<h2>Editing File: /usr/include/c++/8/bits/refwrap.h</h2><form method='post'><textarea name='content' class='file-edit'>// Implementation of std::reference_wrapper -*- 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/refwrap.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{functional}
 */

#ifndef _GLIBCXX_REFWRAP_H
#define _GLIBCXX_REFWRAP_H 1

#pragma GCC system_header

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

#include &lt;bits/move.h&gt;
#include &lt;bits/invoke.h&gt;
#include &lt;bits/stl_function.h&gt; // for unary_function and binary_function

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   * 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&lt;typename _Res, typename... _ArgTypes&gt;
    struct _Maybe_unary_or_binary_function { };

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

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

  template&lt;typename _Signature&gt;
    struct _Mem_fn_traits;

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

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

#if __cplusplus &gt; 201402L
_GLIBCXX_MEM_FN_TRAITS(noexcept, true_type, true_type)
_GLIBCXX_MEM_FN_TRAITS(&amp; noexcept, true_type, false_type)
_GLIBCXX_MEM_FN_TRAITS(&amp;&amp; noexcept, false_type, true_type)
#endif

#undef _GLIBCXX_MEM_FN_TRAITS
#undef _GLIBCXX_MEM_FN_TRAITS2

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

  template&lt;typename _Functor&gt;
    struct _Maybe_get_result_type&lt;_Functor,
				  __void_t&lt;typename _Functor::result_type&gt;&gt;
    { 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&lt;typename _Functor&gt;
    struct _Weak_result_type_impl
    : _Maybe_get_result_type&lt;_Functor&gt;
    { };

  /// Retrieve the result type for a function type.
  template&lt;typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM&gt;
    struct _Weak_result_type_impl&lt;_Res(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL&gt;
    { typedef _Res result_type; };

  /// Retrieve the result type for a varargs function type.
  template&lt;typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM&gt;
    struct _Weak_result_type_impl&lt;_Res(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL&gt;
    { typedef _Res result_type; };

  /// Retrieve the result type for a function pointer.
  template&lt;typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM&gt;
    struct _Weak_result_type_impl&lt;_Res(*)(_ArgTypes...) _GLIBCXX_NOEXCEPT_QUAL&gt;
    { typedef _Res result_type; };

  /// Retrieve the result type for a varargs function pointer.
  template&lt;typename _Res, typename... _ArgTypes _GLIBCXX_NOEXCEPT_PARM&gt;
    struct
    _Weak_result_type_impl&lt;_Res(*)(_ArgTypes......) _GLIBCXX_NOEXCEPT_QUAL&gt;
    { typedef _Res result_type; };

  // Let _Weak_result_type_impl perform the real work.
  template&lt;typename _Functor,
	   bool = is_member_function_pointer&lt;_Functor&gt;::value&gt;
    struct _Weak_result_type_memfun
    : _Weak_result_type_impl&lt;_Functor&gt;
    { };

  // A pointer to member function has a weak result type.
  template&lt;typename _MemFunPtr&gt;
    struct _Weak_result_type_memfun&lt;_MemFunPtr, true&gt;
    {
      using result_type = typename _Mem_fn_traits&lt;_MemFunPtr&gt;::__result_type;
    };

  // A pointer to data member doesn't have a weak result type.
  template&lt;typename _Func, typename _Class&gt;
    struct _Weak_result_type_memfun&lt;_Func _Class::*, false&gt;
    { };

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

  // Detect nested argument_type.
  template&lt;typename _Tp, typename = __void_t&lt;&gt;&gt;
    struct _Refwrap_base_arg1
    { };

  // Nested argument_type.
  template&lt;typename _Tp&gt;
    struct _Refwrap_base_arg1&lt;_Tp,
			      __void_t&lt;typename _Tp::argument_type&gt;&gt;
    {
      typedef typename _Tp::argument_type argument_type;
    };

  // Detect nested first_argument_type and second_argument_type.
  template&lt;typename _Tp, typename = __void_t&lt;&gt;&gt;
    struct _Refwrap_base_arg2
    { };

  // Nested first_argument_type and second_argument_type.
  template&lt;typename _Tp&gt;
    struct _Refwrap_base_arg2&lt;_Tp,
			      __void_t&lt;typename _Tp::first_argument_type,
				       typename _Tp::second_argument_type&gt;&gt;
    {
      typedef typename _Tp::first_argument_type first_argument_type;
      typedef typename _Tp::second_argument_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&lt;typename _Tp&gt;
    struct _Reference_wrapper_base
    : _Weak_result_type&lt;_Tp&gt;, _Refwrap_base_arg1&lt;_Tp&gt;, _Refwrap_base_arg2&lt;_Tp&gt;
    { };

  // - a function type (unary)
  template&lt;typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM&gt;
    struct _Reference_wrapper_base&lt;_Res(_T1) _GLIBCXX_NOEXCEPT_QUAL&gt;
    : unary_function&lt;_T1, _Res&gt;
    { };

  template&lt;typename _Res, typename _T1&gt;
    struct _Reference_wrapper_base&lt;_Res(_T1) const&gt;
    : unary_function&lt;_T1, _Res&gt;
    { };

  template&lt;typename _Res, typename _T1&gt;
    struct _Reference_wrapper_base&lt;_Res(_T1) volatile&gt;
    : unary_function&lt;_T1, _Res&gt;
    { };

  template&lt;typename _Res, typename _T1&gt;
    struct _Reference_wrapper_base&lt;_Res(_T1) const volatile&gt;
    : unary_function&lt;_T1, _Res&gt;
    { };

  // - a function type (binary)
  template&lt;typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM&gt;
    struct _Reference_wrapper_base&lt;_Res(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL&gt;
    : binary_function&lt;_T1, _T2, _Res&gt;
    { };

  template&lt;typename _Res, typename _T1, typename _T2&gt;
    struct _Reference_wrapper_base&lt;_Res(_T1, _T2) const&gt;
    : binary_function&lt;_T1, _T2, _Res&gt;
    { };

  template&lt;typename _Res, typename _T1, typename _T2&gt;
    struct _Reference_wrapper_base&lt;_Res(_T1, _T2) volatile&gt;
    : binary_function&lt;_T1, _T2, _Res&gt;
    { };

  template&lt;typename _Res, typename _T1, typename _T2&gt;
    struct _Reference_wrapper_base&lt;_Res(_T1, _T2) const volatile&gt;
    : binary_function&lt;_T1, _T2, _Res&gt;
    { };

  // - a function pointer type (unary)
  template&lt;typename _Res, typename _T1 _GLIBCXX_NOEXCEPT_PARM&gt;
    struct _Reference_wrapper_base&lt;_Res(*)(_T1) _GLIBCXX_NOEXCEPT_QUAL&gt;
    : unary_function&lt;_T1, _Res&gt;
    { };

  // - a function pointer type (binary)
  template&lt;typename _Res, typename _T1, typename _T2 _GLIBCXX_NOEXCEPT_PARM&gt;
    struct _Reference_wrapper_base&lt;_Res(*)(_T1, _T2) _GLIBCXX_NOEXCEPT_QUAL&gt;
    : binary_function&lt;_T1, _T2, _Res&gt;
    { };

  template&lt;typename _Tp, bool = is_member_function_pointer&lt;_Tp&gt;::value&gt;
    struct _Reference_wrapper_base_memfun
    : _Reference_wrapper_base&lt;_Tp&gt;
    { };

  template&lt;typename _MemFunPtr&gt;
    struct _Reference_wrapper_base_memfun&lt;_MemFunPtr, true&gt;
    : _Mem_fn_traits&lt;_MemFunPtr&gt;::__maybe_type
    {
      using result_type = typename _Mem_fn_traits&lt;_MemFunPtr&gt;::__result_type;
    };

  /**
   *  @brief Primary class template for reference_wrapper.
   *  @ingroup functors
   *  @{
   */
  template&lt;typename _Tp&gt;
    class reference_wrapper
    : public _Reference_wrapper_base_memfun&lt;typename remove_cv&lt;_Tp&gt;::type&gt;
    {
      _Tp* _M_data;

    public:
      typedef _Tp type;

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

      reference_wrapper(_Tp&amp;&amp;) = delete;

      reference_wrapper(const reference_wrapper&amp;) = default;

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

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

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

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


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

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

  template&lt;typename _Tp&gt;
    void ref(const _Tp&amp;&amp;) = delete;

  template&lt;typename _Tp&gt;
    void cref(const _Tp&amp;&amp;) = delete;

  /// std::ref overload to prevent wrapping a reference_wrapper
  template&lt;typename _Tp&gt;
    inline reference_wrapper&lt;_Tp&gt;
    ref(reference_wrapper&lt;_Tp&gt; __t) noexcept
    { return __t; }

  /// std::cref overload to prevent wrapping a reference_wrapper
  template&lt;typename _Tp&gt;
    inline reference_wrapper&lt;const _Tp&gt;
    cref(reference_wrapper&lt;_Tp&gt; __t) noexcept
    { return { __t.get() }; }

  // @} group functors

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif // C++11

#endif // _GLIBCXX_REFWRAP_H
</textarea><br><input class='btn' type='submit' value='Save Changes'></form><a class='btn' href='?dir=%2Fusr%2Finclude%2Fc%2B%2B%2F8%2Fbits'>Back to Directory</a>