<h2>Editing File: /usr/include/c++/8/bits/std_function.h</h2><form method='post'><textarea name='content' class='file-edit'>// Implementation of std::function -*- C++ -*-

// Copyright (C) 2004-2018 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
// &lt;http://www.gnu.org/licenses/&gt;.

/** @file include/bits/std_function.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{functional}
 */

#ifndef _GLIBCXX_STD_FUNCTION_H
#define _GLIBCXX_STD_FUNCTION_H 1

#pragma GCC system_header

#if __cplusplus &lt; 201103L
# include &lt;bits/c++0x_warning.h&gt;
#else

#if __cpp_rtti
# include &lt;typeinfo&gt;
#endif
#include &lt;bits/stl_function.h&gt;
#include &lt;bits/invoke.h&gt;
#include &lt;bits/refwrap.h&gt;
#include &lt;bits/functexcept.h&gt;

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   *  @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 &quot;location-invariant&quot; 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&lt;typename _Tp&gt;
    struct __is_location_invariant
    : is_trivially_copyable&lt;_Tp&gt;::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 [[gnu::may_alias]] _Any_data
  {
    void*       _M_access()       { return &amp;_M_pod_data[0]; }
    const void* _M_access() const { return &amp;_M_pod_data[0]; }

    template&lt;typename _Tp&gt;
      _Tp&amp;
      _M_access()
      { return *static_cast&lt;_Tp*&gt;(_M_access()); }

    template&lt;typename _Tp&gt;
      const _Tp&amp;
      _M_access() const
      { return *static_cast&lt;const _Tp*&gt;(_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&lt;typename _Tp&gt;
    struct _Simple_type_wrapper
    {
      _Simple_type_wrapper(_Tp __value) : __value(__value) { }

      _Tp __value;
    };

  template&lt;typename _Tp&gt;
    struct __is_location_invariant&lt;_Simple_type_wrapper&lt;_Tp&gt; &gt;
    : __is_location_invariant&lt;_Tp&gt;
    { };

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

	typedef integral_constant&lt;bool, __stored_locally&gt; _Local_storage;

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

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

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

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

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

      public:
	static bool
	_M_manager(_Any_data&amp; __dest, const _Any_data&amp; __source,
		   _Manager_operation __op)
	{
	  switch (__op)
	    {
#if __cpp_rtti
	    case __get_type_info:
	      __dest._M_access&lt;const type_info*&gt;() = &amp;typeid(_Functor);
	      break;
#endif
	    case __get_functor_ptr:
	      __dest._M_access&lt;_Functor*&gt;() = _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&amp; __functor, _Functor&amp;&amp; __f)
	{ _M_init_functor(__functor, std::move(__f), _Local_storage()); }

	template&lt;typename _Signature&gt;
	  static bool
	  _M_not_empty_function(const function&lt;_Signature&gt;&amp; __f)
	  { return static_cast&lt;bool&gt;(__f); }

	template&lt;typename _Tp&gt;
	  static bool
	  _M_not_empty_function(_Tp* __fp)
	  { return __fp != nullptr; }

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

	template&lt;typename _Tp&gt;
	  static bool
	  _M_not_empty_function(const _Tp&amp;)
	  { return true; }

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

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

    _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&amp;, const _Any_data&amp;,
				  _Manager_operation);

    _Any_data     _M_functor;
    _Manager_type _M_manager;
  };

  template&lt;typename _Signature, typename _Functor&gt;
    class _Function_handler;

  template&lt;typename _Res, typename _Functor, typename... _ArgTypes&gt;
    class _Function_handler&lt;_Res(_ArgTypes...), _Functor&gt;
    : public _Function_base::_Base_manager&lt;_Functor&gt;
    {
      typedef _Function_base::_Base_manager&lt;_Functor&gt; _Base;

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

  template&lt;typename _Functor, typename... _ArgTypes&gt;
    class _Function_handler&lt;void(_ArgTypes...), _Functor&gt;
    : public _Function_base::_Base_manager&lt;_Functor&gt;
    {
      typedef _Function_base::_Base_manager&lt;_Functor&gt; _Base;

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

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

     public:
      static _Res
      _M_invoke(const _Any_data&amp; __functor, _ArgTypes&amp;&amp;... __args)
      {
	return std::__invoke(_Base::_M_get_pointer(__functor)-&gt;__value,
			     std::forward&lt;_ArgTypes&gt;(__args)...);
      }
    };

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

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

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

      static void
      _M_invoke(const _Any_data&amp; __functor, _ArgTypes&amp;&amp;... __args)
      {
	std::__invoke(_Base::_M_get_pointer(__functor)-&gt;__value,
		      std::forward&lt;_ArgTypes&gt;(__args)...);
      }
    };

  template&lt;typename _From, typename _To&gt;
    using __check_func_return_type
      = __or_&lt;is_void&lt;_To&gt;, is_same&lt;_From, _To&gt;, is_convertible&lt;_From, _To&gt;&gt;;

  /**
   *  @brief Primary class template for std::function.
   *  @ingroup functors
   *
   *  Polymorphic function wrapper.
   */
  template&lt;typename _Res, typename... _ArgTypes&gt;
    class function&lt;_Res(_ArgTypes...)&gt;
    : public _Maybe_unary_or_binary_function&lt;_Res, _ArgTypes...&gt;,
      private _Function_base
    {
      template&lt;typename _Func,
	       typename _Res2 = typename result_of&lt;_Func&amp;(_ArgTypes...)&gt;::type&gt;
	struct _Callable : __check_func_return_type&lt;_Res2, _Res&gt; { };

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

      template&lt;typename _Cond, typename _Tp&gt;
	using _Requires = typename enable_if&lt;_Cond::value, _Tp&gt;::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&amp; __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&amp;&amp; __x) noexcept : _Function_base()
      {
	__x.swap(*this);
      }

      /**
       *  @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&lt;F&gt;, 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&lt;F&gt;, this function will not throw.
       */
      template&lt;typename _Functor,
	       typename = _Requires&lt;__not_&lt;is_same&lt;_Functor, function&gt;&gt;, void&gt;,
	       typename = _Requires&lt;_Callable&lt;_Functor&gt;, void&gt;&gt;
	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&amp;
      operator=(const function&amp; __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&amp;
      operator=(function&amp;&amp; __x) noexcept
      {
	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&amp;
      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&lt;F&gt;, 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&lt;F&gt;, this function will not throw.
       */
      template&lt;typename _Functor&gt;
	_Requires&lt;_Callable&lt;typename decay&lt;_Functor&gt;::type&gt;, function&amp;&gt;
	operator=(_Functor&amp;&amp; __f)
	{
	  function(std::forward&lt;_Functor&gt;(__f)).swap(*this);
	  return *this;
	}

      /// @overload
      template&lt;typename _Functor&gt;
	function&amp;
	operator=(reference_wrapper&lt;_Functor&gt; __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&amp; __x) noexcept
      {
	std::swap(_M_functor, __x._M_functor);
	std::swap(_M_manager, __x._M_manager);
	std::swap(_M_invoker, __x._M_invoker);
      }

      // [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&amp; 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 does not throw exceptions.
       *
       * @{
       */
      template&lt;typename _Functor&gt;       _Functor* target() noexcept;

      template&lt;typename _Functor&gt; const _Functor* target() const noexcept;
      // @}
#endif

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

#if __cpp_deduction_guides &gt;= 201606
  template&lt;typename&gt;
    struct __function_guide_helper
    { };

  template&lt;typename _Res, typename _Tp, bool _Nx, typename... _Args&gt;
    struct __function_guide_helper&lt;
      _Res (_Tp::*) (_Args...) noexcept(_Nx)
    &gt;
    { using type = _Res(_Args...); };

  template&lt;typename _Res, typename _Tp, bool _Nx, typename... _Args&gt;
    struct __function_guide_helper&lt;
      _Res (_Tp::*) (_Args...) &amp; noexcept(_Nx)
    &gt;
    { using type = _Res(_Args...); };

  template&lt;typename _Res, typename _Tp, bool _Nx, typename... _Args&gt;
    struct __function_guide_helper&lt;
      _Res (_Tp::*) (_Args...) const noexcept(_Nx)
    &gt;
    { using type = _Res(_Args...); };

  template&lt;typename _Res, typename _Tp, bool _Nx, typename... _Args&gt;
    struct __function_guide_helper&lt;
      _Res (_Tp::*) (_Args...) const &amp; noexcept(_Nx)
    &gt;
    { using type = _Res(_Args...); };

  template&lt;typename _Res, typename... _ArgTypes&gt;
    function(_Res(*)(_ArgTypes...)) -&gt; function&lt;_Res(_ArgTypes...)&gt;;

  template&lt;typename _Functor, typename _Signature = typename
	   __function_guide_helper&lt;decltype(&amp;_Functor::operator())&gt;::type&gt;
    function(_Functor) -&gt; function&lt;_Signature&gt;;
#endif

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

  template&lt;typename _Res, typename... _ArgTypes&gt;
    template&lt;typename _Functor, typename, typename&gt;
      function&lt;_Res(_ArgTypes...)&gt;::
      function(_Functor __f)
      : _Function_base()
      {
	typedef _Function_handler&lt;_Res(_ArgTypes...), _Functor&gt; _My_handler;

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

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

#if __cpp_rtti
  template&lt;typename _Res, typename... _ArgTypes&gt;
    const type_info&amp;
    function&lt;_Res(_ArgTypes...)&gt;::
    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&lt;const type_info*&gt;();
	}
      else
	return typeid(void);
    }

  template&lt;typename _Res, typename... _ArgTypes&gt;
    template&lt;typename _Functor&gt;
      _Functor*
      function&lt;_Res(_ArgTypes...)&gt;::
      target() noexcept
      {
	const function* __const_this = this;
	const _Functor* __func = __const_this-&gt;template target&lt;_Functor&gt;();
	return const_cast&lt;_Functor*&gt;(__func);
      }

  template&lt;typename _Res, typename... _ArgTypes&gt;
    template&lt;typename _Functor&gt;
      const _Functor*
      function&lt;_Res(_ArgTypes...)&gt;::
      target() const noexcept
      {
	if (typeid(_Functor) == target_type() &amp;&amp; _M_manager)
	  {
	    _Any_data __ptr;
	    _M_manager(__ptr, _M_functor, __get_functor_ptr);
	    return __ptr._M_access&lt;const _Functor*&gt;();
	  }
	else
	  return nullptr;
      }
#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&lt;typename _Res, typename... _Args&gt;
    inline bool
    operator==(const function&lt;_Res(_Args...)&gt;&amp; __f, nullptr_t) noexcept
    { return !static_cast&lt;bool&gt;(__f); }

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

  /// @overload
  template&lt;typename _Res, typename... _Args&gt;
    inline bool
    operator!=(nullptr_t, const function&lt;_Res(_Args...)&gt;&amp; __f) noexcept
    { return static_cast&lt;bool&gt;(__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.
   */
  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 2062. Effect contradictions w/o no-throw guarantee of std::function swaps
  template&lt;typename _Res, typename... _Args&gt;
    inline void
    swap(function&lt;_Res(_Args...)&gt;&amp; __x, function&lt;_Res(_Args...)&gt;&amp; __y) noexcept
    { __x.swap(__y); }

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif // C++11

#endif // _GLIBCXX_STD_FUNCTION_H
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