--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libstdc++-v3/include/std/optional	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,1048 @@
+// <optional> -*- C++ -*-
+
+// Copyright (C) 2013-2017 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/>.
+
+/** @file include/optional
+ *  This is a Standard C++ Library header.
+ */
+
+#ifndef _GLIBCXX_OPTIONAL
+#define _GLIBCXX_OPTIONAL 1
+
+#pragma GCC system_header
+
+#if __cplusplus >= 201703L
+
+#include <utility>
+#include <type_traits>
+#include <stdexcept>
+#include <new>
+#include <initializer_list>
+#include <bits/functexcept.h>
+#include <bits/functional_hash.h>
+#include <bits/enable_special_members.h>
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+  /**
+   *  @addtogroup utilities
+   *  @{
+   */
+
+#define __cpp_lib_optional 201603
+
+  template<typename _Tp>
+    class optional;
+
+  /// Tag type to disengage optional objects.
+  struct nullopt_t
+  {
+    // Do not user-declare default constructor at all for
+    // optional_value = {} syntax to work.
+    // nullopt_t() = delete;
+
+    // Used for constructing nullopt.
+    enum class _Construct { _Token };
+
+    // Must be constexpr for nullopt_t to be literal.
+    explicit constexpr nullopt_t(_Construct) { }
+  };
+
+  /// Tag to disengage optional objects.
+  inline constexpr nullopt_t nullopt { nullopt_t::_Construct::_Token };
+
+  /**
+   *  @brief Exception class thrown when a disengaged optional object is
+   *  dereferenced.
+   *  @ingroup exceptions
+   */
+  class bad_optional_access : public exception
+  {
+  public:
+    bad_optional_access() { }
+    virtual const char* what() const noexcept override
+    {return "bad optional access";}
+
+    virtual ~bad_optional_access() noexcept = default;
+  };
+
+  void
+  __throw_bad_optional_access()
+  __attribute__((__noreturn__));
+
+  // XXX Does not belong here.
+  inline void
+  __throw_bad_optional_access()
+  { _GLIBCXX_THROW_OR_ABORT(bad_optional_access()); }
+
+
+  // Payload for constexpr optionals.
+  template <typename _Tp,
+	    bool /*_TrivialCopyMove*/ =
+	      is_trivially_copy_constructible<_Tp>::value
+	      && is_trivially_move_constructible<_Tp>::value,
+	    bool /*_ShouldProvideDestructor*/ =
+	      is_trivially_destructible<_Tp>::value>
+    struct _Optional_payload
+    {
+      constexpr _Optional_payload()
+	: _M_empty() {}
+
+      template<typename... _Args>
+      constexpr _Optional_payload(in_place_t, _Args&&... __args)
+	: _M_payload(std::forward<_Args>(__args)...),
+	  _M_engaged(true)
+      {}
+
+      template<typename _Up, typename... _Args>
+      constexpr _Optional_payload(std::initializer_list<_Up> __il,
+				  _Args&&... __args)
+	: _M_payload(__il, std::forward<_Args>(__args)...),
+	  _M_engaged(true) {}
+
+      template <class _Up> struct __ctor_tag {};
+
+      constexpr _Optional_payload(__ctor_tag<bool>,
+				  const _Tp& __other)
+	: _M_payload(__other),
+	  _M_engaged(true)
+      {}
+
+      constexpr _Optional_payload(__ctor_tag<void>)
+	: _M_empty()
+      {}
+
+      constexpr _Optional_payload(__ctor_tag<bool>, _Tp&& __other)
+	: _M_payload(std::move(__other)),
+	  _M_engaged(true)
+      {}
+
+      constexpr _Optional_payload(bool __engaged,
+				  const _Optional_payload& __other)
+	: _Optional_payload(__engaged ?
+			    _Optional_payload(__ctor_tag<bool>{},
+					      __other._M_payload) :
+			    _Optional_payload(__ctor_tag<void>{}))
+      {}
+
+      constexpr _Optional_payload(bool __engaged,
+				  _Optional_payload&& __other)
+	: _Optional_payload(__engaged
+			    ? _Optional_payload(__ctor_tag<bool>{},
+						std::move(__other._M_payload))
+			    : _Optional_payload(__ctor_tag<void>{}))
+      {}
+
+      using _Stored_type = remove_const_t<_Tp>;
+      struct _Empty_byte { };
+      union {
+          _Empty_byte _M_empty;
+          _Stored_type _M_payload;
+      };
+      bool _M_engaged = false;
+    };
+
+  // Payload for non-constexpr optionals with non-trivial destructor.
+  template <typename _Tp>
+    struct _Optional_payload<_Tp, false, false>
+    {
+      constexpr _Optional_payload()
+	: _M_empty() {}
+
+      template <typename... _Args>
+      constexpr _Optional_payload(in_place_t, _Args&&... __args)
+	: _M_payload(std::forward<_Args>(__args)...),
+	  _M_engaged(true) {}
+
+      template<typename _Up, typename... _Args>
+      constexpr _Optional_payload(std::initializer_list<_Up> __il,
+				  _Args&&... __args)
+	: _M_payload(__il, std::forward<_Args>(__args)...),
+	  _M_engaged(true) {}
+      constexpr
+      _Optional_payload(bool __engaged, const _Optional_payload& __other)
+	: _Optional_payload(__other)
+      {}
+
+      constexpr
+      _Optional_payload(bool __engaged, _Optional_payload&& __other)
+	: _Optional_payload(std::move(__other))
+      {}
+
+      constexpr _Optional_payload(const _Optional_payload& __other)
+      {
+	if (__other._M_engaged)
+	  this->_M_construct(__other._M_payload);
+      }
+
+      constexpr _Optional_payload(_Optional_payload&& __other)
+      {
+	if (__other._M_engaged)
+	  this->_M_construct(std::move(__other._M_payload));
+      }
+
+      using _Stored_type = remove_const_t<_Tp>;
+      struct _Empty_byte { };
+      union {
+          _Empty_byte _M_empty;
+          _Stored_type _M_payload;
+      };
+      bool _M_engaged = false;
+
+      ~_Optional_payload()
+      {
+        if (_M_engaged)
+          _M_payload.~_Stored_type();
+      }
+
+      template<typename... _Args>
+        void
+        _M_construct(_Args&&... __args)
+        noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
+        {
+          ::new ((void *) std::__addressof(this->_M_payload))
+            _Stored_type(std::forward<_Args>(__args)...);
+          this->_M_engaged = true;
+        }
+    };
+
+  // Payload for non-constexpr optionals with trivial destructor.
+  template <typename _Tp>
+    struct _Optional_payload<_Tp, false, true>
+    {
+      constexpr _Optional_payload()
+	: _M_empty() {}
+
+      template <typename... _Args>
+      constexpr _Optional_payload(in_place_t, _Args&&... __args)
+	: _M_payload(std::forward<_Args>(__args)...),
+	  _M_engaged(true) {}
+
+      template<typename _Up, typename... _Args>
+      constexpr _Optional_payload(std::initializer_list<_Up> __il,
+				  _Args&&... __args)
+	: _M_payload(__il, std::forward<_Args>(__args)...),
+	  _M_engaged(true) {}
+      constexpr
+      _Optional_payload(bool __engaged, const _Optional_payload& __other)
+	: _Optional_payload(__other)
+      {}
+
+      constexpr
+      _Optional_payload(bool __engaged, _Optional_payload&& __other)
+	: _Optional_payload(std::move(__other))
+      {}
+
+      constexpr _Optional_payload(const _Optional_payload& __other)
+      {
+	if (__other._M_engaged)
+	  this->_M_construct(__other._M_payload);
+      }
+
+      constexpr _Optional_payload(_Optional_payload&& __other)
+      {
+	if (__other._M_engaged)
+	  this->_M_construct(std::move(__other._M_payload));
+      }
+
+      using _Stored_type = remove_const_t<_Tp>;
+      struct _Empty_byte { };
+      union {
+          _Empty_byte _M_empty;
+          _Stored_type _M_payload;
+      };
+      bool _M_engaged = false;
+
+      template<typename... _Args>
+        void
+        _M_construct(_Args&&... __args)
+        noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
+        {
+          ::new ((void *) std::__addressof(this->_M_payload))
+            _Stored_type(std::forward<_Args>(__args)...);
+          this->_M_engaged = true;
+        }
+    };
+
+  /**
+    * @brief Class template that holds the necessary state for @ref optional
+    * and that has the responsibility for construction and the special members.
+    *
+    * Such a separate base class template is necessary in order to
+    * conditionally enable the special members (e.g. copy/move constructors).
+    * Note that this means that @ref _Optional_base implements the
+    * functionality for copy and move assignment, but not for converting
+    * assignment.
+    *
+    * @see optional, _Enable_special_members
+    */
+  template<typename _Tp>
+    class _Optional_base
+    {
+    private:
+      // Remove const to avoid prohibition of reusing object storage for
+      // const-qualified types in [3.8/9]. This is strictly internal
+      // and even optional itself is oblivious to it.
+      using _Stored_type = remove_const_t<_Tp>;
+
+    public:
+
+      // Constructors for disengaged optionals.
+      constexpr _Optional_base() noexcept
+      { }
+
+      constexpr _Optional_base(nullopt_t) noexcept
+      { }
+
+      // Constructors for engaged optionals.
+      template<typename... _Args,
+	       enable_if_t<is_constructible_v<_Tp, _Args&&...>, bool> = false>
+        constexpr explicit _Optional_base(in_place_t, _Args&&... __args)
+        : _M_payload(in_place,
+		     std::forward<_Args>(__args)...) { }
+
+      template<typename _Up, typename... _Args,
+               enable_if_t<is_constructible_v<_Tp,
+					      initializer_list<_Up>&,
+					      _Args&&...>, bool> = false>
+        constexpr explicit _Optional_base(in_place_t,
+                                          initializer_list<_Up> __il,
+                                          _Args&&... __args)
+        : _M_payload(in_place,
+		     __il, std::forward<_Args>(__args)...)
+        { }
+
+      // Copy and move constructors.
+      constexpr _Optional_base(const _Optional_base& __other)
+	: _M_payload(__other._M_payload._M_engaged,
+		     __other._M_payload)
+      { }
+
+      constexpr _Optional_base(_Optional_base&& __other)
+      noexcept(is_nothrow_move_constructible<_Tp>())
+	: _M_payload(__other._M_payload._M_engaged,
+		     std::move(__other._M_payload))
+      { }
+
+      // Assignment operators.
+      _Optional_base&
+      operator=(const _Optional_base& __other)
+      {
+        if (this->_M_payload._M_engaged && __other._M_payload._M_engaged)
+          this->_M_get() = __other._M_get();
+        else
+	  {
+	    if (__other._M_payload._M_engaged)
+	      this->_M_construct(__other._M_get());
+	    else
+	      this->_M_reset();
+	  }
+
+        return *this;
+      }
+
+      _Optional_base&
+      operator=(_Optional_base&& __other)
+      noexcept(__and_<is_nothrow_move_constructible<_Tp>,
+		      is_nothrow_move_assignable<_Tp>>())
+      {
+	if (this->_M_payload._M_engaged && __other._M_payload._M_engaged)
+	  this->_M_get() = std::move(__other._M_get());
+	else
+	  {
+	    if (__other._M_payload._M_engaged)
+	      this->_M_construct(std::move(__other._M_get()));
+	    else
+	      this->_M_reset();
+	  }
+	return *this;
+      }
+      // The following functionality is also needed by optional, hence the
+      // protected accessibility.
+    protected:
+      constexpr bool _M_is_engaged() const noexcept
+      { return this->_M_payload._M_engaged; }
+
+      // The _M_get operations have _M_engaged as a precondition.
+      constexpr _Tp&
+      _M_get() noexcept
+      {
+	__glibcxx_assert(_M_is_engaged());
+	return this->_M_payload._M_payload;
+      }
+
+      constexpr const _Tp&
+      _M_get() const noexcept
+      {
+	__glibcxx_assert(_M_is_engaged());
+	return this->_M_payload._M_payload;
+      }
+
+      // The _M_construct operation has !_M_engaged as a precondition
+      // while _M_destruct has _M_engaged as a precondition.
+      template<typename... _Args>
+        void
+        _M_construct(_Args&&... __args)
+        noexcept(is_nothrow_constructible<_Stored_type, _Args...>())
+        {
+          ::new (std::__addressof(this->_M_payload._M_payload))
+            _Stored_type(std::forward<_Args>(__args)...);
+          this->_M_payload._M_engaged = true;
+        }
+
+      void
+      _M_destruct()
+      {
+        this->_M_payload._M_engaged = false;
+        this->_M_payload._M_payload.~_Stored_type();
+      }
+
+      // _M_reset is a 'safe' operation with no precondition.
+      void
+      _M_reset()
+      {
+        if (this->_M_payload._M_engaged)
+          this->_M_destruct();
+      }
+
+    private:
+      _Optional_payload<_Tp> _M_payload;
+    };
+
+  template<typename _Tp>
+  class optional;
+
+  template<typename _Tp, typename _Up>
+    using __converts_from_optional =
+      __or_<is_constructible<_Tp, const optional<_Up>&>,
+	    is_constructible<_Tp, optional<_Up>&>,
+	    is_constructible<_Tp, const optional<_Up>&&>,
+	    is_constructible<_Tp, optional<_Up>&&>,
+	    is_convertible<const optional<_Up>&, _Tp>,
+	    is_convertible<optional<_Up>&, _Tp>,
+	    is_convertible<const optional<_Up>&&, _Tp>,
+	    is_convertible<optional<_Up>&&, _Tp>>;
+
+  template<typename _Tp, typename _Up>
+    using __assigns_from_optional =
+      __or_<is_assignable<_Tp&, const optional<_Up>&>,
+	    is_assignable<_Tp&, optional<_Up>&>,
+	    is_assignable<_Tp&, const optional<_Up>&&>,
+	    is_assignable<_Tp&, optional<_Up>&&>>;
+
+  /**
+    * @brief Class template for optional values.
+    */
+  template<typename _Tp>
+    class optional
+    : private _Optional_base<_Tp>,
+      private _Enable_copy_move<
+        // Copy constructor.
+        is_copy_constructible<_Tp>::value,
+        // Copy assignment.
+        __and_<is_copy_constructible<_Tp>, is_copy_assignable<_Tp>>::value,
+        // Move constructor.
+        is_move_constructible<_Tp>::value,
+        // Move assignment.
+        __and_<is_move_constructible<_Tp>, is_move_assignable<_Tp>>::value,
+        // Unique tag type.
+        optional<_Tp>>
+    {
+      static_assert(!is_same_v<remove_cv_t<_Tp>, nullopt_t>);
+      static_assert(!is_same_v<remove_cv_t<_Tp>, in_place_t>);
+      static_assert(!is_reference_v<_Tp>);
+
+    private:
+      using _Base = _Optional_base<_Tp>;
+
+    public:
+      using value_type = _Tp;
+
+      constexpr optional() = default;
+
+      constexpr optional(nullopt_t) noexcept
+	: _Base(nullopt) { }
+
+      // Converting constructors for engaged optionals.
+      template <typename _Up = _Tp,
+                enable_if_t<__and_<
+			      __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
+			      __not_<is_same<in_place_t, decay_t<_Up>>>,
+			      is_constructible<_Tp, _Up&&>,
+			      is_convertible<_Up&&, _Tp>
+			      >::value, bool> = true>
+      constexpr optional(_Up&& __t)
+        : _Base(std::in_place, std::forward<_Up>(__t)) { }
+
+      template <typename _Up = _Tp,
+                enable_if_t<__and_<
+			      __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
+			      __not_<is_same<in_place_t, decay_t<_Up>>>,
+			      is_constructible<_Tp, _Up&&>,
+			      __not_<is_convertible<_Up&&, _Tp>>
+			      >::value, bool> = false>
+      explicit constexpr optional(_Up&& __t)
+        : _Base(std::in_place, std::forward<_Up>(__t)) { }
+
+      template <typename _Up,
+                enable_if_t<__and_<
+			    __not_<is_same<_Tp, _Up>>,
+			    is_constructible<_Tp, const _Up&>,
+			    is_convertible<const _Up&, _Tp>,
+			    __not_<__converts_from_optional<_Tp, _Up>>
+			    >::value, bool> = true>
+      constexpr optional(const optional<_Up>& __t)
+      {
+	if (__t)
+	  emplace(*__t);
+      }
+
+      template <typename _Up,
+                 enable_if_t<__and_<
+			       __not_<is_same<_Tp, _Up>>,
+			       is_constructible<_Tp, const _Up&>,
+			       __not_<is_convertible<const _Up&, _Tp>>,
+			       __not_<__converts_from_optional<_Tp, _Up>>
+			       >::value, bool> = false>
+      explicit constexpr optional(const optional<_Up>& __t)
+      {
+	if (__t)
+	  emplace(*__t);
+      }
+
+      template <typename _Up,
+                enable_if_t<__and_<
+			      __not_<is_same<_Tp, _Up>>,
+			      is_constructible<_Tp, _Up&&>,
+			      is_convertible<_Up&&, _Tp>,
+			      __not_<__converts_from_optional<_Tp, _Up>>
+			      >::value, bool> = true>
+      constexpr optional(optional<_Up>&& __t)
+      {
+	if (__t)
+	  emplace(std::move(*__t));
+      }
+
+      template <typename _Up,
+                enable_if_t<__and_<
+			    __not_<is_same<_Tp, _Up>>,
+			    is_constructible<_Tp, _Up&&>,
+			    __not_<is_convertible<_Up&&, _Tp>>,
+			    __not_<__converts_from_optional<_Tp, _Up>>
+			    >::value, bool> = false>
+      explicit constexpr optional(optional<_Up>&& __t)
+      {
+	if (__t)
+	  emplace(std::move(*__t));
+      }
+
+      template<typename... _Args,
+	       enable_if_t<is_constructible_v<_Tp, _Args&&...>, bool> = false>
+      explicit constexpr optional(in_place_t, _Args&&... __args)
+        : _Base(std::in_place, std::forward<_Args>(__args)...) { }
+
+      template<typename _Up, typename... _Args,
+               enable_if_t<is_constructible_v<_Tp,
+					      initializer_list<_Up>&,
+					      _Args&&...>, bool> = false>
+      explicit constexpr optional(in_place_t,
+				  initializer_list<_Up> __il,
+				  _Args&&... __args)
+        : _Base(std::in_place, __il, std::forward<_Args>(__args)...) { }
+
+      // Assignment operators.
+      optional&
+      operator=(nullopt_t) noexcept
+      {
+        this->_M_reset();
+        return *this;
+      }
+
+      template<typename _Up = _Tp>
+        enable_if_t<__and_<
+		      __not_<is_same<optional<_Tp>, decay_t<_Up>>>,
+		      is_constructible<_Tp, _Up>,
+		      __not_<__and_<is_scalar<_Tp>,
+				    is_same<_Tp, decay_t<_Up>>>>,
+		      is_assignable<_Tp&, _Up>>::value,
+		    optional&>
+        operator=(_Up&& __u)
+        {
+          if (this->_M_is_engaged())
+            this->_M_get() = std::forward<_Up>(__u);
+          else
+            this->_M_construct(std::forward<_Up>(__u));
+
+          return *this;
+        }
+
+      template<typename _Up>
+	enable_if_t<__and_<
+		      __not_<is_same<_Tp, _Up>>,
+		      is_constructible<_Tp, const _Up&>,
+		      is_assignable<_Tp&, _Up>,
+		      __not_<__converts_from_optional<_Tp, _Up>>,
+		      __not_<__assigns_from_optional<_Tp, _Up>>
+		      >::value,
+		    optional&>
+        operator=(const optional<_Up>& __u)
+        {
+          if (__u)
+            {
+              if (this->_M_is_engaged())
+                this->_M_get() = *__u;
+              else
+                this->_M_construct(*__u);
+            }
+          else
+            {
+              this->_M_reset();
+            }
+          return *this;
+        }
+
+      template<typename _Up>
+	enable_if_t<__and_<
+		      __not_<is_same<_Tp, _Up>>,
+		      is_constructible<_Tp, _Up>,
+		      is_assignable<_Tp&, _Up>,
+		      __not_<__converts_from_optional<_Tp, _Up>>,
+		      __not_<__assigns_from_optional<_Tp, _Up>>
+		      >::value,
+		    optional&>
+        operator=(optional<_Up>&& __u)
+        {
+          if (__u)
+            {
+              if (this->_M_is_engaged())
+                this->_M_get() = std::move(*__u);
+              else
+                this->_M_construct(std::move(*__u));
+            }
+          else
+            {
+              this->_M_reset();
+            }
+
+          return *this;
+        }
+
+      template<typename... _Args>
+	enable_if_t<is_constructible<_Tp, _Args&&...>::value, _Tp&>
+	emplace(_Args&&... __args)
+	{
+	  this->_M_reset();
+	  this->_M_construct(std::forward<_Args>(__args)...);
+	  return this->_M_get();
+	}
+
+      template<typename _Up, typename... _Args>
+	enable_if_t<is_constructible<_Tp, initializer_list<_Up>&,
+				     _Args&&...>::value, _Tp&>
+	emplace(initializer_list<_Up> __il, _Args&&... __args)
+	{
+	  this->_M_reset();
+	  this->_M_construct(__il, std::forward<_Args>(__args)...);
+	  return this->_M_get();
+	}
+
+      // Destructor is implicit, implemented in _Optional_base.
+
+      // Swap.
+      void
+      swap(optional& __other)
+      noexcept(is_nothrow_move_constructible<_Tp>()
+               && is_nothrow_swappable_v<_Tp>)
+      {
+        using std::swap;
+
+        if (this->_M_is_engaged() && __other._M_is_engaged())
+          swap(this->_M_get(), __other._M_get());
+        else if (this->_M_is_engaged())
+	  {
+	    __other._M_construct(std::move(this->_M_get()));
+	    this->_M_destruct();
+	  }
+        else if (__other._M_is_engaged())
+	  {
+	    this->_M_construct(std::move(__other._M_get()));
+	    __other._M_destruct();
+	  }
+      }
+
+      // Observers.
+      constexpr const _Tp*
+      operator->() const
+      { return std::__addressof(this->_M_get()); }
+
+      _Tp*
+      operator->()
+      { return std::__addressof(this->_M_get()); }
+
+      constexpr const _Tp&
+      operator*() const&
+      { return this->_M_get(); }
+
+      constexpr _Tp&
+      operator*()&
+      { return this->_M_get(); }
+
+      constexpr _Tp&&
+      operator*()&&
+      { return std::move(this->_M_get()); }
+
+      constexpr const _Tp&&
+      operator*() const&&
+      { return std::move(this->_M_get()); }
+
+      constexpr explicit operator bool() const noexcept
+      { return this->_M_is_engaged(); }
+
+      constexpr bool has_value() const noexcept
+      { return this->_M_is_engaged(); }
+
+      constexpr const _Tp&
+      value() const&
+      {
+	return this->_M_is_engaged()
+	  ?  this->_M_get()
+	  : (__throw_bad_optional_access(),
+	     this->_M_get());
+      }
+
+      constexpr _Tp&
+      value()&
+      {
+	return this->_M_is_engaged()
+	  ?  this->_M_get()
+	  : (__throw_bad_optional_access(),
+	     this->_M_get());
+      }
+
+      constexpr _Tp&&
+      value()&&
+      {
+	return this->_M_is_engaged()
+	  ?  std::move(this->_M_get())
+	  : (__throw_bad_optional_access(),
+	     std::move(this->_M_get()));
+      }
+
+      constexpr const _Tp&&
+      value() const&&
+      {
+	return this->_M_is_engaged()
+	  ?  std::move(this->_M_get())
+	  : (__throw_bad_optional_access(),
+	     std::move(this->_M_get()));
+      }
+
+      template<typename _Up>
+	constexpr _Tp
+	value_or(_Up&& __u) const&
+	{
+	  static_assert(is_copy_constructible_v<_Tp>);
+	  static_assert(is_convertible_v<_Up&&, _Tp>);
+
+	  return this->_M_is_engaged()
+	    ? this->_M_get()
+	    : static_cast<_Tp>(std::forward<_Up>(__u));
+	}
+
+      template<typename _Up>
+	_Tp
+	value_or(_Up&& __u) &&
+	{
+	  static_assert(is_move_constructible_v<_Tp>);
+	  static_assert(is_convertible_v<_Up&&, _Tp>);
+
+	  return this->_M_is_engaged()
+	    ? std::move(this->_M_get())
+	    : static_cast<_Tp>(std::forward<_Up>(__u));
+	}
+      void reset() noexcept { this->_M_reset(); }
+    };
+
+  template<typename _Tp>
+    using __optional_relop_t =
+    enable_if_t<is_convertible<_Tp, bool>::value, bool>;
+
+  // Comparisons between optional values.
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator==(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() == declval<_Up>())>
+    {
+      return static_cast<bool>(__lhs) == static_cast<bool>(__rhs)
+	     && (!__lhs || *__lhs == *__rhs);
+    }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator!=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() != declval<_Up>())>
+    {
+      return static_cast<bool>(__lhs) != static_cast<bool>(__rhs)
+	|| (static_cast<bool>(__lhs) && *__lhs != *__rhs);
+    }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator<(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() < declval<_Up>())>
+    {
+      return static_cast<bool>(__rhs) && (!__lhs || *__lhs < *__rhs);
+    }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator>(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() > declval<_Up>())>
+    {
+      return static_cast<bool>(__lhs) && (!__rhs || *__lhs > *__rhs);
+    }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator<=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() <= declval<_Up>())>
+    {
+      return !__lhs || (static_cast<bool>(__rhs) && *__lhs <= *__rhs);
+    }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator>=(const optional<_Tp>& __lhs, const optional<_Up>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() >= declval<_Up>())>
+    {
+      return !__rhs || (static_cast<bool>(__lhs) && *__lhs >= *__rhs);
+    }
+
+  // Comparisons with nullopt.
+  template<typename _Tp>
+    constexpr bool
+    operator==(const optional<_Tp>& __lhs, nullopt_t) noexcept
+    { return !__lhs; }
+
+  template<typename _Tp>
+    constexpr bool
+    operator==(nullopt_t, const optional<_Tp>& __rhs) noexcept
+    { return !__rhs; }
+
+  template<typename _Tp>
+    constexpr bool
+    operator!=(const optional<_Tp>& __lhs, nullopt_t) noexcept
+    { return static_cast<bool>(__lhs); }
+
+  template<typename _Tp>
+    constexpr bool
+    operator!=(nullopt_t, const optional<_Tp>& __rhs) noexcept
+    { return static_cast<bool>(__rhs); }
+
+  template<typename _Tp>
+    constexpr bool
+    operator<(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
+    { return false; }
+
+  template<typename _Tp>
+    constexpr bool
+    operator<(nullopt_t, const optional<_Tp>& __rhs) noexcept
+    { return static_cast<bool>(__rhs); }
+
+  template<typename _Tp>
+    constexpr bool
+    operator>(const optional<_Tp>& __lhs, nullopt_t) noexcept
+    { return static_cast<bool>(__lhs); }
+
+  template<typename _Tp>
+    constexpr bool
+    operator>(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
+    { return false; }
+
+  template<typename _Tp>
+    constexpr bool
+    operator<=(const optional<_Tp>& __lhs, nullopt_t) noexcept
+    { return !__lhs; }
+
+  template<typename _Tp>
+    constexpr bool
+    operator<=(nullopt_t, const optional<_Tp>& /* __rhs */) noexcept
+    { return true; }
+
+  template<typename _Tp>
+    constexpr bool
+    operator>=(const optional<_Tp>& /* __lhs */, nullopt_t) noexcept
+    { return true; }
+
+  template<typename _Tp>
+    constexpr bool
+    operator>=(nullopt_t, const optional<_Tp>& __rhs) noexcept
+    { return !__rhs; }
+
+  // Comparisons with value type.
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator==(const optional<_Tp>& __lhs, const _Up& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() == declval<_Up>())>
+    { return __lhs && *__lhs == __rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator==(const _Up& __lhs, const optional<_Tp>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Up>() == declval<_Tp>())>
+    { return __rhs && __lhs == *__rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator!=(const optional<_Tp>& __lhs, const _Up& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() != declval<_Up>())>
+    { return !__lhs || *__lhs != __rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator!=(const _Up& __lhs, const optional<_Tp>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Up>() != declval<_Tp>())>
+    { return !__rhs || __lhs != *__rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator<(const optional<_Tp>& __lhs, const _Up& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() < declval<_Up>())>
+    { return !__lhs || *__lhs < __rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator<(const _Up& __lhs, const optional<_Tp>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Up>() < declval<_Tp>())>
+    { return __rhs && __lhs < *__rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator>(const optional<_Tp>& __lhs, const _Up& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() > declval<_Up>())>
+    { return __lhs && *__lhs > __rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator>(const _Up& __lhs, const optional<_Tp>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Up>() > declval<_Tp>())>
+    { return !__rhs || __lhs > *__rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator<=(const optional<_Tp>& __lhs, const _Up& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() <= declval<_Up>())>
+    { return !__lhs || *__lhs <= __rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator<=(const _Up& __lhs, const optional<_Tp>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Up>() <= declval<_Tp>())>
+    { return __rhs && __lhs <= *__rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator>=(const optional<_Tp>& __lhs, const _Up& __rhs)
+    -> __optional_relop_t<decltype(declval<_Tp>() >= declval<_Up>())>
+    { return __lhs && *__lhs >= __rhs; }
+
+  template<typename _Tp, typename _Up>
+    constexpr auto
+    operator>=(const _Up& __lhs, const optional<_Tp>& __rhs)
+    -> __optional_relop_t<decltype(declval<_Up>() >= declval<_Tp>())>
+    { return !__rhs || __lhs >= *__rhs; }
+
+  // Swap and creation functions.
+
+  // _GLIBCXX_RESOLVE_LIB_DEFECTS
+  // 2748. swappable traits for optionals
+  template<typename _Tp>
+    inline enable_if_t<is_move_constructible_v<_Tp> && is_swappable_v<_Tp>>
+    swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
+    noexcept(noexcept(__lhs.swap(__rhs)))
+    { __lhs.swap(__rhs); }
+
+  template<typename _Tp>
+    enable_if_t<!(is_move_constructible_v<_Tp> && is_swappable_v<_Tp>)>
+    swap(optional<_Tp>&, optional<_Tp>&) = delete;
+
+  template<typename _Tp>
+    constexpr optional<decay_t<_Tp>>
+    make_optional(_Tp&& __t)
+    { return optional<decay_t<_Tp>> { std::forward<_Tp>(__t) }; }
+
+  template<typename _Tp, typename ..._Args>
+    constexpr optional<_Tp>
+    make_optional(_Args&&... __args)
+    { return optional<_Tp> { in_place, std::forward<_Args>(__args)... }; }
+
+  template<typename _Tp, typename _Up, typename ..._Args>
+    constexpr optional<_Tp>
+    make_optional(initializer_list<_Up> __il, _Args&&... __args)
+    { return optional<_Tp> { in_place, __il, std::forward<_Args>(__args)... }; }
+
+  // Hash.
+
+  template<typename _Tp, typename _Up = remove_const_t<_Tp>,
+           bool = __poison_hash<_Up>::__enable_hash_call>
+    struct __optional_hash_call_base
+    {
+      size_t
+      operator()(const optional<_Tp>& __t) const
+      noexcept(noexcept(hash<_Up>{}(*__t)))
+      {
+        // We pick an arbitrary hash for disengaged optionals which hopefully
+        // usual values of _Tp won't typically hash to.
+        constexpr size_t __magic_disengaged_hash = static_cast<size_t>(-3333);
+        return __t ? hash<_Up>{}(*__t) : __magic_disengaged_hash;
+      }
+    };
+
+  template<typename _Tp, typename _Up>
+    struct __optional_hash_call_base<_Tp, _Up, false> {};
+
+  template<typename _Tp>
+    struct hash<optional<_Tp>>
+    : private __poison_hash<remove_const_t<_Tp>>,
+      public __optional_hash_call_base<_Tp>
+    {
+      using result_type [[__deprecated__]] = size_t;
+      using argument_type [[__deprecated__]] = optional<_Tp>;
+    };
+
+  template<typename _Tp>
+    struct __is_fast_hash<hash<optional<_Tp>>> : __is_fast_hash<hash<_Tp>>
+    { };
+
+  /// @}
+
+  template <typename _Tp> optional(_Tp) -> optional<_Tp>;
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+
+#endif // C++17
+
+#endif // _GLIBCXX_OPTIONAL