/* Essentially an internal optional implementation :)
(C) 2017-2025 Niall Douglas <http://www.nedproductions.biz/> (24 commits)
File Created: June 2017


Boost Software License - Version 1.0 - August 17th, 2003

Permission is hereby granted, free of charge, to any person or organization
obtaining a copy of the software and accompanying documentation covered by
this license (the "Software") to use, reproduce, display, distribute,
execute, and transmit the Software, and to prepare derivative works of the
Software, and to permit third-parties to whom the Software is furnished to
do so, all subject to the following:

The copyright notices in the Software and this entire statement, including
the above license grant, this restriction and the following disclaimer,
must be included in all copies of the Software, in whole or in part, and
all derivative works of the Software, unless such copies or derivative
works are solely in the form of machine-executable object code generated by
a source language processor.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
*/

#ifndef BOOST_OUTCOME_VALUE_STORAGE_HPP
#define BOOST_OUTCOME_VALUE_STORAGE_HPP

#include "../config.hpp"

BOOST_OUTCOME_V2_NAMESPACE_EXPORT_BEGIN

namespace detail
{
  // Helpers for move assigning to empty storage
  template <class T, bool isCopyOrMoveConstructible = std::is_copy_constructible<T>::value || std::is_move_constructible<T>::value,
            bool isDefaultConstructibleAndCopyOrMoveAssignable =
            std::is_default_constructible<T>::value && (std::is_copy_assignable<T>::value || std::is_move_assignable<T>::value)>
  struct move_assign_to_empty;
  // Prefer to use move or copy construction
  template <class T> struct move_assign_to_empty<T, true, false>
  {
    move_assign_to_empty(T *dest, T *o) noexcept(std::is_nothrow_move_constructible<T>::value) { new(dest) T(static_cast<T &&>(*o)); }
  };
  template <class T> struct move_assign_to_empty<T, true, true>
  {
    move_assign_to_empty(T *dest, T *o) noexcept(std::is_nothrow_move_constructible<T>::value) { new(dest) T(static_cast<T &&>(*o)); }
  };
  // But fall back on default construction and move assign if necessary
  template <class T> struct move_assign_to_empty<T, false, true>
  {
    move_assign_to_empty(T *dest, T *o) noexcept(std::is_nothrow_default_constructible<T>::value && std::is_nothrow_move_assignable<T>::value)
    {
      new(dest) T;
      *dest = static_cast<T &&>(*o);
    }
  };
  // Void does nothing
  template <> struct move_assign_to_empty<void, false, false>
  {
    move_assign_to_empty(void *, void *) noexcept { /* nothing to assign */ }
  };
  template <> struct move_assign_to_empty<const void, false, false>
  {
    move_assign_to_empty(const void *, const void *) noexcept { /* nothing to assign */ }
  };
  // Helpers for copy assigning to empty storage
  template <class T, bool isCopyConstructible = std::is_copy_constructible<T>::value,
            bool isDefaultConstructibleAndCopyAssignable = std::is_default_constructible<T>::value && std::is_copy_assignable<T>::value>
  struct copy_assign_to_empty;
  // Prefer to use copy construction
  template <class T> struct copy_assign_to_empty<T, true, false>
  {
    copy_assign_to_empty(T *dest, const T *o) noexcept(std::is_nothrow_copy_constructible<T>::value) { new(dest) T(*o); }
  };
  template <class T> struct copy_assign_to_empty<T, true, true>
  {
    copy_assign_to_empty(T *dest, const T *o) noexcept(std::is_nothrow_copy_constructible<T>::value) { new(dest) T(*o); }
  };
  // But fall back on default construction and copy assign if necessary
  template <class T> struct copy_assign_to_empty<T, false, true>
  {
    copy_assign_to_empty(T *dest, const T *o) noexcept(std::is_nothrow_default_constructible<T>::value && std::is_nothrow_copy_assignable<T>::value)
    {
      new(dest) T;
      *dest = *o;
    }
  };
  // Void does nothing
  template <> struct copy_assign_to_empty<void, false, false>
  {
    copy_assign_to_empty(void *, void *) noexcept { /* nothing to assign */ }
  };
  template <> struct copy_assign_to_empty<const void, false, false>
  {
    copy_assign_to_empty(const void *, const void *) noexcept { /* nothing to assign */ }
  };

  template <class T, bool nothrow> struct strong_swap_impl
  {
    constexpr strong_swap_impl(bool &allgood, T &a, T &b)
    {
      allgood = true;
      using std::swap;
      swap(a, b);
    }
  };
  template <class T, bool nothrow> struct strong_placement_impl
  {
    template <class F> constexpr strong_placement_impl(bool &allgood, T *a, T *b, F &&f)
    {
      allgood = true;
      new(a) T(static_cast<T &&>(*b));
      b->~T();
      f();
    }
  };
#ifndef BOOST_NO_EXCEPTIONS
  template <class T> struct strong_swap_impl<T, false>
  {
    strong_swap_impl(bool &allgood, T &a, T &b)
    {
      allgood = true;
      T v(static_cast<T &&>(a));
      try
      {
        a = static_cast<T &&>(b);
      }
      catch(...)
      {
        // Try to put back a
        try
        {
          a = static_cast<T &&>(v);
          // fall through as all good
        }
        catch(...)
        {
          // failed to completely restore
          allgood = false;
          // throw away second exception
        }
        throw;  // rethrow original exception
      }
      // b has been moved to a, try to move v to b
      try
      {
        b = static_cast<T &&>(v);
      }
      catch(...)
      {
        // Try to restore a to b, and v to a
        try
        {
          b = static_cast<T &&>(a);
          a = static_cast<T &&>(v);
          // fall through as all good
        }
        catch(...)
        {
          // failed to completely restore
          allgood = false;
          // throw away second exception
        }
        throw;  // rethrow original exception
      }
    }
  };
  template <class T> struct strong_placement_impl<T, false>
  {
    template <class F> strong_placement_impl(bool &allgood, T *a, T *b, F &&f)
    {
      new(a) T(static_cast<T &&>(*b));
      try
      {
        b->~T();
        f();
      }
      catch(...)
      {
        // Try to put back a, but only if we are still good
        if(allgood)
        {
          try
          {
            new(b) T(static_cast<T &&>(*a));
            // fall through as all good
          }
          catch(...)
          {
            // failed to completely restore
            allgood = false;
            // throw away second exception
          }
          throw;  // rethrow original exception
        }
      }
    }
  };
#endif
}  // namespace detail

/*!
 */
BOOST_OUTCOME_TEMPLATE(class T)
BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(std::is_move_constructible<T>::value &&std::is_move_assignable<T>::value))
constexpr inline void strong_swap(bool &allgood, T &a, T &b) noexcept(detail::is_nothrow_swappable<T>::value)
{
  detail::strong_swap_impl<T, detail::is_nothrow_swappable<T>::value>(allgood, a, b);
}
/*!
 */
BOOST_OUTCOME_TEMPLATE(class T, class F)
BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(std::is_move_constructible<T>::value &&std::is_move_assignable<T>::value))
constexpr inline void strong_placement(bool &allgood, T *a, T *b, F &&f) noexcept(std::is_nothrow_move_constructible<T>::value)
{
  detail::strong_placement_impl<T, std::is_nothrow_move_constructible<T>::value>(allgood, a, b, static_cast<F &&>(f));
}

namespace detail
{
  template <class T>
  constexpr
#ifdef _MSC_VER
  __declspec(noreturn)
#elif defined(__GNUC__) || defined(__clang__)
  __attribute__((noreturn))
#endif
  void
  make_ub(T && /*unused*/)
  {
    BOOST_OUTCOME_ASSERT(false);  // NOLINT
#if defined(__GNUC__) || defined(__clang__)
    __builtin_unreachable();
#elif defined(_MSC_VER)
    __assume(0);
#endif
  }

  /* Outcome v1 used a C bitfield whose values were tracked by compiler optimisers nicely,
  but that produces ICEs when used in constexpr.

  Outcome v2.0-v2.1 used a 32 bit integer and manually set and cleared bits. Unfortunately
  only GCC's optimiser tracks bit values during constant folding, and only per byte, and
  even then unreliably. https://wg21.link/P1886 "Error speed benchmarking" showed just how
  poorly clang and MSVC fails to optimise outcome-using code, if you manually set bits.

  Outcome v2.2 therefore uses an enum with fixed values, and constexpr manipulation functions
  to change the value to one of the enum's values. This is stupid to look at in source code,
  but it make clang's optimiser do the right thing, so it's worth it.
  */
  enum class status : uint16_t
  {
    // WARNING: These bits are not tracked by abi-dumper, but changing them will break ABI!
    // bits 0-5 in use.
    none = 0,

    have_value = (1U << 0U),
    have_error = (1U << 1U),
    have_exception = (2U << 1U),
    have_error_exception = (3U << 1U),

    // failed to complete a strong swap
    have_lost_consistency = (1U << 3U),

    have_value_lost_consistency = (1U << 0U) | (1U << 3U),
    have_error_lost_consistency = (1U << 1U) | (1U << 3U),
    have_exception_lost_consistency = (2U << 1U) | (1U << 3U),
    have_error_exception_lost_consistency = (3U << 1U) | (1U << 3U),

    // can errno be set from this error?
    have_error_is_errno = (1U << 4U),

    have_error_error_is_errno = (1U << 1U) | (1U << 4U),
    have_error_exception_error_is_errno = (3U << 1U) | (1U << 4U),

    have_error_lost_consistency_error_is_errno = (1U << 1U) | (1U << 3U) | (1U << 4U),
    have_error_exception_lost_consistency_error_is_errno = (3U << 1U) | (1U << 3U) | (1U << 4U),

    // value has been moved from
    have_moved_from = (1U << 5U),

    have_value_moved_from = (1U << 0U) | (1U << 5U),
    have_error_moved_from = (1U << 1U) | (1U << 5U),
    have_exception_moved_from = (2U << 1U) | (1U << 5U),
    have_error_exception_moved_from = (3U << 1U) | (1U << 5U),

    have_value_lost_consistency_moved_from = (1U << 0U) | (1U << 3U) | (1U << 5U),
    have_error_lost_consistency_moved_from = (1U << 1U) | (1U << 3U) | (1U << 5U),
    have_exception_lost_consistency_moved_from = (2U << 1U) | (1U << 3U) | (1U << 5U),
    have_error_exception_lost_consistency_moved_from = (3U << 1U) | (1U << 3U) | (1U << 5U),

    have_error_is_errno_moved_from = (1U << 4U) | (1U << 5U),
    have_error_error_is_errno_moved_from = (1U << 1U) | (1U << 4U) | (1U << 5U),
    have_error_exception_error_is_errno_moved_from = (3U << 1U) | (1U << 4U) | (1U << 5U),

    have_error_lost_consistency_error_is_errno_moved_from = (1U << 1U) | (1U << 3U) | (1U << 4U) | (1U << 5U),
    have_error_exception_lost_consistency_error_is_errno_moved_from = (3U << 1U) | (1U << 3U) | (1U << 4U) | (1U << 5U),
  };
  struct status_bitfield_type
  {
    status status_value{status::none};
    uint16_t spare_storage_value{0};  // hooks::spare_storage()

    constexpr status_bitfield_type() = default;
    constexpr status_bitfield_type(status v) noexcept
        : status_value(v)
    {
    }  // NOLINT
    constexpr status_bitfield_type(status v, uint16_t s) noexcept
        : status_value(v)
        , spare_storage_value(s)
    {
    }
    constexpr status_bitfield_type(const status_bitfield_type &) = default;
    constexpr status_bitfield_type(status_bitfield_type &&) = default;
    constexpr status_bitfield_type &operator=(const status_bitfield_type &) = default;
    constexpr status_bitfield_type &operator=(status_bitfield_type &&) = default;
    //~status_bitfield_type() = default;  // Do NOT uncomment this, it breaks older clangs!

    constexpr bool have_value() const noexcept { return (static_cast<uint16_t>(status_value) & static_cast<uint16_t>(status::have_value)) != 0; }
    constexpr bool have_error() const noexcept { return (static_cast<uint16_t>(status_value) & static_cast<uint16_t>(status::have_error)) != 0; }
    constexpr bool have_exception() const noexcept { return (static_cast<uint16_t>(status_value) & static_cast<uint16_t>(status::have_exception)) != 0; }
    constexpr bool have_lost_consistency() const noexcept
    {
      return (static_cast<uint16_t>(status_value) & static_cast<uint16_t>(status::have_lost_consistency)) != 0;
    }
    constexpr bool have_error_is_errno() const noexcept
    {
      return (static_cast<uint16_t>(status_value) & static_cast<uint16_t>(status::have_error_is_errno)) != 0;
    }
    constexpr bool have_moved_from() const noexcept { return (static_cast<uint16_t>(status_value) & static_cast<uint16_t>(status::have_moved_from)) != 0; }

    constexpr status_bitfield_type &set_have_value(bool v) noexcept
    {
      status_value = static_cast<status>(v ? (static_cast<uint16_t>(status_value) | static_cast<uint16_t>(status::have_value)) :
                                             (static_cast<uint16_t>(status_value) & ~static_cast<uint16_t>(status::have_value)));
      return *this;
    }
    constexpr status_bitfield_type &set_have_error(bool v) noexcept
    {
      status_value = static_cast<status>(v ? (static_cast<uint16_t>(status_value) | static_cast<uint16_t>(status::have_error)) :
                                             (static_cast<uint16_t>(status_value) & ~static_cast<uint16_t>(status::have_error)));
      return *this;
    }
    constexpr status_bitfield_type &set_have_exception(bool v) noexcept
    {
      status_value = static_cast<status>(v ? (static_cast<uint16_t>(status_value) | static_cast<uint16_t>(status::have_exception)) :
                                             (static_cast<uint16_t>(status_value) & ~static_cast<uint16_t>(status::have_exception)));
      return *this;
    }
    constexpr status_bitfield_type &set_have_error_is_errno(bool v) noexcept
    {
      status_value = static_cast<status>(v ? (static_cast<uint16_t>(status_value) | static_cast<uint16_t>(status::have_error_is_errno)) :
                                             (static_cast<uint16_t>(status_value) & ~static_cast<uint16_t>(status::have_error_is_errno)));
      return *this;
    }
    constexpr status_bitfield_type &set_have_lost_consistency(bool v) noexcept
    {
      status_value = static_cast<status>(v ? (static_cast<uint16_t>(status_value) | static_cast<uint16_t>(status::have_lost_consistency)) :
                                             (static_cast<uint16_t>(status_value) & ~static_cast<uint16_t>(status::have_lost_consistency)));
      return *this;
    }
    constexpr status_bitfield_type &set_have_moved_from(bool v) noexcept
    {
      status_value = static_cast<status>(v ? (static_cast<uint16_t>(status_value) | static_cast<uint16_t>(status::have_moved_from)) :
                                             (static_cast<uint16_t>(status_value) & ~static_cast<uint16_t>(status::have_moved_from)));
      return *this;
    }
  };
#if !defined(NDEBUG)
  // Check is trivial in all ways except default constructibility
  static_assert(sizeof(status_bitfield_type) == 4, "status_bitfield_type is not sized 4 bytes!");
  static_assert(std::is_trivially_copyable<status_bitfield_type>::value, "status_bitfield_type is not trivially copyable!");
  static_assert(std::is_trivially_assignable<status_bitfield_type, status_bitfield_type>::value, "status_bitfield_type is not trivially assignable!");
  static_assert(std::is_trivially_destructible<status_bitfield_type>::value, "status_bitfield_type is not trivially destructible!");
  static_assert(std::is_trivially_copy_constructible<status_bitfield_type>::value, "status_bitfield_type is not trivially copy constructible!");
  static_assert(std::is_trivially_move_constructible<status_bitfield_type>::value, "status_bitfield_type is not trivially move constructible!");
  static_assert(std::is_trivially_copy_assignable<status_bitfield_type>::value, "status_bitfield_type is not trivially copy assignable!");
  static_assert(std::is_trivially_move_assignable<status_bitfield_type>::value, "status_bitfield_type is not trivially move assignable!");
  // Also check is standard layout
  static_assert(std::is_standard_layout<status_bitfield_type>::value, "status_bitfield_type is not a standard layout type!");
#endif

  template <class State> constexpr inline void _set_error_is_errno(State & /*unused*/) {}

#ifdef _MSC_VER
#pragma warning(push)
#pragma warning(disable : 4127)  // conditional expression is constant
#pragma warning(disable : 4624)  // destructor was implicitly defined as deleted
#endif
  // Used if both T and E are trivial
  template <class T, class E> struct value_storage_trivial
  {
    using value_type = T;
    using error_type = E;

    // Disable in place construction if they are the same type
    struct disable_in_place_value_type
    {
    };
    struct disable_in_place_error_type
    {
    };
    using _value_type = std::conditional_t<std::is_same<value_type, error_type>::value, disable_in_place_value_type, value_type>;
    using _error_type = std::conditional_t<std::is_same<value_type, error_type>::value, disable_in_place_error_type, error_type>;
    using _value_type_ = devoid<value_type>;
    using _error_type_ = devoid<error_type>;

    union
    {
      empty_type _empty;
      _value_type_ _value;
      _error_type_ _error;
    };
    status_bitfield_type _status;
    constexpr value_storage_trivial() noexcept
        : _empty{}
    {
    }
    value_storage_trivial(const value_storage_trivial &) = default;             // NOLINT
    value_storage_trivial(value_storage_trivial &&) = default;                  // NOLINT
    value_storage_trivial &operator=(const value_storage_trivial &) = default;  // NOLINT
    value_storage_trivial &operator=(value_storage_trivial &&) = default;       // NOLINT
    ~value_storage_trivial() = default;
    constexpr explicit value_storage_trivial(status_bitfield_type status)
        : _empty()
        , _status(status)
    {
    }
    template <class... Args>
    constexpr explicit value_storage_trivial(in_place_type_t<_value_type> /*unused*/,
                                             Args &&...args) noexcept(detail::is_nothrow_constructible<_value_type_, Args...>)
        : _value(static_cast<Args &&>(args)...)
        , _status(status::have_value)
    {
    }
    template <class U, class... Args>
    constexpr value_storage_trivial(in_place_type_t<_value_type> /*unused*/, std::initializer_list<U> il,
                                    Args &&...args) noexcept(detail::is_nothrow_constructible<_value_type_, std::initializer_list<U>, Args...>)
        : _value(il, static_cast<Args &&>(args)...)
        , _status(status::have_value)
    {
    }
    template <class... Args>
    constexpr explicit value_storage_trivial(in_place_type_t<_error_type> /*unused*/,
                                             Args &&...args) noexcept(detail::is_nothrow_constructible<_error_type_, Args...>)
        : _error(static_cast<Args &&>(args)...)
        , _status(status::have_error)
    {
      _set_error_is_errno(*this);
    }
    template <class U, class... Args>
    constexpr value_storage_trivial(in_place_type_t<_error_type> /*unused*/, std::initializer_list<U> il,
                                    Args &&...args) noexcept(detail::is_nothrow_constructible<_error_type_, std::initializer_list<U>, Args...>)
        : _error(il, static_cast<Args &&>(args)...)
        , _status(status::have_error)
    {
      _set_error_is_errno(*this);
    }

    struct nonvoid_converting_constructor_tag
    {
    };
    template <class U, class V>
    static constexpr bool enable_nonvoid_converting_constructor =
    !(std::is_same<std::decay_t<U>, value_type>::value && std::is_same<std::decay_t<V>, error_type>::value)  //
    && detail::is_constructible<value_type, U> && detail::is_constructible<error_type, V>;
    BOOST_OUTCOME_TEMPLATE(class U, class V)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_nonvoid_converting_constructor<U, V>))
    constexpr explicit value_storage_trivial(const value_storage_trivial<U, V> &o,
                                             nonvoid_converting_constructor_tag /*unused*/ = {}) noexcept(detail::is_nothrow_constructible<_value_type_, U> &&
                                                                                                          detail::is_nothrow_constructible<_error_type_, V>)
        : value_storage_trivial(o._status.have_value() ?
                                value_storage_trivial(in_place_type<value_type>, o._value) :
                                (o._status.have_error() ? value_storage_trivial(in_place_type<error_type>, o._error) : value_storage_trivial()))  // NOLINT
    {
      _status = o._status;
    }
    BOOST_OUTCOME_TEMPLATE(class U, class V)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_nonvoid_converting_constructor<U, V>))
    constexpr explicit value_storage_trivial(value_storage_trivial<U, V> &&o,
                                             nonvoid_converting_constructor_tag /*unused*/ = {}) noexcept(detail::is_nothrow_constructible<_value_type_, U> &&
                                                                                                          detail::is_nothrow_constructible<_error_type_, V>)
        : value_storage_trivial(
          o._status.have_value() ?
          value_storage_trivial(in_place_type<value_type>, static_cast<U &&>(o._value)) :
          (o._status.have_error() ? value_storage_trivial(in_place_type<error_type>, static_cast<V &&>(o._error)) : value_storage_trivial()))  // NOLINT
    {
      _status = o._status;
    }

    struct void_value_converting_constructor_tag
    {
    };
    template <class V>
    static constexpr bool enable_void_value_converting_constructor =
    std::is_default_constructible<value_type>::value && detail::is_constructible<error_type, V>;
    BOOST_OUTCOME_TEMPLATE(class V)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_void_value_converting_constructor<V>))
    constexpr explicit value_storage_trivial(const value_storage_trivial<void, V> &o, void_value_converting_constructor_tag /*unused*/ = {}) noexcept(
    std::is_nothrow_default_constructible<_value_type_>::value && detail::is_nothrow_constructible<_error_type_, V>)
        : value_storage_trivial(o._status.have_value() ?
                                value_storage_trivial(in_place_type<value_type>) :
                                (o._status.have_error() ? value_storage_trivial(in_place_type<error_type>, o._error) : value_storage_trivial()))  // NOLINT
    {
      _status = o._status;
    }
    BOOST_OUTCOME_TEMPLATE(class V)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_void_value_converting_constructor<V>))
    constexpr explicit value_storage_trivial(value_storage_trivial<void, V> &&o, void_value_converting_constructor_tag /*unused*/ = {}) noexcept(
    std::is_nothrow_default_constructible<_value_type_>::value && detail::is_nothrow_constructible<_error_type_, V>)
        : value_storage_trivial(
          o._status.have_value() ?
          value_storage_trivial(in_place_type<value_type>) :
          (o._status.have_error() ? value_storage_trivial(in_place_type<error_type>, static_cast<V &&>(o._error)) : value_storage_trivial()))  // NOLINT
    {
      _status = o._status;
    }

    struct void_error_converting_constructor_tag
    {
    };
    template <class U>
    static constexpr bool enable_void_error_converting_constructor =
    std::is_default_constructible<error_type>::value && detail::is_constructible<value_type, U>;
    BOOST_OUTCOME_TEMPLATE(class U)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_void_error_converting_constructor<U>))
    constexpr explicit value_storage_trivial(const value_storage_trivial<U, void> &o, void_error_converting_constructor_tag /*unused*/ = {}) noexcept(
    detail::is_nothrow_constructible<_value_type_, U> && std::is_nothrow_default_constructible<_error_type_>::value)
        : value_storage_trivial(o._status.have_value() ?
                                value_storage_trivial(in_place_type<value_type>, o._value) :
                                (o._status.have_error() ? value_storage_trivial(in_place_type<error_type>) : value_storage_trivial()))  // NOLINT
    {
      _status = o._status;
    }
    BOOST_OUTCOME_TEMPLATE(class U)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_void_error_converting_constructor<U>))
    constexpr explicit value_storage_trivial(value_storage_trivial<U, void> &&o, void_error_converting_constructor_tag /*unused*/ = {}) noexcept(
    detail::is_nothrow_constructible<_value_type_, U> && std::is_nothrow_default_constructible<_error_type_>::value)
        : value_storage_trivial(o._status.have_value() ?
                                value_storage_trivial(in_place_type<value_type>, static_cast<U &&>(o._value)) :
                                (o._status.have_error() ? value_storage_trivial(in_place_type<error_type>) : value_storage_trivial()))  // NOLINT
    {
      _status = o._status;
    }
    constexpr void swap(value_storage_trivial &o) noexcept
    {
      // storage is trivial, so just use assignment
      auto temp = static_cast<value_storage_trivial &&>(*this);
      *this = static_cast<value_storage_trivial &&>(o);
      o = static_cast<value_storage_trivial &&>(temp);
    }
  };

  /* Used if T or E is non-trivial. The additional constexpr is injected in C++ 20 to enable Outcome to
  work in constexpr evaluation contexts in C++ 20 where non-trivial constexpr destructors are now allowed.
  */
  template <class T, class E> struct value_storage_nontrivial
  {
    using value_type = T;
    using error_type = E;
    struct disable_in_place_value_type
    {
    };
    struct disable_in_place_error_type
    {
    };
    using _value_type = std::conditional_t<std::is_same<value_type, error_type>::value, disable_in_place_value_type, value_type>;
    using _error_type = std::conditional_t<std::is_same<value_type, error_type>::value, disable_in_place_error_type, error_type>;
    using _value_type_ = devoid<value_type>;
    using _error_type_ = devoid<error_type>;

    union
    {
      empty_type _empty1;
      _value_type_ _value;
    };
    status_bitfield_type _status;
    union
    {
      empty_type _empty2;
      _error_type_ _error;
    };
#if __cplusplus >= 202000L || _HAS_CXX20
    constexpr
#endif
    value_storage_nontrivial() noexcept
        : _empty1{}
        , _empty2{}
    {
    }
    value_storage_nontrivial &operator=(const value_storage_nontrivial &) = default;  // if reaches here, copy assignment is trivial
    value_storage_nontrivial &operator=(value_storage_nontrivial &&) = default;       // NOLINT if reaches here, move assignment is trivial
#if __cplusplus >= 202000L || _HAS_CXX20
    constexpr
#endif
    value_storage_nontrivial(value_storage_nontrivial &&o) noexcept(std::is_nothrow_move_constructible<_value_type_>::value &&
                                                                    std::is_nothrow_move_constructible<_error_type_>::value)  // NOLINT
    {
      if(o._status.have_value())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_value)) _value_type_(static_cast<_value_type_ &&>(o._value));  // NOLINT
      }
      else if(o._status.have_error())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_error)) _error_type_(static_cast<_error_type_ &&>(o._error));  // NOLINT
      }
      _status = o._status;
      o._status.set_have_moved_from(true);
    }
#if __cplusplus >= 202000L || _HAS_CXX20
    constexpr
#endif
    value_storage_nontrivial(const value_storage_nontrivial &o) noexcept(std::is_nothrow_copy_constructible<_value_type_>::value &&
                                                                         std::is_nothrow_copy_constructible<_error_type_>::value)
    {
      if(o._status.have_value())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_value)) _value_type_(o._value);  // NOLINT
      }
      else if(o._status.have_error())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_error)) _error_type_(o._error);  // NOLINT
      }
      _status = o._status;
    }
#if __cplusplus >= 202000L || _HAS_CXX20
    constexpr
#endif
    explicit value_storage_nontrivial(status_bitfield_type status)
        : _empty1()
        , _status(status)
        , _empty2()
    {
    }
    template <class... Args>
    constexpr explicit value_storage_nontrivial(in_place_type_t<_value_type> /*unused*/,
                                                Args &&...args) noexcept(detail::is_nothrow_constructible<_value_type_, Args...>)
        : _value(static_cast<Args &&>(args)...)  // NOLINT
        , _status(status::have_value)
    {
    }
    template <class U, class... Args>
    constexpr value_storage_nontrivial(in_place_type_t<_value_type> /*unused*/, std::initializer_list<U> il,
                                       Args &&...args) noexcept(detail::is_nothrow_constructible<_value_type_, std::initializer_list<U>, Args...>)
        : _value(il, static_cast<Args &&>(args)...)
        , _status(status::have_value)
    {
    }
    template <class... Args>
    constexpr explicit value_storage_nontrivial(in_place_type_t<_error_type> /*unused*/,
                                                Args &&...args) noexcept(detail::is_nothrow_constructible<_error_type_, Args...>)
        : _status(status::have_error)
        , _error(static_cast<Args &&>(args)...)  // NOLINT
    {
      _set_error_is_errno(*this);
    }
    template <class U, class... Args>
    constexpr value_storage_nontrivial(in_place_type_t<_error_type> /*unused*/, std::initializer_list<U> il,
                                       Args &&...args) noexcept(detail::is_nothrow_constructible<_error_type_, std::initializer_list<U>, Args...>)
        : _status(status::have_error)
        , _error(il, static_cast<Args &&>(args)...)
    {
      _set_error_is_errno(*this);
    }

    struct nonvoid_converting_constructor_tag
    {
    };
    template <class U, class V>
    static constexpr bool enable_nonvoid_converting_constructor =
    !(std::is_same<std::decay_t<U>, value_type>::value && std::is_same<std::decay_t<V>, error_type>::value)  //
    && detail::is_constructible<value_type, U> && detail::is_constructible<error_type, V>;
    BOOST_OUTCOME_TEMPLATE(class U, class V)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_nonvoid_converting_constructor<U, V>))
    constexpr explicit value_storage_nontrivial(const value_storage_trivial<U, V> &o, nonvoid_converting_constructor_tag /*unused*/ = {}) noexcept(
    detail::is_nothrow_constructible<_value_type_, U> && detail::is_nothrow_constructible<_error_type_, V>)
        : value_storage_nontrivial(o._status.have_value() ?
                                   value_storage_nontrivial(in_place_type<value_type>, o._value) :
                                   (o._status.have_error() ? value_storage_nontrivial(in_place_type<error_type>, o._error) : value_storage_nontrivial()))
    {
      _status = o._status;
    }
    BOOST_OUTCOME_TEMPLATE(class U, class V)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_nonvoid_converting_constructor<U, V>))
    constexpr explicit value_storage_nontrivial(value_storage_trivial<U, V> &&o, nonvoid_converting_constructor_tag /*unused*/ = {}) noexcept(
    detail::is_nothrow_constructible<_value_type_, U> && detail::is_nothrow_constructible<_error_type_, V>)
        : value_storage_nontrivial(
          o._status.have_value() ?
          value_storage_nontrivial(in_place_type<value_type>, static_cast<U &&>(o._value)) :
          (o._status.have_error() ? value_storage_nontrivial(in_place_type<error_type>, static_cast<V &&>(o._error)) : value_storage_nontrivial()))
    {
      _status = o._status;
    }
    BOOST_OUTCOME_TEMPLATE(class U, class V)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_nonvoid_converting_constructor<U, V>))
    constexpr explicit value_storage_nontrivial(const value_storage_nontrivial<U, V> &o, nonvoid_converting_constructor_tag /*unused*/ = {}) noexcept(
    detail::is_nothrow_constructible<_value_type_, U> && detail::is_nothrow_constructible<_error_type_, V>)
        : value_storage_nontrivial(o._status.have_value() ?
                                   value_storage_nontrivial(in_place_type<value_type>, o._value) :
                                   (o._status.have_error() ? value_storage_nontrivial(in_place_type<error_type>, o._error) : value_storage_nontrivial()))
    {
      _status = o._status;
    }
    BOOST_OUTCOME_TEMPLATE(class U, class V)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_nonvoid_converting_constructor<U, V>))
    constexpr explicit value_storage_nontrivial(value_storage_nontrivial<U, V> &&o, nonvoid_converting_constructor_tag /*unused*/ = {}) noexcept(
    detail::is_nothrow_constructible<_value_type_, U> && detail::is_nothrow_constructible<_error_type_, V>)
        : value_storage_nontrivial(
          o._status.have_value() ?
          value_storage_nontrivial(in_place_type<value_type>, static_cast<U &&>(o._value)) :
          (o._status.have_error() ? value_storage_nontrivial(in_place_type<error_type>, static_cast<V &&>(o._error)) : value_storage_nontrivial()))
    {
      _status = o._status;
    }

    struct void_value_converting_constructor_tag
    {
    };
    template <class V>
    static constexpr bool enable_void_value_converting_constructor =
    std::is_default_constructible<value_type>::value && detail::is_constructible<error_type, V>;
    BOOST_OUTCOME_TEMPLATE(class V)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_void_value_converting_constructor<V>))
    constexpr explicit value_storage_nontrivial(const value_storage_trivial<void, V> &o, void_value_converting_constructor_tag /*unused*/ = {}) noexcept(
    std::is_nothrow_default_constructible<_value_type_>::value && detail::is_nothrow_constructible<_error_type_, V>)
    {
      if(o._status.have_value())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_value)) _value_type_();  // NOLINT
      }
      else if(o._status.have_error())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_error)) _error_type_(o._error);  // NOLINT
      }
      _status = o._status;
    }
    BOOST_OUTCOME_TEMPLATE(class V)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_void_value_converting_constructor<V>))
    constexpr explicit value_storage_nontrivial(value_storage_trivial<void, V> &&o, void_value_converting_constructor_tag /*unused*/ = {}) noexcept(
    std::is_nothrow_default_constructible<_value_type_>::value && detail::is_nothrow_constructible<_error_type_, V>)
    {
      if(o._status.have_value())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_value)) _value_type_();  // NOLINT
      }
      else if(o._status.have_error())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_error)) _error_type_(static_cast<_error_type_ &&>(o._error));  // NOLINT
      }
      _status = o._status;
      o._status.set_have_moved_from(true);
    }

    struct void_error_converting_constructor_tag
    {
    };
    template <class U>
    static constexpr bool enable_void_error_converting_constructor =
    std::is_default_constructible<error_type>::value && detail::is_constructible<value_type, U>;
    BOOST_OUTCOME_TEMPLATE(class U)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_void_error_converting_constructor<U>))
    constexpr explicit value_storage_nontrivial(const value_storage_trivial<U, void> &o, void_error_converting_constructor_tag /*unused*/ = {}) noexcept(
    detail::is_nothrow_constructible<_value_type_, U> && std::is_nothrow_default_constructible<_error_type_>::value)
    {
      if(o._status.have_value())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_value)) _value_type_(o._value);  // NOLINT
      }
      else if(o._status.have_error())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_error)) _error_type_();  // NOLINT
      }
      _status = o._status;
    }
    BOOST_OUTCOME_TEMPLATE(class U)
    BOOST_OUTCOME_TREQUIRES(BOOST_OUTCOME_TPRED(enable_void_error_converting_constructor<U>))
    constexpr explicit value_storage_nontrivial(value_storage_trivial<U, void> &&o, void_error_converting_constructor_tag /*unused*/ = {}) noexcept(
    detail::is_nothrow_constructible<_value_type_, U> && std::is_nothrow_default_constructible<_error_type_>::value)
    {
      if(o._status.have_value())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_value)) _value_type_(static_cast<_value_type_ &&>(o._value));  // NOLINT
      }
      else if(o._status.have_error())
      {
        new(BOOST_OUTCOME_ADDRESS_OF(_error)) _error_type_();  // NOLINT
      }
      _status = o._status;
      o._status.set_have_moved_from(true);
    }

#if __cplusplus >= 202000L || _HAS_CXX20
    constexpr
#endif
    ~value_storage_nontrivial() noexcept(std::is_nothrow_destructible<_value_type_>::value && std::is_nothrow_destructible<_error_type_>::value)
    {
      if(this->_status.have_value())
      {
        if(!trait::is_move_bitcopying<value_type>::value || !this->_status.have_moved_from())
        {
          this->_value.~_value_type_();  // NOLINT
        }
        this->_status.set_have_value(false);
      }
      else if(this->_status.have_error())
      {
        if(!trait::is_move_bitcopying<error_type>::value || !this->_status.have_moved_from())
        {
          this->_error.~_error_type_();  // NOLINT
        }
        this->_status.set_have_error(false);
      }
    }
#if __cplusplus >= 202000L || _HAS_CXX20
    constexpr
#endif
    void
    swap(value_storage_nontrivial &o) noexcept(detail::is_nothrow_swappable<_value_type_>::value && detail::is_nothrow_swappable<_error_type_>::value)
    {
      using std::swap;
      // empty/empty
      if(!_status.have_value() && !o._status.have_value() && !_status.have_error() && !o._status.have_error())
      {
        swap(_status, o._status);
        return;
      }
      // value/value
      if(_status.have_value() && o._status.have_value())
      {
        struct some_type
        {
          status_bitfield_type &a, &b;
          bool all_good{false};
          ~some_type()
          {
            if(!this->all_good)
            {
              // We lost one of the values
              this->a.set_have_lost_consistency(true);
              this->b.set_have_lost_consistency(true);
            }
          }
        } some_type_value{_status, o._status};
        strong_swap(some_type_value.all_good, _value, o._value);
        swap(_status, o._status);
        return;
      }
      // error/error
      if(_status.have_error() && o._status.have_error())
      {
        struct some_type
        {
          status_bitfield_type &a, &b;
          bool all_good{false};
          ~some_type()
          {
            if(!this->all_good)
            {
              // We lost one of the values
              this->a.set_have_lost_consistency(true);
              this->b.set_have_lost_consistency(true);
            }
          }
        } some_type_value{_status, o._status};
        strong_swap(some_type_value.all_good, _error, o._error);
        swap(_status, o._status);
        return;
      }
      // Could be value/empty, error/empty, etc
      if(_status.have_value() && !o._status.have_error())
      {
        // Move construct me into other
        new(BOOST_OUTCOME_ADDRESS_OF(o._value)) _value_type_(static_cast<_value_type_ &&>(_value));  // NOLINT
        if(!trait::is_move_bitcopying<value_type>::value)
        {
          this->_value.~value_type();  // NOLINT
        }
        swap(_status, o._status);
        return;
      }
      if(o._status.have_value() && !_status.have_error())
      {
        // Move construct other into me
        new(BOOST_OUTCOME_ADDRESS_OF(_value)) _value_type_(static_cast<_value_type_ &&>(o._value));  // NOLINT
        if(!trait::is_move_bitcopying<value_type>::value)
        {
          o._value.~value_type();  // NOLINT
        }
        swap(_status, o._status);
        return;
      }
      if(_status.have_error() && !o._status.have_value())
      {
        // Move construct me into other
        new(BOOST_OUTCOME_ADDRESS_OF(o._error)) _error_type_(static_cast<_error_type_ &&>(_error));  // NOLINT
        if(!trait::is_move_bitcopying<error_type>::value)
        {
          this->_error.~error_type();  // NOLINT
        }
        swap(_status, o._status);
        return;
      }
      if(o._status.have_error() && !_status.have_value())
      {
        // Move construct other into me
        new(BOOST_OUTCOME_ADDRESS_OF(_error)) _error_type_(static_cast<_error_type_ &&>(o._error));  // NOLINT
        if(!trait::is_move_bitcopying<error_type>::value)
        {
          o._error.~error_type();  // NOLINT
        }
        swap(_status, o._status);
        return;
      }
      // It can now only be value/error, or error/value
      struct some_type
      {
        status_bitfield_type &a, &b;
        _value_type_ *value, *o_value;
        _error_type_ *error, *o_error;
        bool all_good{true};
        ~some_type()
        {
          if(!this->all_good)
          {
            // We lost one of the values
            this->a.set_have_lost_consistency(true);
            this->b.set_have_lost_consistency(true);
          }
        }
      } some_type_value{_status, o._status, BOOST_OUTCOME_ADDRESS_OF(_value), BOOST_OUTCOME_ADDRESS_OF(o._value), BOOST_OUTCOME_ADDRESS_OF(_error), BOOST_OUTCOME_ADDRESS_OF(o._error)};
      if(_status.have_value() && o._status.have_error())
      {
        strong_placement(some_type_value.all_good, some_type_value.o_value, some_type_value.value, [&some_type_value] {    //
          strong_placement(some_type_value.all_good, some_type_value.error, some_type_value.o_error, [&some_type_value] {  //
            swap(some_type_value.a, some_type_value.b);                                                                    //
          });
        });
        return;
      }
      if(_status.have_error() && o._status.have_value())
      {
        strong_placement(some_type_value.all_good, some_type_value.o_error, some_type_value.error, [&some_type_value] {    //
          strong_placement(some_type_value.all_good, some_type_value.value, some_type_value.o_value, [&some_type_value] {  //
            swap(some_type_value.a, some_type_value.b);                                                                    //
          });
        });
        return;
      }
      // Should never reach here
      make_ub(_value);
    }
  };
  template <class Base> struct value_storage_delete_copy_constructor : Base  // NOLINT
  {
    using Base::Base;
    using value_type = typename Base::value_type;
    using error_type = typename Base::error_type;
    value_storage_delete_copy_constructor() = default;
    value_storage_delete_copy_constructor(const value_storage_delete_copy_constructor &) = delete;
    value_storage_delete_copy_constructor(value_storage_delete_copy_constructor &&) = default;  // NOLINT
    value_storage_delete_copy_constructor &operator=(const value_storage_delete_copy_constructor &o) = default;
    value_storage_delete_copy_constructor &operator=(value_storage_delete_copy_constructor &&o) = default;  // NOLINT
    ~value_storage_delete_copy_constructor() = default;
  };
  template <class Base> struct value_storage_delete_copy_assignment : Base  // NOLINT
  {
    using Base::Base;
    using value_type = typename Base::value_type;
    using error_type = typename Base::error_type;
    value_storage_delete_copy_assignment() = default;
    value_storage_delete_copy_assignment(const value_storage_delete_copy_assignment &) = default;
    value_storage_delete_copy_assignment(value_storage_delete_copy_assignment &&) = default;  // NOLINT
    value_storage_delete_copy_assignment &operator=(const value_storage_delete_copy_assignment &o) = delete;
    value_storage_delete_copy_assignment &operator=(value_storage_delete_copy_assignment &&o) = default;  // NOLINT
    ~value_storage_delete_copy_assignment() = default;
  };
  template <class Base> struct value_storage_delete_move_assignment : Base  // NOLINT
  {
    using Base::Base;
    using value_type = typename Base::value_type;
    using error_type = typename Base::error_type;
    value_storage_delete_move_assignment() = default;
    value_storage_delete_move_assignment(const value_storage_delete_move_assignment &) = default;
    value_storage_delete_move_assignment(value_storage_delete_move_assignment &&) = default;  // NOLINT
    value_storage_delete_move_assignment &operator=(const value_storage_delete_move_assignment &o) = default;
    value_storage_delete_move_assignment &operator=(value_storage_delete_move_assignment &&o) = delete;
    ~value_storage_delete_move_assignment() = default;
  };
  template <class Base> struct value_storage_delete_move_constructor : Base  // NOLINT
  {
    using Base::Base;
    using value_type = typename Base::value_type;
    using error_type = typename Base::error_type;
    value_storage_delete_move_constructor() = default;
    value_storage_delete_move_constructor(const value_storage_delete_move_constructor &) = default;
    value_storage_delete_move_constructor(value_storage_delete_move_constructor &&) = delete;
    value_storage_delete_move_constructor &operator=(const value_storage_delete_move_constructor &o) = default;
    value_storage_delete_move_constructor &operator=(value_storage_delete_move_constructor &&o) = default;
    ~value_storage_delete_move_constructor() = default;
  };
  template <class Base> struct value_storage_nontrivial_move_assignment : Base  // NOLINT
  {
    using Base::Base;
    using value_type = typename Base::value_type;
    using error_type = typename Base::error_type;
    value_storage_nontrivial_move_assignment() = default;
    value_storage_nontrivial_move_assignment(const value_storage_nontrivial_move_assignment &) = default;
    value_storage_nontrivial_move_assignment(value_storage_nontrivial_move_assignment &&) = default;  // NOLINT
    value_storage_nontrivial_move_assignment &operator=(const value_storage_nontrivial_move_assignment &o) = default;
    ~value_storage_nontrivial_move_assignment() = default;
#if __cplusplus >= 202000L || _HAS_CXX20
    constexpr
#endif
    value_storage_nontrivial_move_assignment &
    operator=(value_storage_nontrivial_move_assignment &&o) noexcept(std::is_nothrow_move_assignable<value_type>::value &&
                                                                     std::is_nothrow_move_assignable<error_type>::value &&
                                                                     noexcept(move_assign_to_empty<value_type>(static_cast<value_type *>(nullptr),
                                                                                                               static_cast<value_type *>(nullptr))) &&
                                                                     noexcept(move_assign_to_empty<error_type>(static_cast<error_type *>(nullptr),
                                                                                                               static_cast<error_type *>(nullptr))))  // NOLINT
    {
      using _value_type_ = typename Base::_value_type_;
      using _error_type_ = typename Base::_error_type_;
      if(!this->_status.have_value() && !this->_status.have_error() && !o._status.have_value() && !o._status.have_error())
      {
        this->_status = o._status;
        o._status.set_have_moved_from(true);
        return *this;
      }
      if(this->_status.have_value() && o._status.have_value())
      {
        this->_value = static_cast<_value_type_ &&>(o._value);  // NOLINT
        this->_status = o._status;
        o._status.set_have_moved_from(true);
        return *this;
      }
      if(this->_status.have_error() && o._status.have_error())
      {
        this->_error = static_cast<_error_type_ &&>(o._error);  // NOLINT
        this->_status = o._status;
        o._status.set_have_moved_from(true);
        return *this;
      }
      if(this->_status.have_value() && !o._status.have_value() && !o._status.have_error())
      {
        if(!trait::is_move_bitcopying<value_type>::value || this->_status.have_moved_from())
        {
          this->_value.~_value_type_();  // NOLINT
        }
        this->_status = o._status;
        o._status.set_have_moved_from(true);
        return *this;
      }
      if(!this->_status.have_value() && !this->_status.have_error() && o._status.have_value())
      {
        move_assign_to_empty<_value_type_>(BOOST_OUTCOME_ADDRESS_OF(this->_value), BOOST_OUTCOME_ADDRESS_OF(o._value));
        this->_status = o._status;
        o._status.set_have_moved_from(true);
        return *this;
      }
      if(this->_status.have_error() && !o._status.have_value() && !o._status.have_error())
      {
        if(!trait::is_move_bitcopying<error_type>::value || this->_status.have_moved_from())
        {
          this->_error.~_error_type_();  // NOLINT
        }
        this->_status = o._status;
        o._status.set_have_moved_from(true);
        return *this;
      }
      if(!this->_status.have_value() && !this->_status.have_error() && o._status.have_error())
      {
        move_assign_to_empty<_error_type_>(BOOST_OUTCOME_ADDRESS_OF(this->_error), BOOST_OUTCOME_ADDRESS_OF(o._error));
        this->_status = o._status;
        o._status.set_have_moved_from(true);
        return *this;
      }
      if(this->_status.have_value() && o._status.have_error())
      {
        if(!trait::is_move_bitcopying<value_type>::value || this->_status.have_moved_from())
        {
          this->_value.~_value_type_();  // NOLINT
        }
        move_assign_to_empty<_error_type_>(BOOST_OUTCOME_ADDRESS_OF(this->_error), BOOST_OUTCOME_ADDRESS_OF(o._error));
        this->_status = o._status;
        o._status.set_have_moved_from(true);
        return *this;
      }
      if(this->_status.have_error() && o._status.have_value())
      {
        if(!trait::is_move_bitcopying<error_type>::value || this->_status.have_moved_from())
        {
          this->_error.~_error_type_();  // NOLINT
        }
        move_assign_to_empty<_value_type_>(BOOST_OUTCOME_ADDRESS_OF(this->_value), BOOST_OUTCOME_ADDRESS_OF(o._value));
        this->_status = o._status;
        o._status.set_have_moved_from(true);
        return *this;
      }
      // Should never reach here
      make_ub(this->_value);
    }
  };
  template <class Base> struct value_storage_nontrivial_copy_assignment : Base  // NOLINT
  {
    using Base::Base;
    using value_type = typename Base::value_type;
    using error_type = typename Base::error_type;
    value_storage_nontrivial_copy_assignment() = default;
    value_storage_nontrivial_copy_assignment(const value_storage_nontrivial_copy_assignment &) = default;
    value_storage_nontrivial_copy_assignment(value_storage_nontrivial_copy_assignment &&) = default;              // NOLINT
    value_storage_nontrivial_copy_assignment &operator=(value_storage_nontrivial_copy_assignment &&o) = default;  // NOLINT
    ~value_storage_nontrivial_copy_assignment() = default;
#if __cplusplus >= 202000L || _HAS_CXX20
    constexpr
#endif
    value_storage_nontrivial_copy_assignment &
    operator=(const value_storage_nontrivial_copy_assignment &o) noexcept(
    std::is_nothrow_copy_assignable<value_type>::value && std::is_nothrow_copy_assignable<error_type>::value &&
    noexcept(copy_assign_to_empty<value_type>(static_cast<value_type *>(nullptr), static_cast<value_type *>(nullptr))) &&
    noexcept(copy_assign_to_empty<error_type>(static_cast<error_type *>(nullptr), static_cast<error_type *>(nullptr))))
    {
      using _value_type_ = typename Base::_value_type_;
      using _error_type_ = typename Base::_error_type_;
      if(!this->_status.have_value() && !this->_status.have_error() && !o._status.have_value() && !o._status.have_error())
      {
        this->_status = o._status;
        return *this;
      }
      if(this->_status.have_value() && o._status.have_value())
      {
        this->_value = o._value;  // NOLINT
        this->_status = o._status;
        return *this;
      }
      if(this->_status.have_error() && o._status.have_error())
      {
        this->_error = o._error;  // NOLINT
        this->_status = o._status;
        return *this;
      }
      if(this->_status.have_value() && !o._status.have_value() && !o._status.have_error())
      {
        if(!trait::is_move_bitcopying<value_type>::value || this->_status.have_moved_from())
        {
          this->_value.~_value_type_();  // NOLINT
        }
        this->_status = o._status;
        return *this;
      }
      if(!this->_status.have_value() && !this->_status.have_error() && o._status.have_value())
      {
        copy_assign_to_empty<_value_type_>(BOOST_OUTCOME_ADDRESS_OF(this->_value), BOOST_OUTCOME_ADDRESS_OF(o._value));
        this->_status = o._status;
        return *this;
      }
      if(this->_status.have_error() && !o._status.have_value() && !o._status.have_error())
      {
        if(!trait::is_move_bitcopying<error_type>::value || this->_status.have_moved_from())
        {
          this->_error.~_error_type_();  // NOLINT
        }
        this->_status = o._status;
        return *this;
      }
      if(!this->_status.have_value() && !this->_status.have_error() && o._status.have_error())
      {
        copy_assign_to_empty<_error_type_>(BOOST_OUTCOME_ADDRESS_OF(this->_error), BOOST_OUTCOME_ADDRESS_OF(o._error));
        this->_status = o._status;
        return *this;
      }
      if(this->_status.have_value() && o._status.have_error())
      {
        if(!trait::is_move_bitcopying<value_type>::value || this->_status.have_moved_from())
        {
          this->_value.~_value_type_();  // NOLINT
        }
        copy_assign_to_empty<_error_type_>(BOOST_OUTCOME_ADDRESS_OF(this->_error), BOOST_OUTCOME_ADDRESS_OF(o._error));
        this->_status = o._status;
        return *this;
      }
      if(this->_status.have_error() && o._status.have_value())
      {
        if(!trait::is_move_bitcopying<error_type>::value || this->_status.have_moved_from())
        {
          this->_error.~_error_type_();  // NOLINT
        }
        copy_assign_to_empty<_value_type_>(BOOST_OUTCOME_ADDRESS_OF(this->_value), BOOST_OUTCOME_ADDRESS_OF(o._value));
        this->_status = o._status;
        return *this;
      }
      // Should never reach here
      make_ub(this->_value);
    }
  };
#ifdef _MSC_VER
#pragma warning(pop)
#endif

  // is_trivially_copyable is true even if type is not copyable, so handle that here
  template <class T> struct is_storage_trivial
  {
    static constexpr bool value = std::is_void<T>::value || (std::is_trivially_copy_constructible<T>::value && std::is_trivially_copyable<T>::value);
  };
  // work around libstdc++ 7 bug
  template <> struct is_storage_trivial<void>
  {
    static constexpr bool value = true;
  };
  template <> struct is_storage_trivial<const void>
  {
    static constexpr bool value = true;
  };
  // Ability to do copy assigns needs more than just copy assignment
  template <class T> struct is_copy_assignable
  {
    static constexpr bool value = std::is_copy_assignable<T>::value && (std::is_copy_constructible<T>::value || std::is_default_constructible<T>::value);
  };
  // Ability to do move assigns needs more than just move assignment
  template <class T> struct is_move_assignable
  {
    static constexpr bool value = std::is_move_assignable<T>::value && (std::is_move_constructible<T>::value || std::is_default_constructible<T>::value);
  };

  template <class T, class E>
  using value_storage_select_trivality =
  std::conditional_t<is_storage_trivial<T>::value && is_storage_trivial<E>::value, value_storage_trivial<T, E>, value_storage_nontrivial<T, E>>;
  template <class T, class E>
  using value_storage_select_move_constructor =
  std::conditional_t<std::is_move_constructible<devoid<T>>::value && std::is_move_constructible<devoid<E>>::value, value_storage_select_trivality<T, E>,
                     value_storage_delete_move_constructor<value_storage_select_trivality<T, E>>>;
  template <class T, class E>
  using value_storage_select_copy_constructor =
  std::conditional_t<std::is_copy_constructible<devoid<T>>::value && std::is_copy_constructible<devoid<E>>::value, value_storage_select_move_constructor<T, E>,
                     value_storage_delete_copy_constructor<value_storage_select_move_constructor<T, E>>>;
  template <class T, class E>
  using value_storage_select_move_assignment =
  std::conditional_t<std::is_trivially_move_assignable<devoid<T>>::value && std::is_trivially_move_assignable<devoid<E>>::value,
                     value_storage_select_copy_constructor<T, E>,
                     std::conditional_t<is_move_assignable<devoid<T>>::value && is_move_assignable<devoid<E>>::value,
                                        value_storage_nontrivial_move_assignment<value_storage_select_copy_constructor<T, E>>,
                                        value_storage_delete_move_assignment<value_storage_select_copy_constructor<T, E>>>>;
  template <class T, class E>
  using value_storage_select_copy_assignment =
  std::conditional_t<std::is_trivially_copy_assignable<devoid<T>>::value && std::is_trivially_copy_assignable<devoid<E>>::value,
                     value_storage_select_move_assignment<T, E>,
                     std::conditional_t<is_copy_assignable<devoid<T>>::value && is_copy_assignable<devoid<E>>::value,
                                        value_storage_nontrivial_copy_assignment<value_storage_select_move_assignment<T, E>>,
                                        value_storage_delete_copy_assignment<value_storage_select_move_assignment<T, E>>>>;
  template <class T, class E> using value_storage_select_impl = value_storage_select_copy_assignment<T, E>;
#ifndef NDEBUG
  // Check is trivial in all ways except default constructibility
  // static_assert(std::is_trivial<value_storage_select_impl<int, long>>::value, "value_storage_select_impl<int, long> is not trivial!");
  // static_assert(std::is_trivially_default_constructible<value_storage_select_impl<int, long>>::value, "value_storage_select_impl<int, long> is not
  // trivially default constructible!");
  static_assert(std::is_trivially_copyable<value_storage_select_impl<int, long>>::value, "value_storage_select_impl<int, long> is not trivially copyable!");
  static_assert(std::is_trivially_assignable<value_storage_select_impl<int, long>, value_storage_select_impl<int, long>>::value,
                "value_storage_select_impl<int, long> is not trivially assignable!");
  static_assert(std::is_trivially_destructible<value_storage_select_impl<int, long>>::value,
                "value_storage_select_impl<int, long> is not trivially destructible!");
  static_assert(std::is_trivially_copy_constructible<value_storage_select_impl<int, long>>::value,
                "value_storage_select_impl<int, long> is not trivially copy constructible!");
  static_assert(std::is_trivially_move_constructible<value_storage_select_impl<int, long>>::value,
                "value_storage_select_impl<int, long> is not trivially move constructible!");
  static_assert(std::is_trivially_copy_assignable<value_storage_select_impl<int, long>>::value,
                "value_storage_select_impl<int, long> is not trivially copy assignable!");
  static_assert(std::is_trivially_move_assignable<value_storage_select_impl<int, long>>::value,
                "value_storage_select_impl<int, long> is not trivially move assignable!");
  // Also check is standard layout
  static_assert(std::is_standard_layout<value_storage_select_impl<int, long>>::value, "value_storage_select_impl<int, long> is not a standard layout type!");
#endif
}  // namespace detail

BOOST_OUTCOME_V2_NAMESPACE_END

#endif
