// <functional> -*- C++ -*-

// Copyright (C) 2001-2016 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/*
 * Copyright (c) 1997
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 */

/** @file include/functional
 *  This is a Standard C++ Library header.
 */

#ifndef _GLIBCXX_FUNCTIONAL
#define _GLIBCXX_FUNCTIONAL 1

#pragma GCC system_header

#include <bits/c++config.h>
#include <bits/stl_function.h>

#if __cplusplus >= 201103L

#include <typeinfo>
#include <new>
#include <tuple>
#include <type_traits>
#include <bits/functexcept.h>
#include <bits/functional_hash.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  template<typename _MemberPointer>
    class _Mem_fn;
  template<typename _Tp, typename _Class>
    _Mem_fn<_Tp _Class::*>
    mem_fn(_Tp _Class::*) noexcept;

  /// If we have found a result_type, extract it.
  template<typename _Functor, typename = __void_t<>>
    struct _Maybe_get_result_type
    { };

  template<typename _Functor>
    struct _Maybe_get_result_type<_Functor,
				  __void_t<typename _Functor::result_type>>
    { typedef typename _Functor::result_type result_type; };

  /**
   *  Base class for any function object that has a weak result type, as
   *  defined in 20.8.2 [func.require] of C++11.
  */
  template<typename _Functor>
    struct _Weak_result_type_impl
    : _Maybe_get_result_type<_Functor>
    { };

  /// Retrieve the result type for a function type.
  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(_ArgTypes...)>
    { typedef _Res result_type; };

  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(_ArgTypes......)>
    { typedef _Res result_type; };

  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(_ArgTypes...) const>
    { typedef _Res result_type; };

  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(_ArgTypes......) const>
    { typedef _Res result_type; };

  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(_ArgTypes...) volatile>
    { typedef _Res result_type; };

  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(_ArgTypes......) volatile>
    { typedef _Res result_type; };

  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(_ArgTypes...) const volatile>
    { typedef _Res result_type; };

  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(_ArgTypes......) const volatile>
    { typedef _Res result_type; };

  /// Retrieve the result type for a function reference.
  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(&)(_ArgTypes...)>
    { typedef _Res result_type; };

  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(&)(_ArgTypes......)>
    { typedef _Res result_type; };

  /// Retrieve the result type for a function pointer.
  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(*)(_ArgTypes...)>
    { typedef _Res result_type; };

  template<typename _Res, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res(*)(_ArgTypes......)>
    { typedef _Res result_type; };

  /// Retrieve result type for a member function pointer.
  template<typename _Res, typename _Class, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res (_Class::*)(_ArgTypes...)>
    { typedef _Res result_type; };

  template<typename _Res, typename _Class, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res (_Class::*)(_ArgTypes......)>
    { typedef _Res result_type; };

  /// Retrieve result type for a const member function pointer.
  template<typename _Res, typename _Class, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res (_Class::*)(_ArgTypes...) const>
    { typedef _Res result_type; };

  template<typename _Res, typename _Class, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res (_Class::*)(_ArgTypes......) const>
    { typedef _Res result_type; };

  /// Retrieve result type for a volatile member function pointer.
  template<typename _Res, typename _Class, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res (_Class::*)(_ArgTypes...) volatile>
    { typedef _Res result_type; };

  template<typename _Res, typename _Class, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res (_Class::*)(_ArgTypes......) volatile>
    { typedef _Res result_type; };

  /// Retrieve result type for a const volatile member function pointer.
  template<typename _Res, typename _Class, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res (_Class::*)(_ArgTypes...)
				  const volatile>
    { typedef _Res result_type; };

  template<typename _Res, typename _Class, typename... _ArgTypes>
    struct _Weak_result_type_impl<_Res (_Class::*)(_ArgTypes......)
				  const volatile>
    { typedef _Res result_type; };

  /**
   *  Strip top-level cv-qualifiers from the function object and let
   *  _Weak_result_type_impl perform the real work.
  */
  template<typename _Functor>
    struct _Weak_result_type
    : _Weak_result_type_impl<typename remove_cv<_Functor>::type>
    { };

  template<typename _Tp, typename _Up = typename decay<_Tp>::type>
    struct _Unwrap
    {
      using type = _Tp&&;

      // Equivalent to std::forward<_Tp>
      static constexpr _Tp&&
      _S_fwd(_Tp& __t) noexcept { return static_cast<_Tp&&>(__t); }
    };

  template<typename _Tp, typename _Up>
    struct _Unwrap<_Tp, reference_wrapper<_Up>>
    {
      using type = _Up&;

      // Get an lvalue-reference from a reference_wrapper.
      static _Up&
      _S_fwd(const _Tp& __t) noexcept { __t.get(); }
    };

  // Used by __invoke_impl instead of std::forward<_Tp> so that a
  // reference_wrapper is converted to an lvalue-reference.
  template<typename _Tp>
    inline typename _Unwrap<_Tp>::type
    __invfwd(typename remove_reference<_Tp>::type& __t) noexcept
    { return _Unwrap<_Tp>::_S_fwd(__t); }

  template<typename _Res, typename _Fn, typename... _Args>
    inline _Res
    __invoke_impl(__invoke_other, _Fn&& __f, _Args&&... __args)
    noexcept(noexcept(std::forward<_Fn>(__f)(std::forward<_Args>(__args)...)))
    { return std::forward<_Fn>(__f)(std::forward<_Args>(__args)...); }

  template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
    inline _Res
    __invoke_impl(__invoke_memfun_ref, _MemFun&& __f, _Tp&& __t,
		  _Args&&... __args)
    noexcept(noexcept(
	  (__invfwd<_Tp>(__t).*__f)(std::forward<_Args>(__args)...)))
    { return (__invfwd<_Tp>(__t).*__f)(std::forward<_Args>(__args)...); }

  template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
    inline _Res
    __invoke_impl(__invoke_memfun_deref, _MemFun&& __f, _Tp&& __t,
		  _Args&&... __args)
    noexcept(noexcept(
	  ((*std::forward<_Tp>(__t)).*__f)(std::forward<_Args>(__args)...)))
    {
      return ((*std::forward<_Tp>(__t)).*__f)(std::forward<_Args>(__args)...);
    }

  template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
    inline _Res
    __invoke_impl(__invoke_memobj_ref, _MemFun&& __f, _Tp&& __t)
    noexcept(noexcept(__invfwd<_Tp>(__t).*__f))
    { return __invfwd<_Tp>(__t).*__f; }

  template<typename _Res, typename _MemFun, typename _Tp, typename... _Args>
    inline _Res
    __invoke_impl(__invoke_memobj_deref, _MemFun&& __f, _Tp&& __t,
		  _Args&&... __args)
    noexcept(noexcept((*std::forward<_Tp>(__t)).*__f))
    { return (*std::forward<_Tp>(__t)).*__f; }

  /// Invoke a callable object.
  template<typename _Callable, typename... _Args>
    inline typename result_of<_Callable&&(_Args&&...)>::type
    __invoke(_Callable&& __fn, _Args&&... __args)
    {
      using __result_of = result_of<_Callable&&(_Args&&...)>;
      using __type = typename __result_of::type;
      using __tag = typename __result_of::__invoke_type;
      return std::__invoke_impl<__type>(__tag{}, std::forward<_Callable>(__fn),
					std::forward<_Args>(__args)...);
    }

#if __cplusplus > 201402L
# define __cpp_lib_invoke 201411

  /// Invoke a callable object.
  template<typename _Callable, typename... _Args>
    inline result_of_t<_Callable&&(_Args&&...)>
    invoke(_Callable&& __fn, _Args&&... __args)
    {
      return std::__invoke(std::forward<_Callable>(__fn),
			   std::forward<_Args>(__args)...);
    }
#endif

  /**
   *  Knowing which of unary_function and binary_function _Tp derives
   *  from, derives from the same and ensures that reference_wrapper
   *  will have a weak result type. See cases below.
   */
  template<bool _Unary, bool _Binary, typename _Tp>
    struct _Reference_wrapper_base_impl;

  // None of the nested argument types.
  template<typename _Tp>
    struct _Reference_wrapper_base_impl<false, false, _Tp>
    : _Weak_result_type<_Tp>
    { };

  // Nested argument_type only.
  template<typename _Tp>
    struct _Reference_wrapper_base_impl<true, false, _Tp>
    : _Weak_result_type<_Tp>
    {
      typedef typename _Tp::argument_type argument_type;
    };

  // Nested first_argument_type and second_argument_type only.
  template<typename _Tp>
    struct _Reference_wrapper_base_impl<false, true, _Tp>
    : _Weak_result_type<_Tp>
    {
      typedef typename _Tp::first_argument_type first_argument_type;
      typedef typename _Tp::second_argument_type second_argument_type;
    };

  // All the nested argument types.
   template<typename _Tp>
    struct _Reference_wrapper_base_impl<true, true, _Tp>
    : _Weak_result_type<_Tp>
    {
      typedef typename _Tp::argument_type argument_type;
      typedef typename _Tp::first_argument_type first_argument_type;
      typedef typename _Tp::second_argument_type second_argument_type;
    };

  _GLIBCXX_HAS_NESTED_TYPE(argument_type)
  _GLIBCXX_HAS_NESTED_TYPE(first_argument_type)
  _GLIBCXX_HAS_NESTED_TYPE(second_argument_type)

  /**
   *  Derives from unary_function or binary_function when it
   *  can. Specializations handle all of the easy cases. The primary
   *  template determines what to do with a class type, which may
   *  derive from both unary_function and binary_function.
  */
  template<typename _Tp>
    struct _Reference_wrapper_base
    : _Reference_wrapper_base_impl<
      __has_argument_type<_Tp>::value,
      __has_first_argument_type<_Tp>::value
      && __has_second_argument_type<_Tp>::value,
      _Tp>
    { };

  // - a function type (unary)
  template<typename _Res, typename _T1>
    struct _Reference_wrapper_base<_Res(_T1)>
    : unary_function<_T1, _Res>
    { };

  template<typename _Res, typename _T1>
    struct _Reference_wrapper_base<_Res(_T1) const>
    : unary_function<_T1, _Res>
    { };

  template<typename _Res, typename _T1>
    struct _Reference_wrapper_base<_Res(_T1) volatile>
    : unary_function<_T1, _Res>
    { };

  template<typename _Res, typename _T1>
    struct _Reference_wrapper_base<_Res(_T1) const volatile>
    : unary_function<_T1, _Res>
    { };

  // - a function type (binary)
  template<typename _Res, typename _T1, typename _T2>
    struct _Reference_wrapper_base<_Res(_T1, _T2)>
    : binary_function<_T1, _T2, _Res>
    { };

  template<typename _Res, typename _T1, typename _T2>
    struct _Reference_wrapper_base<_Res(_T1, _T2) const>
    : binary_function<_T1, _T2, _Res>
    { };

  template<typename _Res, typename _T1, typename _T2>
    struct _Reference_wrapper_base<_Res(_T1, _T2) volatile>
    : binary_function<_T1, _T2, _Res>
    { };

  template<typename _Res, typename _T1, typename _T2>
    struct _Reference_wrapper_base<_Res(_T1, _T2) const volatile>
    : binary_function<_T1, _T2, _Res>
    { };

  // - a function pointer type (unary)
  template<typename _Res, typename _T1>
    struct _Reference_wrapper_base<_Res(*)(_T1)>
    : unary_function<_T1, _Res>
    { };

  // - a function pointer type (binary)
  template<typename _Res, typename _T1, typename _T2>
    struct _Reference_wrapper_base<_Res(*)(_T1, _T2)>
    : binary_function<_T1, _T2, _Res>
    { };

  // - a pointer to member function type (unary, no qualifiers)
  template<typename _Res, typename _T1>
    struct _Reference_wrapper_base<_Res (_T1::*)()>
    : unary_function<_T1*, _Res>
    { };

  // - a pointer to member function type (binary, no qualifiers)
  template<typename _Res, typename _T1, typename _T2>
    struct _Reference_wrapper_base<_Res (_T1::*)(_T2)>
    : binary_function<_T1*, _T2, _Res>
    { };

  // - a pointer to member function type (unary, const)
  template<typename _Res, typename _T1>
    struct _Reference_wrapper_base<_Res (_T1::*)() const>
    : unary_function<const _T1*, _Res>
    { };

  // - a pointer to member function type (binary, const)
  template<typename _Res, typename _T1, typename _T2>
    struct _Reference_wrapper_base<_Res (_T1::*)(_T2) const>
    : binary_function<const _T1*, _T2, _Res>
    { };

  // - a pointer to member function type (unary, volatile)
  template<typename _Res, typename _T1>
    struct _Reference_wrapper_base<_Res (_T1::*)() volatile>
    : unary_function<volatile _T1*, _Res>
    { };

  // - a pointer to member function type (binary, volatile)
  template<typename _Res, typename _T1, typename _T2>
    struct _Reference_wrapper_base<_Res (_T1::*)(_T2) volatile>
    : binary_function<volatile _T1*, _T2, _Res>
    { };

  // - a pointer to member function type (unary, const volatile)
  template<typename _Res, typename _T1>
    struct _Reference_wrapper_base<_Res (_T1::*)() const volatile>
    : unary_function<const volatile _T1*, _Res>
    { };

  // - a pointer to member function type (binary, const volatile)
  template<typename _Res, typename _T1, typename _T2>
    struct _Reference_wrapper_base<_Res (_T1::*)(_T2) const volatile>
    : binary_function<const volatile _T1*, _T2, _Res>
    { };

  /**
   *  @brief Primary class template for reference_wrapper.
   *  @ingroup functors
   *  @{
   */
  template<typename _Tp>
    class reference_wrapper
    : public _Reference_wrapper_base<typename remove_cv<_Tp>::type>
    {
      _Tp* _M_data;

    public:
      typedef _Tp type;

      reference_wrapper(_Tp& __indata) noexcept
      : _M_data(std::__addressof(__indata))
      { }

      reference_wrapper(_Tp&&) = delete;

      reference_wrapper(const reference_wrapper&) = default;

      reference_wrapper&
      operator=(const reference_wrapper&) = default;

      operator _Tp&() const noexcept
      { return this->get(); }

      _Tp&
      get() const noexcept
      { return *_M_data; }

      template<typename... _Args>
	typename result_of<_Tp&(_Args&&...)>::type
	operator()(_Args&&... __args) const
	{
	  return std::__invoke(get(), std::forward<_Args>(__args)...);
	}
    };


  /// Denotes a reference should be taken to a variable.
  template<typename _Tp>
    inline reference_wrapper<_Tp>
    ref(_Tp& __t) noexcept
    { return reference_wrapper<_Tp>(__t); }

  /// Denotes a const reference should be taken to a variable.
  template<typename _Tp>
    inline reference_wrapper<const _Tp>
    cref(const _Tp& __t) noexcept
    { return reference_wrapper<const _Tp>(__t); }

  template<typename _Tp>
    void ref(const _Tp&&) = delete;

  template<typename _Tp>
    void cref(const _Tp&&) = delete;

  /// Partial specialization.
  template<typename _Tp>
    inline reference_wrapper<_Tp>
    ref(reference_wrapper<_Tp> __t) noexcept
    { return ref(__t.get()); }

  /// Partial specialization.
  template<typename _Tp>
    inline reference_wrapper<const _Tp>
    cref(reference_wrapper<_Tp> __t) noexcept
    { return cref(__t.get()); }

  // @} group functors

  template<typename... _Types>
    struct _Pack : integral_constant<size_t, sizeof...(_Types)>
    { };

  template<typename _From, typename _To, bool = _From::value == _To::value>
    struct _AllConvertible : false_type
    { };

  template<typename... _From, typename... _To>
    struct _AllConvertible<_Pack<_From...>, _Pack<_To...>, true>
    : __and_<is_convertible<_From, _To>...>
    { };

  template<typename _Tp1, typename _Tp2>
    using _NotSame = __not_<is_same<typename std::decay<_Tp1>::type,
				    typename std::decay<_Tp2>::type>>;

  /**
   * Derives from @c unary_function or @c binary_function, or perhaps
   * nothing, depending on the number of arguments provided. The
   * primary template is the basis case, which derives nothing.
   */
  template<typename _Res, typename... _ArgTypes>
    struct _Maybe_unary_or_binary_function { };

  /// Derives from @c unary_function, as appropriate.
  template<typename _Res, typename _T1>
    struct _Maybe_unary_or_binary_function<_Res, _T1>
    : std::unary_function<_T1, _Res> { };

  /// Derives from @c binary_function, as appropriate.
  template<typename _Res, typename _T1, typename _T2>
    struct _Maybe_unary_or_binary_function<_Res, _T1, _T2>
    : std::binary_function<_T1, _T2, _Res> { };

  template<typename _Signature>
    struct _Mem_fn_traits;

  template<typename _Res, typename _Class, typename... _ArgTypes>
    struct _Mem_fn_traits_base
    {
      using __result_type = _Res;
      using __maybe_type
	= _Maybe_unary_or_binary_function<_Res, _Class*, _ArgTypes...>;
      using __arity = integral_constant<size_t, sizeof...(_ArgTypes)>;
    };

#define _GLIBCXX_MEM_FN_TRAITS2(_CV, _REF, _LVAL, _RVAL)		\
  template<typename _Res, typename _Class, typename... _ArgTypes>	\
    struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes...) _CV _REF>	\
    : _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...>		\
    {									\
      using __vararg = false_type;					\
    };									\
  template<typename _Res, typename _Class, typename... _ArgTypes>	\
    struct _Mem_fn_traits<_Res (_Class::*)(_ArgTypes... ...) _CV _REF>	\
    : _Mem_fn_traits_base<_Res, _CV _Class, _ArgTypes...>		\
    {									\
      using __vararg = true_type;					\
    };

#define _GLIBCXX_MEM_FN_TRAITS(_REF, _LVAL, _RVAL)		\
  _GLIBCXX_MEM_FN_TRAITS2(		, _REF, _LVAL, _RVAL)	\
  _GLIBCXX_MEM_FN_TRAITS2(const		, _REF, _LVAL, _RVAL)	\
  _GLIBCXX_MEM_FN_TRAITS2(volatile	, _REF, _LVAL, _RVAL)	\
  _GLIBCXX_MEM_FN_TRAITS2(const volatile, _REF, _LVAL, _RVAL)

_GLIBCXX_MEM_FN_TRAITS( , true_type, true_type)
_GLIBCXX_MEM_FN_TRAITS(&, true_type, false_type)
_GLIBCXX_MEM_FN_TRAITS(&&, false_type, true_type)

#undef _GLIBCXX_MEM_FN_TRAITS
#undef _GLIBCXX_MEM_FN_TRAITS2

  template<typename _MemFunPtr,
	   bool __is_mem_fn = is_member_function_pointer<_MemFunPtr>::value>
    class _Mem_fn_base
    : public _Mem_fn_traits<_MemFunPtr>::__maybe_type
    {
      using _Traits = _Mem_fn_traits<_MemFunPtr>;

      using _Arity = typename _Traits::__arity;
      using _Varargs = typename _Traits::__vararg;

      template<typename _Func, typename... _BoundArgs>
	friend struct _Bind_check_arity;

      _MemFunPtr _M_pmf;

    public:

      using result_type = typename _Traits::__result_type;

      explicit constexpr
      _Mem_fn_base(_MemFunPtr __pmf) noexcept : _M_pmf(__pmf) { }

      template<typename... _Args>
	auto
	operator()(_Args&&... __args) const
	noexcept(noexcept(
	      std::__invoke(_M_pmf, std::forward<_Args>(__args)...)))
	-> decltype(std::__invoke(_M_pmf, std::forward<_Args>(__args)...))
	{ return std::__invoke(_M_pmf, std::forward<_Args>(__args)...); }
    };

  // Partial specialization for member object pointers.
  template<typename _MemObjPtr>
    class _Mem_fn_base<_MemObjPtr, false>
    {
      using _Arity = integral_constant<size_t, 0>;
      using _Varargs = false_type;

      template<typename _Func, typename... _BoundArgs>
	friend struct _Bind_check_arity;

      _MemObjPtr _M_pm;

    public:
      explicit constexpr
      _Mem_fn_base(_MemObjPtr __pm) noexcept : _M_pm(__pm) { }

      template<typename _Tp>
	auto
	operator()(_Tp&& __obj) const
	noexcept(noexcept(std::__invoke(_M_pm, std::forward<_Tp>(__obj))))
	-> decltype(std::__invoke(_M_pm, std::forward<_Tp>(__obj)))
	{ return std::__invoke(_M_pm, std::forward<_Tp>(__obj)); }
    };

  template<typename _Res, typename _Class>
    struct _Mem_fn<_Res _Class::*>
    : _Mem_fn_base<_Res _Class::*>
    {
      using _Mem_fn_base<_Res _Class::*>::_Mem_fn_base;
    };

  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 2048.  Unnecessary mem_fn overloads
  /**
   *  @brief Returns a function object that forwards to the member
   *  pointer @a pm.
   *  @ingroup functors
   */
  template<typename _Tp, typename _Class>
    inline _Mem_fn<_Tp _Class::*>
    mem_fn(_Tp _Class::* __pm) noexcept
    {
      return _Mem_fn<_Tp _Class::*>(__pm);
    }

  /**
   *  @brief Determines if the given type _Tp is a function object that
   *  should be treated as a subexpression when evaluating calls to
   *  function objects returned by bind().
   *
   *  C++11 [func.bind.isbind].
   *  @ingroup binders
   */
  template<typename _Tp>
    struct is_bind_expression
    : public false_type { };

  /**
   *  @brief Determines if the given type _Tp is a placeholder in a
   *  bind() expression and, if so, which placeholder it is.
   *
   *  C++11 [func.bind.isplace].
   *  @ingroup binders
   */
  template<typename _Tp>
    struct is_placeholder
    : public integral_constant<int, 0>
    { };

  /** @brief The type of placeholder objects defined by libstdc++.
   *  @ingroup binders
   */
  template<int _Num> struct _Placeholder { };

  _GLIBCXX_END_NAMESPACE_VERSION

  /** @namespace std::placeholders
   *  @brief ISO C++11 entities sub-namespace for functional.
   *  @ingroup binders
   */
  namespace placeholders
  {
  _GLIBCXX_BEGIN_NAMESPACE_VERSION
  /* Define a large number of placeholders. There is no way to
   * simplify this with variadic templates, because we're introducing
   * unique names for each.
   */
    extern const _Placeholder<1> _1;
    extern const _Placeholder<2> _2;
    extern const _Placeholder<3> _3;
    extern const _Placeholder<4> _4;
    extern const _Placeholder<5> _5;
    extern const _Placeholder<6> _6;
    extern const _Placeholder<7> _7;
    extern const _Placeholder<8> _8;
    extern const _Placeholder<9> _9;
    extern const _Placeholder<10> _10;
    extern const _Placeholder<11> _11;
    extern const _Placeholder<12> _12;
    extern const _Placeholder<13> _13;
    extern const _Placeholder<14> _14;
    extern const _Placeholder<15> _15;
    extern const _Placeholder<16> _16;
    extern const _Placeholder<17> _17;
    extern const _Placeholder<18> _18;
    extern const _Placeholder<19> _19;
    extern const _Placeholder<20> _20;
    extern const _Placeholder<21> _21;
    extern const _Placeholder<22> _22;
    extern const _Placeholder<23> _23;
    extern const _Placeholder<24> _24;
    extern const _Placeholder<25> _25;
    extern const _Placeholder<26> _26;
    extern const _Placeholder<27> _27;
    extern const _Placeholder<28> _28;
    extern const _Placeholder<29> _29;
  _GLIBCXX_END_NAMESPACE_VERSION
  }

  _GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   *  Partial specialization of is_placeholder that provides the placeholder
   *  number for the placeholder objects defined by libstdc++.
   *  @ingroup binders
   */
  template<int _Num>
    struct is_placeholder<_Placeholder<_Num> >
    : public integral_constant<int, _Num>
    { };

  template<int _Num>
    struct is_placeholder<const _Placeholder<_Num> >
    : public integral_constant<int, _Num>
    { };


  // Like tuple_element_t but SFINAE-friendly.
 template<std::size_t __i, typename _Tuple>
   using _Safe_tuple_element_t
     = typename enable_if<(__i < tuple_size<_Tuple>::value),
			  tuple_element<__i, _Tuple>>::type::type;

  /**
   *  Maps an argument to bind() into an actual argument to the bound
   *  function object [func.bind.bind]/10. Only the first parameter should
   *  be specified: the rest are used to determine among the various
   *  implementations. Note that, although this class is a function
   *  object, it isn't entirely normal because it takes only two
   *  parameters regardless of the number of parameters passed to the
   *  bind expression. The first parameter is the bound argument and
   *  the second parameter is a tuple containing references to the
   *  rest of the arguments.
   */
  template<typename _Arg,
	   bool _IsBindExp = is_bind_expression<_Arg>::value,
	   bool _IsPlaceholder = (is_placeholder<_Arg>::value > 0)>
    class _Mu;

  /**
   *  If the argument is reference_wrapper<_Tp>, returns the
   *  underlying reference.
   *  C++11 [func.bind.bind] p10 bullet 1.
   */
  template<typename _Tp>
    class _Mu<reference_wrapper<_Tp>, false, false>
    {
    public:
      /* Note: This won't actually work for const volatile
       * reference_wrappers, because reference_wrapper::get() is const
       * but not volatile-qualified. This might be a defect in the TR.
       */
      template<typename _CVRef, typename _Tuple>
	_Tp&
	operator()(_CVRef& __arg, _Tuple&) const volatile
	{ return __arg.get(); }
    };

  /**
   *  If the argument is a bind expression, we invoke the underlying
   *  function object with the same cv-qualifiers as we are given and
   *  pass along all of our arguments (unwrapped).
   *  C++11 [func.bind.bind] p10 bullet 2.
   */
  template<typename _Arg>
    class _Mu<_Arg, true, false>
    {
    public:
      template<typename _CVArg, typename... _Args>
	auto
	operator()(_CVArg& __arg,
		   tuple<_Args...>& __tuple) const volatile
	-> decltype(__arg(declval<_Args>()...))
	{
	  // Construct an index tuple and forward to __call
	  typedef typename _Build_index_tuple<sizeof...(_Args)>::__type
	    _Indexes;
	  return this->__call(__arg, __tuple, _Indexes());
	}

    private:
      // Invokes the underlying function object __arg by unpacking all
      // of the arguments in the tuple.
      template<typename _CVArg, typename... _Args, std::size_t... _Indexes>
	auto
	__call(_CVArg& __arg, tuple<_Args...>& __tuple,
	       const _Index_tuple<_Indexes...>&) const volatile
	-> decltype(__arg(declval<_Args>()...))
	{
	  return __arg(std::forward<_Args>(std::get<_Indexes>(__tuple))...);
	}
    };

  /**
   *  If the argument is a placeholder for the Nth argument, returns
   *  a reference to the Nth argument to the bind function object.
   *  C++11 [func.bind.bind] p10 bullet 3.
   */
  template<typename _Arg>
    class _Mu<_Arg, false, true>
    {
    public:
      template<typename _Tuple>
	_Safe_tuple_element_t<(is_placeholder<_Arg>::value - 1), _Tuple>&&
	operator()(const volatile _Arg&, _Tuple& __tuple) const volatile
	{
	  using __type
	    = __tuple_element_t<(is_placeholder<_Arg>::value - 1), _Tuple>;
	  return std::forward<__type>(
	      ::std::get<(is_placeholder<_Arg>::value - 1)>(__tuple));
	}
    };

  /**
   *  If the argument is just a value, returns a reference to that
   *  value. The cv-qualifiers on the reference are determined by the caller.
   *  C++11 [func.bind.bind] p10 bullet 4.
   */
  template<typename _Arg>
    class _Mu<_Arg, false, false>
    {
    public:
      template<typename _CVArg, typename _Tuple>
	_CVArg&&
	operator()(_CVArg&& __arg, _Tuple&) const volatile
	{ return std::forward<_CVArg>(__arg); }
    };

  /**
   *  Maps member pointers into instances of _Mem_fn but leaves all
   *  other function objects untouched. Used by std::bind(). The
   *  primary template handles the non-member-pointer case.
   */
  template<typename _Tp>
    struct _Maybe_wrap_member_pointer
    {
      typedef _Tp type;

      static constexpr const _Tp&
      __do_wrap(const _Tp& __x)
      { return __x; }

      static constexpr _Tp&&
      __do_wrap(_Tp&& __x)
      { return static_cast<_Tp&&>(__x); }
    };

  /**
   *  Maps member pointers into instances of _Mem_fn but leaves all
   *  other function objects untouched. Used by std::bind(). This
   *  partial specialization handles the member pointer case.
   */
  template<typename _Tp, typename _Class>
    struct _Maybe_wrap_member_pointer<_Tp _Class::*>
    {
      typedef _Mem_fn<_Tp _Class::*> type;

      static constexpr type
      __do_wrap(_Tp _Class::* __pm)
      { return type(__pm); }
    };

  // Specialization needed to prevent "forming reference to void" errors when
  // bind<void>() is called, because argument deduction instantiates
  // _Maybe_wrap_member_pointer<void> outside the immediate context where
  // SFINAE applies.
  template<>
    struct _Maybe_wrap_member_pointer<void>
    {
      typedef void type;
    };

  // std::get<I> for volatile-qualified tuples
  template<std::size_t _Ind, typename... _Tp>
    inline auto
    __volget(volatile tuple<_Tp...>& __tuple)
    -> __tuple_element_t<_Ind, tuple<_Tp...>> volatile&
    { return std::get<_Ind>(const_cast<tuple<_Tp...>&>(__tuple)); }

  // std::get<I> for const-volatile-qualified tuples
  template<std::size_t _Ind, typename... _Tp>
    inline auto
    __volget(const volatile tuple<_Tp...>& __tuple)
    -> __tuple_element_t<_Ind, tuple<_Tp...>> const volatile&
    { return std::get<_Ind>(const_cast<const tuple<_Tp...>&>(__tuple)); }

  /// Type of the function object returned from bind().
  template<typename _Signature>
    struct _Bind;

   template<typename _Functor, typename... _Bound_args>
    class _Bind<_Functor(_Bound_args...)>
    : public _Weak_result_type<_Functor>
    {
      typedef _Bind __self_type;
      typedef typename _Build_index_tuple<sizeof...(_Bound_args)>::__type
	_Bound_indexes;

      _Functor _M_f;
      tuple<_Bound_args...> _M_bound_args;

      // Call unqualified
      template<typename _Result, typename... _Args, std::size_t... _Indexes>
	_Result
	__call(tuple<_Args...>&& __args, _Index_tuple<_Indexes...>)
	{
	  return _M_f(_Mu<_Bound_args>()
		      (std::get<_Indexes>(_M_bound_args), __args)...);
	}

      // Call as const
      template<typename _Result, typename... _Args, std::size_t... _Indexes>
	_Result
	__call_c(tuple<_Args...>&& __args, _Index_tuple<_Indexes...>) const
	{
	  return _M_f(_Mu<_Bound_args>()
		      (std::get<_Indexes>(_M_bound_args), __args)...);
	}

      // Call as volatile
      template<typename _Result, typename... _Args, std::size_t... _Indexes>
	_Result
	__call_v(tuple<_Args...>&& __args,
		 _Index_tuple<_Indexes...>) volatile
	{
	  return _M_f(_Mu<_Bound_args>()
		      (__volget<_Indexes>(_M_bound_args), __args)...);
	}

      // Call as const volatile
      template<typename _Result, typename... _Args, std::size_t... _Indexes>
	_Result
	__call_c_v(tuple<_Args...>&& __args,
		   _Index_tuple<_Indexes...>) const volatile
	{
	  return _M_f(_Mu<_Bound_args>()
		      (__volget<_Indexes>(_M_bound_args), __args)...);
	}

     public:
      template<typename... _Args>
	explicit _Bind(const _Functor& __f, _Args&&... __args)
	: _M_f(__f), _M_bound_args(std::forward<_Args>(__args)...)
	{ }

      template<typename... _Args>
	explicit _Bind(_Functor&& __f, _Args&&... __args)
	: _M_f(std::move(__f)), _M_bound_args(std::forward<_Args>(__args)...)
	{ }

      _Bind(const _Bind&) = default;

      _Bind(_Bind&& __b)
      : _M_f(std::move(__b._M_f)), _M_bound_args(std::move(__b._M_bound_args))
      { }

      // Call unqualified
      template<typename... _Args, typename _Result
	= decltype( std::declval<_Functor&>()(
	      _Mu<_Bound_args>()( std::declval<_Bound_args&>(),
				  std::declval<tuple<_Args...>&>() )... ) )>
	_Result
	operator()(_Args&&... __args)
	{
	  return this->__call<_Result>(
	      std::forward_as_tuple(std::forward<_Args>(__args)...),
	      _Bound_indexes());
	}

      // Call as const
      template<typename... _Args, typename _Result
	= decltype( std::declval<typename enable_if<(sizeof...(_Args) >= 0),
		       typename add_const<_Functor>::type&>::type>()(
	      _Mu<_Bound_args>()( std::declval<const _Bound_args&>(),
				  std::declval<tuple<_Args...>&>() )... ) )>
	_Result
	operator()(_Args&&... __args) const
	{
	  return this->__call_c<_Result>(
	      std::forward_as_tuple(std::forward<_Args>(__args)...),
	      _Bound_indexes());
	}

      // Call as volatile
      template<typename... _Args, typename _Result
	= decltype( std::declval<typename enable_if<(sizeof...(_Args) >= 0),
                       typename add_volatile<_Functor>::type&>::type>()(
	      _Mu<_Bound_args>()( std::declval<volatile _Bound_args&>(),
				  std::declval<tuple<_Args...>&>() )... ) )>
	_Result
	operator()(_Args&&... __args) volatile
	{
	  return this->__call_v<_Result>(
	      std::forward_as_tuple(std::forward<_Args>(__args)...),
	      _Bound_indexes());
	}

      // Call as const volatile
      template<typename... _Args, typename _Result
	= decltype( std::declval<typename enable_if<(sizeof...(_Args) >= 0),
                       typename add_cv<_Functor>::type&>::type>()(
	      _Mu<_Bound_args>()( std::declval<const volatile _Bound_args&>(),
				  std::declval<tuple<_Args...>&>() )... ) )>
	_Result
	operator()(_Args&&... __args) const volatile
	{
	  return this->__call_c_v<_Result>(
	      std::forward_as_tuple(std::forward<_Args>(__args)...),
	      _Bound_indexes());
	}
    };

  /// Type of the function object returned from bind<R>().
  template<typename _Result, typename _Signature>
    struct _Bind_result;

  template<typename _Result, typename _Functor, typename... _Bound_args>
    class _Bind_result<_Result, _Functor(_Bound_args...)>
    {
      typedef _Bind_result __self_type;
      typedef typename _Build_index_tuple<sizeof...(_Bound_args)>::__type
	_Bound_indexes;

      _Functor _M_f;
      tuple<_Bound_args...> _M_bound_args;

      // sfinae types
      template<typename _Res>
	struct __enable_if_void : enable_if<is_void<_Res>::value, int> { };
      template<typename _Res>
	struct __disable_if_void : enable_if<!is_void<_Res>::value, int> { };

      // Call unqualified
      template<typename _Res, typename... _Args, std::size_t... _Indexes>
	_Result
	__call(tuple<_Args...>&& __args, _Index_tuple<_Indexes...>,
	    typename __disable_if_void<_Res>::type = 0)
	{
	  return _M_f(_Mu<_Bound_args>()
		      (std::get<_Indexes>(_M_bound_args), __args)...);
	}

      // Call unqualified, return void
      template<typename _Res, typename... _Args, std::size_t... _Indexes>
	void
	__call(tuple<_Args...>&& __args, _Index_tuple<_Indexes...>,
	    typename __enable_if_void<_Res>::type = 0)
	{
	  _M_f(_Mu<_Bound_args>()
	       (std::get<_Indexes>(_M_bound_args), __args)...);
	}

      // Call as const
      template<typename _Res, typename... _Args, std::size_t... _Indexes>
	_Result
	__call(tuple<_Args...>&& __args, _Index_tuple<_Indexes...>,
	    typename __disable_if_void<_Res>::type = 0) const
	{
	  return _M_f(_Mu<_Bound_args>()
		      (std::get<_Indexes>(_M_bound_args), __args)...);
	}

      // Call as const, return void
      template<typename _Res, typename... _Args, std::size_t... _Indexes>
	void
	__call(tuple<_Args...>&& __args, _Index_tuple<_Indexes...>,
	    typename __enable_if_void<_Res>::type = 0) const
	{
	  _M_f(_Mu<_Bound_args>()
	       (std::get<_Indexes>(_M_bound_args),  __args)...);
	}

      // Call as volatile
      template<typename _Res, typename... _Args, std::size_t... _Indexes>
	_Result
	__call(tuple<_Args...>&& __args, _Index_tuple<_Indexes...>,
	    typename __disable_if_void<_Res>::type = 0) volatile
	{
	  return _M_f(_Mu<_Bound_args>()
		      (__volget<_Indexes>(_M_bound_args), __args)...);
	}

      // Call as volatile, return void
      template<typename _Res, typename... _Args, std::size_t... _Indexes>
	void
	__call(tuple<_Args...>&& __args, _Index_tuple<_Indexes...>,
	    typename __enable_if_void<_Res>::type = 0) volatile
	{
	  _M_f(_Mu<_Bound_args>()
	       (__volget<_Indexes>(_M_bound_args), __args)...);
	}

      // Call as const volatile
      template<typename _Res, typename... _Args, std::size_t... _Indexes>
	_Result
	__call(tuple<_Args...>&& __args, _Index_tuple<_Indexes...>,
	    typename __disable_if_void<_Res>::type = 0) const volatile
	{
	  return _M_f(_Mu<_Bound_args>()
		      (__volget<_Indexes>(_M_bound_args), __args)...);
	}

      // Call as const volatile, return void
      template<typename _Res, typename... _Args, std::size_t... _Indexes>
	void
	__call(tuple<_Args...>&& __args,
	       _Index_tuple<_Indexes...>,
	    typename __enable_if_void<_Res>::type = 0) const volatile
	{
	  _M_f(_Mu<_Bound_args>()
	       (__volget<_Indexes>(_M_bound_args), __args)...);
	}

    public:
      typedef _Result result_type;

      template<typename... _Args>
	explicit _Bind_result(const _Functor& __f, _Args&&... __args)
	: _M_f(__f), _M_bound_args(std::forward<_Args>(__args)...)
	{ }

      template<typename... _Args>
	explicit _Bind_result(_Functor&& __f, _Args&&... __args)
	: _M_f(std::move(__f)), _M_bound_args(std::forward<_Args>(__args)...)
	{ }

      _Bind_result(const _Bind_result&) = default;

      _Bind_result(_Bind_result&& __b)
      : _M_f(std::move(__b._M_f)), _M_bound_args(std::move(__b._M_bound_args))
      { }

      // Call unqualified
      template<typename... _Args>
	result_type
	operator()(_Args&&... __args)
	{
	  return this->__call<_Result>(
	      std::forward_as_tuple(std::forward<_Args>(__args)...),
	      _Bound_indexes());
	}

      // Call as const
      template<typename... _Args>
	result_type
	operator()(_Args&&... __args) const
	{
	  return this->__call<_Result>(
	      std::forward_as_tuple(std::forward<_Args>(__args)...),
	      _Bound_indexes());
	}

      // Call as volatile
      template<typename... _Args>
	result_type
	operator()(_Args&&... __args) volatile
	{
	  return this->__call<_Result>(
	      std::forward_as_tuple(std::forward<_Args>(__args)...),
	      _Bound_indexes());
	}

      // Call as const volatile
      template<typename... _Args>
	result_type
	operator()(_Args&&... __args) const volatile
	{
	  return this->__call<_Result>(
	      std::forward_as_tuple(std::forward<_Args>(__args)...),
	      _Bound_indexes());
	}
    };

  /**
   *  @brief Class template _Bind is always a bind expression.
   *  @ingroup binders
   */
  template<typename _Signature>
    struct is_bind_expression<_Bind<_Signature> >
    : public true_type { };

  /**
   *  @brief Class template _Bind is always a bind expression.
   *  @ingroup binders
   */
  template<typename _Signature>
    struct is_bind_expression<const _Bind<_Signature> >
    : public true_type { };

  /**
   *  @brief Class template _Bind is always a bind expression.
   *  @ingroup binders
   */
  template<typename _Signature>
    struct is_bind_expression<volatile _Bind<_Signature> >
    : public true_type { };

  /**
   *  @brief Class template _Bind is always a bind expression.
   *  @ingroup binders
   */
  template<typename _Signature>
    struct is_bind_expression<const volatile _Bind<_Signature>>
    : public true_type { };

  /**
   *  @brief Class template _Bind_result is always a bind expression.
   *  @ingroup binders
   */
  template<typename _Result, typename _Signature>
    struct is_bind_expression<_Bind_result<_Result, _Signature>>
    : public true_type { };

  /**
   *  @brief Class template _Bind_result is always a bind expression.
   *  @ingroup binders
   */
  template<typename _Result, typename _Signature>
    struct is_bind_expression<const _Bind_result<_Result, _Signature>>
    : public true_type { };

  /**
   *  @brief Class template _Bind_result is always a bind expression.
   *  @ingroup binders
   */
  template<typename _Result, typename _Signature>
    struct is_bind_expression<volatile _Bind_result<_Result, _Signature>>
    : public true_type { };

  /**
   *  @brief Class template _Bind_result is always a bind expression.
   *  @ingroup binders
   */
  template<typename _Result, typename _Signature>
    struct is_bind_expression<const volatile _Bind_result<_Result, _Signature>>
    : public true_type { };

  template<typename _Func, typename... _BoundArgs>
    struct _Bind_check_arity { };

  template<typename _Ret, typename... _Args, typename... _BoundArgs>
    struct _Bind_check_arity<_Ret (*)(_Args...), _BoundArgs...>
    {
      static_assert(sizeof...(_BoundArgs) == sizeof...(_Args),
                   "Wrong number of arguments for function");
    };

  template<typename _Ret, typename... _Args, typename... _BoundArgs>
    struct _Bind_check_arity<_Ret (*)(_Args......), _BoundArgs...>
    {
      static_assert(sizeof...(_BoundArgs) >= sizeof...(_Args),
                   "Wrong number of arguments for function");
    };

  template<typename _Tp, typename _Class, typename... _BoundArgs>
    struct _Bind_check_arity<_Tp _Class::*, _BoundArgs...>
    {
      using _Arity = typename _Mem_fn<_Tp _Class::*>::_Arity;
      using _Varargs = typename _Mem_fn<_Tp _Class::*>::_Varargs;
      static_assert(_Varargs::value
		    ? sizeof...(_BoundArgs) >= _Arity::value + 1
		    : sizeof...(_BoundArgs) == _Arity::value + 1,
		    "Wrong number of arguments for pointer-to-member");
    };

  // Trait type used to remove std::bind() from overload set via SFINAE
  // when first argument has integer type, so that std::bind() will
  // not be a better match than ::bind() from the BSD Sockets API.
  template<typename _Tp, typename _Tp2 = typename decay<_Tp>::type>
    using __is_socketlike = __or_<is_integral<_Tp2>, is_enum<_Tp2>>;

  template<bool _SocketLike, typename _Func, typename... _BoundArgs>
    struct _Bind_helper
    : _Bind_check_arity<typename decay<_Func>::type, _BoundArgs...>
    {
      typedef _Maybe_wrap_member_pointer<typename decay<_Func>::type>
	__maybe_type;
      typedef typename __maybe_type::type __func_type;
      typedef _Bind<__func_type(typename decay<_BoundArgs>::type...)> type;
    };

  // Partial specialization for is_socketlike == true, does not define
  // nested type so std::bind() will not participate in overload resolution
  // when the first argument might be a socket file descriptor.
  template<typename _Func, typename... _BoundArgs>
    struct _Bind_helper<true, _Func, _BoundArgs...>
    { };

  /**
   *  @brief Function template for std::bind.
   *  @ingroup binders
   */
  template<typename _Func, typename... _BoundArgs>
    inline typename
    _Bind_helper<__is_socketlike<_Func>::value, _Func, _BoundArgs...>::type
    bind(_Func&& __f, _BoundArgs&&... __args)
    {
      typedef _Bind_helper<false, _Func, _BoundArgs...> __helper_type;
      typedef typename __helper_type::__maybe_type __maybe_type;
      typedef typename __helper_type::type __result_type;
      return __result_type(__maybe_type::__do_wrap(std::forward<_Func>(__f)),
			   std::forward<_BoundArgs>(__args)...);
    }

  template<typename _Result, typename _Func, typename... _BoundArgs>
    struct _Bindres_helper
    : _Bind_check_arity<typename decay<_Func>::type, _BoundArgs...>
    {
      typedef _Maybe_wrap_member_pointer<typename decay<_Func>::type>
	__maybe_type;
      typedef typename __maybe_type::type __functor_type;
      typedef _Bind_result<_Result,
			   __functor_type(typename decay<_BoundArgs>::type...)>
	type;
    };

  /**
   *  @brief Function template for std::bind<R>.
   *  @ingroup binders
   */
  template<typename _Result, typename _Func, typename... _BoundArgs>
    inline
    typename _Bindres_helper<_Result, _Func, _BoundArgs...>::type
    bind(_Func&& __f, _BoundArgs&&... __args)
    {
      typedef _Bindres_helper<_Result, _Func, _BoundArgs...> __helper_type;
      typedef typename __helper_type::__maybe_type __maybe_type;
      typedef typename __helper_type::type __result_type;
      return __result_type(__maybe_type::__do_wrap(std::forward<_Func>(__f)),
			   std::forward<_BoundArgs>(__args)...);
    }

  template<typename _Signature>
    struct _Bind_simple;

  template<typename _Callable, typename... _Args>
    struct _Bind_simple<_Callable(_Args...)>
    {
      typedef typename result_of<_Callable(_Args...)>::type result_type;

      template<typename _Tp, typename... _Up>
        explicit
        _Bind_simple(_Tp&& __f, _Up&&... __args)
        : _M_bound(std::forward<_Tp>(__f), std::forward<_Up>(__args)...)
        { }

      _Bind_simple(const _Bind_simple&) = default;
      _Bind_simple(_Bind_simple&&) = default;

      result_type
      operator()()
      {
        typedef typename _Build_index_tuple<sizeof...(_Args)>::__type _Indices;
        return _M_invoke(_Indices());
      }

    private:
      template<std::size_t... _Indices>
        typename result_of<_Callable(_Args...)>::type
        _M_invoke(_Index_tuple<_Indices...>)
        {
	  // std::bind always forwards bound arguments as lvalues,
	  // but this type can call functions which only accept rvalues.
          return std::forward<_Callable>(std::get<0>(_M_bound))(
              std::forward<_Args>(std::get<_Indices+1>(_M_bound))...);
        }

      std::tuple<_Callable, _Args...> _M_bound;
    };

  template<typename _Func, typename... _BoundArgs>
    struct _Bind_simple_helper
    : _Bind_check_arity<typename decay<_Func>::type, _BoundArgs...>
    {
      typedef _Maybe_wrap_member_pointer<typename decay<_Func>::type>
        __maybe_type;
      typedef typename __maybe_type::type __func_type;
      typedef _Bind_simple<__func_type(typename decay<_BoundArgs>::type...)>
       	__type;
    };

  // Simplified version of std::bind for internal use, without support for
  // unbound arguments, placeholders or nested bind expressions.
  template<typename _Callable, typename... _Args>
    typename _Bind_simple_helper<_Callable, _Args...>::__type
    __bind_simple(_Callable&& __callable, _Args&&... __args)
    {
      typedef _Bind_simple_helper<_Callable, _Args...> __helper_type;
      typedef typename __helper_type::__maybe_type __maybe_type;
      typedef typename __helper_type::__type __result_type;
      return __result_type(
          __maybe_type::__do_wrap( std::forward<_Callable>(__callable)),
          std::forward<_Args>(__args)...);
    }

  /**
   *  @brief Exception class thrown when class template function's
   *  operator() is called with an empty target.
   *  @ingroup exceptions
   */
  class bad_function_call : public std::exception
  {
  public:
    virtual ~bad_function_call() noexcept;

    const char* what() const noexcept;
  };

  /**
   *  Trait identifying "location-invariant" types, meaning that the
   *  address of the object (or any of its members) will not escape.
   *  Trivially copyable types are location-invariant and users can
   *  specialize this trait for other types.
   */
  template<typename _Tp>
    struct __is_location_invariant
    : is_trivially_copyable<_Tp>::type
    { };

  class _Undefined_class;

  union _Nocopy_types
  {
    void*       _M_object;
    const void* _M_const_object;
    void (*_M_function_pointer)();
    void (_Undefined_class::*_M_member_pointer)();
  };

  union _Any_data
  {
    void*       _M_access()       { return &_M_pod_data[0]; }
    const void* _M_access() const { return &_M_pod_data[0]; }

    template<typename _Tp>
      _Tp&
      _M_access()
      { return *static_cast<_Tp*>(_M_access()); }

    template<typename _Tp>
      const _Tp&
      _M_access() const
      { return *static_cast<const _Tp*>(_M_access()); }

    _Nocopy_types _M_unused;
    char _M_pod_data[sizeof(_Nocopy_types)];
  };

  enum _Manager_operation
  {
    __get_type_info,
    __get_functor_ptr,
    __clone_functor,
    __destroy_functor
  };

  // Simple type wrapper that helps avoid annoying const problems
  // when casting between void pointers and pointers-to-pointers.
  template<typename _Tp>
    struct _Simple_type_wrapper
    {
      _Simple_type_wrapper(_Tp __value) : __value(__value) { }

      _Tp __value;
    };

  template<typename _Tp>
    struct __is_location_invariant<_Simple_type_wrapper<_Tp> >
    : __is_location_invariant<_Tp>
    { };

  // Converts a reference to a function object into a callable
  // function object.
  template<typename _Functor>
    inline _Functor&
    __callable_functor(_Functor& __f)
    { return __f; }

  template<typename _Member, typename _Class>
    inline _Mem_fn<_Member _Class::*>
    __callable_functor(_Member _Class::* &__p)
    { return std::mem_fn(__p); }

  template<typename _Member, typename _Class>
    inline _Mem_fn<_Member _Class::*>
    __callable_functor(_Member _Class::* const &__p)
    { return std::mem_fn(__p); }

  template<typename _Member, typename _Class>
    inline _Mem_fn<_Member _Class::*>
    __callable_functor(_Member _Class::* volatile &__p)
    { return std::mem_fn(__p); }

  template<typename _Member, typename _Class>
    inline _Mem_fn<_Member _Class::*>
    __callable_functor(_Member _Class::* const volatile &__p)
    { return std::mem_fn(__p); }

  template<typename _Signature>
    class function;

  /// Base class of all polymorphic function object wrappers.
  class _Function_base
  {
  public:
    static const std::size_t _M_max_size = sizeof(_Nocopy_types);
    static const std::size_t _M_max_align = __alignof__(_Nocopy_types);

    template<typename _Functor>
      class _Base_manager
      {
      protected:
	static const bool __stored_locally =
	(__is_location_invariant<_Functor>::value
	 && sizeof(_Functor) <= _M_max_size
	 && __alignof__(_Functor) <= _M_max_align
	 && (_M_max_align % __alignof__(_Functor) == 0));

	typedef integral_constant<bool, __stored_locally> _Local_storage;

	// Retrieve a pointer to the function object
	static _Functor*
	_M_get_pointer(const _Any_data& __source)
	{
	  const _Functor* __ptr =
	    __stored_locally? std::__addressof(__source._M_access<_Functor>())
	    /* have stored a pointer */ : __source._M_access<_Functor*>();
	  return const_cast<_Functor*>(__ptr);
	}

	// Clone a location-invariant function object that fits within
	// an _Any_data structure.
	static void
	_M_clone(_Any_data& __dest, const _Any_data& __source, true_type)
	{
	  new (__dest._M_access()) _Functor(__source._M_access<_Functor>());
	}

	// Clone a function object that is not location-invariant or
	// that cannot fit into an _Any_data structure.
	static void
	_M_clone(_Any_data& __dest, const _Any_data& __source, false_type)
	{
	  __dest._M_access<_Functor*>() =
	    new _Functor(*__source._M_access<_Functor*>());
	}

	// Destroying a location-invariant object may still require
	// destruction.
	static void
	_M_destroy(_Any_data& __victim, true_type)
	{
	  __victim._M_access<_Functor>().~_Functor();
	}

	// Destroying an object located on the heap.
	static void
	_M_destroy(_Any_data& __victim, false_type)
	{
	  delete __victim._M_access<_Functor*>();
	}

      public:
	static bool
	_M_manager(_Any_data& __dest, const _Any_data& __source,
		   _Manager_operation __op)
	{
	  switch (__op)
	    {
#if __cpp_rtti
	    case __get_type_info:
	      __dest._M_access<const type_info*>() = &typeid(_Functor);
	      break;
#endif
	    case __get_functor_ptr:
	      __dest._M_access<_Functor*>() = _M_get_pointer(__source);
	      break;

	    case __clone_functor:
	      _M_clone(__dest, __source, _Local_storage());
	      break;

	    case __destroy_functor:
	      _M_destroy(__dest, _Local_storage());
	      break;
	    }
	  return false;
	}

	static void
	_M_init_functor(_Any_data& __functor, _Functor&& __f)
	{ _M_init_functor(__functor, std::move(__f), _Local_storage()); }

	template<typename _Signature>
	  static bool
	  _M_not_empty_function(const function<_Signature>& __f)
	  { return static_cast<bool>(__f); }

	template<typename _Tp>
	  static bool
	  _M_not_empty_function(_Tp* __fp)
	  { return __fp != nullptr; }

	template<typename _Class, typename _Tp>
	  static bool
	  _M_not_empty_function(_Tp _Class::* __mp)
	  { return __mp != nullptr; }

	template<typename _Tp>
	  static bool
	  _M_not_empty_function(const _Tp&)
	  { return true; }

      private:
	static void
	_M_init_functor(_Any_data& __functor, _Functor&& __f, true_type)
	{ new (__functor._M_access()) _Functor(std::move(__f)); }

	static void
	_M_init_functor(_Any_data& __functor, _Functor&& __f, false_type)
	{ __functor._M_access<_Functor*>() = new _Functor(std::move(__f)); }
      };

    template<typename _Functor>
      class _Ref_manager : public _Base_manager<_Functor*>
      {
	typedef _Function_base::_Base_manager<_Functor*> _Base;

      public:
	static bool
	_M_manager(_Any_data& __dest, const _Any_data& __source,
		   _Manager_operation __op)
	{
	  switch (__op)
	    {
#if __cpp_rtti
	    case __get_type_info:
	      __dest._M_access<const type_info*>() = &typeid(_Functor);
	      break;
#endif
	    case __get_functor_ptr:
	      __dest._M_access<_Functor*>() = *_Base::_M_get_pointer(__source);
	      return is_const<_Functor>::value;
	      break;

	    default:
	      _Base::_M_manager(__dest, __source, __op);
	    }
	  return false;
	}

	static void
	_M_init_functor(_Any_data& __functor, reference_wrapper<_Functor> __f)
	{
	  _Base::_M_init_functor(__functor, std::__addressof(__f.get()));
	}
      };

    _Function_base() : _M_manager(nullptr) { }

    ~_Function_base()
    {
      if (_M_manager)
	_M_manager(_M_functor, _M_functor, __destroy_functor);
    }


    bool _M_empty() const { return !_M_manager; }

    typedef bool (*_Manager_type)(_Any_data&, const _Any_data&,
				  _Manager_operation);

    _Any_data     _M_functor;
    _Manager_type _M_manager;
  };

  template<typename _Signature, typename _Functor>
    class _Function_handler;

  template<typename _Res, typename _Functor, typename... _ArgTypes>
    class _Function_handler<_Res(_ArgTypes...), _Functor>
    : public _Function_base::_Base_manager<_Functor>
    {
      typedef _Function_base::_Base_manager<_Functor> _Base;

    public:
      static _Res
      _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
      {
	return (*_Base::_M_get_pointer(__functor))(
	    std::forward<_ArgTypes>(__args)...);
      }
    };

  template<typename _Functor, typename... _ArgTypes>
    class _Function_handler<void(_ArgTypes...), _Functor>
    : public _Function_base::_Base_manager<_Functor>
    {
      typedef _Function_base::_Base_manager<_Functor> _Base;

     public:
      static void
      _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
      {
	(*_Base::_M_get_pointer(__functor))(
	    std::forward<_ArgTypes>(__args)...);
      }
    };

  template<typename _Res, typename _Functor, typename... _ArgTypes>
    class _Function_handler<_Res(_ArgTypes...), reference_wrapper<_Functor> >
    : public _Function_base::_Ref_manager<_Functor>
    {
      typedef _Function_base::_Ref_manager<_Functor> _Base;

     public:
      static _Res
      _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
      {
	return std::__callable_functor(**_Base::_M_get_pointer(__functor))(
	      std::forward<_ArgTypes>(__args)...);
      }
    };

  template<typename _Functor, typename... _ArgTypes>
    class _Function_handler<void(_ArgTypes...), reference_wrapper<_Functor> >
    : public _Function_base::_Ref_manager<_Functor>
    {
      typedef _Function_base::_Ref_manager<_Functor> _Base;

     public:
      static void
      _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
      {
	std::__callable_functor(**_Base::_M_get_pointer(__functor))(
	    std::forward<_ArgTypes>(__args)...);
      }
    };

  template<typename _Class, typename _Member, typename _Res,
	   typename... _ArgTypes>
    class _Function_handler<_Res(_ArgTypes...), _Member _Class::*>
    : public _Function_handler<void(_ArgTypes...), _Member _Class::*>
    {
      typedef _Function_handler<void(_ArgTypes...), _Member _Class::*>
	_Base;

     public:
      static _Res
      _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
      {
	return std::mem_fn(_Base::_M_get_pointer(__functor)->__value)(
	    std::forward<_ArgTypes>(__args)...);
      }
    };

  template<typename _Class, typename _Member, typename... _ArgTypes>
    class _Function_handler<void(_ArgTypes...), _Member _Class::*>
    : public _Function_base::_Base_manager<
		 _Simple_type_wrapper< _Member _Class::* > >
    {
      typedef _Member _Class::* _Functor;
      typedef _Simple_type_wrapper<_Functor> _Wrapper;
      typedef _Function_base::_Base_manager<_Wrapper> _Base;

    public:
      static bool
      _M_manager(_Any_data& __dest, const _Any_data& __source,
		 _Manager_operation __op)
      {
	switch (__op)
	  {
#if __cpp_rtti
	  case __get_type_info:
	    __dest._M_access<const type_info*>() = &typeid(_Functor);
	    break;
#endif
	  case __get_functor_ptr:
	    __dest._M_access<_Functor*>() =
	      &_Base::_M_get_pointer(__source)->__value;
	    break;

	  default:
	    _Base::_M_manager(__dest, __source, __op);
	  }
	return false;
      }

      static void
      _M_invoke(const _Any_data& __functor, _ArgTypes&&... __args)
      {
	std::mem_fn(_Base::_M_get_pointer(__functor)->__value)(
	    std::forward<_ArgTypes>(__args)...);
      }
    };

  template<typename _From, typename _To>
    using __check_func_return_type
      = __or_<is_void<_To>, is_same<_From, _To>, is_convertible<_From, _To>>;

  /**
   *  @brief Primary class template for std::function.
   *  @ingroup functors
   *
   *  Polymorphic function wrapper.
   */
  template<typename _Res, typename... _ArgTypes>
    class function<_Res(_ArgTypes...)>
    : public _Maybe_unary_or_binary_function<_Res, _ArgTypes...>,
      private _Function_base
    {
      typedef _Res _Signature_type(_ArgTypes...);

      template<typename _Func,
	       typename _Res2 = typename result_of<_Func(_ArgTypes...)>::type>
	struct _Callable : __check_func_return_type<_Res2, _Res> { };

      // Used so the return type convertibility checks aren't done when
      // performing overload resolution for copy construction/assignment.
      template<typename _Tp>
	struct _Callable<function, _Tp> : false_type { };

      template<typename _Cond, typename _Tp>
	using _Requires = typename enable_if<_Cond::value, _Tp>::type;

    public:
      typedef _Res result_type;

      // [3.7.2.1] construct/copy/destroy

      /**
       *  @brief Default construct creates an empty function call wrapper.
       *  @post @c !(bool)*this
       */
      function() noexcept
      : _Function_base() { }

      /**
       *  @brief Creates an empty function call wrapper.
       *  @post @c !(bool)*this
       */
      function(nullptr_t) noexcept
      : _Function_base() { }

      /**
       *  @brief %Function copy constructor.
       *  @param __x A %function object with identical call signature.
       *  @post @c bool(*this) == bool(__x)
       *
       *  The newly-created %function contains a copy of the target of @a
       *  __x (if it has one).
       */
      function(const function& __x);

      /**
       *  @brief %Function move constructor.
       *  @param __x A %function object rvalue with identical call signature.
       *
       *  The newly-created %function contains the target of @a __x
       *  (if it has one).
       */
      function(function&& __x) : _Function_base()
      {
	__x.swap(*this);
      }

      // TODO: needs allocator_arg_t

      /**
       *  @brief Builds a %function that targets a copy of the incoming
       *  function object.
       *  @param __f A %function object that is callable with parameters of
       *  type @c T1, @c T2, ..., @c TN and returns a value convertible
       *  to @c Res.
       *
       *  The newly-created %function object will target a copy of 
       *  @a __f. If @a __f is @c reference_wrapper<F>, then this function
       *  object will contain a reference to the function object @c
       *  __f.get(). If @a __f is a NULL function pointer or NULL
       *  pointer-to-member, the newly-created object will be empty.
       *
       *  If @a __f is a non-NULL function pointer or an object of type @c
       *  reference_wrapper<F>, this function will not throw.
       */
      template<typename _Functor,
	       typename = _Requires<__not_<is_same<_Functor, function>>, void>,
	       typename = _Requires<_Callable<_Functor>, void>>
	function(_Functor);

      /**
       *  @brief %Function assignment operator.
       *  @param __x A %function with identical call signature.
       *  @post @c (bool)*this == (bool)x
       *  @returns @c *this
       *
       *  The target of @a __x is copied to @c *this. If @a __x has no
       *  target, then @c *this will be empty.
       *
       *  If @a __x targets a function pointer or a reference to a function
       *  object, then this operation will not throw an %exception.
       */
      function&
      operator=(const function& __x)
      {
	function(__x).swap(*this);
	return *this;
      }

      /**
       *  @brief %Function move-assignment operator.
       *  @param __x A %function rvalue with identical call signature.
       *  @returns @c *this
       *
       *  The target of @a __x is moved to @c *this. If @a __x has no
       *  target, then @c *this will be empty.
       *
       *  If @a __x targets a function pointer or a reference to a function
       *  object, then this operation will not throw an %exception.
       */
      function&
      operator=(function&& __x)
      {
	function(std::move(__x)).swap(*this);
	return *this;
      }

      /**
       *  @brief %Function assignment to zero.
       *  @post @c !(bool)*this
       *  @returns @c *this
       *
       *  The target of @c *this is deallocated, leaving it empty.
       */
      function&
      operator=(nullptr_t) noexcept
      {
	if (_M_manager)
	  {
	    _M_manager(_M_functor, _M_functor, __destroy_functor);
	    _M_manager = nullptr;
	    _M_invoker = nullptr;
	  }
	return *this;
      }

      /**
       *  @brief %Function assignment to a new target.
       *  @param __f A %function object that is callable with parameters of
       *  type @c T1, @c T2, ..., @c TN and returns a value convertible
       *  to @c Res.
       *  @return @c *this
       *
       *  This  %function object wrapper will target a copy of @a
       *  __f. If @a __f is @c reference_wrapper<F>, then this function
       *  object will contain a reference to the function object @c
       *  __f.get(). If @a __f is a NULL function pointer or NULL
       *  pointer-to-member, @c this object will be empty.
       *
       *  If @a __f is a non-NULL function pointer or an object of type @c
       *  reference_wrapper<F>, this function will not throw.
       */
      template<typename _Functor>
	_Requires<_Callable<typename decay<_Functor>::type>, function&>
	operator=(_Functor&& __f)
	{
	  function(std::forward<_Functor>(__f)).swap(*this);
	  return *this;
	}

      /// @overload
      template<typename _Functor>
	function&
	operator=(reference_wrapper<_Functor> __f) noexcept
	{
	  function(__f).swap(*this);
	  return *this;
	}

      // [3.7.2.2] function modifiers

      /**
       *  @brief Swap the targets of two %function objects.
       *  @param __x A %function with identical call signature.
       *
       *  Swap the targets of @c this function object and @a __f. This
       *  function will not throw an %exception.
       */
      void swap(function& __x)
      {
	std::swap(_M_functor, __x._M_functor);
	std::swap(_M_manager, __x._M_manager);
	std::swap(_M_invoker, __x._M_invoker);
      }

      // TODO: needs allocator_arg_t
      /*
      template<typename _Functor, typename _Alloc>
	void
	assign(_Functor&& __f, const _Alloc& __a)
	{
	  function(allocator_arg, __a,
		   std::forward<_Functor>(__f)).swap(*this);
	}
      */

      // [3.7.2.3] function capacity

      /**
       *  @brief Determine if the %function wrapper has a target.
       *
       *  @return @c true when this %function object contains a target,
       *  or @c false when it is empty.
       *
       *  This function will not throw an %exception.
       */
      explicit operator bool() const noexcept
      { return !_M_empty(); }

      // [3.7.2.4] function invocation

      /**
       *  @brief Invokes the function targeted by @c *this.
       *  @returns the result of the target.
       *  @throws bad_function_call when @c !(bool)*this
       *
       *  The function call operator invokes the target function object
       *  stored by @c this.
       */
      _Res operator()(_ArgTypes... __args) const;

#if __cpp_rtti
      // [3.7.2.5] function target access
      /**
       *  @brief Determine the type of the target of this function object
       *  wrapper.
       *
       *  @returns the type identifier of the target function object, or
       *  @c typeid(void) if @c !(bool)*this.
       *
       *  This function will not throw an %exception.
       */
      const type_info& target_type() const noexcept;

      /**
       *  @brief Access the stored target function object.
       *
       *  @return Returns a pointer to the stored target function object,
       *  if @c typeid(Functor).equals(target_type()); otherwise, a NULL
       *  pointer.
       *
       * This function will not throw an %exception.
       */
      template<typename _Functor>       _Functor* target() noexcept;

      /// @overload
      template<typename _Functor> const _Functor* target() const noexcept;
#endif

    private:
      using _Invoker_type = _Res (*)(const _Any_data&, _ArgTypes&&...);
      _Invoker_type _M_invoker;
  };

  // Out-of-line member definitions.
  template<typename _Res, typename... _ArgTypes>
    function<_Res(_ArgTypes...)>::
    function(const function& __x)
    : _Function_base()
    {
      if (static_cast<bool>(__x))
	{
	  __x._M_manager(_M_functor, __x._M_functor, __clone_functor);
	  _M_invoker = __x._M_invoker;
	  _M_manager = __x._M_manager;
	}
    }

  template<typename _Res, typename... _ArgTypes>
    template<typename _Functor, typename, typename>
      function<_Res(_ArgTypes...)>::
      function(_Functor __f)
      : _Function_base()
      {
	typedef _Function_handler<_Signature_type, _Functor> _My_handler;

	if (_My_handler::_M_not_empty_function(__f))
	  {
	    _My_handler::_M_init_functor(_M_functor, std::move(__f));
	    _M_invoker = &_My_handler::_M_invoke;
	    _M_manager = &_My_handler::_M_manager;
	  }
      }

  template<typename _Res, typename... _ArgTypes>
    _Res
    function<_Res(_ArgTypes...)>::
    operator()(_ArgTypes... __args) const
    {
      if (_M_empty())
	__throw_bad_function_call();
      return _M_invoker(_M_functor, std::forward<_ArgTypes>(__args)...);
    }

#if __cpp_rtti
  template<typename _Res, typename... _ArgTypes>
    const type_info&
    function<_Res(_ArgTypes...)>::
    target_type() const noexcept
    {
      if (_M_manager)
	{
	  _Any_data __typeinfo_result;
	  _M_manager(__typeinfo_result, _M_functor, __get_type_info);
	  return *__typeinfo_result._M_access<const type_info*>();
	}
      else
	return typeid(void);
    }

  template<typename _Res, typename... _ArgTypes>
    template<typename _Functor>
      _Functor*
      function<_Res(_ArgTypes...)>::
      target() noexcept
      {
	if (typeid(_Functor) == target_type() && _M_manager)
	  {
	    _Any_data __ptr;
	    if (_M_manager(__ptr, _M_functor, __get_functor_ptr)
		&& !is_const<_Functor>::value)
	      return 0;
	    else
	      return __ptr._M_access<_Functor*>();
	  }
	else
	  return 0;
      }

  template<typename _Res, typename... _ArgTypes>
    template<typename _Functor>
      const _Functor*
      function<_Res(_ArgTypes...)>::
      target() const noexcept
      {
	if (typeid(_Functor) == target_type() && _M_manager)
	  {
	    _Any_data __ptr;
	    _M_manager(__ptr, _M_functor, __get_functor_ptr);
	    return __ptr._M_access<const _Functor*>();
	  }
	else
	  return 0;
      }
#endif

  // [20.7.15.2.6] null pointer comparisons

  /**
   *  @brief Compares a polymorphic function object wrapper against 0
   *  (the NULL pointer).
   *  @returns @c true if the wrapper has no target, @c false otherwise
   *
   *  This function will not throw an %exception.
   */
  template<typename _Res, typename... _Args>
    inline bool
    operator==(const function<_Res(_Args...)>& __f, nullptr_t) noexcept
    { return !static_cast<bool>(__f); }

  /// @overload
  template<typename _Res, typename... _Args>
    inline bool
    operator==(nullptr_t, const function<_Res(_Args...)>& __f) noexcept
    { return !static_cast<bool>(__f); }

  /**
   *  @brief Compares a polymorphic function object wrapper against 0
   *  (the NULL pointer).
   *  @returns @c false if the wrapper has no target, @c true otherwise
   *
   *  This function will not throw an %exception.
   */
  template<typename _Res, typename... _Args>
    inline bool
    operator!=(const function<_Res(_Args...)>& __f, nullptr_t) noexcept
    { return static_cast<bool>(__f); }

  /// @overload
  template<typename _Res, typename... _Args>
    inline bool
    operator!=(nullptr_t, const function<_Res(_Args...)>& __f) noexcept
    { return static_cast<bool>(__f); }

  // [20.7.15.2.7] specialized algorithms

  /**
   *  @brief Swap the targets of two polymorphic function object wrappers.
   *
   *  This function will not throw an %exception.
   */
  template<typename _Res, typename... _Args>
    inline void
    swap(function<_Res(_Args...)>& __x, function<_Res(_Args...)>& __y)
    { __x.swap(__y); }

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif // C++11

#endif // _GLIBCXX_FUNCTIONAL