Split libcxx on msvc/other

1 files changed, 1566 insertions, 0 deletions

diff --git a/contrib/libs/cxxsupp/libcxxmsvc/include/optional b/contrib/libs/cxxsupp/libcxxmsvc/include/optional
new file mode 100644
index 0000000000..fd17b0821a
--- /dev/null
+++ b/contrib/libs/cxxsupp/libcxxmsvc/include/optional
@@ -0,0 +1,1566 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_OPTIONAL
+#define _LIBCPP_OPTIONAL
+
+/*
+    optional synopsis
+
+// C++1z
+
+namespace std {
+  // 23.6.3, optional for object types
+  template <class T> class optional;
+
+  // 23.6.4, no-value state indicator
+  struct nullopt_t{see below };
+  inline constexpr nullopt_t nullopt(unspecified );
+
+  // 23.6.5, class bad_optional_access
+  class bad_optional_access;
+
+  // 23.6.6, relational operators
+  template <class T, class U>
+  constexpr bool operator==(const optional<T>&, const optional<U>&);
+  template <class T, class U>
+  constexpr bool operator!=(const optional<T>&, const optional<U>&);
+  template <class T, class U>
+  constexpr bool operator<(const optional<T>&, const optional<U>&);
+  template <class T, class U>
+  constexpr bool operator>(const optional<T>&, const optional<U>&);
+  template <class T, class U>
+  constexpr bool operator<=(const optional<T>&, const optional<U>&);
+  template <class T, class U>
+  constexpr bool operator>=(const optional<T>&, const optional<U>&);
+
+  // 23.6.7 comparison with nullopt
+  template <class T> constexpr bool operator==(const optional<T>&, nullopt_t) noexcept;
+  template <class T> constexpr bool operator==(nullopt_t, const optional<T>&) noexcept;
+  template <class T> constexpr bool operator!=(const optional<T>&, nullopt_t) noexcept;
+  template <class T> constexpr bool operator!=(nullopt_t, const optional<T>&) noexcept;
+  template <class T> constexpr bool operator<(const optional<T>&, nullopt_t) noexcept;
+  template <class T> constexpr bool operator<(nullopt_t, const optional<T>&) noexcept;
+  template <class T> constexpr bool operator<=(const optional<T>&, nullopt_t) noexcept;
+  template <class T> constexpr bool operator<=(nullopt_t, const optional<T>&) noexcept;
+  template <class T> constexpr bool operator>(const optional<T>&, nullopt_t) noexcept;
+  template <class T> constexpr bool operator>(nullopt_t, const optional<T>&) noexcept;
+  template <class T> constexpr bool operator>=(const optional<T>&, nullopt_t) noexcept;
+  template <class T> constexpr bool operator>=(nullopt_t, const optional<T>&) noexcept;
+
+  // 23.6.8, comparison with T
+  template <class T, class U> constexpr bool operator==(const optional<T>&, const U&);
+  template <class T, class U> constexpr bool operator==(const T&, const optional<U>&);
+  template <class T, class U> constexpr bool operator!=(const optional<T>&, const U&);
+  template <class T, class U> constexpr bool operator!=(const T&, const optional<U>&);
+  template <class T, class U> constexpr bool operator<(const optional<T>&, const U&);
+  template <class T, class U> constexpr bool operator<(const T&, const optional<U>&);
+  template <class T, class U> constexpr bool operator<=(const optional<T>&, const U&);
+  template <class T, class U> constexpr bool operator<=(const T&, const optional<U>&);
+  template <class T, class U> constexpr bool operator>(const optional<T>&, const U&);
+  template <class T, class U> constexpr bool operator>(const T&, const optional<U>&);
+  template <class T, class U> constexpr bool operator>=(const optional<T>&, const U&);
+  template <class T, class U> constexpr bool operator>=(const T&, const optional<U>&);
+
+  // 23.6.9, specialized algorithms
+  template <class T> void swap(optional<T>&, optional<T>&) noexcept(see below ); // constexpr in C++20
+  template <class T> constexpr optional<see below > make_optional(T&&);
+  template <class T, class... Args>
+    constexpr optional<T> make_optional(Args&&... args);
+  template <class T, class U, class... Args>
+    constexpr optional<T> make_optional(initializer_list<U> il, Args&&... args);
+
+  // 23.6.10, hash support
+  template <class T> struct hash;
+  template <class T> struct hash<optional<T>>;
+
+  template <class T> class optional {
+  public:
+    using value_type = T;
+
+    // 23.6.3.1, constructors
+    constexpr optional() noexcept;
+    constexpr optional(nullopt_t) noexcept;
+    optional(const optional &);
+    optional(optional &&) noexcept(see below);
+    template <class... Args> constexpr explicit optional(in_place_t, Args &&...);
+    template <class U, class... Args>
+      constexpr explicit optional(in_place_t, initializer_list<U>, Args &&...);
+    template <class U = T>
+      constexpr EXPLICIT optional(U &&);
+    template <class U>
+      EXPLICIT optional(const optional<U> &);   // constexpr in C++20
+    template <class U>
+      EXPLICIT optional(optional<U> &&);        // constexpr in C++20
+
+    // 23.6.3.2, destructor
+    ~optional(); // constexpr in C++20
+
+    // 23.6.3.3, assignment
+    optional &operator=(nullopt_t) noexcept;                     // constexpr in C++20
+    optional &operator=(const optional &);                       // constexpr in C++20
+    optional &operator=(optional &&) noexcept(see below);        // constexpr in C++20
+    template <class U = T> optional &operator=(U &&);            // constexpr in C++20
+    template <class U> optional &operator=(const optional<U> &); // constexpr in C++20
+    template <class U> optional &operator=(optional<U> &&);      // constexpr in C++20
+    template <class... Args> T& emplace(Args &&...);             // constexpr in C++20
+    template <class U, class... Args>
+      T& emplace(initializer_list<U>, Args &&...);               // constexpr in C++20
+
+    // 23.6.3.4, swap
+    void swap(optional &) noexcept(see below ); // constexpr in C++20
+
+    // 23.6.3.5, observers
+    constexpr T const *operator->() const;
+    constexpr T *operator->();
+    constexpr T const &operator*() const &;
+    constexpr T &operator*() &;
+    constexpr T &&operator*() &&;
+    constexpr const T &&operator*() const &&;
+    constexpr explicit operator bool() const noexcept;
+    constexpr bool has_value() const noexcept;
+    constexpr T const &value() const &;
+    constexpr T &value() &;
+    constexpr T &&value() &&;
+    constexpr const T &&value() const &&;
+    template <class U> constexpr T value_or(U &&) const &;
+    template <class U> constexpr T value_or(U &&) &&;
+
+    // [optional.monadic], monadic operations
+    template<class F> constexpr auto and_then(F&& f) &;         // since C++23
+    template<class F> constexpr auto and_then(F&& f) &&;        // since C++23
+    template<class F> constexpr auto and_then(F&& f) const&;    // since C++23
+    template<class F> constexpr auto and_then(F&& f) const&&;   // since C++23
+    template<class F> constexpr auto transform(F&& f) &;        // since C++23
+    template<class F> constexpr auto transform(F&& f) &&;       // since C++23
+    template<class F> constexpr auto transform(F&& f) const&;   // since C++23
+    template<class F> constexpr auto transform(F&& f) const&&;  // since C++23
+    template<class F> constexpr optional or_else(F&& f) &&;     // since C++23
+    template<class F> constexpr optional or_else(F&& f) const&; // since C++23
+
+    // 23.6.3.6, modifiers
+    void reset() noexcept; // constexpr in C++20
+
+  private:
+    T *val; // exposition only
+  };
+
+template<class T>
+  optional(T) -> optional<T>;
+
+} // namespace std
+
+*/
+
+#include <__assert>
+#include <__availability>
+#include <__concepts/invocable.h>
+#include <__config>
+#include <compare>
+#include <functional>
+#include <initializer_list>
+#include <new>
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
+#include <version>
+
+// TODO: remove these headers
+#include <__memory/allocator_arg_t.h>
+#include <__memory/uses_allocator.h>
+#include <typeinfo>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+namespace std  // purposefully not using versioning namespace
+{
+
+class _LIBCPP_EXCEPTION_ABI _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS bad_optional_access
+    : public exception
+{
+public:
+    // Get the key function ~bad_optional_access() into the dylib
+    virtual ~bad_optional_access() _NOEXCEPT;
+    virtual const char* what() const _NOEXCEPT;
+};
+
+} // namespace std
+
+#if _LIBCPP_STD_VER > 14
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+_LIBCPP_NORETURN
+inline _LIBCPP_INLINE_VISIBILITY
+_LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+void __throw_bad_optional_access() {
+#ifndef _LIBCPP_NO_EXCEPTIONS
+        throw bad_optional_access();
+#else
+        _VSTD::abort();
+#endif
+}
+
+struct nullopt_t
+{
+    struct __secret_tag { _LIBCPP_INLINE_VISIBILITY explicit __secret_tag() = default; };
+    _LIBCPP_INLINE_VISIBILITY constexpr explicit nullopt_t(__secret_tag, __secret_tag) noexcept {}
+};
+
+inline constexpr nullopt_t nullopt{nullopt_t::__secret_tag{}, nullopt_t::__secret_tag{}};
+
+struct __optional_construct_from_invoke_tag {};
+
+template <class _Tp, bool = is_trivially_destructible<_Tp>::value>
+struct __optional_destruct_base;
+
+template <class _Tp>
+struct __optional_destruct_base<_Tp, false>
+{
+    typedef _Tp value_type;
+    static_assert(is_object_v<value_type>,
+        "instantiation of optional with a non-object type is undefined behavior");
+    union
+    {
+        char __null_state_;
+        value_type __val_;
+    };
+    bool __engaged_;
+
+    _LIBCPP_INLINE_VISIBILITY
+    /* _LIBCPP_CONSTEXPR_AFTER_CXX17 */ ~__optional_destruct_base()
+    {
+        if (__engaged_)
+            __val_.~value_type();
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr __optional_destruct_base() noexcept
+        :  __null_state_(),
+           __engaged_(false) {}
+
+    template <class... _Args>
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr explicit __optional_destruct_base(in_place_t, _Args&&... __args)
+        :  __val_(_VSTD::forward<_Args>(__args)...),
+           __engaged_(true) {}
+
+#if _LIBCPP_STD_VER > 20
+  template <class _Fp, class... _Args>
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr __optional_destruct_base(__optional_construct_from_invoke_tag, _Fp&& __f, _Args&&... __args)
+      : __val_(_VSTD::invoke(_VSTD::forward<_Fp>(__f), _VSTD::forward<_Args>(__args)...)), __engaged_(true) {}
+#endif
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 void reset() noexcept
+    {
+        if (__engaged_)
+        {
+            __val_.~value_type();
+            __engaged_ = false;
+        }
+    }
+};
+
+template <class _Tp>
+struct __optional_destruct_base<_Tp, true>
+{
+    typedef _Tp value_type;
+    static_assert(is_object_v<value_type>,
+        "instantiation of optional with a non-object type is undefined behavior");
+    union
+    {
+        char __null_state_;
+        value_type __val_;
+    };
+    bool __engaged_;
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr __optional_destruct_base() noexcept
+        :  __null_state_(),
+           __engaged_(false) {}
+
+    template <class... _Args>
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr explicit __optional_destruct_base(in_place_t, _Args&&... __args)
+        :  __val_(_VSTD::forward<_Args>(__args)...),
+           __engaged_(true) {}
+
+#if _LIBCPP_STD_VER > 20
+  template <class _Fp, class... _Args>
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr __optional_destruct_base(__optional_construct_from_invoke_tag, _Fp&& __f, _Args&&... __args)
+      : __val_(_VSTD::invoke(_VSTD::forward<_Fp>(__f), _VSTD::forward<_Args>(__args)...)), __engaged_(true) {}
+#endif
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 void reset() noexcept
+    {
+        if (__engaged_)
+        {
+            __engaged_ = false;
+        }
+    }
+};
+
+template <class _Tp, bool = is_reference<_Tp>::value>
+struct __optional_storage_base : __optional_destruct_base<_Tp>
+{
+    using __base = __optional_destruct_base<_Tp>;
+    using value_type = _Tp;
+    using __base::__base;
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr bool has_value() const noexcept
+    {
+        return this->__engaged_;
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr value_type& __get() & noexcept
+    {
+        return this->__val_;
+    }
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr const value_type& __get() const& noexcept
+    {
+        return this->__val_;
+    }
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr value_type&& __get() && noexcept
+    {
+        return _VSTD::move(this->__val_);
+    }
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr const value_type&& __get() const&& noexcept
+    {
+        return _VSTD::move(this->__val_);
+    }
+
+    template <class... _Args>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 void __construct(_Args&&... __args)
+    {
+        _LIBCPP_ASSERT(!has_value(), "__construct called for engaged __optional_storage");
+#if _LIBCPP_STD_VER > 17
+        _VSTD::construct_at(_VSTD::addressof(this->__val_), _VSTD::forward<_Args>(__args)...);
+#else
+        ::new ((void*)_VSTD::addressof(this->__val_)) value_type(_VSTD::forward<_Args>(__args)...);
+#endif
+        this->__engaged_ = true;
+    }
+
+    template <class _That>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 void __construct_from(_That&& __opt)
+    {
+        if (__opt.has_value())
+            __construct(_VSTD::forward<_That>(__opt).__get());
+    }
+
+    template <class _That>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 void __assign_from(_That&& __opt)
+    {
+        if (this->__engaged_ == __opt.has_value())
+        {
+            if (this->__engaged_)
+                this->__val_ = _VSTD::forward<_That>(__opt).__get();
+        }
+        else
+        {
+            if (this->__engaged_)
+                this->reset();
+            else
+                __construct(_VSTD::forward<_That>(__opt).__get());
+        }
+    }
+};
+
+// optional<T&> is currently required ill-formed, however it may to be in the
+// future. For this reason it has already been implemented to ensure we can
+// make the change in an ABI compatible manner.
+template <class _Tp>
+struct __optional_storage_base<_Tp, true>
+{
+    using value_type = _Tp;
+    using __raw_type = remove_reference_t<_Tp>;
+    __raw_type* __value_;
+
+    template <class _Up>
+    static constexpr bool __can_bind_reference() {
+        using _RawUp = typename remove_reference<_Up>::type;
+        using _UpPtr = _RawUp*;
+        using _RawTp = typename remove_reference<_Tp>::type;
+        using _TpPtr = _RawTp*;
+        using _CheckLValueArg = integral_constant<bool,
+            (is_lvalue_reference<_Up>::value && is_convertible<_UpPtr, _TpPtr>::value)
+        ||  is_same<_RawUp, reference_wrapper<_RawTp>>::value
+        ||  is_same<_RawUp, reference_wrapper<typename remove_const<_RawTp>::type>>::value
+        >;
+        return (is_lvalue_reference<_Tp>::value && _CheckLValueArg::value)
+            || (is_rvalue_reference<_Tp>::value && !is_lvalue_reference<_Up>::value &&
+                is_convertible<_UpPtr, _TpPtr>::value);
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr __optional_storage_base() noexcept
+        :  __value_(nullptr) {}
+
+    template <class _UArg>
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr explicit __optional_storage_base(in_place_t, _UArg&& __uarg)
+        :  __value_(_VSTD::addressof(__uarg))
+    {
+      static_assert(__can_bind_reference<_UArg>(),
+        "Attempted to construct a reference element in tuple from a "
+        "possible temporary");
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 void reset() noexcept { __value_ = nullptr; }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr bool has_value() const noexcept
+      { return __value_ != nullptr; }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr value_type& __get() const& noexcept
+      { return *__value_; }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr value_type&& __get() const&& noexcept
+      { return _VSTD::forward<value_type>(*__value_); }
+
+    template <class _UArg>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 void __construct(_UArg&& __val)
+    {
+        _LIBCPP_ASSERT(!has_value(), "__construct called for engaged __optional_storage");
+        static_assert(__can_bind_reference<_UArg>(),
+            "Attempted to construct a reference element in tuple from a "
+            "possible temporary");
+        __value_ = _VSTD::addressof(__val);
+    }
+
+    template <class _That>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 void __construct_from(_That&& __opt)
+    {
+        if (__opt.has_value())
+            __construct(_VSTD::forward<_That>(__opt).__get());
+    }
+
+    template <class _That>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 void __assign_from(_That&& __opt)
+    {
+        if (has_value() == __opt.has_value())
+        {
+            if (has_value())
+                *__value_ = _VSTD::forward<_That>(__opt).__get();
+        }
+        else
+        {
+            if (has_value())
+                reset();
+            else
+                __construct(_VSTD::forward<_That>(__opt).__get());
+        }
+    }
+};
+
+template <class _Tp, bool = is_trivially_copy_constructible<_Tp>::value>
+struct __optional_copy_base : __optional_storage_base<_Tp>
+{
+    using __optional_storage_base<_Tp>::__optional_storage_base;
+};
+
+template <class _Tp>
+struct __optional_copy_base<_Tp, false> : __optional_storage_base<_Tp>
+{
+    using __optional_storage_base<_Tp>::__optional_storage_base;
+
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_copy_base() = default;
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 __optional_copy_base(const __optional_copy_base& __opt)
+    {
+        this->__construct_from(__opt);
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_copy_base(__optional_copy_base&&) = default;
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_copy_base& operator=(const __optional_copy_base&) = default;
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_copy_base& operator=(__optional_copy_base&&) = default;
+};
+
+template <class _Tp, bool = is_trivially_move_constructible<_Tp>::value>
+struct __optional_move_base : __optional_copy_base<_Tp>
+{
+    using __optional_copy_base<_Tp>::__optional_copy_base;
+};
+
+template <class _Tp>
+struct __optional_move_base<_Tp, false> : __optional_copy_base<_Tp>
+{
+    using value_type = _Tp;
+    using __optional_copy_base<_Tp>::__optional_copy_base;
+
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_move_base() = default;
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_move_base(const __optional_move_base&) = default;
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 __optional_move_base(__optional_move_base&& __opt)
+        noexcept(is_nothrow_move_constructible_v<value_type>)
+    {
+        this->__construct_from(_VSTD::move(__opt));
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_move_base& operator=(const __optional_move_base&) = default;
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_move_base& operator=(__optional_move_base&&) = default;
+};
+
+template <class _Tp, bool =
+    is_trivially_destructible<_Tp>::value &&
+    is_trivially_copy_constructible<_Tp>::value &&
+    is_trivially_copy_assignable<_Tp>::value>
+struct __optional_copy_assign_base : __optional_move_base<_Tp>
+{
+    using __optional_move_base<_Tp>::__optional_move_base;
+};
+
+template <class _Tp>
+struct __optional_copy_assign_base<_Tp, false> : __optional_move_base<_Tp>
+{
+    using __optional_move_base<_Tp>::__optional_move_base;
+
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_copy_assign_base() = default;
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_copy_assign_base(const __optional_copy_assign_base&) = default;
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_copy_assign_base(__optional_copy_assign_base&&) = default;
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 __optional_copy_assign_base& operator=(const __optional_copy_assign_base& __opt)
+    {
+        this->__assign_from(__opt);
+        return *this;
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_copy_assign_base& operator=(__optional_copy_assign_base&&) = default;
+};
+
+template <class _Tp, bool =
+    is_trivially_destructible<_Tp>::value &&
+    is_trivially_move_constructible<_Tp>::value &&
+    is_trivially_move_assignable<_Tp>::value>
+struct __optional_move_assign_base : __optional_copy_assign_base<_Tp>
+{
+    using __optional_copy_assign_base<_Tp>::__optional_copy_assign_base;
+};
+
+template <class _Tp>
+struct __optional_move_assign_base<_Tp, false> : __optional_copy_assign_base<_Tp>
+{
+    using value_type = _Tp;
+    using __optional_copy_assign_base<_Tp>::__optional_copy_assign_base;
+
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_move_assign_base() = default;
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_move_assign_base(const __optional_move_assign_base& __opt) = default;
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_move_assign_base(__optional_move_assign_base&&) = default;
+    _LIBCPP_INLINE_VISIBILITY
+    __optional_move_assign_base& operator=(const __optional_move_assign_base&) = default;
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 __optional_move_assign_base& operator=(__optional_move_assign_base&& __opt)
+        noexcept(is_nothrow_move_assignable_v<value_type> &&
+                 is_nothrow_move_constructible_v<value_type>)
+    {
+        this->__assign_from(_VSTD::move(__opt));
+        return *this;
+    }
+};
+
+template <class _Tp>
+using __optional_sfinae_ctor_base_t = __sfinae_ctor_base<
+    is_copy_constructible<_Tp>::value,
+    is_move_constructible<_Tp>::value
+>;
+
+template <class _Tp>
+using __optional_sfinae_assign_base_t = __sfinae_assign_base<
+    (is_copy_constructible<_Tp>::value && is_copy_assignable<_Tp>::value),
+    (is_move_constructible<_Tp>::value && is_move_assignable<_Tp>::value)
+>;
+
+template<class _Tp>
+class optional;
+template <class _Tp>
+struct __is_std_optional : false_type {};
+template <class _Tp> struct __is_std_optional<optional<_Tp>> : true_type {};
+
+template <class _Tp>
+class optional
+    : private __optional_move_assign_base<_Tp>
+    , private __optional_sfinae_ctor_base_t<_Tp>
+    , private __optional_sfinae_assign_base_t<_Tp>
+{
+    using __base = __optional_move_assign_base<_Tp>;
+public:
+    using value_type = _Tp;
+
+private:
+     // Disable the reference extension using this static assert.
+    static_assert(!is_same_v<__uncvref_t<value_type>, in_place_t>,
+        "instantiation of optional with in_place_t is ill-formed");
+    static_assert(!is_same_v<__uncvref_t<value_type>, nullopt_t>,
+        "instantiation of optional with nullopt_t is ill-formed");
+    static_assert(!is_reference_v<value_type>,
+        "instantiation of optional with a reference type is ill-formed");
+    static_assert(is_destructible_v<value_type>,
+        "instantiation of optional with a non-destructible type is ill-formed");
+    static_assert(!is_array_v<value_type>,
+        "instantiation of optional with an array type is ill-formed");
+
+    // LWG2756: conditionally explicit conversion from _Up
+    struct _CheckOptionalArgsConstructor {
+      template <class _Up>
+      static constexpr bool __enable_implicit =
+          is_constructible_v<_Tp, _Up&&> &&
+          is_convertible_v<_Up&&, _Tp>;
+
+      template <class _Up>
+      static constexpr bool __enable_explicit =
+          is_constructible_v<_Tp, _Up&&> &&
+          !is_convertible_v<_Up&&, _Tp>;
+    };
+    template <class _Up>
+    using _CheckOptionalArgsCtor = _If<
+        _IsNotSame<__uncvref_t<_Up>, in_place_t>::value &&
+        _IsNotSame<__uncvref_t<_Up>, optional>::value,
+        _CheckOptionalArgsConstructor,
+        __check_tuple_constructor_fail
+    >;
+    template <class _QualUp>
+    struct _CheckOptionalLikeConstructor {
+      template <class _Up, class _Opt = optional<_Up>>
+      using __check_constructible_from_opt = _Or<
+          is_constructible<_Tp, _Opt&>,
+          is_constructible<_Tp, _Opt const&>,
+          is_constructible<_Tp, _Opt&&>,
+          is_constructible<_Tp, _Opt const&&>,
+          is_convertible<_Opt&, _Tp>,
+          is_convertible<_Opt const&, _Tp>,
+          is_convertible<_Opt&&, _Tp>,
+          is_convertible<_Opt const&&, _Tp>
+      >;
+      template <class _Up, class _Opt = optional<_Up>>
+      using __check_assignable_from_opt = _Or<
+          is_assignable<_Tp&, _Opt&>,
+          is_assignable<_Tp&, _Opt const&>,
+          is_assignable<_Tp&, _Opt&&>,
+          is_assignable<_Tp&, _Opt const&&>
+      >;
+      template <class _Up, class _QUp = _QualUp>
+      static constexpr bool __enable_implicit =
+          is_convertible<_QUp, _Tp>::value &&
+          !__check_constructible_from_opt<_Up>::value;
+
+      template <class _Up, class _QUp = _QualUp>
+      static constexpr bool __enable_explicit =
+          !is_convertible<_QUp, _Tp>::value &&
+          !__check_constructible_from_opt<_Up>::value;
+
+      template <class _Up, class _QUp = _QualUp>
+      static constexpr bool __enable_assign =
+          !__check_constructible_from_opt<_Up>::value &&
+          !__check_assignable_from_opt<_Up>::value;
+    };
+
+    template <class _Up, class _QualUp>
+    using _CheckOptionalLikeCtor = _If<
+      _And<
+         _IsNotSame<_Up, _Tp>,
+          is_constructible<_Tp, _QualUp>
+      >::value,
+      _CheckOptionalLikeConstructor<_QualUp>,
+      __check_tuple_constructor_fail
+    >;
+    template <class _Up, class _QualUp>
+    using _CheckOptionalLikeAssign = _If<
+      _And<
+          _IsNotSame<_Up, _Tp>,
+          is_constructible<_Tp, _QualUp>,
+          is_assignable<_Tp&, _QualUp>
+      >::value,
+      _CheckOptionalLikeConstructor<_QualUp>,
+      __check_tuple_constructor_fail
+    >;
+
+public:
+
+    _LIBCPP_INLINE_VISIBILITY constexpr optional() noexcept {}
+    _LIBCPP_INLINE_VISIBILITY constexpr optional(const optional&) = default;
+    _LIBCPP_INLINE_VISIBILITY constexpr optional(optional&&) = default;
+    _LIBCPP_INLINE_VISIBILITY constexpr optional(nullopt_t) noexcept {}
+
+    template <class _InPlaceT, class... _Args, class = enable_if_t<
+          _And<
+              _IsSame<_InPlaceT, in_place_t>,
+            is_constructible<value_type, _Args...>
+            >::value
+        >
+    >
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr explicit optional(_InPlaceT, _Args&&... __args)
+        : __base(in_place, _VSTD::forward<_Args>(__args)...) {}
+
+    template <class _Up, class... _Args, class = enable_if_t<
+        is_constructible_v<value_type, initializer_list<_Up>&, _Args...>>
+    >
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr explicit optional(in_place_t, initializer_list<_Up> __il, _Args&&... __args)
+        : __base(in_place, __il, _VSTD::forward<_Args>(__args)...) {}
+
+    template <class _Up = value_type, enable_if_t<
+        _CheckOptionalArgsCtor<_Up>::template __enable_implicit<_Up>
+    , int> = 0>
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr optional(_Up&& __v)
+        : __base(in_place, _VSTD::forward<_Up>(__v)) {}
+
+    template <class _Up, enable_if_t<
+        _CheckOptionalArgsCtor<_Up>::template __enable_explicit<_Up>
+    , int> = 0>
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr explicit optional(_Up&& __v)
+        : __base(in_place, _VSTD::forward<_Up>(__v)) {}
+
+    // LWG2756: conditionally explicit conversion from const optional<_Up>&
+    template <class _Up, enable_if_t<
+        _CheckOptionalLikeCtor<_Up, _Up const&>::template __enable_implicit<_Up>
+    , int> = 0>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 optional(const optional<_Up>& __v)
+    {
+        this->__construct_from(__v);
+    }
+    template <class _Up, enable_if_t<
+        _CheckOptionalLikeCtor<_Up, _Up const&>::template __enable_explicit<_Up>
+    , int> = 0>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 explicit optional(const optional<_Up>& __v)
+    {
+        this->__construct_from(__v);
+    }
+
+    // LWG2756: conditionally explicit conversion from optional<_Up>&&
+    template <class _Up, enable_if_t<
+        _CheckOptionalLikeCtor<_Up, _Up &&>::template __enable_implicit<_Up>
+    , int> = 0>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 optional(optional<_Up>&& __v)
+    {
+        this->__construct_from(_VSTD::move(__v));
+    }
+    template <class _Up, enable_if_t<
+        _CheckOptionalLikeCtor<_Up, _Up &&>::template __enable_explicit<_Up>
+    , int> = 0>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 explicit optional(optional<_Up>&& __v)
+    {
+        this->__construct_from(_VSTD::move(__v));
+    }
+
+#if _LIBCPP_STD_VER > 20
+  template<class _Fp, class... _Args>
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr explicit optional(__optional_construct_from_invoke_tag, _Fp&& __f, _Args&&... __args)
+      : __base(__optional_construct_from_invoke_tag{}, _VSTD::forward<_Fp>(__f), _VSTD::forward<_Args>(__args)...) {
+  }
+#endif
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 optional& operator=(nullopt_t) noexcept
+    {
+        reset();
+        return *this;
+    }
+
+    _LIBCPP_INLINE_VISIBILITY optional& operator=(const optional&) = default;
+    _LIBCPP_INLINE_VISIBILITY optional& operator=(optional&&) = default;
+
+    // LWG2756
+    template <class _Up = value_type,
+              class = enable_if_t<
+                      _And<
+                          _IsNotSame<__uncvref_t<_Up>, optional>,
+                          _Or<
+                              _IsNotSame<__uncvref_t<_Up>, value_type>,
+                              _Not<is_scalar<value_type>>
+                          >,
+                          is_constructible<value_type, _Up>,
+                          is_assignable<value_type&, _Up>
+                      >::value>
+             >
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 optional&
+    operator=(_Up&& __v)
+    {
+        if (this->has_value())
+            this->__get() = _VSTD::forward<_Up>(__v);
+        else
+            this->__construct(_VSTD::forward<_Up>(__v));
+        return *this;
+    }
+
+    // LWG2756
+    template <class _Up, enable_if_t<
+        _CheckOptionalLikeAssign<_Up, _Up const&>::template __enable_assign<_Up>
+    , int> = 0>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 optional&
+    operator=(const optional<_Up>& __v)
+    {
+        this->__assign_from(__v);
+        return *this;
+    }
+
+    // LWG2756
+    template <class _Up, enable_if_t<
+        _CheckOptionalLikeCtor<_Up, _Up &&>::template __enable_assign<_Up>
+    , int> = 0>
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 optional&
+    operator=(optional<_Up>&& __v)
+    {
+        this->__assign_from(_VSTD::move(__v));
+        return *this;
+    }
+
+    template <class... _Args,
+              class = enable_if_t
+                      <
+                          is_constructible_v<value_type, _Args...>
+                      >
+             >
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 _Tp &
+    emplace(_Args&&... __args)
+    {
+        reset();
+        this->__construct(_VSTD::forward<_Args>(__args)...);
+        return this->__get();
+    }
+
+    template <class _Up, class... _Args,
+              class = enable_if_t
+                      <
+                          is_constructible_v<value_type, initializer_list<_Up>&, _Args...>
+                      >
+             >
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 _Tp &
+    emplace(initializer_list<_Up> __il, _Args&&... __args)
+    {
+        reset();
+        this->__construct(__il, _VSTD::forward<_Args>(__args)...);
+        return this->__get();
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX17 void swap(optional& __opt)
+        noexcept(is_nothrow_move_constructible_v<value_type> &&
+                 is_nothrow_swappable_v<value_type>)
+    {
+        if (this->has_value() == __opt.has_value())
+        {
+            using _VSTD::swap;
+            if (this->has_value())
+                swap(this->__get(), __opt.__get());
+        }
+        else
+        {
+            if (this->has_value())
+            {
+                __opt.__construct(_VSTD::move(this->__get()));
+                reset();
+            }
+            else
+            {
+                this->__construct(_VSTD::move(__opt.__get()));
+                __opt.reset();
+            }
+        }
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr
+    add_pointer_t<value_type const>
+    operator->() const
+    {
+        _LIBCPP_ASSERT(this->has_value(), "optional operator-> called on a disengaged value");
+        return _VSTD::addressof(this->__get());
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr
+    add_pointer_t<value_type>
+    operator->()
+    {
+        _LIBCPP_ASSERT(this->has_value(), "optional operator-> called on a disengaged value");
+        return _VSTD::addressof(this->__get());
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr
+    const value_type&
+    operator*() const& noexcept
+    {
+        _LIBCPP_ASSERT(this->has_value(), "optional operator* called on a disengaged value");
+        return this->__get();
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr
+    value_type&
+    operator*() & noexcept
+    {
+        _LIBCPP_ASSERT(this->has_value(), "optional operator* called on a disengaged value");
+        return this->__get();
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr
+    value_type&&
+    operator*() && noexcept
+    {
+        _LIBCPP_ASSERT(this->has_value(), "optional operator* called on a disengaged value");
+        return _VSTD::move(this->__get());
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr
+    const value_type&&
+    operator*() const&& noexcept
+    {
+        _LIBCPP_ASSERT(this->has_value(), "optional operator* called on a disengaged value");
+        return _VSTD::move(this->__get());
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr explicit operator bool() const noexcept { return has_value(); }
+
+    using __base::has_value;
+    using __base::__get;
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+    constexpr value_type const& value() const&
+    {
+        if (!this->has_value())
+            __throw_bad_optional_access();
+        return this->__get();
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+    constexpr value_type& value() &
+    {
+        if (!this->has_value())
+            __throw_bad_optional_access();
+        return this->__get();
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+    constexpr value_type&& value() &&
+    {
+        if (!this->has_value())
+            __throw_bad_optional_access();
+        return _VSTD::move(this->__get());
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+    constexpr value_type const&& value() const&&
+    {
+        if (!this->has_value())
+            __throw_bad_optional_access();
+        return _VSTD::move(this->__get());
+    }
+
+    template <class _Up>
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr value_type value_or(_Up&& __v) const&
+    {
+        static_assert(is_copy_constructible_v<value_type>,
+                      "optional<T>::value_or: T must be copy constructible");
+        static_assert(is_convertible_v<_Up, value_type>,
+                      "optional<T>::value_or: U must be convertible to T");
+        return this->has_value() ? this->__get() :
+                                  static_cast<value_type>(_VSTD::forward<_Up>(__v));
+    }
+
+    template <class _Up>
+    _LIBCPP_INLINE_VISIBILITY
+    constexpr value_type value_or(_Up&& __v) &&
+    {
+        static_assert(is_move_constructible_v<value_type>,
+                      "optional<T>::value_or: T must be move constructible");
+        static_assert(is_convertible_v<_Up, value_type>,
+                      "optional<T>::value_or: U must be convertible to T");
+        return this->has_value() ? _VSTD::move(this->__get()) :
+                                  static_cast<value_type>(_VSTD::forward<_Up>(__v));
+    }
+
+#if _LIBCPP_STD_VER > 20
+  template<class _Func>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+  constexpr auto and_then(_Func&& __f) & {
+    using _Up = invoke_result_t<_Func, value_type&>;
+    static_assert(__is_std_optional<remove_cvref_t<_Up>>::value,
+                  "Result of f(value()) must be a specialization of std::optional");
+    if (*this)
+      return _VSTD::invoke(_VSTD::forward<_Func>(__f), value());
+    return remove_cvref_t<_Up>();
+  }
+
+  template<class _Func>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+  constexpr auto and_then(_Func&& __f) const& {
+    using _Up = invoke_result_t<_Func, const value_type&>;
+    static_assert(__is_std_optional<remove_cvref_t<_Up>>::value,
+                  "Result of f(value()) must be a specialization of std::optional");
+    if (*this)
+      return _VSTD::invoke(_VSTD::forward<_Func>(__f), value());
+    return remove_cvref_t<_Up>();
+  }
+
+  template<class _Func>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+  constexpr auto and_then(_Func&& __f) && {
+    using _Up = invoke_result_t<_Func, value_type&&>;
+    static_assert(__is_std_optional<remove_cvref_t<_Up>>::value,
+                  "Result of f(std::move(value())) must be a specialization of std::optional");
+    if (*this)
+      return _VSTD::invoke(_VSTD::forward<_Func>(__f), _VSTD::move(value()));
+    return remove_cvref_t<_Up>();
+  }
+
+  template<class _Func>
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr auto and_then(_Func&& __f) const&& {
+    using _Up = invoke_result_t<_Func, const value_type&&>;
+    static_assert(__is_std_optional<remove_cvref_t<_Up>>::value,
+                  "Result of f(std::move(value())) must be a specialization of std::optional");
+    if (*this)
+      return _VSTD::invoke(_VSTD::forward<_Func>(__f), _VSTD::move(value()));
+    return remove_cvref_t<_Up>();
+  }
+
+  template<class _Func>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+  constexpr auto transform(_Func&& __f) & {
+    using _Up = remove_cv_t<invoke_result_t<_Func, value_type&>>;
+    static_assert(!is_array_v<_Up>, "Result of f(value()) should not be an Array");
+    static_assert(!is_same_v<_Up, in_place_t>,
+                  "Result of f(value()) should not be std::in_place_t");
+    static_assert(!is_same_v<_Up, nullopt_t>,
+                  "Result of f(value()) should not be std::nullopt_t");
+    static_assert(is_object_v<_Up>, "Result of f(value()) should be an object type");
+    if (*this)
+      return optional<_Up>(__optional_construct_from_invoke_tag{}, _VSTD::forward<_Func>(__f), value());
+    return optional<_Up>();
+  }
+
+  template<class _Func>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+  constexpr auto transform(_Func&& __f) const& {
+    using _Up = remove_cv_t<invoke_result_t<_Func, const value_type&>>;
+    static_assert(!is_array_v<_Up>, "Result of f(value()) should not be an Array");
+    static_assert(!is_same_v<_Up, in_place_t>,
+                  "Result of f(value()) should not be std::in_place_t");
+    static_assert(!is_same_v<_Up, nullopt_t>,
+                  "Result of f(value()) should not be std::nullopt_t");
+    static_assert(is_object_v<_Up>, "Result of f(value()) should be an object type");
+    if (*this)
+      return optional<_Up>(__optional_construct_from_invoke_tag{}, _VSTD::forward<_Func>(__f), value());
+    return optional<_Up>();
+  }
+
+  template<class _Func>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+  constexpr auto transform(_Func&& __f) && {
+    using _Up = remove_cv_t<invoke_result_t<_Func, value_type&&>>;
+    static_assert(!is_array_v<_Up>, "Result of f(std::move(value())) should not be an Array");
+    static_assert(!is_same_v<_Up, in_place_t>,
+                  "Result of f(std::move(value())) should not be std::in_place_t");
+    static_assert(!is_same_v<_Up, nullopt_t>,
+                  "Result of f(std::move(value())) should not be std::nullopt_t");
+    static_assert(is_object_v<_Up>, "Result of f(std::move(value())) should be an object type");
+    if (*this)
+      return optional<_Up>(__optional_construct_from_invoke_tag{}, _VSTD::forward<_Func>(__f), _VSTD::move(value()));
+    return optional<_Up>();
+  }
+
+  template<class _Func>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_THROW_BAD_OPTIONAL_ACCESS
+  constexpr auto transform(_Func&& __f) const&& {
+    using _Up = remove_cvref_t<invoke_result_t<_Func, const value_type&&>>;
+    static_assert(!is_array_v<_Up>, "Result of f(std::move(value())) should not be an Array");
+    static_assert(!is_same_v<_Up, in_place_t>,
+                  "Result of f(std::move(value())) should not be std::in_place_t");
+    static_assert(!is_same_v<_Up, nullopt_t>,
+                  "Result of f(std::move(value())) should not be std::nullopt_t");
+    static_assert(is_object_v<_Up>, "Result of f(std::move(value())) should be an object type");
+    if (*this)
+      return optional<_Up>(__optional_construct_from_invoke_tag{}, _VSTD::forward<_Func>(__f), _VSTD::move(value()));
+    return optional<_Up>();
+  }
+
+  template<invocable _Func>
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr optional or_else(_Func&& __f) const& requires is_copy_constructible_v<value_type> {
+    static_assert(is_same_v<remove_cvref_t<invoke_result_t<_Func>>, optional>,
+                  "Result of f() should be the same type as this optional");
+    if (*this)
+      return *this;
+    return _VSTD::forward<_Func>(__f)();
+  }
+
+  template<invocable _Func>
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr optional or_else(_Func&& __f) && requires is_move_constructible_v<value_type> {
+    static_assert(is_same_v<remove_cvref_t<invoke_result_t<_Func>>, optional>,
+                  "Result of f() should be the same type as this optional");
+    if (*this)
+      return _VSTD::move(*this);
+    return _VSTD::forward<_Func>(__f)();
+  }
+#endif // _LIBCPP_STD_VER > 20
+
+    using __base::reset;
+};
+
+#if _LIBCPP_STD_VER >= 17
+template<class _Tp>
+    optional(_Tp) -> optional<_Tp>;
+#endif
+
+// Comparisons between optionals
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() ==
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator==(const optional<_Tp>& __x, const optional<_Up>& __y)
+{
+    if (static_cast<bool>(__x) != static_cast<bool>(__y))
+        return false;
+    if (!static_cast<bool>(__x))
+        return true;
+    return *__x == *__y;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() !=
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator!=(const optional<_Tp>& __x, const optional<_Up>& __y)
+{
+    if (static_cast<bool>(__x) != static_cast<bool>(__y))
+        return true;
+    if (!static_cast<bool>(__x))
+        return false;
+    return *__x != *__y;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() <
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator<(const optional<_Tp>& __x, const optional<_Up>& __y)
+{
+    if (!static_cast<bool>(__y))
+        return false;
+    if (!static_cast<bool>(__x))
+        return true;
+    return *__x < *__y;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() >
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator>(const optional<_Tp>& __x, const optional<_Up>& __y)
+{
+    if (!static_cast<bool>(__x))
+        return false;
+    if (!static_cast<bool>(__y))
+        return true;
+    return *__x > *__y;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() <=
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator<=(const optional<_Tp>& __x, const optional<_Up>& __y)
+{
+    if (!static_cast<bool>(__x))
+        return true;
+    if (!static_cast<bool>(__y))
+        return false;
+    return *__x <= *__y;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() >=
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator>=(const optional<_Tp>& __x, const optional<_Up>& __y)
+{
+    if (!static_cast<bool>(__y))
+        return true;
+    if (!static_cast<bool>(__x))
+        return false;
+    return *__x >= *__y;
+}
+
+// Comparisons with nullopt
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator==(const optional<_Tp>& __x, nullopt_t) noexcept
+{
+    return !static_cast<bool>(__x);
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator==(nullopt_t, const optional<_Tp>& __x) noexcept
+{
+    return !static_cast<bool>(__x);
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator!=(const optional<_Tp>& __x, nullopt_t) noexcept
+{
+    return static_cast<bool>(__x);
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator!=(nullopt_t, const optional<_Tp>& __x) noexcept
+{
+    return static_cast<bool>(__x);
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator<(const optional<_Tp>&, nullopt_t) noexcept
+{
+    return false;
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator<(nullopt_t, const optional<_Tp>& __x) noexcept
+{
+    return static_cast<bool>(__x);
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator<=(const optional<_Tp>& __x, nullopt_t) noexcept
+{
+    return !static_cast<bool>(__x);
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator<=(nullopt_t, const optional<_Tp>&) noexcept
+{
+    return true;
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator>(const optional<_Tp>& __x, nullopt_t) noexcept
+{
+    return static_cast<bool>(__x);
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator>(nullopt_t, const optional<_Tp>&) noexcept
+{
+    return false;
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator>=(const optional<_Tp>&, nullopt_t) noexcept
+{
+    return true;
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+bool
+operator>=(nullopt_t, const optional<_Tp>& __x) noexcept
+{
+    return !static_cast<bool>(__x);
+}
+
+// Comparisons with T
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() ==
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator==(const optional<_Tp>& __x, const _Up& __v)
+{
+    return static_cast<bool>(__x) ? *__x == __v : false;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() ==
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator==(const _Tp& __v, const optional<_Up>& __x)
+{
+    return static_cast<bool>(__x) ? __v == *__x : false;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() !=
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator!=(const optional<_Tp>& __x, const _Up& __v)
+{
+    return static_cast<bool>(__x) ? *__x != __v : true;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() !=
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator!=(const _Tp& __v, const optional<_Up>& __x)
+{
+    return static_cast<bool>(__x) ? __v != *__x : true;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() <
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator<(const optional<_Tp>& __x, const _Up& __v)
+{
+    return static_cast<bool>(__x) ? *__x < __v : true;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() <
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator<(const _Tp& __v, const optional<_Up>& __x)
+{
+    return static_cast<bool>(__x) ? __v < *__x : false;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() <=
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator<=(const optional<_Tp>& __x, const _Up& __v)
+{
+    return static_cast<bool>(__x) ? *__x <= __v : true;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() <=
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator<=(const _Tp& __v, const optional<_Up>& __x)
+{
+    return static_cast<bool>(__x) ? __v <= *__x : false;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() >
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator>(const optional<_Tp>& __x, const _Up& __v)
+{
+    return static_cast<bool>(__x) ? *__x > __v : false;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() >
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator>(const _Tp& __v, const optional<_Up>& __x)
+{
+    return static_cast<bool>(__x) ? __v > *__x : true;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() >=
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator>=(const optional<_Tp>& __x, const _Up& __v)
+{
+    return static_cast<bool>(__x) ? *__x >= __v : false;
+}
+
+template <class _Tp, class _Up>
+_LIBCPP_INLINE_VISIBILITY constexpr
+enable_if_t<
+    is_convertible_v<decltype(declval<const _Tp&>() >=
+        declval<const _Up&>()), bool>,
+    bool
+>
+operator>=(const _Tp& __v, const optional<_Up>& __x)
+{
+    return static_cast<bool>(__x) ? __v >= *__x : true;
+}
+
+
+template <class _Tp>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
+enable_if_t<
+    is_move_constructible_v<_Tp> && is_swappable_v<_Tp>,
+    void
+>
+swap(optional<_Tp>& __x, optional<_Tp>& __y) noexcept(noexcept(__x.swap(__y)))
+{
+    __x.swap(__y);
+}
+
+template <class _Tp>
+_LIBCPP_INLINE_VISIBILITY constexpr
+optional<decay_t<_Tp>> make_optional(_Tp&& __v)
+{
+    return optional<decay_t<_Tp>>(_VSTD::forward<_Tp>(__v));
+}
+
+template <class _Tp, class... _Args>
+_LIBCPP_INLINE_VISIBILITY constexpr
+optional<_Tp> make_optional(_Args&&... __args)
+{
+    return optional<_Tp>(in_place, _VSTD::forward<_Args>(__args)...);
+}
+
+template <class _Tp, class _Up, class... _Args>
+_LIBCPP_INLINE_VISIBILITY constexpr
+optional<_Tp> make_optional(initializer_list<_Up> __il,  _Args&&... __args)
+{
+    return optional<_Tp>(in_place, __il, _VSTD::forward<_Args>(__args)...);
+}
+
+template <class _Tp>
+struct _LIBCPP_TEMPLATE_VIS hash<
+    __enable_hash_helper<optional<_Tp>, remove_const_t<_Tp>>
+>
+{
+#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_BINDER_TYPEDEFS)
+    _LIBCPP_DEPRECATED_IN_CXX17 typedef optional<_Tp> argument_type;
+    _LIBCPP_DEPRECATED_IN_CXX17 typedef size_t        result_type;
+#endif
+
+    _LIBCPP_INLINE_VISIBILITY
+    size_t operator()(const optional<_Tp>& __opt) const
+    {
+        return static_cast<bool>(__opt) ? hash<remove_const_t<_Tp>>()(*__opt) : 0;
+    }
+};
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER > 14
+
+#endif // _LIBCPP_OPTIONAL