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 // -*- 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___CXX03___EXPECTED_EXPECTED_H
 #define _LIBCPP___CXX03___EXPECTED_EXPECTED_H
 
 #include <__cxx03/__assert>
 #include <__cxx03/__config>
 #include <__cxx03/__expected/bad_expected_access.h>
 #include <__cxx03/__expected/unexpect.h>
 #include <__cxx03/__expected/unexpected.h>
 #include <__cxx03/__functional/invoke.h>
 #include <__cxx03/__memory/addressof.h>
 #include <__cxx03/__memory/construct_at.h>
 #include <__cxx03/__type_traits/conjunction.h>
 #include <__cxx03/__type_traits/disjunction.h>
 #include <__cxx03/__type_traits/integral_constant.h>
 #include <__cxx03/__type_traits/is_assignable.h>
 #include <__cxx03/__type_traits/is_constructible.h>
 #include <__cxx03/__type_traits/is_convertible.h>
 #include <__cxx03/__type_traits/is_function.h>
 #include <__cxx03/__type_traits/is_nothrow_assignable.h>
 #include <__cxx03/__type_traits/is_nothrow_constructible.h>
 #include <__cxx03/__type_traits/is_reference.h>
 #include <__cxx03/__type_traits/is_same.h>
 #include <__cxx03/__type_traits/is_swappable.h>
 #include <__cxx03/__type_traits/is_trivially_constructible.h>
 #include <__cxx03/__type_traits/is_trivially_destructible.h>
 #include <__cxx03/__type_traits/is_trivially_relocatable.h>
 #include <__cxx03/__type_traits/is_void.h>
 #include <__cxx03/__type_traits/lazy.h>
 #include <__cxx03/__type_traits/negation.h>
 #include <__cxx03/__type_traits/remove_cv.h>
 #include <__cxx03/__type_traits/remove_cvref.h>
 #include <__cxx03/__utility/as_const.h>
 #include <__cxx03/__utility/exception_guard.h>
 #include <__cxx03/__utility/forward.h>
 #include <__cxx03/__utility/in_place.h>
 #include <__cxx03/__utility/move.h>
 #include <__cxx03/__utility/swap.h>
 #include <__cxx03/__verbose_abort>
 #include <__cxx03/initializer_list>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_PUSH_MACROS
 #include <__cxx03/__undef_macros>
 
 #if _LIBCPP_STD_VER >= 23
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp, class _Err>
 class expected;
 
 template <class _Tp>
 struct __is_std_expected : false_type {};
 
 template <class _Tp, class _Err>
 struct __is_std_expected<expected<_Tp, _Err>> : true_type {};
 
 struct __expected_construct_in_place_from_invoke_tag {};
 struct __expected_construct_unexpected_from_invoke_tag {};
 
 template <class _Err, class _Arg>
 _LIBCPP_HIDE_FROM_ABI void __throw_bad_expected_access(_Arg&& __arg) {
 #  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   throw bad_expected_access<_Err>(std::forward<_Arg>(__arg));
 #  else
   (void)__arg;
   _LIBCPP_VERBOSE_ABORT("bad_expected_access was thrown in -fno-exceptions mode");
 #  endif
 }
 
 // If parameter type `_Tp` of `__conditional_no_unique_address` is neither
 // copyable nor movable, a constructor with this tag is provided. For that
 // constructor, the user has to provide a function and arguments. The function
 // must return an object of type `_Tp`. When the function is invoked by the
 // constructor, guaranteed copy elision kicks in and the `_Tp` is constructed
 // in place.
 struct __conditional_no_unique_address_invoke_tag {};
 
 // This class implements an object with `[[no_unique_address]]` conditionally applied to it,
 // based on the value of `_NoUnique`.
 //
 // A member of this class must always have `[[no_unique_address]]` applied to
 // it. Otherwise, the `[[no_unique_address]]` in the "`_NoUnique == true`" case
 // would not have any effect. In the `false` case, the `__v` is not
 // `[[no_unique_address]]`, so nullifies the effects of the "outer"
 // `[[no_unique_address]]` regarding data layout.
 //
 // If we had a language feature, this class would basically be replaced by `[[no_unique_address(condition)]]`.
 template <bool _NoUnique, class _Tp>
 struct __conditional_no_unique_address;
 
 template <class _Tp>
 struct __conditional_no_unique_address<true, _Tp> {
   template <class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit __conditional_no_unique_address(in_place_t, _Args&&... __args)
       : __v(std::forward<_Args>(__args)...) {}
 
   template <class _Func, class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit __conditional_no_unique_address(
       __conditional_no_unique_address_invoke_tag, _Func&& __f, _Args&&... __args)
       : __v(std::invoke(std::forward<_Func>(__f), std::forward<_Args>(__args)...)) {}
 
   _LIBCPP_NO_UNIQUE_ADDRESS _Tp __v;
 };
 
 template <class _Tp>
 struct __conditional_no_unique_address<false, _Tp> {
   template <class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit __conditional_no_unique_address(in_place_t, _Args&&... __args)
       : __v(std::forward<_Args>(__args)...) {}
 
   template <class _Func, class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit __conditional_no_unique_address(
       __conditional_no_unique_address_invoke_tag, _Func&& __f, _Args&&... __args)
       : __v(std::invoke(std::forward<_Func>(__f), std::forward<_Args>(__args)...)) {}
 
   _Tp __v;
 };
 
 // This function returns whether the type `_Second` can be stuffed into the tail padding
 // of the `_First` type if both of them are given `[[no_unique_address]]`.
 template <class _First, class _Second>
 inline constexpr bool __fits_in_tail_padding = []() {
   struct __x {
     _LIBCPP_NO_UNIQUE_ADDRESS _First __first;
     _LIBCPP_NO_UNIQUE_ADDRESS _Second __second;
   };
   return sizeof(__x) == sizeof(_First);
 }();
 
 // This class implements the storage used by `std::expected`. We have a few
 // goals for this storage:
 // 1. Whenever the underlying {_Tp | _Unex} combination has free bytes in its
 //    tail padding, we should reuse it to store the bool discriminator of the
 //    expected, so as to save space.
 // 2. Whenever the `expected<_Tp, _Unex>` as a whole has free bytes in its tail
 //    padding, we should allow an object following the expected to be stored in
 //    its tail padding.
 // 3. However, we never want a user object (say `X`) that would follow an
 //    `expected<_Tp, _Unex>` to be stored in the padding bytes of the
 //    underlying {_Tp | _Unex} union, if any. That is because we use
 //    `construct_at` on that union, which would end up overwriting the `X`
 //    member if it is stored in the tail padding of the union.
 //
 // To achieve this, `__expected_base`'s logic is implemented in an inner
 // `__repr` class. `__expected_base` holds one `__repr` member which is
 // conditionally `[[no_unique_address]]`. The `__repr` class holds the
 // underlying {_Tp | _Unex} union and a boolean "has value" flag.
 //
 // Which one of the `__repr_`/`__union_` members is `[[no_unique_address]]`
 // depends on whether the "has value" boolean fits into the tail padding of
 // the underlying {_Tp | _Unex} union:
 //
 // - In case the "has value" bool fits into the tail padding of the union, the
 //   whole `__repr_` member is _not_ `[[no_unique_address]]` as it needs to be
 //   transparently replaced on `emplace()`/`swap()` etc.
 // - In case the "has value" bool does not fit into the tail padding of the
 //   union, only the union member must be transparently replaced (therefore is
 //   _not_ `[[no_unique_address]]`) and the "has value" flag must be adjusted
 //   manually.
 //
 // This way, the member that is transparently replaced on mutating operations
 // is never `[[no_unique_address]]`, satisfying the requirements from
 // "[basic.life]" in the standard.
 //
 // Stripped away of all superfluous elements, the layout of `__expected_base`
 // then looks like this:
 //
 //     template <class Tp, class Err>
 //     class expected_base {
 //       union union_t {
 //         [[no_unique_address]] Tp val;
 //         [[no_unique_address]] Err unex;
 //       };
 //
 //       static constexpr bool put_flag_in_tail                    = fits_in_tail_padding<union_t, bool>;
 //       static constexpr bool allow_reusing_expected_tail_padding = !put_flag_in_tail;
 //
 //       struct repr {
 //       private:
 //         // If "has value" fits into the tail, this should be
 //         // `[[no_unique_address]]`, otherwise not.
 //         [[no_unique_address]] conditional_no_unique_address<
 //             put_flag_in_tail,
 //             union_t>::type union_;
 //         [[no_unique_address]] bool has_val_;
 //       };
 //
 //     protected:
 //       // If "has value" fits into the tail, this must _not_ be
 //       // `[[no_unique_address]]` so that we fill out the
 //       // complete `expected` object.
 //       [[no_unique_address]] conditional_no_unique_address<
 //           allow_reusing_expected_tail_padding,
 //           repr>::type repr_;
 //     };
 //
 template <class _Tp, class _Err>
 class __expected_base {
   // use named union because [[no_unique_address]] cannot be applied to an unnamed union,
   // also guaranteed elision into a potentially-overlapping subobject is unsettled (and
   // it's not clear that it's implementable, given that the function is allowed to clobber
   // the tail padding) - see https://github.com/itanium-cxx-abi/cxx-abi/issues/107.
   union __union_t {
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t(const __union_t&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t(const __union_t&)
       requires(is_copy_constructible_v<_Tp> && is_copy_constructible_v<_Err> &&
                is_trivially_copy_constructible_v<_Tp> && is_trivially_copy_constructible_v<_Err>)
     = default;
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t(__union_t&&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t(__union_t&&)
       requires(is_move_constructible_v<_Tp> && is_move_constructible_v<_Err> &&
                is_trivially_move_constructible_v<_Tp> && is_trivially_move_constructible_v<_Err>)
     = default;
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t& operator=(const __union_t&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t& operator=(__union_t&&)      = delete;
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __union_t(in_place_t, _Args&&... __args)
         : __val_(std::forward<_Args>(__args)...) {}
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __union_t(unexpect_t, _Args&&... __args)
         : __unex_(std::forward<_Args>(__args)...) {}
 
     template <class _Func, class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __union_t(
         std::__expected_construct_in_place_from_invoke_tag, _Func&& __f, _Args&&... __args)
         : __val_(std::invoke(std::forward<_Func>(__f), std::forward<_Args>(__args)...)) {}
 
     template <class _Func, class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __union_t(
         std::__expected_construct_unexpected_from_invoke_tag, _Func&& __f, _Args&&... __args)
         : __unex_(std::invoke(std::forward<_Func>(__f), std::forward<_Args>(__args)...)) {}
 
     _LIBCPP_HIDE_FROM_ABI constexpr ~__union_t()
       requires(is_trivially_destructible_v<_Tp> && is_trivially_destructible_v<_Err>)
     = default;
 
     // __repr's destructor handles this
     _LIBCPP_HIDE_FROM_ABI constexpr ~__union_t() {}
 
     _LIBCPP_NO_UNIQUE_ADDRESS _Tp __val_;
     _LIBCPP_NO_UNIQUE_ADDRESS _Err __unex_;
   };
 
   static constexpr bool __put_flag_in_tail                    = __fits_in_tail_padding<__union_t, bool>;
   static constexpr bool __allow_reusing_expected_tail_padding = !__put_flag_in_tail;
 
   struct __repr {
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr() = delete;
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr(in_place_t __tag, _Args&&... __args)
         : __union_(in_place, __tag, std::forward<_Args>(__args)...), __has_val_(true) {}
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr(unexpect_t __tag, _Args&&... __args)
         : __union_(in_place, __tag, std::forward<_Args>(__args)...), __has_val_(false) {}
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr(std::__expected_construct_in_place_from_invoke_tag __tag,
                                                     _Args&&... __args)
         : __union_(in_place, __tag, std::forward<_Args>(__args)...), __has_val_(true) {}
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr(std::__expected_construct_unexpected_from_invoke_tag __tag,
                                                     _Args&&... __args)
         : __union_(in_place, __tag, std::forward<_Args>(__args)...), __has_val_(false) {}
 
     // The return value of `__make_union` must be constructed in place in the
     // `__v` member of `__union_`, relying on guaranteed copy elision. To do
     // this, the `__conditional_no_unique_address_invoke_tag` constructor is
     // called with a lambda that is immediately called inside
     // `__conditional_no_unique_address`'s constructor.
     template <class _OtherUnion>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr(bool __has_val, _OtherUnion&& __other)
       requires(__allow_reusing_expected_tail_padding)
         : __union_(__conditional_no_unique_address_invoke_tag{},
                    [&] { return __make_union(__has_val, std::forward<_OtherUnion>(__other)); }),
           __has_val_(__has_val) {}
 
     _LIBCPP_HIDE_FROM_ABI constexpr __repr(const __repr&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __repr(const __repr&)
       requires(is_copy_constructible_v<_Tp> && is_copy_constructible_v<_Err> &&
                is_trivially_copy_constructible_v<_Tp> && is_trivially_copy_constructible_v<_Err>)
     = default;
     _LIBCPP_HIDE_FROM_ABI constexpr __repr(__repr&&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __repr(__repr&&)
       requires(is_move_constructible_v<_Tp> && is_move_constructible_v<_Err> &&
                is_trivially_move_constructible_v<_Tp> && is_trivially_move_constructible_v<_Err>)
     = default;
 
     _LIBCPP_HIDE_FROM_ABI constexpr __repr& operator=(const __repr&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __repr& operator=(__repr&&)      = delete;
 
     _LIBCPP_HIDE_FROM_ABI constexpr ~__repr()
       requires(is_trivially_destructible_v<_Tp> && is_trivially_destructible_v<_Err>)
     = default;
 
     _LIBCPP_HIDE_FROM_ABI constexpr ~__repr()
       requires(!is_trivially_destructible_v<_Tp> || !is_trivially_destructible_v<_Err>)
     {
       __destroy_union_member();
     }
 
     _LIBCPP_HIDE_FROM_ABI constexpr void __destroy_union()
       requires(__allow_reusing_expected_tail_padding &&
                (is_trivially_destructible_v<_Tp> && is_trivially_destructible_v<_Err>))
     {
       // Note: Since the destructor of the union is trivial, this does nothing
       // except to end the lifetime of the union.
       std::destroy_at(&__union_.__v);
     }
 
     _LIBCPP_HIDE_FROM_ABI constexpr void __destroy_union()
       requires(__allow_reusing_expected_tail_padding &&
                (!is_trivially_destructible_v<_Tp> || !is_trivially_destructible_v<_Err>))
     {
       __destroy_union_member();
       std::destroy_at(&__union_.__v);
     }
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr void __construct_union(in_place_t, _Args&&... __args)
       requires(__allow_reusing_expected_tail_padding)
     {
       std::construct_at(&__union_.__v, in_place, std::forward<_Args>(__args)...);
       __has_val_ = true;
     }
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr void __construct_union(unexpect_t, _Args&&... __args)
       requires(__allow_reusing_expected_tail_padding)
     {
       std::construct_at(&__union_.__v, unexpect, std::forward<_Args>(__args)...);
       __has_val_ = false;
     }
 
   private:
     template <class, class>
     friend class __expected_base;
 
     _LIBCPP_HIDE_FROM_ABI constexpr void __destroy_union_member()
       requires(!is_trivially_destructible_v<_Tp> || !is_trivially_destructible_v<_Err>)
     {
       if (__has_val_) {
         std::destroy_at(std::addressof(__union_.__v.__val_));
       } else {
         std::destroy_at(std::addressof(__union_.__v.__unex_));
       }
     }
 
     template <class _OtherUnion>
     _LIBCPP_HIDE_FROM_ABI static constexpr __union_t __make_union(bool __has_val, _OtherUnion&& __other)
       requires(__allow_reusing_expected_tail_padding)
     {
       if (__has_val)
         return __union_t(in_place, std::forward<_OtherUnion>(__other).__val_);
       else
         return __union_t(unexpect, std::forward<_OtherUnion>(__other).__unex_);
     }
 
     _LIBCPP_NO_UNIQUE_ADDRESS __conditional_no_unique_address<__put_flag_in_tail, __union_t> __union_;
     _LIBCPP_NO_UNIQUE_ADDRESS bool __has_val_;
   };
 
   template <class _OtherUnion>
   _LIBCPP_HIDE_FROM_ABI static constexpr __repr __make_repr(bool __has_val, _OtherUnion&& __other)
     requires(__put_flag_in_tail)
   {
     if (__has_val)
       return __repr(in_place, std::forward<_OtherUnion>(__other).__val_);
     else
       return __repr(unexpect, std::forward<_OtherUnion>(__other).__unex_);
   }
 
 protected:
   template <class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit __expected_base(_Args&&... __args)
       : __repr_(in_place, std::forward<_Args>(__args)...) {}
 
   // In case we copy/move construct from another `expected` we need to create
   // our `expected` so that it either has a value or not, depending on the "has
   // value" flag of the other `expected`. To do this without falling back on
   // `std::construct_at` we rely on guaranteed copy elision using two helper
   // functions `__make_repr` and `__make_union`. There have to be two since
   // there are two data layouts with different members being
   // `[[no_unique_address]]`. GCC (as of version 13) does not do guaranteed
   // copy elision when initializing `[[no_unique_address]]` members. The two
   // cases are:
   //
   // - `__make_repr`: This is used when the "has value" flag lives in the tail
   //   of the union. In this case, the `__repr` member is _not_
   //   `[[no_unique_address]]`.
   // - `__make_union`: When the "has value" flag does _not_ fit in the tail of
   //   the union, the `__repr` member is `[[no_unique_address]]` and the union
   //   is not.
   //
   // This constructor "catches" the first case and leaves the second case to
   // `__union_t`, its constructors and `__make_union`.
   template <class _OtherUnion>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit __expected_base(bool __has_val, _OtherUnion&& __other)
     requires(__put_flag_in_tail)
       : __repr_(__conditional_no_unique_address_invoke_tag{},
                 [&] { return __make_repr(__has_val, std::forward<_OtherUnion>(__other)); }) {}
 
   _LIBCPP_HIDE_FROM_ABI constexpr void __destroy() {
     if constexpr (__put_flag_in_tail)
       std::destroy_at(&__repr_.__v);
     else
       __repr_.__v.__destroy_union();
   }
 
   template <class _Tag, class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr void __construct(_Tag __tag, _Args&&... __args) {
     if constexpr (__put_flag_in_tail)
       std::construct_at(&__repr_.__v, __tag, std::forward<_Args>(__args)...);
     else
       __repr_.__v.__construct_union(__tag, std::forward<_Args>(__args)...);
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr bool __has_val() const { return __repr_.__v.__has_val_; }
   _LIBCPP_HIDE_FROM_ABI constexpr __union_t& __union() { return __repr_.__v.__union_.__v; }
   _LIBCPP_HIDE_FROM_ABI constexpr const __union_t& __union() const { return __repr_.__v.__union_.__v; }
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp& __val() { return __repr_.__v.__union_.__v.__val_; }
   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& __val() const { return __repr_.__v.__union_.__v.__val_; }
   _LIBCPP_HIDE_FROM_ABI constexpr _Err& __unex() { return __repr_.__v.__union_.__v.__unex_; }
   _LIBCPP_HIDE_FROM_ABI constexpr const _Err& __unex() const { return __repr_.__v.__union_.__v.__unex_; }
 
 private:
   _LIBCPP_NO_UNIQUE_ADDRESS __conditional_no_unique_address<__allow_reusing_expected_tail_padding, __repr> __repr_;
 };
 
 template <class _Tp, class _Err>
 class expected : private __expected_base<_Tp, _Err> {
   static_assert(!is_reference_v<_Tp> && !is_function_v<_Tp> && !is_same_v<remove_cv_t<_Tp>, in_place_t> &&
                     !is_same_v<remove_cv_t<_Tp>, unexpect_t> && !__is_std_unexpected<remove_cv_t<_Tp>>::value &&
                     __valid_std_unexpected<_Err>::value,
                 "[expected.object.general] A program that instantiates the definition of template expected<T, E> for a "
                 "reference type, a function type, or for possibly cv-qualified types in_place_t, unexpect_t, or a "
                 "specialization of unexpected for the T parameter is ill-formed. A program that instantiates the "
                 "definition of the template expected<T, E> with a type for the E parameter that is not a valid "
                 "template argument for unexpected is ill-formed.");
 
   template <class _Up, class _OtherErr>
   friend class expected;
 
   using __base = __expected_base<_Tp, _Err>;
 
 public:
   using value_type      = _Tp;
   using error_type      = _Err;
   using unexpected_type = unexpected<_Err>;
 
   using __trivially_relocatable =
       __conditional_t<__libcpp_is_trivially_relocatable<_Tp>::value && __libcpp_is_trivially_relocatable<_Err>::value,
                       expected,
                       void>;
 
   template <class _Up>
   using rebind = expected<_Up, error_type>;
 
   // [expected.object.ctor], constructors
   _LIBCPP_HIDE_FROM_ABI constexpr expected() noexcept(is_nothrow_default_constructible_v<_Tp>) // strengthened
     requires is_default_constructible_v<_Tp>
       : __base(in_place) {}
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected(const expected&) = delete;
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected(const expected&)
     requires(is_copy_constructible_v<_Tp> && is_copy_constructible_v<_Err> && is_trivially_copy_constructible_v<_Tp> &&
              is_trivially_copy_constructible_v<_Err>)
   = default;
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected(const expected& __other) noexcept(
       is_nothrow_copy_constructible_v<_Tp> && is_nothrow_copy_constructible_v<_Err>) // strengthened
     requires(is_copy_constructible_v<_Tp> && is_copy_constructible_v<_Err> &&
              !(is_trivially_copy_constructible_v<_Tp> && is_trivially_copy_constructible_v<_Err>))
       : __base(__other.__has_val(), __other.__union()) {}
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected(expected&&)
     requires(is_move_constructible_v<_Tp> && is_move_constructible_v<_Err> && is_trivially_move_constructible_v<_Tp> &&
              is_trivially_move_constructible_v<_Err>)
   = default;
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected(expected&& __other) noexcept(
       is_nothrow_move_constructible_v<_Tp> && is_nothrow_move_constructible_v<_Err>)
     requires(is_move_constructible_v<_Tp> && is_move_constructible_v<_Err> &&
              !(is_trivially_move_constructible_v<_Tp> && is_trivially_move_constructible_v<_Err>))
       : __base(__other.__has_val(), std::move(__other.__union())) {}
 
 private:
   template <class _Up, class _OtherErr, class _UfQual, class _OtherErrQual>
   using __can_convert = _And<
       is_constructible<_Tp, _UfQual>,
       is_constructible<_Err, _OtherErrQual>,
       _If<_Not<is_same<remove_cv_t<_Tp>, bool>>::value,
           _And< _Not<_And<is_same<_Tp, _Up>, is_same<_Err, _OtherErr>>>, // use the copy constructor instead, see #92676
                 _Not<is_constructible<_Tp, expected<_Up, _OtherErr>&>>,
                 _Not<is_constructible<_Tp, expected<_Up, _OtherErr>>>,
                 _Not<is_constructible<_Tp, const expected<_Up, _OtherErr>&>>,
                 _Not<is_constructible<_Tp, const expected<_Up, _OtherErr>>>,
                 _Not<is_convertible<expected<_Up, _OtherErr>&, _Tp>>,
                 _Not<is_convertible<expected<_Up, _OtherErr>&&, _Tp>>,
                 _Not<is_convertible<const expected<_Up, _OtherErr>&, _Tp>>,
                 _Not<is_convertible<const expected<_Up, _OtherErr>&&, _Tp>>>,
           true_type>,
       _Not<is_constructible<unexpected<_Err>, expected<_Up, _OtherErr>&>>,
       _Not<is_constructible<unexpected<_Err>, expected<_Up, _OtherErr>>>,
       _Not<is_constructible<unexpected<_Err>, const expected<_Up, _OtherErr>&>>,
       _Not<is_constructible<unexpected<_Err>, const expected<_Up, _OtherErr>>> >;
 
   template <class _Func, class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit expected(
       std::__expected_construct_in_place_from_invoke_tag __tag, _Func&& __f, _Args&&... __args)
       : __base(__tag, std::forward<_Func>(__f), std::forward<_Args>(__args)...) {}
 
   template <class _Func, class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit expected(
       std::__expected_construct_unexpected_from_invoke_tag __tag, _Func&& __f, _Args&&... __args)
       : __base(__tag, std::forward<_Func>(__f), std::forward<_Args>(__args)...) {}
 
 public:
   template <class _Up, class _OtherErr>
     requires __can_convert<_Up, _OtherErr, const _Up&, const _OtherErr&>::value
   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<const _Up&, _Tp> ||
                                            !is_convertible_v<const _OtherErr&, _Err>)
       expected(const expected<_Up, _OtherErr>& __other) noexcept(
           is_nothrow_constructible_v<_Tp, const _Up&> &&
           is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
       : __base(__other.__has_val(), __other.__union()) {}
 
   template <class _Up, class _OtherErr>
     requires __can_convert<_Up, _OtherErr, _Up, _OtherErr>::value
   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_Up, _Tp> || !is_convertible_v<_OtherErr, _Err>)
       expected(expected<_Up, _OtherErr>&& __other) noexcept(
           is_nothrow_constructible_v<_Tp, _Up> && is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
       : __base(__other.__has_val(), std::move(__other.__union())) {}
 
   template <class _Up = _Tp>
     requires(!is_same_v<remove_cvref_t<_Up>, in_place_t> && !is_same_v<expected, remove_cvref_t<_Up>> &&
              is_constructible_v<_Tp, _Up> && !__is_std_unexpected<remove_cvref_t<_Up>>::value &&
              (!is_same_v<remove_cv_t<_Tp>, bool> || !__is_std_expected<remove_cvref_t<_Up>>::value))
   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_Up, _Tp>)
       expected(_Up&& __u) noexcept(is_nothrow_constructible_v<_Tp, _Up>) // strengthened
       : __base(in_place, std::forward<_Up>(__u)) {}
 
   template <class _OtherErr>
     requires is_constructible_v<_Err, const _OtherErr&>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<const _OtherErr&, _Err>) expected(
       const unexpected<_OtherErr>& __unex) noexcept(is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
       : __base(unexpect, __unex.error()) {}
 
   template <class _OtherErr>
     requires is_constructible_v<_Err, _OtherErr>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_OtherErr, _Err>)
       expected(unexpected<_OtherErr>&& __unex) noexcept(is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
       : __base(unexpect, std::move(__unex.error())) {}
 
   template <class... _Args>
     requires is_constructible_v<_Tp, _Args...>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit expected(in_place_t, _Args&&... __args) noexcept(
       is_nothrow_constructible_v<_Tp, _Args...>) // strengthened
       : __base(in_place, std::forward<_Args>(__args)...) {}
 
   template <class _Up, class... _Args>
     requires is_constructible_v< _Tp, initializer_list<_Up>&, _Args... >
   _LIBCPP_HIDE_FROM_ABI constexpr explicit expected(in_place_t, initializer_list<_Up> __il, _Args&&... __args) noexcept(
       is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>) // strengthened
       : __base(in_place, __il, std::forward<_Args>(__args)...) {}
 
   template <class... _Args>
     requires is_constructible_v<_Err, _Args...>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit expected(unexpect_t, _Args&&... __args) noexcept(
       is_nothrow_constructible_v<_Err, _Args...>) // strengthened
       : __base(unexpect, std::forward<_Args>(__args)...) {}
 
   template <class _Up, class... _Args>
     requires is_constructible_v< _Err, initializer_list<_Up>&, _Args... >
   _LIBCPP_HIDE_FROM_ABI constexpr explicit expected(unexpect_t, initializer_list<_Up> __il, _Args&&... __args) noexcept(
       is_nothrow_constructible_v<_Err, initializer_list<_Up>&, _Args...>) // strengthened
       : __base(unexpect, __il, std::forward<_Args>(__args)...) {}
 
   // [expected.object.dtor], destructor
 
   _LIBCPP_HIDE_FROM_ABI constexpr ~expected() = default;
 
 private:
   template <class _Tag, class _OtherTag, class _T1, class _T2, class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr void __reinit_expected(_T2& __oldval, _Args&&... __args) {
     if constexpr (is_nothrow_constructible_v<_T1, _Args...>) {
       this->__destroy();
       this->__construct(_Tag{}, std::forward<_Args>(__args)...);
     } else if constexpr (is_nothrow_move_constructible_v<_T1>) {
       _T1 __tmp(std::forward<_Args>(__args)...);
       this->__destroy();
       this->__construct(_Tag{}, std::move(__tmp));
     } else {
       static_assert(
           is_nothrow_move_constructible_v<_T2>,
           "To provide strong exception guarantee, T2 has to satisfy `is_nothrow_move_constructible_v` so that it can "
           "be reverted to the previous state in case an exception is thrown during the assignment.");
       _T2 __tmp(std::move(__oldval));
       this->__destroy();
       auto __trans = std::__make_exception_guard([&] { this->__construct(_OtherTag{}, std::move(__tmp)); });
       this->__construct(_Tag{}, std::forward<_Args>(__args)...);
       __trans.__complete();
     }
   }
 
 public:
   // [expected.object.assign], assignment
   _LIBCPP_HIDE_FROM_ABI constexpr expected& operator=(const expected&) = delete;
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected& operator=(const expected& __rhs) noexcept(
       is_nothrow_copy_assignable_v<_Tp> && is_nothrow_copy_constructible_v<_Tp> && is_nothrow_copy_assignable_v<_Err> &&
       is_nothrow_copy_constructible_v<_Err>) // strengthened
     requires(is_copy_assignable_v<_Tp> && is_copy_constructible_v<_Tp> && is_copy_assignable_v<_Err> &&
              is_copy_constructible_v<_Err> &&
              (is_nothrow_move_constructible_v<_Tp> || is_nothrow_move_constructible_v<_Err>))
   {
     if (this->__has_val() && __rhs.__has_val()) {
       this->__val() = __rhs.__val();
     } else if (this->__has_val()) {
       __reinit_expected<unexpect_t, in_place_t, _Err, _Tp>(this->__val(), __rhs.__unex());
     } else if (__rhs.__has_val()) {
       __reinit_expected<in_place_t, unexpect_t, _Tp, _Err>(this->__unex(), __rhs.__val());
     } else {
       this->__unex() = __rhs.__unex();
     }
     return *this;
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected&
   operator=(expected&& __rhs) noexcept(is_nothrow_move_assignable_v<_Tp> && is_nothrow_move_constructible_v<_Tp> &&
                                        is_nothrow_move_assignable_v<_Err> && is_nothrow_move_constructible_v<_Err>)
     requires(is_move_constructible_v<_Tp> && is_move_assignable_v<_Tp> && is_move_constructible_v<_Err> &&
              is_move_assignable_v<_Err> &&
              (is_nothrow_move_constructible_v<_Tp> || is_nothrow_move_constructible_v<_Err>))
   {
     if (this->__has_val() && __rhs.__has_val()) {
       this->__val() = std::move(__rhs.__val());
     } else if (this->__has_val()) {
       __reinit_expected<unexpect_t, in_place_t, _Err, _Tp>(this->__val(), std::move(__rhs.__unex()));
     } else if (__rhs.__has_val()) {
       __reinit_expected<in_place_t, unexpect_t, _Tp, _Err>(this->__unex(), std::move(__rhs.__val()));
     } else {
       this->__unex() = std::move(__rhs.__unex());
     }
     return *this;
   }
 
   template <class _Up = _Tp>
   _LIBCPP_HIDE_FROM_ABI constexpr expected& operator=(_Up&& __v)
     requires(!is_same_v<expected, remove_cvref_t<_Up>> && !__is_std_unexpected<remove_cvref_t<_Up>>::value &&
              is_constructible_v<_Tp, _Up> && is_assignable_v<_Tp&, _Up> &&
              (is_nothrow_constructible_v<_Tp, _Up> || is_nothrow_move_constructible_v<_Tp> ||
               is_nothrow_move_constructible_v<_Err>))
   {
     if (this->__has_val()) {
       this->__val() = std::forward<_Up>(__v);
     } else {
       __reinit_expected<in_place_t, unexpect_t, _Tp, _Err>(this->__unex(), std::forward<_Up>(__v));
     }
     return *this;
   }
 
 private:
   template <class _OtherErrQual>
   static constexpr bool __can_assign_from_unexpected =
       _And< is_constructible<_Err, _OtherErrQual>,
             is_assignable<_Err&, _OtherErrQual>,
             _Lazy<_Or,
                   is_nothrow_constructible<_Err, _OtherErrQual>,
                   is_nothrow_move_constructible<_Tp>,
                   is_nothrow_move_constructible<_Err>> >::value;
 
 public:
   template <class _OtherErr>
     requires(__can_assign_from_unexpected<const _OtherErr&>)
   _LIBCPP_HIDE_FROM_ABI constexpr expected& operator=(const unexpected<_OtherErr>& __un) {
     if (this->__has_val()) {
       __reinit_expected<unexpect_t, in_place_t, _Err, _Tp>(this->__val(), __un.error());
     } else {
       this->__unex() = __un.error();
     }
     return *this;
   }
 
   template <class _OtherErr>
     requires(__can_assign_from_unexpected<_OtherErr>)
   _LIBCPP_HIDE_FROM_ABI constexpr expected& operator=(unexpected<_OtherErr>&& __un) {
     if (this->__has_val()) {
       __reinit_expected<unexpect_t, in_place_t, _Err, _Tp>(this->__val(), std::move(__un.error()));
     } else {
       this->__unex() = std::move(__un.error());
     }
     return *this;
   }
 
   template <class... _Args>
     requires is_nothrow_constructible_v<_Tp, _Args...>
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp& emplace(_Args&&... __args) noexcept {
     this->__destroy();
     this->__construct(in_place, std::forward<_Args>(__args)...);
     return this->__val();
   }
 
   template <class _Up, class... _Args>
     requires is_nothrow_constructible_v<_Tp, initializer_list<_Up>&, _Args...>
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp& emplace(initializer_list<_Up> __il, _Args&&... __args) noexcept {
     this->__destroy();
     this->__construct(in_place, __il, std::forward<_Args>(__args)...);
     return this->__val();
   }
 
 public:
   // [expected.object.swap], swap
   _LIBCPP_HIDE_FROM_ABI constexpr void
   swap(expected& __rhs) noexcept(is_nothrow_move_constructible_v<_Tp> && is_nothrow_swappable_v<_Tp> &&
                                  is_nothrow_move_constructible_v<_Err> && is_nothrow_swappable_v<_Err>)
     requires(is_swappable_v<_Tp> && is_swappable_v<_Err> && is_move_constructible_v<_Tp> &&
              is_move_constructible_v<_Err> &&
              (is_nothrow_move_constructible_v<_Tp> || is_nothrow_move_constructible_v<_Err>))
   {
     auto __swap_val_unex_impl = [](expected& __with_val, expected& __with_err) {
       if constexpr (is_nothrow_move_constructible_v<_Err>) {
         _Err __tmp(std::move(__with_err.__unex()));
         __with_err.__destroy();
         auto __trans = std::__make_exception_guard([&] { __with_err.__construct(unexpect, std::move(__tmp)); });
         __with_err.__construct(in_place, std::move(__with_val.__val()));
         __trans.__complete();
         __with_val.__destroy();
         __with_val.__construct(unexpect, std::move(__tmp));
       } else {
         static_assert(is_nothrow_move_constructible_v<_Tp>,
                       "To provide strong exception guarantee, Tp has to satisfy `is_nothrow_move_constructible_v` so "
                       "that it can be reverted to the previous state in case an exception is thrown during swap.");
         _Tp __tmp(std::move(__with_val.__val()));
         __with_val.__destroy();
         auto __trans = std::__make_exception_guard([&] { __with_val.__construct(in_place, std::move(__tmp)); });
         __with_val.__construct(unexpect, std::move(__with_err.__unex()));
         __trans.__complete();
         __with_err.__destroy();
         __with_err.__construct(in_place, std::move(__tmp));
       }
     };
 
     if (this->__has_val()) {
       if (__rhs.__has_val()) {
         using std::swap;
         swap(this->__val(), __rhs.__val());
       } else {
         __swap_val_unex_impl(*this, __rhs);
       }
     } else {
       if (__rhs.__has_val()) {
         __swap_val_unex_impl(__rhs, *this);
       } else {
         using std::swap;
         swap(this->__unex(), __rhs.__unex());
       }
     }
   }
 
   _LIBCPP_HIDE_FROM_ABI friend constexpr void swap(expected& __x, expected& __y) noexcept(noexcept(__x.swap(__y)))
     requires requires { __x.swap(__y); }
   {
     __x.swap(__y);
   }
 
   // [expected.object.obs], observers
   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp* operator->() const noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         this->__has_val(), "expected::operator-> requires the expected to contain a value");
     return std::addressof(this->__val());
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* operator->() noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         this->__has_val(), "expected::operator-> requires the expected to contain a value");
     return std::addressof(this->__val());
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& operator*() const& noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         this->__has_val(), "expected::operator* requires the expected to contain a value");
     return this->__val();
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp& operator*() & noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         this->__has_val(), "expected::operator* requires the expected to contain a value");
     return this->__val();
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp&& operator*() const&& noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         this->__has_val(), "expected::operator* requires the expected to contain a value");
     return std::move(this->__val());
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp&& operator*() && noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         this->__has_val(), "expected::operator* requires the expected to contain a value");
     return std::move(this->__val());
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr explicit operator bool() const noexcept { return this->__has_val(); }
 
   _LIBCPP_HIDE_FROM_ABI constexpr bool has_value() const noexcept { return this->__has_val(); }
 
   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp& value() const& {
     static_assert(is_copy_constructible_v<_Err>, "error_type has to be copy constructible");
     if (!this->__has_val()) {
       std::__throw_bad_expected_access<_Err>(std::as_const(error()));
     }
     return this->__val();
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp& value() & {
     static_assert(is_copy_constructible_v<_Err>, "error_type has to be copy constructible");
     if (!this->__has_val()) {
       std::__throw_bad_expected_access<_Err>(std::as_const(error()));
     }
     return this->__val();
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr const _Tp&& value() const&& {
     static_assert(is_copy_constructible_v<_Err> && is_constructible_v<_Err, decltype(std::move(error()))>,
                   "error_type has to be both copy constructible and constructible from decltype(std::move(error()))");
     if (!this->__has_val()) {
       std::__throw_bad_expected_access<_Err>(std::move(error()));
     }
     return std::move(this->__val());
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp&& value() && {
     static_assert(is_copy_constructible_v<_Err> && is_constructible_v<_Err, decltype(std::move(error()))>,
                   "error_type has to be both copy constructible and constructible from decltype(std::move(error()))");
     if (!this->__has_val()) {
       std::__throw_bad_expected_access<_Err>(std::move(error()));
     }
     return std::move(this->__val());
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr const _Err& error() const& noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         !this->__has_val(), "expected::error requires the expected to contain an error");
     return this->__unex();
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr _Err& error() & noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         !this->__has_val(), "expected::error requires the expected to contain an error");
     return this->__unex();
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr const _Err&& error() const&& noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         !this->__has_val(), "expected::error requires the expected to contain an error");
     return std::move(this->__unex());
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr _Err&& error() && noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         !this->__has_val(), "expected::error requires the expected to contain an error");
     return std::move(this->__unex());
   }
 
   template <class _Up>
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp value_or(_Up&& __v) const& {
     static_assert(is_copy_constructible_v<_Tp>, "value_type has to be copy constructible");
     static_assert(is_convertible_v<_Up, _Tp>, "argument has to be convertible to value_type");
     return this->__has_val() ? this->__val() : static_cast<_Tp>(std::forward<_Up>(__v));
   }
 
   template <class _Up>
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp value_or(_Up&& __v) && {
     static_assert(is_move_constructible_v<_Tp>, "value_type has to be move constructible");
     static_assert(is_convertible_v<_Up, _Tp>, "argument has to be convertible to value_type");
     return this->__has_val() ? std::move(this->__val()) : static_cast<_Tp>(std::forward<_Up>(__v));
   }
 
   template <class _Up = _Err>
   _LIBCPP_HIDE_FROM_ABI constexpr _Err error_or(_Up&& __error) const& {
     static_assert(is_copy_constructible_v<_Err>, "error_type has to be copy constructible");
     static_assert(is_convertible_v<_Up, _Err>, "argument has to be convertible to error_type");
     if (has_value())
       return std::forward<_Up>(__error);
     return error();
   }
 
   template <class _Up = _Err>
   _LIBCPP_HIDE_FROM_ABI constexpr _Err error_or(_Up&& __error) && {
     static_assert(is_move_constructible_v<_Err>, "error_type has to be move constructible");
     static_assert(is_convertible_v<_Up, _Err>, "argument has to be convertible to error_type");
     if (has_value())
       return std::forward<_Up>(__error);
     return std::move(error());
   }
 
   // [expected.void.monadic], monadic
   template <class _Func>
     requires is_constructible_v<_Err, _Err&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto and_then(_Func&& __f) & {
     using _Up = remove_cvref_t<invoke_result_t<_Func, _Tp&>>;
     static_assert(__is_std_expected<_Up>::value, "The result of f(**this) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Up::error_type, _Err>,
                   "The result of f(**this) must have the same error_type as this expected");
     if (has_value()) {
       return std::invoke(std::forward<_Func>(__f), this->__val());
     }
     return _Up(unexpect, error());
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, const _Err&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto and_then(_Func&& __f) const& {
     using _Up = remove_cvref_t<invoke_result_t<_Func, const _Tp&>>;
     static_assert(__is_std_expected<_Up>::value, "The result of f(**this) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Up::error_type, _Err>,
                   "The result of f(**this) must have the same error_type as this expected");
     if (has_value()) {
       return std::invoke(std::forward<_Func>(__f), this->__val());
     }
     return _Up(unexpect, error());
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, _Err&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto and_then(_Func&& __f) && {
     using _Up = remove_cvref_t<invoke_result_t<_Func, _Tp&&>>;
     static_assert(
         __is_std_expected<_Up>::value, "The result of f(std::move(**this)) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Up::error_type, _Err>,
                   "The result of f(std::move(**this)) must have the same error_type as this expected");
     if (has_value()) {
       return std::invoke(std::forward<_Func>(__f), std::move(this->__val()));
     }
     return _Up(unexpect, std::move(error()));
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, const _Err&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto and_then(_Func&& __f) const&& {
     using _Up = remove_cvref_t<invoke_result_t<_Func, const _Tp&&>>;
     static_assert(
         __is_std_expected<_Up>::value, "The result of f(std::move(**this)) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Up::error_type, _Err>,
                   "The result of f(std::move(**this)) must have the same error_type as this expected");
     if (has_value()) {
       return std::invoke(std::forward<_Func>(__f), std::move(this->__val()));
     }
     return _Up(unexpect, std::move(error()));
   }
 
   template <class _Func>
     requires is_constructible_v<_Tp, _Tp&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto or_else(_Func&& __f) & {
     using _Gp = remove_cvref_t<invoke_result_t<_Func, _Err&>>;
     static_assert(__is_std_expected<_Gp>::value, "The result of f(error()) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Gp::value_type, _Tp>,
                   "The result of f(error()) must have the same value_type as this expected");
     if (has_value()) {
       return _Gp(in_place, this->__val());
     }
     return std::invoke(std::forward<_Func>(__f), error());
   }
 
   template <class _Func>
     requires is_constructible_v<_Tp, const _Tp&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto or_else(_Func&& __f) const& {
     using _Gp = remove_cvref_t<invoke_result_t<_Func, const _Err&>>;
     static_assert(__is_std_expected<_Gp>::value, "The result of f(error()) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Gp::value_type, _Tp>,
                   "The result of f(error()) must have the same value_type as this expected");
     if (has_value()) {
       return _Gp(in_place, this->__val());
     }
     return std::invoke(std::forward<_Func>(__f), error());
   }
 
   template <class _Func>
     requires is_constructible_v<_Tp, _Tp&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto or_else(_Func&& __f) && {
     using _Gp = remove_cvref_t<invoke_result_t<_Func, _Err&&>>;
     static_assert(
         __is_std_expected<_Gp>::value, "The result of f(std::move(error())) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Gp::value_type, _Tp>,
                   "The result of f(std::move(error())) must have the same value_type as this expected");
     if (has_value()) {
       return _Gp(in_place, std::move(this->__val()));
     }
     return std::invoke(std::forward<_Func>(__f), std::move(error()));
   }
 
   template <class _Func>
     requires is_constructible_v<_Tp, const _Tp&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto or_else(_Func&& __f) const&& {
     using _Gp = remove_cvref_t<invoke_result_t<_Func, const _Err&&>>;
     static_assert(
         __is_std_expected<_Gp>::value, "The result of f(std::move(error())) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Gp::value_type, _Tp>,
                   "The result of f(std::move(error())) must have the same value_type as this expected");
     if (has_value()) {
       return _Gp(in_place, std::move(this->__val()));
     }
     return std::invoke(std::forward<_Func>(__f), std::move(error()));
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, _Err&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform(_Func&& __f) & {
     using _Up = remove_cv_t<invoke_result_t<_Func, _Tp&>>;
     if (!has_value()) {
       return expected<_Up, _Err>(unexpect, error());
     }
     if constexpr (!is_void_v<_Up>) {
       return expected<_Up, _Err>(
           __expected_construct_in_place_from_invoke_tag{}, std::forward<_Func>(__f), this->__val());
     } else {
       std::invoke(std::forward<_Func>(__f), this->__val());
       return expected<_Up, _Err>();
     }
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, const _Err&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform(_Func&& __f) const& {
     using _Up = remove_cv_t<invoke_result_t<_Func, const _Tp&>>;
     if (!has_value()) {
       return expected<_Up, _Err>(unexpect, error());
     }
     if constexpr (!is_void_v<_Up>) {
       return expected<_Up, _Err>(
           __expected_construct_in_place_from_invoke_tag{}, std::forward<_Func>(__f), this->__val());
     } else {
       std::invoke(std::forward<_Func>(__f), this->__val());
       return expected<_Up, _Err>();
     }
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, _Err&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform(_Func&& __f) && {
     using _Up = remove_cv_t<invoke_result_t<_Func, _Tp&&>>;
     if (!has_value()) {
       return expected<_Up, _Err>(unexpect, std::move(error()));
     }
     if constexpr (!is_void_v<_Up>) {
       return expected<_Up, _Err>(
           __expected_construct_in_place_from_invoke_tag{}, std::forward<_Func>(__f), std::move(this->__val()));
     } else {
       std::invoke(std::forward<_Func>(__f), std::move(this->__val()));
       return expected<_Up, _Err>();
     }
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, const _Err&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform(_Func&& __f) const&& {
     using _Up = remove_cv_t<invoke_result_t<_Func, const _Tp&&>>;
     if (!has_value()) {
       return expected<_Up, _Err>(unexpect, std::move(error()));
     }
     if constexpr (!is_void_v<_Up>) {
       return expected<_Up, _Err>(
           __expected_construct_in_place_from_invoke_tag{}, std::forward<_Func>(__f), std::move(this->__val()));
     } else {
       std::invoke(std::forward<_Func>(__f), std::move(this->__val()));
       return expected<_Up, _Err>();
     }
   }
 
   template <class _Func>
     requires is_constructible_v<_Tp, _Tp&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform_error(_Func&& __f) & {
     using _Gp = remove_cv_t<invoke_result_t<_Func, _Err&>>;
     static_assert(__valid_std_unexpected<_Gp>::value,
                   "The result of f(error()) must be a valid template argument for unexpected");
     if (has_value()) {
       return expected<_Tp, _Gp>(in_place, this->__val());
     }
     return expected<_Tp, _Gp>(__expected_construct_unexpected_from_invoke_tag{}, std::forward<_Func>(__f), error());
   }
 
   template <class _Func>
     requires is_constructible_v<_Tp, const _Tp&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform_error(_Func&& __f) const& {
     using _Gp = remove_cv_t<invoke_result_t<_Func, const _Err&>>;
     static_assert(__valid_std_unexpected<_Gp>::value,
                   "The result of f(error()) must be a valid template argument for unexpected");
     if (has_value()) {
       return expected<_Tp, _Gp>(in_place, this->__val());
     }
     return expected<_Tp, _Gp>(__expected_construct_unexpected_from_invoke_tag{}, std::forward<_Func>(__f), error());
   }
 
   template <class _Func>
     requires is_constructible_v<_Tp, _Tp&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform_error(_Func&& __f) && {
     using _Gp = remove_cv_t<invoke_result_t<_Func, _Err&&>>;
     static_assert(__valid_std_unexpected<_Gp>::value,
                   "The result of f(std::move(error())) must be a valid template argument for unexpected");
     if (has_value()) {
       return expected<_Tp, _Gp>(in_place, std::move(this->__val()));
     }
     return expected<_Tp, _Gp>(
         __expected_construct_unexpected_from_invoke_tag{}, std::forward<_Func>(__f), std::move(error()));
   }
 
   template <class _Func>
     requires is_constructible_v<_Tp, const _Tp&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform_error(_Func&& __f) const&& {
     using _Gp = remove_cv_t<invoke_result_t<_Func, const _Err&&>>;
     static_assert(__valid_std_unexpected<_Gp>::value,
                   "The result of f(std::move(error())) must be a valid template argument for unexpected");
     if (has_value()) {
       return expected<_Tp, _Gp>(in_place, std::move(this->__val()));
     }
     return expected<_Tp, _Gp>(
         __expected_construct_unexpected_from_invoke_tag{}, std::forward<_Func>(__f), std::move(error()));
   }
 
   // [expected.object.eq], equality operators
   template <class _T2, class _E2>
     requires(!is_void_v<_T2>)
   _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const expected<_T2, _E2>& __y) {
     if (__x.__has_val() != __y.__has_val()) {
       return false;
     } else {
       if (__x.__has_val()) {
         return __x.__val() == __y.__val();
       } else {
         return __x.__unex() == __y.__unex();
       }
     }
   }
 
   template <class _T2>
   _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const _T2& __v) {
     return __x.__has_val() && static_cast<bool>(__x.__val() == __v);
   }
 
   template <class _E2>
   _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const unexpected<_E2>& __e) {
     return !__x.__has_val() && static_cast<bool>(__x.__unex() == __e.error());
   }
 };
 
 template <class _Err>
 class __expected_void_base {
   struct __empty_t {};
   // use named union because [[no_unique_address]] cannot be applied to an unnamed union,
   // also guaranteed elision into a potentially-overlapping subobject is unsettled (and
   // it's not clear that it's implementable, given that the function is allowed to clobber
   // the tail padding) - see https://github.com/itanium-cxx-abi/cxx-abi/issues/107.
   union __union_t {
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t(const __union_t&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t(const __union_t&)
       requires(is_copy_constructible_v<_Err> && is_trivially_copy_constructible_v<_Err>)
     = default;
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t(__union_t&&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t(__union_t&&)
       requires(is_move_constructible_v<_Err> && is_trivially_move_constructible_v<_Err>)
     = default;
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t& operator=(const __union_t&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __union_t& operator=(__union_t&&)      = delete;
 
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __union_t(in_place_t) : __empty_() {}
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __union_t(unexpect_t, _Args&&... __args)
         : __unex_(std::forward<_Args>(__args)...) {}
 
     template <class _Func, class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __union_t(
         __expected_construct_unexpected_from_invoke_tag, _Func&& __f, _Args&&... __args)
         : __unex_(std::invoke(std::forward<_Func>(__f), std::forward<_Args>(__args)...)) {}
 
     _LIBCPP_HIDE_FROM_ABI constexpr ~__union_t()
       requires(is_trivially_destructible_v<_Err>)
     = default;
 
     // __repr's destructor handles this
     _LIBCPP_HIDE_FROM_ABI constexpr ~__union_t()
       requires(!is_trivially_destructible_v<_Err>)
     {}
 
     _LIBCPP_NO_UNIQUE_ADDRESS __empty_t __empty_;
     _LIBCPP_NO_UNIQUE_ADDRESS _Err __unex_;
   };
 
   static constexpr bool __put_flag_in_tail                    = __fits_in_tail_padding<__union_t, bool>;
   static constexpr bool __allow_reusing_expected_tail_padding = !__put_flag_in_tail;
 
   struct __repr {
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr() = delete;
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr(in_place_t __tag) : __union_(in_place, __tag), __has_val_(true) {}
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr(unexpect_t __tag, _Args&&... __args)
         : __union_(in_place, __tag, std::forward<_Args>(__args)...), __has_val_(false) {}
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr(std::__expected_construct_unexpected_from_invoke_tag __tag,
                                                     _Args&&... __args)
         : __union_(in_place, __tag, std::forward<_Args>(__args)...), __has_val_(false) {}
 
     template <class _OtherUnion>
     _LIBCPP_HIDE_FROM_ABI constexpr explicit __repr(bool __has_val, _OtherUnion&& __other)
       requires(__allow_reusing_expected_tail_padding)
         : __union_(__conditional_no_unique_address_invoke_tag{},
                    [&] { return __make_union(__has_val, std::forward<_OtherUnion>(__other)); }),
           __has_val_(__has_val) {}
 
     _LIBCPP_HIDE_FROM_ABI constexpr __repr(const __repr&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __repr(const __repr&)
       requires(is_copy_constructible_v<_Err> && is_trivially_copy_constructible_v<_Err>)
     = default;
     _LIBCPP_HIDE_FROM_ABI constexpr __repr(__repr&&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __repr(__repr&&)
       requires(is_move_constructible_v<_Err> && is_trivially_move_constructible_v<_Err>)
     = default;
 
     _LIBCPP_HIDE_FROM_ABI constexpr __repr& operator=(const __repr&) = delete;
     _LIBCPP_HIDE_FROM_ABI constexpr __repr& operator=(__repr&&)      = delete;
 
     _LIBCPP_HIDE_FROM_ABI constexpr ~__repr()
       requires(is_trivially_destructible_v<_Err>)
     = default;
 
     _LIBCPP_HIDE_FROM_ABI constexpr ~__repr()
       requires(!is_trivially_destructible_v<_Err>)
     {
       __destroy_union_member();
     }
 
     _LIBCPP_HIDE_FROM_ABI constexpr void __destroy_union()
       requires(__allow_reusing_expected_tail_padding && is_trivially_destructible_v<_Err>)
     {
       std::destroy_at(&__union_.__v);
     }
 
     _LIBCPP_HIDE_FROM_ABI constexpr void __destroy_union()
       requires(__allow_reusing_expected_tail_padding && !is_trivially_destructible_v<_Err>)
     {
       __destroy_union_member();
       std::destroy_at(&__union_.__v);
     }
 
     _LIBCPP_HIDE_FROM_ABI constexpr void __construct_union(in_place_t)
       requires(__allow_reusing_expected_tail_padding)
     {
       std::construct_at(&__union_.__v, in_place);
       __has_val_ = true;
     }
 
     template <class... _Args>
     _LIBCPP_HIDE_FROM_ABI constexpr void __construct_union(unexpect_t, _Args&&... __args)
       requires(__allow_reusing_expected_tail_padding)
     {
       std::construct_at(&__union_.__v, unexpect, std::forward<_Args>(__args)...);
       __has_val_ = false;
     }
 
   private:
     template <class>
     friend class __expected_void_base;
 
     _LIBCPP_HIDE_FROM_ABI constexpr void __destroy_union_member()
       requires(!is_trivially_destructible_v<_Err>)
     {
       if (!__has_val_)
         std::destroy_at(std::addressof(__union_.__v.__unex_));
     }
 
     template <class _OtherUnion>
     _LIBCPP_HIDE_FROM_ABI static constexpr __union_t __make_union(bool __has_val, _OtherUnion&& __other)
       requires(__allow_reusing_expected_tail_padding)
     {
       if (__has_val)
         return __union_t(in_place);
       else
         return __union_t(unexpect, std::forward<_OtherUnion>(__other).__unex_);
     }
 
     _LIBCPP_NO_UNIQUE_ADDRESS __conditional_no_unique_address<__put_flag_in_tail, __union_t> __union_;
     _LIBCPP_NO_UNIQUE_ADDRESS bool __has_val_;
   };
 
   template <class _OtherUnion>
   _LIBCPP_HIDE_FROM_ABI static constexpr __repr __make_repr(bool __has_val, _OtherUnion&& __other)
     requires(__put_flag_in_tail)
   {
     if (__has_val)
       return __repr(in_place);
     else
       return __repr(unexpect, std::forward<_OtherUnion>(__other).__unex_);
   }
 
 protected:
   template <class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit __expected_void_base(_Args&&... __args)
       : __repr_(in_place, std::forward<_Args>(__args)...) {}
 
   template <class _OtherUnion>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit __expected_void_base(bool __has_val, _OtherUnion&& __other)
     requires(__put_flag_in_tail)
       : __repr_(__conditional_no_unique_address_invoke_tag{},
                 [&] { return __make_repr(__has_val, std::forward<_OtherUnion>(__other)); }) {}
 
   _LIBCPP_HIDE_FROM_ABI constexpr void __destroy() {
     if constexpr (__put_flag_in_tail)
       std::destroy_at(&__repr_.__v);
     else
       __repr_.__v.__destroy_union();
   }
 
   template <class _Tag, class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr void __construct(_Tag __tag, _Args&&... __args) {
     if constexpr (__put_flag_in_tail)
       std::construct_at(&__repr_.__v, __tag, std::forward<_Args>(__args)...);
     else
       __repr_.__v.__construct_union(__tag, std::forward<_Args>(__args)...);
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr bool __has_val() const { return __repr_.__v.__has_val_; }
   _LIBCPP_HIDE_FROM_ABI constexpr __union_t& __union() { return __repr_.__v.__union_.__v; }
   _LIBCPP_HIDE_FROM_ABI constexpr const __union_t& __union() const { return __repr_.__v.__union_.__v; }
   _LIBCPP_HIDE_FROM_ABI constexpr _Err& __unex() { return __repr_.__v.__union_.__v.__unex_; }
   _LIBCPP_HIDE_FROM_ABI constexpr const _Err& __unex() const { return __repr_.__v.__union_.__v.__unex_; }
 
 private:
   _LIBCPP_NO_UNIQUE_ADDRESS __conditional_no_unique_address<__allow_reusing_expected_tail_padding, __repr> __repr_;
 };
 
 template <class _Tp, class _Err>
   requires is_void_v<_Tp>
 class expected<_Tp, _Err> : private __expected_void_base<_Err> {
   static_assert(__valid_std_unexpected<_Err>::value,
                 "[expected.void.general] A program that instantiates expected<T, E> with a E that is not a "
                 "valid argument for unexpected<E> is ill-formed");
 
   template <class, class>
   friend class expected;
 
   template <class _Up, class _OtherErr, class _OtherErrQual>
   using __can_convert =
       _And< is_void<_Up>,
             is_constructible<_Err, _OtherErrQual>,
             _Not<is_constructible<unexpected<_Err>, expected<_Up, _OtherErr>&>>,
             _Not<is_constructible<unexpected<_Err>, expected<_Up, _OtherErr>>>,
             _Not<is_constructible<unexpected<_Err>, const expected<_Up, _OtherErr>&>>,
             _Not<is_constructible<unexpected<_Err>, const expected<_Up, _OtherErr>>>>;
 
   using __base = __expected_void_base<_Err>;
 
 public:
   using value_type      = _Tp;
   using error_type      = _Err;
   using unexpected_type = unexpected<_Err>;
 
   template <class _Up>
   using rebind = expected<_Up, error_type>;
 
   // [expected.void.ctor], constructors
   _LIBCPP_HIDE_FROM_ABI constexpr expected() noexcept : __base(in_place) {}
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected(const expected&) = delete;
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected(const expected&)
     requires(is_copy_constructible_v<_Err> && is_trivially_copy_constructible_v<_Err>)
   = default;
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected(const expected& __rhs) noexcept(
       is_nothrow_copy_constructible_v<_Err>) // strengthened
     requires(is_copy_constructible_v<_Err> && !is_trivially_copy_constructible_v<_Err>)
       : __base(__rhs.__has_val(), __rhs.__union()) {}
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected(expected&&)
     requires(is_move_constructible_v<_Err> && is_trivially_move_constructible_v<_Err>)
   = default;
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected(expected&& __rhs) noexcept(is_nothrow_move_constructible_v<_Err>)
     requires(is_move_constructible_v<_Err> && !is_trivially_move_constructible_v<_Err>)
       : __base(__rhs.__has_val(), std::move(__rhs.__union())) {}
 
   template <class _Up, class _OtherErr>
     requires __can_convert<_Up, _OtherErr, const _OtherErr&>::value
   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<const _OtherErr&, _Err>)
       expected(const expected<_Up, _OtherErr>& __rhs) noexcept(
           is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
       : __base(__rhs.__has_val(), __rhs.__union()) {}
 
   template <class _Up, class _OtherErr>
     requires __can_convert<_Up, _OtherErr, _OtherErr>::value
   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_OtherErr, _Err>)
       expected(expected<_Up, _OtherErr>&& __rhs) noexcept(is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
       : __base(__rhs.__has_val(), std::move(__rhs.__union())) {}
 
   template <class _OtherErr>
     requires is_constructible_v<_Err, const _OtherErr&>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<const _OtherErr&, _Err>) expected(
       const unexpected<_OtherErr>& __unex) noexcept(is_nothrow_constructible_v<_Err, const _OtherErr&>) // strengthened
       : __base(unexpect, __unex.error()) {}
 
   template <class _OtherErr>
     requires is_constructible_v<_Err, _OtherErr>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit(!is_convertible_v<_OtherErr, _Err>)
       expected(unexpected<_OtherErr>&& __unex) noexcept(is_nothrow_constructible_v<_Err, _OtherErr>) // strengthened
       : __base(unexpect, std::move(__unex.error())) {}
 
   _LIBCPP_HIDE_FROM_ABI constexpr explicit expected(in_place_t) noexcept : __base(in_place) {}
 
   template <class... _Args>
     requires is_constructible_v<_Err, _Args...>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit expected(unexpect_t, _Args&&... __args) noexcept(
       is_nothrow_constructible_v<_Err, _Args...>) // strengthened
       : __base(unexpect, std::forward<_Args>(__args)...) {}
 
   template <class _Up, class... _Args>
     requires is_constructible_v< _Err, initializer_list<_Up>&, _Args... >
   _LIBCPP_HIDE_FROM_ABI constexpr explicit expected(unexpect_t, initializer_list<_Up> __il, _Args&&... __args) noexcept(
       is_nothrow_constructible_v<_Err, initializer_list<_Up>&, _Args...>) // strengthened
       : __base(unexpect, __il, std::forward<_Args>(__args)...) {}
 
 private:
   template <class _Func, class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr explicit expected(
       __expected_construct_unexpected_from_invoke_tag __tag, _Func&& __f, _Args&&... __args)
       : __base(__tag, std::forward<_Func>(__f), std::forward<_Args>(__args)...) {}
 
 public:
   // [expected.void.dtor], destructor
 
   _LIBCPP_HIDE_FROM_ABI constexpr ~expected() = default;
 
 private:
   template <class... _Args>
   _LIBCPP_HIDE_FROM_ABI constexpr void __reinit_expected(unexpect_t, _Args&&... __args) {
     _LIBCPP_ASSERT_INTERNAL(this->__has_val(), "__reinit_expected(unexpect_t, ...) needs value to be set");
 
     this->__destroy();
     auto __trans = std::__make_exception_guard([&] { this->__construct(in_place); });
     this->__construct(unexpect, std::forward<_Args>(__args)...);
     __trans.__complete();
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr void __reinit_expected(in_place_t) {
     _LIBCPP_ASSERT_INTERNAL(!this->__has_val(), "__reinit_expected(in_place_t, ...) needs value to be unset");
 
     this->__destroy();
     this->__construct(in_place);
   }
 
 public:
   // [expected.void.assign], assignment
   _LIBCPP_HIDE_FROM_ABI constexpr expected& operator=(const expected&) = delete;
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected& operator=(const expected& __rhs) noexcept(
       is_nothrow_copy_assignable_v<_Err> && is_nothrow_copy_constructible_v<_Err>) // strengthened
     requires(is_copy_assignable_v<_Err> && is_copy_constructible_v<_Err>)
   {
     if (this->__has_val()) {
       if (!__rhs.__has_val()) {
         __reinit_expected(unexpect, __rhs.__unex());
       }
     } else {
       if (__rhs.__has_val()) {
         __reinit_expected(in_place);
       } else {
         this->__unex() = __rhs.__unex();
       }
     }
     return *this;
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected& operator=(expected&&) = delete;
 
   _LIBCPP_HIDE_FROM_ABI constexpr expected&
   operator=(expected&& __rhs) noexcept(is_nothrow_move_assignable_v<_Err> && is_nothrow_move_constructible_v<_Err>)
     requires(is_move_assignable_v<_Err> && is_move_constructible_v<_Err>)
   {
     if (this->__has_val()) {
       if (!__rhs.__has_val()) {
         __reinit_expected(unexpect, std::move(__rhs.__unex()));
       }
     } else {
       if (__rhs.__has_val()) {
         __reinit_expected(in_place);
       } else {
         this->__unex() = std::move(__rhs.__unex());
       }
     }
     return *this;
   }
 
   template <class _OtherErr>
     requires(is_constructible_v<_Err, const _OtherErr&> && is_assignable_v<_Err&, const _OtherErr&>)
   _LIBCPP_HIDE_FROM_ABI constexpr expected& operator=(const unexpected<_OtherErr>& __un) {
     if (this->__has_val()) {
       __reinit_expected(unexpect, __un.error());
     } else {
       this->__unex() = __un.error();
     }
     return *this;
   }
 
   template <class _OtherErr>
     requires(is_constructible_v<_Err, _OtherErr> && is_assignable_v<_Err&, _OtherErr>)
   _LIBCPP_HIDE_FROM_ABI constexpr expected& operator=(unexpected<_OtherErr>&& __un) {
     if (this->__has_val()) {
       __reinit_expected(unexpect, std::move(__un.error()));
     } else {
       this->__unex() = std::move(__un.error());
     }
     return *this;
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr void emplace() noexcept {
     if (!this->__has_val()) {
       __reinit_expected(in_place);
     }
   }
 
   // [expected.void.swap], swap
   _LIBCPP_HIDE_FROM_ABI constexpr void
   swap(expected& __rhs) noexcept(is_nothrow_move_constructible_v<_Err> && is_nothrow_swappable_v<_Err>)
     requires(is_swappable_v<_Err> && is_move_constructible_v<_Err>)
   {
     auto __swap_val_unex_impl = [](expected& __with_val, expected& __with_err) {
       // May throw, but will re-engage `__with_val` in that case.
       __with_val.__reinit_expected(unexpect, std::move(__with_err.__unex()));
       // Will not throw.
       __with_err.__reinit_expected(in_place);
     };
 
     if (this->__has_val()) {
       if (!__rhs.__has_val()) {
         __swap_val_unex_impl(*this, __rhs);
       }
     } else {
       if (__rhs.__has_val()) {
         __swap_val_unex_impl(__rhs, *this);
       } else {
         using std::swap;
         swap(this->__unex(), __rhs.__unex());
       }
     }
   }
 
   _LIBCPP_HIDE_FROM_ABI friend constexpr void swap(expected& __x, expected& __y) noexcept(noexcept(__x.swap(__y)))
     requires requires { __x.swap(__y); }
   {
     __x.swap(__y);
   }
 
   // [expected.void.obs], observers
   _LIBCPP_HIDE_FROM_ABI constexpr explicit operator bool() const noexcept { return this->__has_val(); }
 
   _LIBCPP_HIDE_FROM_ABI constexpr bool has_value() const noexcept { return this->__has_val(); }
 
   _LIBCPP_HIDE_FROM_ABI constexpr void operator*() const noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         this->__has_val(), "expected::operator* requires the expected to contain a value");
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr void value() const& {
     static_assert(is_copy_constructible_v<_Err>);
     if (!this->__has_val()) {
       std::__throw_bad_expected_access<_Err>(this->__unex());
     }
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr void value() && {
     static_assert(is_copy_constructible_v<_Err> && is_move_constructible_v<_Err>);
     if (!this->__has_val()) {
       std::__throw_bad_expected_access<_Err>(std::move(this->__unex()));
     }
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr const _Err& error() const& noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         !this->__has_val(), "expected::error requires the expected to contain an error");
     return this->__unex();
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr _Err& error() & noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         !this->__has_val(), "expected::error requires the expected to contain an error");
     return this->__unex();
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr const _Err&& error() const&& noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         !this->__has_val(), "expected::error requires the expected to contain an error");
     return std::move(this->__unex());
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr _Err&& error() && noexcept {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         !this->__has_val(), "expected::error requires the expected to contain an error");
     return std::move(this->__unex());
   }
 
   template <class _Up = _Err>
   _LIBCPP_HIDE_FROM_ABI constexpr _Err error_or(_Up&& __error) const& {
     static_assert(is_copy_constructible_v<_Err>, "error_type has to be copy constructible");
     static_assert(is_convertible_v<_Up, _Err>, "argument has to be convertible to error_type");
     if (has_value()) {
       return std::forward<_Up>(__error);
     }
     return error();
   }
 
   template <class _Up = _Err>
   _LIBCPP_HIDE_FROM_ABI constexpr _Err error_or(_Up&& __error) && {
     static_assert(is_move_constructible_v<_Err>, "error_type has to be move constructible");
     static_assert(is_convertible_v<_Up, _Err>, "argument has to be convertible to error_type");
     if (has_value()) {
       return std::forward<_Up>(__error);
     }
     return std::move(error());
   }
 
   // [expected.void.monadic], monadic
   template <class _Func>
     requires is_constructible_v<_Err, _Err&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto and_then(_Func&& __f) & {
     using _Up = remove_cvref_t<invoke_result_t<_Func>>;
     static_assert(__is_std_expected<_Up>::value, "The result of f() must be a specialization of std::expected");
     static_assert(
         is_same_v<typename _Up::error_type, _Err>, "The result of f() must have the same error_type as this expected");
     if (has_value()) {
       return std::invoke(std::forward<_Func>(__f));
     }
     return _Up(unexpect, error());
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, const _Err&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto and_then(_Func&& __f) const& {
     using _Up = remove_cvref_t<invoke_result_t<_Func>>;
     static_assert(__is_std_expected<_Up>::value, "The result of f() must be a specialization of std::expected");
     static_assert(
         is_same_v<typename _Up::error_type, _Err>, "The result of f() must have the same error_type as this expected");
     if (has_value()) {
       return std::invoke(std::forward<_Func>(__f));
     }
     return _Up(unexpect, error());
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, _Err&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto and_then(_Func&& __f) && {
     using _Up = remove_cvref_t<invoke_result_t<_Func>>;
     static_assert(__is_std_expected<_Up>::value, "The result of f() must be a specialization of std::expected");
     static_assert(
         is_same_v<typename _Up::error_type, _Err>, "The result of f() must have the same error_type as this expected");
     if (has_value()) {
       return std::invoke(std::forward<_Func>(__f));
     }
     return _Up(unexpect, std::move(error()));
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, const _Err&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto and_then(_Func&& __f) const&& {
     using _Up = remove_cvref_t<invoke_result_t<_Func>>;
     static_assert(__is_std_expected<_Up>::value, "The result of f() must be a specialization of std::expected");
     static_assert(
         is_same_v<typename _Up::error_type, _Err>, "The result of f() must have the same error_type as this expected");
     if (has_value()) {
       return std::invoke(std::forward<_Func>(__f));
     }
     return _Up(unexpect, std::move(error()));
   }
 
   template <class _Func>
   _LIBCPP_HIDE_FROM_ABI constexpr auto or_else(_Func&& __f) & {
     using _Gp = remove_cvref_t<invoke_result_t<_Func, _Err&>>;
     static_assert(__is_std_expected<_Gp>::value, "The result of f(error()) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Gp::value_type, _Tp>,
                   "The result of f(error()) must have the same value_type as this expected");
     if (has_value()) {
       return _Gp();
     }
     return std::invoke(std::forward<_Func>(__f), error());
   }
 
   template <class _Func>
   _LIBCPP_HIDE_FROM_ABI constexpr auto or_else(_Func&& __f) const& {
     using _Gp = remove_cvref_t<invoke_result_t<_Func, const _Err&>>;
     static_assert(__is_std_expected<_Gp>::value, "The result of f(error()) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Gp::value_type, _Tp>,
                   "The result of f(error()) must have the same value_type as this expected");
     if (has_value()) {
       return _Gp();
     }
     return std::invoke(std::forward<_Func>(__f), error());
   }
 
   template <class _Func>
   _LIBCPP_HIDE_FROM_ABI constexpr auto or_else(_Func&& __f) && {
     using _Gp = remove_cvref_t<invoke_result_t<_Func, _Err&&>>;
     static_assert(
         __is_std_expected<_Gp>::value, "The result of f(std::move(error())) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Gp::value_type, _Tp>,
                   "The result of f(std::move(error())) must have the same value_type as this expected");
     if (has_value()) {
       return _Gp();
     }
     return std::invoke(std::forward<_Func>(__f), std::move(error()));
   }
 
   template <class _Func>
   _LIBCPP_HIDE_FROM_ABI constexpr auto or_else(_Func&& __f) const&& {
     using _Gp = remove_cvref_t<invoke_result_t<_Func, const _Err&&>>;
     static_assert(
         __is_std_expected<_Gp>::value, "The result of f(std::move(error())) must be a specialization of std::expected");
     static_assert(is_same_v<typename _Gp::value_type, _Tp>,
                   "The result of f(std::move(error())) must have the same value_type as this expected");
     if (has_value()) {
       return _Gp();
     }
     return std::invoke(std::forward<_Func>(__f), std::move(error()));
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, _Err&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform(_Func&& __f) & {
     using _Up = remove_cv_t<invoke_result_t<_Func>>;
     if (!has_value()) {
       return expected<_Up, _Err>(unexpect, error());
     }
     if constexpr (!is_void_v<_Up>) {
       return expected<_Up, _Err>(__expected_construct_in_place_from_invoke_tag{}, std::forward<_Func>(__f));
     } else {
       std::invoke(std::forward<_Func>(__f));
       return expected<_Up, _Err>();
     }
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, const _Err&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform(_Func&& __f) const& {
     using _Up = remove_cv_t<invoke_result_t<_Func>>;
     if (!has_value()) {
       return expected<_Up, _Err>(unexpect, error());
     }
     if constexpr (!is_void_v<_Up>) {
       return expected<_Up, _Err>(__expected_construct_in_place_from_invoke_tag{}, std::forward<_Func>(__f));
     } else {
       std::invoke(std::forward<_Func>(__f));
       return expected<_Up, _Err>();
     }
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, _Err&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform(_Func&& __f) && {
     using _Up = remove_cv_t<invoke_result_t<_Func>>;
     if (!has_value()) {
       return expected<_Up, _Err>(unexpect, std::move(error()));
     }
     if constexpr (!is_void_v<_Up>) {
       return expected<_Up, _Err>(__expected_construct_in_place_from_invoke_tag{}, std::forward<_Func>(__f));
     } else {
       std::invoke(std::forward<_Func>(__f));
       return expected<_Up, _Err>();
     }
   }
 
   template <class _Func>
     requires is_constructible_v<_Err, const _Err&&>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform(_Func&& __f) const&& {
     using _Up = remove_cv_t<invoke_result_t<_Func>>;
     if (!has_value()) {
       return expected<_Up, _Err>(unexpect, std::move(error()));
     }
     if constexpr (!is_void_v<_Up>) {
       return expected<_Up, _Err>(__expected_construct_in_place_from_invoke_tag{}, std::forward<_Func>(__f));
     } else {
       std::invoke(std::forward<_Func>(__f));
       return expected<_Up, _Err>();
     }
   }
 
   template <class _Func>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform_error(_Func&& __f) & {
     using _Gp = remove_cv_t<invoke_result_t<_Func, _Err&>>;
     static_assert(__valid_std_unexpected<_Gp>::value,
                   "The result of f(error()) must be a valid template argument for unexpected");
     if (has_value()) {
       return expected<_Tp, _Gp>();
     }
     return expected<_Tp, _Gp>(__expected_construct_unexpected_from_invoke_tag{}, std::forward<_Func>(__f), error());
   }
 
   template <class _Func>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform_error(_Func&& __f) const& {
     using _Gp = remove_cv_t<invoke_result_t<_Func, const _Err&>>;
     static_assert(__valid_std_unexpected<_Gp>::value,
                   "The result of f(error()) must be a valid template argument for unexpected");
     if (has_value()) {
       return expected<_Tp, _Gp>();
     }
     return expected<_Tp, _Gp>(__expected_construct_unexpected_from_invoke_tag{}, std::forward<_Func>(__f), error());
   }
 
   template <class _Func>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform_error(_Func&& __f) && {
     using _Gp = remove_cv_t<invoke_result_t<_Func, _Err&&>>;
     static_assert(__valid_std_unexpected<_Gp>::value,
                   "The result of f(std::move(error())) must be a valid template argument for unexpected");
     if (has_value()) {
       return expected<_Tp, _Gp>();
     }
     return expected<_Tp, _Gp>(
         __expected_construct_unexpected_from_invoke_tag{}, std::forward<_Func>(__f), std::move(error()));
   }
 
   template <class _Func>
   _LIBCPP_HIDE_FROM_ABI constexpr auto transform_error(_Func&& __f) const&& {
     using _Gp = remove_cv_t<invoke_result_t<_Func, const _Err&&>>;
     static_assert(__valid_std_unexpected<_Gp>::value,
                   "The result of f(std::move(error())) must be a valid template argument for unexpected");
     if (has_value()) {
       return expected<_Tp, _Gp>();
     }
     return expected<_Tp, _Gp>(
         __expected_construct_unexpected_from_invoke_tag{}, std::forward<_Func>(__f), std::move(error()));
   }
 
   // [expected.void.eq], equality operators
   template <class _T2, class _E2>
     requires is_void_v<_T2>
   _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const expected<_T2, _E2>& __y) {
     if (__x.__has_val() != __y.__has_val()) {
       return false;
     } else {
       return __x.__has_val() || static_cast<bool>(__x.__unex() == __y.__unex());
     }
   }
 
   template <class _E2>
   _LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(const expected& __x, const unexpected<_E2>& __y) {
     return !__x.__has_val() && static_cast<bool>(__x.__unex() == __y.error());
   }
 };
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP_STD_VER >= 23
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP___CXX03___EXPECTED_EXPECTED_H

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