first1 == __s)
                return _VSTD::make_pair(__last1, __last1);
            if (__pred(*__first1, *__first2))
                break;
            ++__first1;
        }

        _RandomAccessIterator1 __m1 = __first1;
        _RandomAccessIterator2 __m2 = __first2;
         while (true)
         {
             if (++__m2 == __last2)
                 return _VSTD::make_pair(__first1, __first1 + __len2);
             ++__m1;          // no need to check range on __m1 because __s guarantees we have enough source
             if (!__pred(*__m1, *__m2))
             {
                 ++__first1;
                 break;
             }
         }
    }
}

#if _LIBCPP_STD_VER > 14

// default searcher
template<class _ForwardIterator, class _BinaryPredicate = equal_to<>>
class _LIBCPP_TEMPLATE_VIS default_searcher {
public:
    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
    default_searcher(_ForwardIterator __f, _ForwardIterator __l,
                       _BinaryPredicate __p = _BinaryPredicate())
        : __first_(__f), __last_(__l), __pred_(__p) {}

    template <typename _ForwardIterator2>
    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
    pair<_ForwardIterator2, _ForwardIterator2>
    operator () (_ForwardIterator2 __f, _ForwardIterator2 __l) const
    {
        return _VSTD::__search(__f, __l, __first_, __last_, __pred_,
            typename iterator_traits<_ForwardIterator>::iterator_category(),
            typename iterator_traits<_ForwardIterator2>::iterator_category());
    }

private:
    _ForwardIterator __first_;
    _ForwardIterator __last_;
    _BinaryPredicate __pred_;
    };

#endif // _LIBCPP_STD_VER > 14

#if _LIBCPP_STD_VER > 17
template <class _Tp>
using unwrap_reference_t = typename unwrap_reference<_Tp>::type;

template <class _Tp>
using unwrap_ref_decay_t = typename unwrap_ref_decay<_Tp>::type;
#endif // > C++17

#if _LIBCPP_STD_VER > 17
// [func.identity]
struct identity {
    template<class _Tp>
    _LIBCPP_NODISCARD_EXT constexpr _Tp&& operator()(_Tp&& __t) const noexcept
    {
        return _VSTD::forward<_Tp>(__t);
    }

    using is_transparent = void;
};
#endif // _LIBCPP_STD_VER > 17

#if !defined(_LIBCPP_HAS_NO_RANGES)

namespace ranges {

struct equal_to {
  template <class _Tp, class _Up>
  requires equality_comparable_with<_Tp, _Up>
  [[nodiscard]] constexpr bool operator()(_Tp &&__t, _Up &&__u) const
      noexcept(noexcept(bool(_VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u)))) {
    return _VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u);
  }

  using is_transparent = void;
};

struct not_equal_to {
  template <class _Tp, class _Up>
  requires equality_comparable_with<_Tp, _Up>
  [[nodiscard]] constexpr bool operator()(_Tp &&__t, _Up &&__u) const
      noexcept(noexcept(bool(!(_VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u))))) {
    return !(_VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u));
  }

  using is_transparent = void;
};

struct greater {
  template <class _Tp, class _Up>
  requires totally_ordered_with<_Tp, _Up>
  [[nodiscard]] constexpr bool operator()(_Tp &&__t, _Up &&__u) const
      noexcept(noexcept(bool(_VSTD::forward<_Up>(__u) < _VSTD::forward<_Tp>(__t)))) {
    return _VSTD::forward<_Up>(__u) < _VSTD::forward<_Tp>(__t);
  }

  using is_transparent = void;
};

struct less {
  template <class _Tp, class _Up>
  requires totally_ordered_with<_Tp, _Up>
  [[nodiscard]] constexpr bool operator()(_Tp &&__t, _Up &&__u) const
      noexcept(noexcept(bool(_VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u)))) {
    return _VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u);
  }

  using is_transparent = void;
};

struct greater_equal {
  template <class _Tp, class _Up>
  requires totally_ordered_with<_Tp, _Up>
  [[nodiscard]] constexpr bool operator()(_Tp &&__t, _Up &&__u) const
      noexcept(noexcept(bool(!(_VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u))))) {
    return !(_VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u));
  }

  using is_transparent = void;
};

struct less_equal {
  template <class _Tp, class _Up>
  requires totally_ordered_with<_Tp, _Up>
  [[nodiscard]] constexpr bool operator()(_Tp &&__t, _Up &&__u) const
      noexcept(noexcept(bool(!(_VSTD::forward<_Up>(__u) < _VSTD::forward<_Tp>(__t))))) {
    return !(_VSTD::forward<_Up>(__u) < _VSTD::forward<_Tp>(__t));
  }

  using is_transparent = void;
};

} // namespace ranges

#endif // !defined(_LIBCPP_HAS_NO_RANGES)

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP_FUNCTIONAL