///
// expected - An implementation of std::expected with extensions
// Written in 2017 by Simon Brand (simonrbrand@gmail.com, @TartanLlama)
//
// Documentation available at http://tl.tartanllama.xyz/
//
// To the extent possible under law, the author(s) have dedicated all
// copyright and related and neighboring rights to this software to the
// public domain worldwide. This software is distributed without any warranty.
//
// You should have received a copy of the CC0 Public Domain Dedication
// along with this software. If not, see
// <http://creativecommons.org/publicdomain/zero/1.0/>.
///

#ifndef TL_EXPECTED_HPP
#define TL_EXPECTED_HPP

#define TL_EXPECTED_VERSION_MAJOR 1
#define TL_EXPECTED_VERSION_MINOR 0
#define TL_EXPECTED_VERSION_PATCH 1

#include <exception>
#include <functional>
#include <type_traits>
#include <utility>

#if defined(__EXCEPTIONS) || defined(_CPPUNWIND)
#define TL_EXPECTED_EXCEPTIONS_ENABLED
#endif

#if (defined(_MSC_VER) && _MSC_VER == 1900)
#define TL_EXPECTED_MSVC2015
#define TL_EXPECTED_MSVC2015_CONSTEXPR
#else
#define TL_EXPECTED_MSVC2015_CONSTEXPR constexpr
#endif

#if (defined(__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ <= 9 && !defined(__clang__))
#define TL_EXPECTED_GCC49
#endif

#if (defined(__GNUC__) && __GNUC__ == 5 && __GNUC_MINOR__ <= 4 && !defined(__clang__))
#define TL_EXPECTED_GCC54
#endif

#if (defined(__GNUC__) && __GNUC__ == 5 && __GNUC_MINOR__ <= 5 && !defined(__clang__))
#define TL_EXPECTED_GCC55
#endif

#if (defined(__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ <= 9 && !defined(__clang__))
// GCC < 5 doesn't support overloading on const&& for member functions

#define TL_EXPECTED_NO_CONSTRR
// GCC < 5 doesn't support some standard C++11 type traits
#define TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T) std::has_trivial_copy_constructor<T>
#define TL_EXPECTED_IS_TRIVIALLY_COPY_ASSIGNABLE(T) std::has_trivial_copy_assign<T>

// This one will be different for GCC 5.7 if it's ever supported
#define TL_EXPECTED_IS_TRIVIALLY_DESTRUCTIBLE(T) std::is_trivially_destructible<T>

// GCC 5 < v < 8 has a bug in is_trivially_copy_constructible which breaks std::vector
// for non-copyable types
#elif (defined(__GNUC__) && __GNUC__ < 8 && !defined(__clang__))
#ifndef TL_GCC_LESS_8_TRIVIALLY_COPY_CONSTRUCTIBLE_MUTEX
#define TL_GCC_LESS_8_TRIVIALLY_COPY_CONSTRUCTIBLE_MUTEX
namespace tl
{
namespace detail
{
template<class T>
struct is_trivially_copy_constructible : std::is_trivially_copy_constructible<T> {
};
#ifdef _GLIBCXX_VECTOR
template<class T, class A>
struct is_trivially_copy_constructible<std::vector<T, A>> : std::false_type {
};
#endif
} // namespace detail
} // namespace tl
#endif

#define TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T)                                             \
  tl::detail::is_trivially_copy_constructible<T>
#define TL_EXPECTED_IS_TRIVIALLY_COPY_ASSIGNABLE(T) std::is_trivially_copy_assignable<T>
#define TL_EXPECTED_IS_TRIVIALLY_DESTRUCTIBLE(T) std::is_trivially_destructible<T>
#else
#define TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T) std::is_trivially_copy_constructible<T>
#define TL_EXPECTED_IS_TRIVIALLY_COPY_ASSIGNABLE(T) std::is_trivially_copy_assignable<T>
#define TL_EXPECTED_IS_TRIVIALLY_DESTRUCTIBLE(T) std::is_trivially_destructible<T>
#endif

#if __cplusplus > 201103L
#define TL_EXPECTED_CXX14
#endif

#ifdef TL_EXPECTED_GCC49
#define TL_EXPECTED_GCC49_CONSTEXPR
#else
#define TL_EXPECTED_GCC49_CONSTEXPR constexpr
#endif

#if (__cplusplus == 201103L || defined(TL_EXPECTED_MSVC2015) || defined(TL_EXPECTED_GCC49))
#define TL_EXPECTED_11_CONSTEXPR
#else
#define TL_EXPECTED_11_CONSTEXPR constexpr
#endif

namespace tl
{
template<class T, class E>
class expected;

#ifndef TL_MONOSTATE_INPLACE_MUTEX
#define TL_MONOSTATE_INPLACE_MUTEX
class monostate
{
};

struct in_place_t {
  explicit in_place_t() = default;
};
static constexpr in_place_t in_place{};
#endif

template<class E>
class unexpected
{
public:
  static_assert(!std::is_same<E, void>::value, "E must not be void");

  unexpected() = delete;
  constexpr explicit unexpected(const E& e)
    : m_val(e)
  {
  }

  constexpr explicit unexpected(E&& e)
    : m_val(std::move(e))
  {
  }

  constexpr const E& value() const&
  {
    return m_val;
  }
  TL_EXPECTED_11_CONSTEXPR E& value() &
  {
    return m_val;
  }
  TL_EXPECTED_11_CONSTEXPR E&& value() &&
  {
    return std::move(m_val);
  }
  constexpr const E&& value() const&&
  {
    return std::move(m_val);
  }

private:
  E m_val;
};

template<class E>
constexpr bool
operator==(const unexpected<E>& lhs, const unexpected<E>& rhs)
{
  return lhs.value() == rhs.value();
}
template<class E>
constexpr bool
operator!=(const unexpected<E>& lhs, const unexpected<E>& rhs)
{
  return lhs.value() != rhs.value();
}
template<class E>
constexpr bool
operator<(const unexpected<E>& lhs, const unexpected<E>& rhs)
{
  return lhs.value() < rhs.value();
}
template<class E>
constexpr bool
operator<=(const unexpected<E>& lhs, const unexpected<E>& rhs)
{
  return lhs.value() <= rhs.value();
}
template<class E>
constexpr bool
operator>(const unexpected<E>& lhs, const unexpected<E>& rhs)
{
  return lhs.value() > rhs.value();
}
template<class E>
constexpr bool
operator>=(const unexpected<E>& lhs, const unexpected<E>& rhs)
{
  return lhs.value() >= rhs.value();
}

template<class E>
unexpected<typename std::decay<E>::type>
make_unexpected(E&& e)
{
  return unexpected<typename std::decay<E>::type>(std::forward<E>(e));
}

struct unexpect_t {
  unexpect_t() = default;
};
static constexpr unexpect_t unexpect{};

namespace detail
{
template<typename E>
[[noreturn]] TL_EXPECTED_11_CONSTEXPR void
throw_exception(E&& e)
{
#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
  throw std::forward<E>(e);
#else
#ifdef _MSC_VER
  __assume(0);
#else
  __builtin_unreachable();
#endif
#endif
}

#ifndef TL_TRAITS_MUTEX
#define TL_TRAITS_MUTEX
// C++14-style aliases for brevity
template<class T>
using remove_const_t = typename std::remove_const<T>::type;
template<class T>
using remove_reference_t = typename std::remove_reference<T>::type;
template<class T>
using decay_t = typename std::decay<T>::type;
template<bool E, class T = void>
using enable_if_t = typename std::enable_if<E, T>::type;
template<bool B, class T, class F>
using conditional_t = typename std::conditional<B, T, F>::type;

// std::conjunction from C++17
template<class...>
struct conjunction : std::true_type {
};
template<class B>
struct conjunction<B> : B {
};
template<class B, class... Bs>
struct conjunction<B, Bs...> : std::conditional<bool(B::value), conjunction<Bs...>, B>::type {
};

#if defined(_LIBCPP_VERSION) && __cplusplus == 201103L
#define TL_TRAITS_LIBCXX_MEM_FN_WORKAROUND
#endif

// In C++11 mode, there's an issue in libc++'s std::mem_fn
// which results in a hard-error when using it in a noexcept expression
// in some cases. This is a check to workaround the common failing case.
#ifdef TL_TRAITS_LIBCXX_MEM_FN_WORKAROUND
template<class T>
struct is_pointer_to_non_const_member_func : std::false_type {
};
template<class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...)> : std::true_type {
};
template<class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...)&> : std::true_type {
};
template<class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...) &&> : std::true_type {
};
template<class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...) volatile> : std::true_type {
};
template<class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...) volatile&> : std::true_type {
};
template<class T, class Ret, class... Args>
struct is_pointer_to_non_const_member_func<Ret (T::*)(Args...) volatile&&> : std::true_type {
};

template<class T>
struct is_const_or_const_ref : std::false_type {
};
template<class T>
struct is_const_or_const_ref<T const&> : std::true_type {
};
template<class T>
struct is_const_or_const_ref<T const> : std::true_type {
};
#endif

// std::invoke from C++17
// https://stackoverflow.com/questions/38288042/c11-14-invoke-workaround
template<typename Fn,
         typename... Args,
#ifdef TL_TRAITS_LIBCXX_MEM_FN_WORKAROUND
         typename = enable_if_t<!(is_pointer_to_non_const_member_func<Fn>::value &&
                                  is_const_or_const_ref<Args...>::value)>,
#endif
         typename = enable_if_t<std::is_member_pointer<decay_t<Fn>>::value>,
         int = 0>
constexpr auto
invoke(Fn&& f, Args&&... args) noexcept(noexcept(std::mem_fn(f)(std::forward<Args>(args)...)))
  -> decltype(std::mem_fn(f)(std::forward<Args>(args)...))
{
  return std::mem_fn(f)(std::forward<Args>(args)...);
}

template<typename Fn,
         typename... Args,
         typename = enable_if_t<!std::is_member_pointer<decay_t<Fn>>::value>>
constexpr auto
invoke(Fn&& f, Args&&... args) noexcept(noexcept(std::forward<Fn>(f)(std::forward<Args>(args)...)))
  -> decltype(std::forward<Fn>(f)(std::forward<Args>(args)...))
{
  return std::forward<Fn>(f)(std::forward<Args>(args)...);
}

// std::invoke_result from C++17
template<class F, class, class... Us>
struct invoke_result_impl;

template<class F, class... Us>
struct invoke_result_impl<F,
                          decltype(detail::invoke(std::declval<F>(), std::declval<Us>()...),
                                   void()),
                          Us...> {
  using type = decltype(detail::invoke(std::declval<F>(), std::declval<Us>()...));
};

template<class F, class... Us>
using invoke_result = invoke_result_impl<F, void, Us...>;

template<class F, class... Us>
using invoke_result_t = typename invoke_result<F, Us...>::type;

#if defined(_MSC_VER) && _MSC_VER <= 1900
// TODO make a version which works with MSVC 2015
template<class T, class U = T>
struct is_swappable : std::true_type {
};

template<class T, class U = T>
struct is_nothrow_swappable : std::true_type {
};
#else
// https://stackoverflow.com/questions/26744589/what-is-a-proper-way-to-implement-is-swappable-to-test-for-the-swappable-concept
namespace swap_adl_tests
{
// if swap ADL finds this then it would call std::swap otherwise (same
// signature)
struct tag {
};

template<class T>
tag
swap(T&, T&);
template<class T, std::size_t N>
tag swap(T (&a)[N], T (&b)[N]);

// helper functions to test if an unqualified swap is possible, and if it
// becomes std::swap
template<class, class>
std::false_type
can_swap(...) noexcept(false);
template<class T, class U, class = decltype(swap(std::declval<T&>(), std::declval<U&>()))>
std::true_type
can_swap(int) noexcept(noexcept(swap(std::declval<T&>(), std::declval<U&>())));

template<class, class>
std::false_type
uses_std(...);
template<class T, class U>
std::is_same<decltype(swap(std::declval<T&>(), std::declval<U&>())), tag>
uses_std(int);

template<class T>
struct is_std_swap_noexcept
  : std::integral_constant<bool,
                           std::is_nothrow_move_constructible<T>::value &&
                             std::is_nothrow_move_assignable<T>::value> {
};

template<class T, std::size_t N>
struct is_std_swap_noexcept<T[N]> : is_std_swap_noexcept<T> {
};

template<class T, class U>
struct is_adl_swap_noexcept : std::integral_constant<bool, noexcept(can_swap<T, U>(0))> {
};
} // namespace swap_adl_tests

template<class T, class U = T>
struct is_swappable
  : std::integral_constant<bool,
                           decltype(detail::swap_adl_tests::can_swap<T, U>(0))::value &&
                             (!decltype(detail::swap_adl_tests::uses_std<T, U>(0))::value ||
                              (std::is_move_assignable<T>::value &&
                               std::is_move_constructible<T>::value))> {
};

template<class T, std::size_t N>
struct is_swappable<T[N], T[N]>
  : std::integral_constant<bool,
                           decltype(detail::swap_adl_tests::can_swap<T[N], T[N]>(0))::value &&
                             (!decltype(detail::swap_adl_tests::uses_std<T[N], T[N]>(0))::value ||
                              is_swappable<T, T>::value)> {
};

template<class T, class U = T>
struct is_nothrow_swappable
  : std::integral_constant<bool,
                           is_swappable<T, U>::value &&
                             ((decltype(detail::swap_adl_tests::uses_std<T, U>(0))::value &&
                               detail::swap_adl_tests::is_std_swap_noexcept<T>::value) ||
                              (!decltype(detail::swap_adl_tests::uses_std<T, U>(0))::value &&
                               detail::swap_adl_tests::is_adl_swap_noexcept<T, U>::value))> {
};
#endif
#endif

// Trait for checking if a type is a tl::expected
template<class T>
struct is_expected_impl : std::false_type {
};
template<class T, class E>
struct is_expected_impl<expected<T, E>> : std::true_type {
};
template<class T>
using is_expected = is_expected_impl<decay_t<T>>;

template<class T, class E, class U>
using expected_enable_forward_value =
  detail::enable_if_t<std::is_constructible<T, U&&>::value &&
                      !std::is_same<detail::decay_t<U>, in_place_t>::value &&
                      !std::is_same<expected<T, E>, detail::decay_t<U>>::value &&
                      !std::is_same<unexpected<E>, detail::decay_t<U>>::value>;

template<class T, class E, class U, class G, class UR, class GR>
using expected_enable_from_other =
  detail::enable_if_t<std::is_constructible<T, UR>::value && std::is_constructible<E, GR>::value &&
                      !std::is_constructible<T, expected<U, G>&>::value &&
                      !std::is_constructible<T, expected<U, G>&&>::value &&
                      !std::is_constructible<T, const expected<U, G>&>::value &&
                      !std::is_constructible<T, const expected<U, G>&&>::value &&
                      !std::is_convertible<expected<U, G>&, T>::value &&
                      !std::is_convertible<expected<U, G>&&, T>::value &&
                      !std::is_convertible<const expected<U, G>&, T>::value &&
                      !std::is_convertible<const expected<U, G>&&, T>::value>;

template<class T, class U>
using is_void_or = conditional_t<std::is_void<T>::value, std::true_type, U>;

template<class T>
using is_copy_constructible_or_void = is_void_or<T, std::is_copy_constructible<T>>;

template<class T>
using is_move_constructible_or_void = is_void_or<T, std::is_move_constructible<T>>;

template<class T>
using is_copy_assignable_or_void = is_void_or<T, std::is_copy_assignable<T>>;

template<class T>
using is_move_assignable_or_void = is_void_or<T, std::is_move_assignable<T>>;

} // namespace detail

namespace detail
{
struct no_init_t {
};
static constexpr no_init_t no_init{};

// Implements the storage of the values, and ensures that the destructor is
// trivial if it can be.
//
// This specialization is for where neither `T` or `E` is trivially
// destructible, so the destructors must be called on destruction of the
// `expected`
template<class T,
         class E,
         bool = std::is_trivially_destructible<T>::value,
         bool = std::is_trivially_destructible<E>::value>
struct expected_storage_base {
  constexpr expected_storage_base()
    : m_val(T{})
    , m_has_val(true)
  {
  }
  constexpr expected_storage_base(no_init_t)
    : m_no_init()
    , m_has_val(false)
  {
  }

  template<class... Args,
           detail::enable_if_t<std::is_constructible<T, Args&&...>::value>* = nullptr>
  constexpr expected_storage_base(in_place_t, Args&&... args)
    : m_val(std::forward<Args>(args)...)
    , m_has_val(true)
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr expected_storage_base(in_place_t, std::initializer_list<U> il, Args&&... args)
    : m_val(il, std::forward<Args>(args)...)
    , m_has_val(true)
  {
  }
  template<class... Args,
           detail::enable_if_t<std::is_constructible<E, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, Args&&... args)
    : m_unexpect(std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<E, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, std::initializer_list<U> il, Args&&... args)
    : m_unexpect(il, std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  ~expected_storage_base()
  {
    if (m_has_val) {
      m_val.~T();
    } else {
      m_unexpect.~unexpected<E>();
    }
  }
  union {
    T m_val;
    unexpected<E> m_unexpect;
    char m_no_init;
  };
  bool m_has_val;
};

// This specialization is for when both `T` and `E` are trivially-destructible,
// so the destructor of the `expected` can be trivial.
template<class T, class E>
struct expected_storage_base<T, E, true, true> {
  constexpr expected_storage_base()
    : m_val(T{})
    , m_has_val(true)
  {
  }
  constexpr expected_storage_base(no_init_t)
    : m_no_init()
    , m_has_val(false)
  {
  }

  template<class... Args,
           detail::enable_if_t<std::is_constructible<T, Args&&...>::value>* = nullptr>
  constexpr expected_storage_base(in_place_t, Args&&... args)
    : m_val(std::forward<Args>(args)...)
    , m_has_val(true)
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr expected_storage_base(in_place_t, std::initializer_list<U> il, Args&&... args)
    : m_val(il, std::forward<Args>(args)...)
    , m_has_val(true)
  {
  }
  template<class... Args,
           detail::enable_if_t<std::is_constructible<E, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, Args&&... args)
    : m_unexpect(std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<E, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, std::initializer_list<U> il, Args&&... args)
    : m_unexpect(il, std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  ~expected_storage_base() = default;
  union {
    T m_val;
    unexpected<E> m_unexpect;
    char m_no_init;
  };
  bool m_has_val;
};

// T is trivial, E is not.
template<class T, class E>
struct expected_storage_base<T, E, true, false> {
  constexpr expected_storage_base()
    : m_val(T{})
    , m_has_val(true)
  {
  }
  TL_EXPECTED_MSVC2015_CONSTEXPR expected_storage_base(no_init_t)
    : m_no_init()
    , m_has_val(false)
  {
  }

  template<class... Args,
           detail::enable_if_t<std::is_constructible<T, Args&&...>::value>* = nullptr>
  constexpr expected_storage_base(in_place_t, Args&&... args)
    : m_val(std::forward<Args>(args)...)
    , m_has_val(true)
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr expected_storage_base(in_place_t, std::initializer_list<U> il, Args&&... args)
    : m_val(il, std::forward<Args>(args)...)
    , m_has_val(true)
  {
  }
  template<class... Args,
           detail::enable_if_t<std::is_constructible<E, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, Args&&... args)
    : m_unexpect(std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<E, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, std::initializer_list<U> il, Args&&... args)
    : m_unexpect(il, std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  ~expected_storage_base()
  {
    if (!m_has_val) {
      m_unexpect.~unexpected<E>();
    }
  }

  union {
    T m_val;
    unexpected<E> m_unexpect;
    char m_no_init;
  };
  bool m_has_val;
};

// E is trivial, T is not.
template<class T, class E>
struct expected_storage_base<T, E, false, true> {
  constexpr expected_storage_base()
    : m_val(T{})
    , m_has_val(true)
  {
  }
  constexpr expected_storage_base(no_init_t)
    : m_no_init()
    , m_has_val(false)
  {
  }

  template<class... Args,
           detail::enable_if_t<std::is_constructible<T, Args&&...>::value>* = nullptr>
  constexpr expected_storage_base(in_place_t, Args&&... args)
    : m_val(std::forward<Args>(args)...)
    , m_has_val(true)
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr expected_storage_base(in_place_t, std::initializer_list<U> il, Args&&... args)
    : m_val(il, std::forward<Args>(args)...)
    , m_has_val(true)
  {
  }
  template<class... Args,
           detail::enable_if_t<std::is_constructible<E, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, Args&&... args)
    : m_unexpect(std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<E, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, std::initializer_list<U> il, Args&&... args)
    : m_unexpect(il, std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  ~expected_storage_base()
  {
    if (m_has_val) {
      m_val.~T();
    }
  }
  union {
    T m_val;
    unexpected<E> m_unexpect;
    char m_no_init;
  };
  bool m_has_val;
};

// `T` is `void`, `E` is trivially-destructible
template<class E>
struct expected_storage_base<void, E, false, true> {
  TL_EXPECTED_MSVC2015_CONSTEXPR expected_storage_base()
    : m_has_val(true)
  {
  }
  constexpr expected_storage_base(no_init_t)
    : m_val()
    , m_has_val(false)
  {
  }

  constexpr expected_storage_base(in_place_t)
    : m_has_val(true)
  {
  }

  template<class... Args,
           detail::enable_if_t<std::is_constructible<E, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, Args&&... args)
    : m_unexpect(std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<E, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, std::initializer_list<U> il, Args&&... args)
    : m_unexpect(il, std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  ~expected_storage_base() = default;
  struct dummy {
  };
  union {
    unexpected<E> m_unexpect;
    dummy m_val;
  };
  bool m_has_val;
};

// `T` is `void`, `E` is not trivially-destructible
template<class E>
struct expected_storage_base<void, E, false, false> {
  constexpr expected_storage_base()
    : m_dummy()
    , m_has_val(true)
  {
  }
  constexpr expected_storage_base(no_init_t)
    : m_dummy()
    , m_has_val(false)
  {
  }

  constexpr expected_storage_base(in_place_t)
    : m_dummy()
    , m_has_val(true)
  {
  }

  template<class... Args,
           detail::enable_if_t<std::is_constructible<E, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, Args&&... args)
    : m_unexpect(std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<E, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr explicit expected_storage_base(unexpect_t, std::initializer_list<U> il, Args&&... args)
    : m_unexpect(il, std::forward<Args>(args)...)
    , m_has_val(false)
  {
  }

  ~expected_storage_base()
  {
    if (!m_has_val) {
      m_unexpect.~unexpected<E>();
    }
  }

  union {
    unexpected<E> m_unexpect;
    char m_dummy;
  };
  bool m_has_val;
};

// This base class provides some handy member functions which can be used in
// further derived classes
template<class T, class E>
struct expected_operations_base : expected_storage_base<T, E> {
  using expected_storage_base<T, E>::expected_storage_base;

  template<class... Args>
  void construct(Args&&... args) noexcept
  {
    new (std::addressof(this->m_val)) T(std::forward<Args>(args)...);
    this->m_has_val = true;
  }

  template<class Rhs>
  void construct_with(Rhs&& rhs) noexcept
  {
    new (std::addressof(this->m_val)) T(std::forward<Rhs>(rhs).get());
    this->m_has_val = true;
  }

  template<class... Args>
  void construct_error(Args&&... args) noexcept
  {
    new (std::addressof(this->m_unexpect)) unexpected<E>(std::forward<Args>(args)...);
    this->m_has_val = false;
  }

#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED

  // These assign overloads ensure that the most efficient assignment
  // implementation is used while maintaining the strong exception guarantee.
  // The problematic case is where rhs has a value, but *this does not.
  //
  // This overload handles the case where we can just copy-construct `T`
  // directly into place without throwing.
  template<class U = T,
           detail::enable_if_t<std::is_nothrow_copy_constructible<U>::value>* = nullptr>
  void assign(const expected_operations_base& rhs) noexcept
  {
    if (!this->m_has_val && rhs.m_has_val) {
      geterr().~unexpected<E>();
      construct(rhs.get());
    } else {
      assign_common(rhs);
    }
  }

  // This overload handles the case where we can attempt to create a copy of
  // `T`, then no-throw move it into place if the copy was successful.
  template<class U = T,
           detail::enable_if_t<!std::is_nothrow_copy_constructible<U>::value &&
                               std::is_nothrow_move_constructible<U>::value>* = nullptr>
  void assign(const expected_operations_base& rhs) noexcept
  {
    if (!this->m_has_val && rhs.m_has_val) {
      T tmp = rhs.get();
      geterr().~unexpected<E>();
      construct(std::move(tmp));
    } else {
      assign_common(rhs);
    }
  }

  // This overload is the worst-case, where we have to move-construct the
  // unexpected value into temporary storage, then try to copy the T into place.
  // If the construction succeeds, then everything is fine, but if it throws,
  // then we move the old unexpected value back into place before rethrowing the
  // exception.
  template<class U = T,
           detail::enable_if_t<!std::is_nothrow_copy_constructible<U>::value &&
                               !std::is_nothrow_move_constructible<U>::value>* = nullptr>
  void assign(const expected_operations_base& rhs)
  {
    if (!this->m_has_val && rhs.m_has_val) {
      auto tmp = std::move(geterr());
      geterr().~unexpected<E>();

#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
      try {
        construct(rhs.get());
      } catch (...) {
        geterr() = std::move(tmp);
        throw;
      }
#else
      construct(rhs.get());
#endif
    } else {
      assign_common(rhs);
    }
  }

  // These overloads do the same as above, but for rvalues
  template<class U = T,
           detail::enable_if_t<std::is_nothrow_move_constructible<U>::value>* = nullptr>
  void assign(expected_operations_base&& rhs) noexcept
  {
    if (!this->m_has_val && rhs.m_has_val) {
      geterr().~unexpected<E>();
      construct(std::move(rhs).get());
    } else {
      assign_common(std::move(rhs));
    }
  }

  template<class U = T,
           detail::enable_if_t<!std::is_nothrow_move_constructible<U>::value>* = nullptr>
  void assign(expected_operations_base&& rhs)
  {
    if (!this->m_has_val && rhs.m_has_val) {
      auto tmp = std::move(geterr());
      geterr().~unexpected<E>();
#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
      try {
        construct(std::move(rhs).get());
      } catch (...) {
        geterr() = std::move(tmp);
        throw;
      }
#else
      construct(std::move(rhs).get());
#endif
    } else {
      assign_common(std::move(rhs));
    }
  }

#else

  // If exceptions are disabled then we can just copy-construct
  void assign(const expected_operations_base& rhs) noexcept
  {
    if (!this->m_has_val && rhs.m_has_val) {
      geterr().~unexpected<E>();
      construct(rhs.get());
    } else {
      assign_common(rhs);
    }
  }

  void assign(expected_operations_base&& rhs) noexcept
  {
    if (!this->m_has_val && rhs.m_has_val) {
      geterr().~unexpected<E>();
      construct(std::move(rhs).get());
    } else {
      assign_common(rhs);
    }
  }

#endif

  // The common part of move/copy assigning
  template<class Rhs>
  void assign_common(Rhs&& rhs)
  {
    if (this->m_has_val) {
      if (rhs.m_has_val) {
        get() = std::forward<Rhs>(rhs).get();
      } else {
        destroy_val();
        construct_error(std::forward<Rhs>(rhs).geterr());
      }
    } else {
      if (!rhs.m_has_val) {
        geterr() = std::forward<Rhs>(rhs).geterr();
      }
    }
  }

  bool has_value() const
  {
    return this->m_has_val;
  }

  TL_EXPECTED_11_CONSTEXPR T& get() &
  {
    return this->m_val;
  }
  constexpr const T& get() const&
  {
    return this->m_val;
  }
  TL_EXPECTED_11_CONSTEXPR T&& get() &&
  {
    return std::move(this->m_val);
  }
#ifndef TL_EXPECTED_NO_CONSTRR
  constexpr const T&& get() const&&
  {
    return std::move(this->m_val);
  }
#endif

  TL_EXPECTED_11_CONSTEXPR unexpected<E>& geterr() &
  {
    return this->m_unexpect;
  }
  constexpr const unexpected<E>& geterr() const&
  {
    return this->m_unexpect;
  }
  TL_EXPECTED_11_CONSTEXPR unexpected<E>&& geterr() &&
  {
    return std::move(this->m_unexpect);
  }
#ifndef TL_EXPECTED_NO_CONSTRR
  constexpr const unexpected<E>&& geterr() const&&
  {
    return std::move(this->m_unexpect);
  }
#endif

  TL_EXPECTED_11_CONSTEXPR void destroy_val()
  {
    get().~T();
  }
};

// This base class provides some handy member functions which can be used in
// further derived classes
template<class E>
struct expected_operations_base<void, E> : expected_storage_base<void, E> {
  using expected_storage_base<void, E>::expected_storage_base;

  template<class... Args>
  void construct() noexcept
  {
    this->m_has_val = true;
  }

  // This function doesn't use its argument, but needs it so that code in
  // levels above this can work independently of whether T is void
  template<class Rhs>
  void construct_with(Rhs&&) noexcept
  {
    this->m_has_val = true;
  }

  template<class... Args>
  void construct_error(Args&&... args) noexcept
  {
    new (std::addressof(this->m_unexpect)) unexpected<E>(std::forward<Args>(args)...);
    this->m_has_val = false;
  }

  template<class Rhs>
  void assign(Rhs&& rhs) noexcept
  {
    if (!this->m_has_val) {
      if (rhs.m_has_val) {
        geterr().~unexpected<E>();
        construct();
      } else {
        geterr() = std::forward<Rhs>(rhs).geterr();
      }
    } else {
      if (!rhs.m_has_val) {
        construct_error(std::forward<Rhs>(rhs).geterr());
      }
    }
  }

  bool has_value() const
  {
    return this->m_has_val;
  }

  TL_EXPECTED_11_CONSTEXPR unexpected<E>& geterr() &
  {
    return this->m_unexpect;
  }
  constexpr const unexpected<E>& geterr() const&
  {
    return this->m_unexpect;
  }
  TL_EXPECTED_11_CONSTEXPR unexpected<E>&& geterr() &&
  {
    return std::move(this->m_unexpect);
  }
#ifndef TL_EXPECTED_NO_CONSTRR
  constexpr const unexpected<E>&& geterr() const&&
  {
    return std::move(this->m_unexpect);
  }
#endif

  TL_EXPECTED_11_CONSTEXPR void destroy_val()
  {
    // no-op
  }
};

// This class manages conditionally having a trivial copy constructor
// This specialization is for when T and E are trivially copy constructible
template<class T,
         class E,
         bool = is_void_or<T, TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T)>::value &&
                TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(E)::value>
struct expected_copy_base : expected_operations_base<T, E> {
  using expected_operations_base<T, E>::expected_operations_base;
};

// This specialization is for when T or E are not trivially copy constructible
template<class T, class E>
struct expected_copy_base<T, E, false> : expected_operations_base<T, E> {
  using expected_operations_base<T, E>::expected_operations_base;

  expected_copy_base() = default;
  expected_copy_base(const expected_copy_base& rhs)
    : expected_operations_base<T, E>(no_init)
  {
    if (rhs.has_value()) {
      this->construct_with(rhs);
    } else {
      this->construct_error(rhs.geterr());
    }
  }

  expected_copy_base(expected_copy_base&& rhs) = default;
  expected_copy_base& operator=(const expected_copy_base& rhs) = default;
  expected_copy_base& operator=(expected_copy_base&& rhs) = default;
};

// This class manages conditionally having a trivial move constructor
// Unfortunately there's no way to achieve this in GCC < 5 AFAIK, since it
// doesn't implement an analogue to std::is_trivially_move_constructible. We
// have to make do with a non-trivial move constructor even if T is trivially
// move constructible
#ifndef TL_EXPECTED_GCC49
template<class T,
         class E,
         bool = is_void_or<T, std::is_trivially_move_constructible<T>>::value &&
                std::is_trivially_move_constructible<E>::value>
struct expected_move_base : expected_copy_base<T, E> {
  using expected_copy_base<T, E>::expected_copy_base;
};
#else
template<class T, class E, bool = false>
struct expected_move_base;
#endif
template<class T, class E>
struct expected_move_base<T, E, false> : expected_copy_base<T, E> {
  using expected_copy_base<T, E>::expected_copy_base;

  expected_move_base() = default;
  expected_move_base(const expected_move_base& rhs) = default;

  expected_move_base(expected_move_base&& rhs) noexcept(
    std::is_nothrow_move_constructible<T>::value)
    : expected_copy_base<T, E>(no_init)
  {
    if (rhs.has_value()) {
      this->construct_with(std::move(rhs));
    } else {
      this->construct_error(std::move(rhs.geterr()));
    }
  }
  expected_move_base& operator=(const expected_move_base& rhs) = default;
  expected_move_base& operator=(expected_move_base&& rhs) = default;
};

// This class manages conditionally having a trivial copy assignment operator
template<class T,
         class E,
         bool = is_void_or<T,
                           conjunction<TL_EXPECTED_IS_TRIVIALLY_COPY_ASSIGNABLE(T),
                                       TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T),
                                       TL_EXPECTED_IS_TRIVIALLY_DESTRUCTIBLE(T)>>::value &&
                TL_EXPECTED_IS_TRIVIALLY_COPY_ASSIGNABLE(E)::value &&
                TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(E)::value &&
                TL_EXPECTED_IS_TRIVIALLY_DESTRUCTIBLE(E)::value>
struct expected_copy_assign_base : expected_move_base<T, E> {
  using expected_move_base<T, E>::expected_move_base;
};

template<class T, class E>
struct expected_copy_assign_base<T, E, false> : expected_move_base<T, E> {
  using expected_move_base<T, E>::expected_move_base;

  expected_copy_assign_base() = default;
  expected_copy_assign_base(const expected_copy_assign_base& rhs) = default;

  expected_copy_assign_base(expected_copy_assign_base&& rhs) = default;
  expected_copy_assign_base& operator=(const expected_copy_assign_base& rhs)
  {
    this->assign(rhs);
    return *this;
  }
  expected_copy_assign_base& operator=(expected_copy_assign_base&& rhs) = default;
};

// This class manages conditionally having a trivial move assignment operator
// Unfortunately there's no way to achieve this in GCC < 5 AFAIK, since it
// doesn't implement an analogue to std::is_trivially_move_assignable. We have
// to make do with a non-trivial move assignment operator even if T is trivially
// move assignable
#ifndef TL_EXPECTED_GCC49
template<class T,
         class E,
         bool = is_void_or<T,
                           conjunction<std::is_trivially_destructible<T>,
                                       std::is_trivially_move_constructible<T>,
                                       std::is_trivially_move_assignable<T>>>::value &&
                std::is_trivially_destructible<E>::value &&
                std::is_trivially_move_constructible<E>::value &&
                std::is_trivially_move_assignable<E>::value>
struct expected_move_assign_base : expected_copy_assign_base<T, E> {
  using expected_copy_assign_base<T, E>::expected_copy_assign_base;
};
#else
template<class T, class E, bool = false>
struct expected_move_assign_base;
#endif

template<class T, class E>
struct expected_move_assign_base<T, E, false> : expected_copy_assign_base<T, E> {
  using expected_copy_assign_base<T, E>::expected_copy_assign_base;

  expected_move_assign_base() = default;
  expected_move_assign_base(const expected_move_assign_base& rhs) = default;

  expected_move_assign_base(expected_move_assign_base&& rhs) = default;

  expected_move_assign_base& operator=(const expected_move_assign_base& rhs) = default;

  expected_move_assign_base& operator=(expected_move_assign_base&& rhs) noexcept(
    std::is_nothrow_move_constructible<T>::value && std::is_nothrow_move_assignable<T>::value)
  {
    this->assign(std::move(rhs));
    return *this;
  }
};

// expected_delete_ctor_base will conditionally delete copy and move
// constructors depending on whether T is copy/move constructible
template<class T,
         class E,
         bool EnableCopy =
           (is_copy_constructible_or_void<T>::value && std::is_copy_constructible<E>::value),
         bool EnableMove =
           (is_move_constructible_or_void<T>::value && std::is_move_constructible<E>::value)>
struct expected_delete_ctor_base {
  expected_delete_ctor_base() = default;
  expected_delete_ctor_base(const expected_delete_ctor_base&) = default;
  expected_delete_ctor_base(expected_delete_ctor_base&&) noexcept = default;
  expected_delete_ctor_base& operator=(const expected_delete_ctor_base&) = default;
  expected_delete_ctor_base& operator=(expected_delete_ctor_base&&) noexcept = default;
};

template<class T, class E>
struct expected_delete_ctor_base<T, E, true, false> {
  expected_delete_ctor_base() = default;
  expected_delete_ctor_base(const expected_delete_ctor_base&) = default;
  expected_delete_ctor_base(expected_delete_ctor_base&&) noexcept = delete;
  expected_delete_ctor_base& operator=(const expected_delete_ctor_base&) = default;
  expected_delete_ctor_base& operator=(expected_delete_ctor_base&&) noexcept = default;
};

template<class T, class E>
struct expected_delete_ctor_base<T, E, false, true> {
  expected_delete_ctor_base() = default;
  expected_delete_ctor_base(const expected_delete_ctor_base&) = delete;
  expected_delete_ctor_base(expected_delete_ctor_base&&) noexcept = default;
  expected_delete_ctor_base& operator=(const expected_delete_ctor_base&) = default;
  expected_delete_ctor_base& operator=(expected_delete_ctor_base&&) noexcept = default;
};

template<class T, class E>
struct expected_delete_ctor_base<T, E, false, false> {
  expected_delete_ctor_base() = default;
  expected_delete_ctor_base(const expected_delete_ctor_base&) = delete;
  expected_delete_ctor_base(expected_delete_ctor_base&&) noexcept = delete;
  expected_delete_ctor_base& operator=(const expected_delete_ctor_base&) = default;
  expected_delete_ctor_base& operator=(expected_delete_ctor_base&&) noexcept = default;
};

// expected_delete_assign_base will conditionally delete copy and move
// constructors depending on whether T and E are copy/move constructible +
// assignable
template<class T,
         class E,
         bool EnableCopy =
           (is_copy_constructible_or_void<T>::value && std::is_copy_constructible<E>::value &&
            is_copy_assignable_or_void<T>::value && std::is_copy_assignable<E>::value),
         bool EnableMove =
           (is_move_constructible_or_void<T>::value && std::is_move_constructible<E>::value &&
            is_move_assignable_or_void<T>::value && std::is_move_assignable<E>::value)>
struct expected_delete_assign_base {
  expected_delete_assign_base() = default;
  expected_delete_assign_base(const expected_delete_assign_base&) = default;
  expected_delete_assign_base(expected_delete_assign_base&&) noexcept = default;
  expected_delete_assign_base& operator=(const expected_delete_assign_base&) = default;
  expected_delete_assign_base& operator=(expected_delete_assign_base&&) noexcept = default;
};

template<class T, class E>
struct expected_delete_assign_base<T, E, true, false> {
  expected_delete_assign_base() = default;
  expected_delete_assign_base(const expected_delete_assign_base&) = default;
  expected_delete_assign_base(expected_delete_assign_base&&) noexcept = default;
  expected_delete_assign_base& operator=(const expected_delete_assign_base&) = default;
  expected_delete_assign_base& operator=(expected_delete_assign_base&&) noexcept = delete;
};

template<class T, class E>
struct expected_delete_assign_base<T, E, false, true> {
  expected_delete_assign_base() = default;
  expected_delete_assign_base(const expected_delete_assign_base&) = default;
  expected_delete_assign_base(expected_delete_assign_base&&) noexcept = default;
  expected_delete_assign_base& operator=(const expected_delete_assign_base&) = delete;
  expected_delete_assign_base& operator=(expected_delete_assign_base&&) noexcept = default;
};

template<class T, class E>
struct expected_delete_assign_base<T, E, false, false> {
  expected_delete_assign_base() = default;
  expected_delete_assign_base(const expected_delete_assign_base&) = default;
  expected_delete_assign_base(expected_delete_assign_base&&) noexcept = default;
  expected_delete_assign_base& operator=(const expected_delete_assign_base&) = delete;
  expected_delete_assign_base& operator=(expected_delete_assign_base&&) noexcept = delete;
};

// This is needed to be able to construct the expected_default_ctor_base which
// follows, while still conditionally deleting the default constructor.
struct default_constructor_tag {
  explicit constexpr default_constructor_tag() = default;
};

// expected_default_ctor_base will ensure that expected has a deleted default
// consturctor if T is not default constructible.
// This specialization is for when T is default constructible
template<class T,
         class E,
         bool Enable = std::is_default_constructible<T>::value || std::is_void<T>::value>
struct expected_default_ctor_base {
  constexpr expected_default_ctor_base() noexcept = default;
  constexpr expected_default_ctor_base(expected_default_ctor_base const&) noexcept = default;
  constexpr expected_default_ctor_base(expected_default_ctor_base&&) noexcept = default;
  expected_default_ctor_base& operator=(expected_default_ctor_base const&) noexcept = default;
  expected_default_ctor_base& operator=(expected_default_ctor_base&&) noexcept = default;

  constexpr explicit expected_default_ctor_base(default_constructor_tag)
  {
  }
};

// This specialization is for when T is not default constructible
template<class T, class E>
struct expected_default_ctor_base<T, E, false> {
  constexpr expected_default_ctor_base() noexcept = delete;
  constexpr expected_default_ctor_base(expected_default_ctor_base const&) noexcept = default;
  constexpr expected_default_ctor_base(expected_default_ctor_base&&) noexcept = default;
  expected_default_ctor_base& operator=(expected_default_ctor_base const&) noexcept = default;
  expected_default_ctor_base& operator=(expected_default_ctor_base&&) noexcept = default;

  constexpr explicit expected_default_ctor_base(default_constructor_tag)
  {
  }
};
} // namespace detail

template<class E>
class bad_expected_access : public std::exception
{
public:
  explicit bad_expected_access(E e)
    : m_val(std::move(e))
  {
  }

  virtual const char* what() const noexcept override
  {
    return "Bad expected access";
  }

  const E& error() const&
  {
    return m_val;
  }
  E& error() &
  {
    return m_val;
  }
  const E&& error() const&&
  {
    return std::move(m_val);
  }
  E&& error() &&
  {
    return std::move(m_val);
  }

private:
  E m_val;
};

/// An `expected<T, E>` object is an object that contains the storage for
/// another object and manages the lifetime of this contained object `T`.
/// Alternatively it could contain the storage for another unexpected object
/// `E`. The contained object may not be initialized after the expected object
/// has been initialized, and may not be destroyed before the expected object
/// has been destroyed. The initialization state of the contained object is
/// tracked by the expected object.
template<class T, class E>
class expected
  : private detail::expected_move_assign_base<T, E>
  , private detail::expected_delete_ctor_base<T, E>
  , private detail::expected_delete_assign_base<T, E>
  , private detail::expected_default_ctor_base<T, E>
{
  static_assert(!std::is_reference<T>::value, "T must not be a reference");
  static_assert(!std::is_same<T, std::remove_cv<in_place_t>::type>::value,
                "T must not be in_place_t");
  static_assert(!std::is_same<T, std::remove_cv<unexpect_t>::type>::value,
                "T must not be unexpect_t");
  static_assert(!std::is_same<T, typename std::remove_cv<unexpected<E>>::type>::value,
                "T must not be unexpected<E>");
  static_assert(!std::is_reference<E>::value, "E must not be a reference");

  T* valptr()
  {
    return std::addressof(this->m_val);
  }
  const T* valptr() const
  {
    return std::addressof(this->m_val);
  }
  unexpected<E>* errptr()
  {
    return std::addressof(this->m_unexpect);
  }
  const unexpected<E>* errptr() const
  {
    return std::addressof(this->m_unexpect);
  }

  template<class U = T, detail::enable_if_t<!std::is_void<U>::value>* = nullptr>
  TL_EXPECTED_11_CONSTEXPR U& val()
  {
    return this->m_val;
  }
  TL_EXPECTED_11_CONSTEXPR unexpected<E>& err()
  {
    return this->m_unexpect;
  }

  template<class U = T, detail::enable_if_t<!std::is_void<U>::value>* = nullptr>
  constexpr const U& val() const
  {
    return this->m_val;
  }
  constexpr const unexpected<E>& err() const
  {
    return this->m_unexpect;
  }

  using impl_base = detail::expected_move_assign_base<T, E>;
  using ctor_base = detail::expected_default_ctor_base<T, E>;

public:
  typedef T value_type;
  typedef E error_type;
  typedef unexpected<E> unexpected_type;

#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) && !defined(TL_EXPECTED_GCC54) &&    \
  !defined(TL_EXPECTED_GCC55)
  template<class F>
  TL_EXPECTED_11_CONSTEXPR auto and_then(F&& f) &
  {
    return and_then_impl(*this, std::forward<F>(f));
  }
  template<class F>
  TL_EXPECTED_11_CONSTEXPR auto and_then(F&& f) &&
  {
    return and_then_impl(std::move(*this), std::forward<F>(f));
  }
  template<class F>
  constexpr auto and_then(F&& f) const&
  {
    return and_then_impl(*this, std::forward<F>(f));
  }

#ifndef TL_EXPECTED_NO_CONSTRR
  template<class F>
  constexpr auto and_then(F&& f) const&&
  {
    return and_then_impl(std::move(*this), std::forward<F>(f));
  }
#endif

#else
  template<class F>
  TL_EXPECTED_11_CONSTEXPR auto and_then(
    F&& f) & -> decltype(and_then_impl(std::declval<expected&>(), std::forward<F>(f)))
  {
    return and_then_impl(*this, std::forward<F>(f));
  }
  template<class F>
  TL_EXPECTED_11_CONSTEXPR auto and_then(
    F&& f) && -> decltype(and_then_impl(std::declval<expected&&>(), std::forward<F>(f)))
  {
    return and_then_impl(std::move(*this), std::forward<F>(f));
  }
  template<class F>
  constexpr auto and_then(F&& f) const& -> decltype(and_then_impl(std::declval<expected const&>(),
                                                                  std::forward<F>(f)))
  {
    return and_then_impl(*this, std::forward<F>(f));
  }

#ifndef TL_EXPECTED_NO_CONSTRR
  template<class F>
  constexpr auto and_then(F&& f) const&& -> decltype(and_then_impl(std::declval<expected const&&>(),
                                                                   std::forward<F>(f)))
  {
    return and_then_impl(std::move(*this), std::forward<F>(f));
  }
#endif
#endif

#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) && !defined(TL_EXPECTED_GCC54) &&    \
  !defined(TL_EXPECTED_GCC55)
  template<class F>
  TL_EXPECTED_11_CONSTEXPR auto map(F&& f) &
  {
    return expected_map_impl(*this, std::forward<F>(f));
  }
  template<class F>
  TL_EXPECTED_11_CONSTEXPR auto map(F&& f) &&
  {
    return expected_map_impl(std::move(*this), std::forward<F>(f));
  }
  template<class F>
  constexpr auto map(F&& f) const&
  {
    return expected_map_impl(*this, std::forward<F>(f));
  }
  template<class F>
  constexpr auto map(F&& f) const&&
  {
    return expected_map_impl(std::move(*this), std::forward<F>(f));
  }
#else
  template<class F>
  TL_EXPECTED_11_CONSTEXPR decltype(expected_map_impl(std::declval<expected&>(),
                                                      std::declval<F&&>()))
  map(F&& f) &
  {
    return expected_map_impl(*this, std::forward<F>(f));
  }
  template<class F>
  TL_EXPECTED_11_CONSTEXPR decltype(expected_map_impl(std::declval<expected>(),
                                                      std::declval<F&&>()))
  map(F&& f) &&
  {
    return expected_map_impl(std::move(*this), std::forward<F>(f));
  }
  template<class F>
  constexpr decltype(expected_map_impl(std::declval<const expected&>(), std::declval<F&&>())) map(
    F&& f) const&
  {
    return expected_map_impl(*this, std::forward<F>(f));
  }

#ifndef TL_EXPECTED_NO_CONSTRR
  template<class F>
  constexpr decltype(expected_map_impl(std::declval<const expected&&>(), std::declval<F&&>())) map(
    F&& f) const&&
  {
    return expected_map_impl(std::move(*this), std::forward<F>(f));
  }
#endif
#endif

#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) && !defined(TL_EXPECTED_GCC54) &&    \
  !defined(TL_EXPECTED_GCC55)
  template<class F>
  TL_EXPECTED_11_CONSTEXPR auto transform(F&& f) &
  {
    return expected_map_impl(*this, std::forward<F>(f));
  }
  template<class F>
  TL_EXPECTED_11_CONSTEXPR auto transform(F&& f) &&
  {
    return expected_map_impl(std::move(*this), std::forward<F>(f));
  }
  template<class F>
  constexpr auto transform(F&& f) const&
  {
    return expected_map_impl(*this, std::forward<F>(f));
  }
  template<class F>
  constexpr auto transform(F&& f) const&&
  {
    return expected_map_impl(std::move(*this), std::forward<F>(f));
  }
#else
  template<class F>
  TL_EXPECTED_11_CONSTEXPR decltype(expected_map_impl(std::declval<expected&>(),
                                                      std::declval<F&&>()))
  transform(F&& f) &
  {
    return expected_map_impl(*this, std::forward<F>(f));
  }
  template<class F>
  TL_EXPECTED_11_CONSTEXPR decltype(expected_map_impl(std::declval<expected>(),
                                                      std::declval<F&&>()))
  transform(F&& f) &&
  {
    return expected_map_impl(std::move(*this), std::forward<F>(f));
  }
  template<class F>
  constexpr decltype(expected_map_impl(std::declval<const expected&>(), std::declval<F&&>()))
  transform(F&& f) const&
  {
    return expected_map_impl(*this, std::forward<F>(f));
  }

#ifndef TL_EXPECTED_NO_CONSTRR
  template<class F>
  constexpr decltype(expected_map_impl(std::declval<const expected&&>(), std::declval<F&&>()))
  transform(F&& f) const&&
  {
    return expected_map_impl(std::move(*this), std::forward<F>(f));
  }
#endif
#endif

#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) && !defined(TL_EXPECTED_GCC54) &&    \
  !defined(TL_EXPECTED_GCC55)
  template<class F>
  TL_EXPECTED_11_CONSTEXPR auto map_error(F&& f) &
  {
    return map_error_impl(*this, std::forward<F>(f));
  }
  template<class F>
  TL_EXPECTED_11_CONSTEXPR auto map_error(F&& f) &&
  {
    return map_error_impl(std::move(*this), std::forward<F>(f));
  }
  template<class F>
  constexpr auto map_error(F&& f) const&
  {
    return map_error_impl(*this, std::forward<F>(f));
  }
  template<class F>
  constexpr auto map_error(F&& f) const&&
  {
    return map_error_impl(std::move(*this), std::forward<F>(f));
  }
#else
  template<class F>
  TL_EXPECTED_11_CONSTEXPR decltype(map_error_impl(std::declval<expected&>(), std::declval<F&&>()))
  map_error(F&& f) &
  {
    return map_error_impl(*this, std::forward<F>(f));
  }
  template<class F>
  TL_EXPECTED_11_CONSTEXPR decltype(map_error_impl(std::declval<expected&&>(), std::declval<F&&>()))
  map_error(F&& f) &&
  {
    return map_error_impl(std::move(*this), std::forward<F>(f));
  }
  template<class F>
  constexpr decltype(map_error_impl(std::declval<const expected&>(), std::declval<F&&>()))
  map_error(F&& f) const&
  {
    return map_error_impl(*this, std::forward<F>(f));
  }

#ifndef TL_EXPECTED_NO_CONSTRR
  template<class F>
  constexpr decltype(map_error_impl(std::declval<const expected&&>(), std::declval<F&&>()))
  map_error(F&& f) const&&
  {
    return map_error_impl(std::move(*this), std::forward<F>(f));
  }
#endif
#endif
  template<class F>
  expected TL_EXPECTED_11_CONSTEXPR or_else(F&& f) &
  {
    return or_else_impl(*this, std::forward<F>(f));
  }

  template<class F>
  expected TL_EXPECTED_11_CONSTEXPR or_else(F&& f) &&
  {
    return or_else_impl(std::move(*this), std::forward<F>(f));
  }

  template<class F>
  expected constexpr or_else(F&& f) const&
  {
    return or_else_impl(*this, std::forward<F>(f));
  }

#ifndef TL_EXPECTED_NO_CONSTRR
  template<class F>
  expected constexpr or_else(F&& f) const&&
  {
    return or_else_impl(std::move(*this), std::forward<F>(f));
  }
#endif
  constexpr expected() = default;
  constexpr expected(const expected& rhs) = default;
  constexpr expected(expected&& rhs) = default;
  expected& operator=(const expected& rhs) = default;
  expected& operator=(expected&& rhs) = default;

  template<class... Args,
           detail::enable_if_t<std::is_constructible<T, Args&&...>::value>* = nullptr>
  constexpr expected(in_place_t, Args&&... args)
    : impl_base(in_place, std::forward<Args>(args)...)
    , ctor_base(detail::default_constructor_tag{})
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<T, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr expected(in_place_t, std::initializer_list<U> il, Args&&... args)
    : impl_base(in_place, il, std::forward<Args>(args)...)
    , ctor_base(detail::default_constructor_tag{})
  {
  }

  template<class G = E,
           detail::enable_if_t<std::is_constructible<E, const G&>::value>* = nullptr,
           detail::enable_if_t<!std::is_convertible<const G&, E>::value>* = nullptr>
  explicit constexpr expected(const unexpected<G>& e)
    : impl_base(unexpect, e.value())
    , ctor_base(detail::default_constructor_tag{})
  {
  }

  template<class G = E,
           detail::enable_if_t<std::is_constructible<E, const G&>::value>* = nullptr,
           detail::enable_if_t<std::is_convertible<const G&, E>::value>* = nullptr>
  constexpr expected(unexpected<G> const& e)
    : impl_base(unexpect, e.value())
    , ctor_base(detail::default_constructor_tag{})
  {
  }

  template<class G = E,
           detail::enable_if_t<std::is_constructible<E, G&&>::value>* = nullptr,
           detail::enable_if_t<!std::is_convertible<G&&, E>::value>* = nullptr>
  explicit constexpr expected(unexpected<G>&& e) noexcept(
    std::is_nothrow_constructible<E, G&&>::value)
    : impl_base(unexpect, std::move(e.value()))
    , ctor_base(detail::default_constructor_tag{})
  {
  }

  template<class G = E,
           detail::enable_if_t<std::is_constructible<E, G&&>::value>* = nullptr,
           detail::enable_if_t<std::is_convertible<G&&, E>::value>* = nullptr>
  constexpr expected(unexpected<G>&& e) noexcept(std::is_nothrow_constructible<E, G&&>::value)
    : impl_base(unexpect, std::move(e.value()))
    , ctor_base(detail::default_constructor_tag{})
  {
  }

  template<class... Args,
           detail::enable_if_t<std::is_constructible<E, Args&&...>::value>* = nullptr>
  constexpr explicit expected(unexpect_t, Args&&... args)
    : impl_base(unexpect, std::forward<Args>(args)...)
    , ctor_base(detail::default_constructor_tag{})
  {
  }

  template<class U,
           class... Args,
           detail::enable_if_t<
             std::is_constructible<E, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  constexpr explicit expected(unexpect_t, std::initializer_list<U> il, Args&&... args)
    : impl_base(unexpect, il, std::forward<Args>(args)...)
    , ctor_base(detail::default_constructor_tag{})
  {
  }

  template<class U,
           class G,
           detail::enable_if_t<!(std::is_convertible<U const&, T>::value &&
                                 std::is_convertible<G const&, E>::value)>* = nullptr,
           detail::expected_enable_from_other<T, E, U, G, const U&, const G&>* = nullptr>
  explicit TL_EXPECTED_11_CONSTEXPR expected(const expected<U, G>& rhs)
    : ctor_base(detail::default_constructor_tag{})
  {
    if (rhs.has_value()) {
      this->construct(*rhs);
    } else {
      this->construct_error(rhs.error());
    }
  }

  template<class U,
           class G,
           detail::enable_if_t<(std::is_convertible<U const&, T>::value &&
                                std::is_convertible<G const&, E>::value)>* = nullptr,
           detail::expected_enable_from_other<T, E, U, G, const U&, const G&>* = nullptr>
  TL_EXPECTED_11_CONSTEXPR expected(const expected<U, G>& rhs)
    : ctor_base(detail::default_constructor_tag{})
  {
    if (rhs.has_value()) {
      this->construct(*rhs);
    } else {
      this->construct_error(rhs.error());
    }
  }

  template<class U,
           class G,
           detail::enable_if_t<!(std::is_convertible<U&&, T>::value &&
                                 std::is_convertible<G&&, E>::value)>* = nullptr,
           detail::expected_enable_from_other<T, E, U, G, U&&, G&&>* = nullptr>
  explicit TL_EXPECTED_11_CONSTEXPR expected(expected<U, G>&& rhs)
    : ctor_base(detail::default_constructor_tag{})
  {
    if (rhs.has_value()) {
      this->construct(std::move(*rhs));
    } else {
      this->construct_error(std::move(rhs.error()));
    }
  }

  template<class U,
           class G,
           detail::enable_if_t<(std::is_convertible<U&&, T>::value &&
                                std::is_convertible<G&&, E>::value)>* = nullptr,
           detail::expected_enable_from_other<T, E, U, G, U&&, G&&>* = nullptr>
  TL_EXPECTED_11_CONSTEXPR expected(expected<U, G>&& rhs)
    : ctor_base(detail::default_constructor_tag{})
  {
    if (rhs.has_value()) {
      this->construct(std::move(*rhs));
    } else {
      this->construct_error(std::move(rhs.error()));
    }
  }

  template<class U = T,
           detail::enable_if_t<!std::is_convertible<U&&, T>::value>* = nullptr,
           detail::expected_enable_forward_value<T, E, U>* = nullptr>
  explicit TL_EXPECTED_MSVC2015_CONSTEXPR expected(U&& v)
    : expected(in_place, std::forward<U>(v))
  {
  }

  template<class U = T,
           detail::enable_if_t<std::is_convertible<U&&, T>::value>* = nullptr,
           detail::expected_enable_forward_value<T, E, U>* = nullptr>
  TL_EXPECTED_MSVC2015_CONSTEXPR expected(U&& v)
    : expected(in_place, std::forward<U>(v))
  {
  }

  template<class U = T,
           class G = T,
           detail::enable_if_t<std::is_nothrow_constructible<T, U&&>::value>* = nullptr,
           detail::enable_if_t<!std::is_void<G>::value>* = nullptr,
           detail::enable_if_t<
             (!std::is_same<expected<T, E>, detail::decay_t<U>>::value &&
              !detail::conjunction<std::is_scalar<T>, std::is_same<T, detail::decay_t<U>>>::value &&
              std::is_constructible<T, U>::value && std::is_assignable<G&, U>::value &&
              std::is_nothrow_move_constructible<E>::value)>* = nullptr>
  expected& operator=(U&& v)
  {
    if (has_value()) {
      val() = std::forward<U>(v);
    } else {
      err().~unexpected<E>();
      ::new (valptr()) T(std::forward<U>(v));
      this->m_has_val = true;
    }

    return *this;
  }

  template<class U = T,
           class G = T,
           detail::enable_if_t<!std::is_nothrow_constructible<T, U&&>::value>* = nullptr,
           detail::enable_if_t<!std::is_void<U>::value>* = nullptr,
           detail::enable_if_t<
             (!std::is_same<expected<T, E>, detail::decay_t<U>>::value &&
              !detail::conjunction<std::is_scalar<T>, std::is_same<T, detail::decay_t<U>>>::value &&
              std::is_constructible<T, U>::value && std::is_assignable<G&, U>::value &&
              std::is_nothrow_move_constructible<E>::value)>* = nullptr>
  expected& operator=(U&& v)
  {
    if (has_value()) {
      val() = std::forward<U>(v);
    } else {
      auto tmp = std::move(err());
      err().~unexpected<E>();

#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
      try {
        ::new (valptr()) T(std::forward<U>(v));
        this->m_has_val = true;
      } catch (...) {
        err() = std::move(tmp);
        throw;
      }
#else
      ::new (valptr()) T(std::forward<U>(v));
      this->m_has_val = true;
#endif
    }

    return *this;
  }

  template<class G = E,
           detail::enable_if_t<std::is_nothrow_copy_constructible<G>::value &&
                               std::is_assignable<G&, G>::value>* = nullptr>
  expected& operator=(const unexpected<G>& rhs)
  {
    if (!has_value()) {
      err() = rhs;
    } else {
      this->destroy_val();
      ::new (errptr()) unexpected<E>(rhs);
      this->m_has_val = false;
    }

    return *this;
  }

  template<class G = E,
           detail::enable_if_t<std::is_nothrow_move_constructible<G>::value &&
                               std::is_move_assignable<G>::value>* = nullptr>
  expected& operator=(unexpected<G>&& rhs) noexcept
  {
    if (!has_value()) {
      err() = std::move(rhs);
    } else {
      this->destroy_val();
      ::new (errptr()) unexpected<E>(std::move(rhs));
      this->m_has_val = false;
    }

    return *this;
  }

  template<class... Args,
           detail::enable_if_t<std::is_nothrow_constructible<T, Args&&...>::value>* = nullptr>
  void emplace(Args&&... args)
  {
    if (has_value()) {
      val() = T(std::forward<Args>(args)...);
    } else {
      err().~unexpected<E>();
      ::new (valptr()) T(std::forward<Args>(args)...);
      this->m_has_val = true;
    }
  }

  template<class... Args,
           detail::enable_if_t<!std::is_nothrow_constructible<T, Args&&...>::value>* = nullptr>
  void emplace(Args&&... args)
  {
    if (has_value()) {
      val() = T(std::forward<Args>(args)...);
    } else {
      auto tmp = std::move(err());
      err().~unexpected<E>();

#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
      try {
        ::new (valptr()) T(std::forward<Args>(args)...);
        this->m_has_val = true;
      } catch (...) {
        err() = std::move(tmp);
        throw;
      }
#else
      ::new (valptr()) T(std::forward<Args>(args)...);
      this->m_has_val = true;
#endif
    }
  }

  template<
    class U,
    class... Args,
    detail::enable_if_t<
      std::is_nothrow_constructible<T, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  void emplace(std::initializer_list<U> il, Args&&... args)
  {
    if (has_value()) {
      T t(il, std::forward<Args>(args)...);
      val() = std::move(t);
    } else {
      err().~unexpected<E>();
      ::new (valptr()) T(il, std::forward<Args>(args)...);
      this->m_has_val = true;
    }
  }

  template<
    class U,
    class... Args,
    detail::enable_if_t<
      !std::is_nothrow_constructible<T, std::initializer_list<U>&, Args&&...>::value>* = nullptr>
  void emplace(std::initializer_list<U> il, Args&&... args)
  {
    if (has_value()) {
      T t(il, std::forward<Args>(args)...);
      val() = std::move(t);
    } else {
      auto tmp = std::move(err());
      err().~unexpected<E>();

#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
      try {
        ::new (valptr()) T(il, std::forward<Args>(args)...);
        this->m_has_val = true;
      } catch (...) {
        err() = std::move(tmp);
        throw;
      }
#else
      ::new (valptr()) T(il, std::forward<Args>(args)...);
      this->m_has_val = true;
#endif
    }
  }

private:
  using t_is_void = std::true_type;
  using t_is_not_void = std::false_type;
  using t_is_nothrow_move_constructible = std::true_type;
  using move_constructing_t_can_throw = std::false_type;
  using e_is_nothrow_move_constructible = std::true_type;
  using move_constructing_e_can_throw = std::false_type;

  void swap_where_both_have_value(expected& /*rhs*/, t_is_void) noexcept
  {
    // swapping void is a no-op
  }

  void swap_where_both_have_value(expected& rhs, t_is_not_void)
  {
    using std::swap;
    swap(val(), rhs.val());
  }

  void swap_where_only_one_has_value(expected& rhs, t_is_void) noexcept(
    std::is_nothrow_move_constructible<E>::value)
  {
    ::new (errptr()) unexpected_type(std::move(rhs.err()));
    rhs.err().~unexpected_type();
    std::swap(this->m_has_val, rhs.m_has_val);
  }

  void swap_where_only_one_has_value(expected& rhs, t_is_not_void)
  {
    swap_where_only_one_has_value_and_t_is_not_void(
      rhs,
      typename std::is_nothrow_move_constructible<T>::type{},
      typename std::is_nothrow_move_constructible<E>::type{});
  }

  void swap_where_only_one_has_value_and_t_is_not_void(expected& rhs,
                                                       t_is_nothrow_move_constructible,
                                                       e_is_nothrow_move_constructible) noexcept
  {
    auto temp = std::move(val());
    val().~T();
    ::new (errptr()) unexpected_type(std::move(rhs.err()));
    rhs.err().~unexpected_type();
    ::new (rhs.valptr()) T(std::move(temp));
    std::swap(this->m_has_val, rhs.m_has_val);
  }

  void swap_where_only_one_has_value_and_t_is_not_void(expected& rhs,
                                                       t_is_nothrow_move_constructible,
                                                       move_constructing_e_can_throw)
  {
    auto temp = std::move(val());
    val().~T();
#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
    try {
      ::new (errptr()) unexpected_type(std::move(rhs.err()));
      rhs.err().~unexpected_type();
      ::new (rhs.valptr()) T(std::move(temp));
      std::swap(this->m_has_val, rhs.m_has_val);
    } catch (...) {
      val() = std::move(temp);
      throw;
    }
#else
    ::new (errptr()) unexpected_type(std::move(rhs.err()));
    rhs.err().~unexpected_type();
    ::new (rhs.valptr()) T(std::move(temp));
    std::swap(this->m_has_val, rhs.m_has_val);
#endif
  }

  void swap_where_only_one_has_value_and_t_is_not_void(expected& rhs,
                                                       move_constructing_t_can_throw,
                                                       t_is_nothrow_move_constructible)
  {
    auto temp = std::move(rhs.err());
    rhs.err().~unexpected_type();
#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
    try {
      ::new (rhs.valptr()) T(val());
      val().~T();
      ::new (errptr()) unexpected_type(std::move(temp));
      std::swap(this->m_has_val, rhs.m_has_val);
    } catch (...) {
      rhs.err() = std::move(temp);
      throw;
    }
#else
    ::new (rhs.valptr()) T(val());
    val().~T();
    ::new (errptr()) unexpected_type(std::move(temp));
    std::swap(this->m_has_val, rhs.m_has_val);
#endif
  }

public:
  template<class OT = T, class OE = E>
  detail::enable_if_t<detail::is_swappable<OT>::value && detail::is_swappable<OE>::value &&
                      (std::is_nothrow_move_constructible<OT>::value ||
                       std::is_nothrow_move_constructible<OE>::value)>
  swap(expected& rhs) noexcept(std::is_nothrow_move_constructible<T>::value &&
                               detail::is_nothrow_swappable<T>::value &&
                               std::is_nothrow_move_constructible<E>::value &&
                               detail::is_nothrow_swappable<E>::value)
  {
    if (has_value() && rhs.has_value()) {
      swap_where_both_have_value(rhs, typename std::is_void<T>::type{});
    } else if (!has_value() && rhs.has_value()) {
      rhs.swap(*this);
    } else if (has_value()) {
      swap_where_only_one_has_value(rhs, typename std::is_void<T>::type{});
    } else {
      using std::swap;
      swap(err(), rhs.err());
    }
  }

  constexpr const T* operator->() const
  {
    return valptr();
  }
  TL_EXPECTED_11_CONSTEXPR T* operator->()
  {
    return valptr();
  }

  template<class U = T, detail::enable_if_t<!std::is_void<U>::value>* = nullptr>
  constexpr const U& operator*() const&
  {
    return val();
  }
  template<class U = T, detail::enable_if_t<!std::is_void<U>::value>* = nullptr>
  TL_EXPECTED_11_CONSTEXPR U& operator*() &
  {
    return val();
  }
  template<class U = T, detail::enable_if_t<!std::is_void<U>::value>* = nullptr>
  constexpr const U&& operator*() const&&
  {
    return std::move(val());
  }
  template<class U = T, detail::enable_if_t<!std::is_void<U>::value>* = nullptr>
  TL_EXPECTED_11_CONSTEXPR U&& operator*() &&
  {
    return std::move(val());
  }

  constexpr bool has_value() const noexcept
  {
    return this->m_has_val;
  }
  constexpr explicit operator bool() const noexcept
  {
    return this->m_has_val;
  }

  template<class U = T, detail::enable_if_t<!std::is_void<U>::value>* = nullptr>
  TL_EXPECTED_11_CONSTEXPR const U& value() const&
  {
    if (!has_value())
      detail::throw_exception(bad_expected_access<E>(err().value()));
    return val();
  }
  template<class U = T, detail::enable_if_t<!std::is_void<U>::value>* = nullptr>
  TL_EXPECTED_11_CONSTEXPR U& value() &
  {
    if (!has_value())
      detail::throw_exception(bad_expected_access<E>(err().value()));
    return val();
  }
  template<class U = T, detail::enable_if_t<!std::is_void<U>::value>* = nullptr>
  TL_EXPECTED_11_CONSTEXPR const U&& value() const&&
  {
    if (!has_value())
      detail::throw_exception(bad_expected_access<E>(std::move(err()).value()));
    return std::move(val());
  }
  template<class U = T, detail::enable_if_t<!std::is_void<U>::value>* = nullptr>
  TL_EXPECTED_11_CONSTEXPR U&& value() &&
  {
    if (!has_value())
      detail::throw_exception(bad_expected_access<E>(std::move(err()).value()));
    return std::move(val());
  }

  constexpr const E& error() const&
  {
    return err().value();
  }
  TL_EXPECTED_11_CONSTEXPR E& error() &
  {
    return err().value();
  }
  constexpr const E&& error() const&&
  {
    return std::move(err().value());
  }
  TL_EXPECTED_11_CONSTEXPR E&& error() &&
  {
    return std::move(err().value());
  }

  template<class U>
  constexpr T value_or(U&& v) const&
  {
    static_assert(std::is_copy_constructible<T>::value && std::is_convertible<U&&, T>::value,
                  "T must be copy-constructible and convertible to from U&&");
    return bool(*this) ? **this : static_cast<T>(std::forward<U>(v));
  }
  template<class U>
  TL_EXPECTED_11_CONSTEXPR T value_or(U&& v) &&
  {
    static_assert(std::is_move_constructible<T>::value && std::is_convertible<U&&, T>::value,
                  "T must be move-constructible and convertible to from U&&");
    return bool(*this) ? std::move(**this) : static_cast<T>(std::forward<U>(v));
  }
};

namespace detail
{
template<class Exp>
using exp_t = typename detail::decay_t<Exp>::value_type;
template<class Exp>
using err_t = typename detail::decay_t<Exp>::error_type;
template<class Exp, class Ret>
using ret_t = expected<Ret, err_t<Exp>>;

#ifdef TL_EXPECTED_CXX14
template<class Exp,
         class F,
         detail::enable_if_t<!std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), *std::declval<Exp>()))>
constexpr auto
and_then_impl(Exp&& exp, F&& f)
{
  static_assert(detail::is_expected<Ret>::value, "F must return an expected");

  return exp.has_value() ? detail::invoke(std::forward<F>(f), *std::forward<Exp>(exp))
                         : Ret(unexpect, std::forward<Exp>(exp).error());
}

template<class Exp,
         class F,
         detail::enable_if_t<std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>()))>
constexpr auto
and_then_impl(Exp&& exp, F&& f)
{
  static_assert(detail::is_expected<Ret>::value, "F must return an expected");

  return exp.has_value() ? detail::invoke(std::forward<F>(f))
                         : Ret(unexpect, std::forward<Exp>(exp).error());
}
#else
template<class>
struct TC;
template<class Exp,
         class F,
         class Ret = decltype(detail::invoke(std::declval<F>(), *std::declval<Exp>())),
         detail::enable_if_t<!std::is_void<exp_t<Exp>>::value>* = nullptr>
auto
and_then_impl(Exp&& exp, F&& f) -> Ret
{
  static_assert(detail::is_expected<Ret>::value, "F must return an expected");

  return exp.has_value() ? detail::invoke(std::forward<F>(f), *std::forward<Exp>(exp))
                         : Ret(unexpect, std::forward<Exp>(exp).error());
}

template<class Exp,
         class F,
         class Ret = decltype(detail::invoke(std::declval<F>())),
         detail::enable_if_t<std::is_void<exp_t<Exp>>::value>* = nullptr>
constexpr auto
and_then_impl(Exp&& exp, F&& f) -> Ret
{
  static_assert(detail::is_expected<Ret>::value, "F must return an expected");

  return exp.has_value() ? detail::invoke(std::forward<F>(f))
                         : Ret(unexpect, std::forward<Exp>(exp).error());
}
#endif

#ifdef TL_EXPECTED_CXX14
template<class Exp,
         class F,
         detail::enable_if_t<!std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), *std::declval<Exp>())),
         detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>
constexpr auto
expected_map_impl(Exp&& exp, F&& f)
{
  using result = ret_t<Exp, detail::decay_t<Ret>>;
  return exp.has_value() ? result(detail::invoke(std::forward<F>(f), *std::forward<Exp>(exp)))
                         : result(unexpect, std::forward<Exp>(exp).error());
}

template<class Exp,
         class F,
         detail::enable_if_t<!std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), *std::declval<Exp>())),
         detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>
auto
expected_map_impl(Exp&& exp, F&& f)
{
  using result = expected<void, err_t<Exp>>;
  if (exp.has_value()) {
    detail::invoke(std::forward<F>(f), *std::forward<Exp>(exp));
    return result();
  }

  return result(unexpect, std::forward<Exp>(exp).error());
}

template<class Exp,
         class F,
         detail::enable_if_t<std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>())),
         detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>
constexpr auto
expected_map_impl(Exp&& exp, F&& f)
{
  using result = ret_t<Exp, detail::decay_t<Ret>>;
  return exp.has_value() ? result(detail::invoke(std::forward<F>(f)))
                         : result(unexpect, std::forward<Exp>(exp).error());
}

template<class Exp,
         class F,
         detail::enable_if_t<std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>())),
         detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>
auto
expected_map_impl(Exp&& exp, F&& f)
{
  using result = expected<void, err_t<Exp>>;
  if (exp.has_value()) {
    detail::invoke(std::forward<F>(f));
    return result();
  }

  return result(unexpect, std::forward<Exp>(exp).error());
}
#else
template<class Exp,
         class F,
         detail::enable_if_t<!std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), *std::declval<Exp>())),
         detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>

constexpr auto
expected_map_impl(Exp&& exp, F&& f) -> ret_t<Exp, detail::decay_t<Ret>>
{
  using result = ret_t<Exp, detail::decay_t<Ret>>;

  return exp.has_value() ? result(detail::invoke(std::forward<F>(f), *std::forward<Exp>(exp)))
                         : result(unexpect, std::forward<Exp>(exp).error());
}

template<class Exp,
         class F,
         detail::enable_if_t<!std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), *std::declval<Exp>())),
         detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>

auto
expected_map_impl(Exp&& exp, F&& f) -> expected<void, err_t<Exp>>
{
  if (exp.has_value()) {
    detail::invoke(std::forward<F>(f), *std::forward<Exp>(exp));
    return {};
  }

  return unexpected<err_t<Exp>>(std::forward<Exp>(exp).error());
}

template<class Exp,
         class F,
         detail::enable_if_t<std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>())),
         detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>

constexpr auto
expected_map_impl(Exp&& exp, F&& f) -> ret_t<Exp, detail::decay_t<Ret>>
{
  using result = ret_t<Exp, detail::decay_t<Ret>>;

  return exp.has_value() ? result(detail::invoke(std::forward<F>(f)))
                         : result(unexpect, std::forward<Exp>(exp).error());
}

template<class Exp,
         class F,
         detail::enable_if_t<std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>())),
         detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>

auto
expected_map_impl(Exp&& exp, F&& f) -> expected<void, err_t<Exp>>
{
  if (exp.has_value()) {
    detail::invoke(std::forward<F>(f));
    return {};
  }

  return unexpected<err_t<Exp>>(std::forward<Exp>(exp).error());
}
#endif

#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) && !defined(TL_EXPECTED_GCC54) &&    \
  !defined(TL_EXPECTED_GCC55)
template<class Exp,
         class F,
         detail::enable_if_t<!std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>
constexpr auto
map_error_impl(Exp&& exp, F&& f)
{
  using result = expected<exp_t<Exp>, detail::decay_t<Ret>>;
  return exp.has_value()
           ? result(*std::forward<Exp>(exp))
           : result(unexpect, detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error()));
}
template<class Exp,
         class F,
         detail::enable_if_t<!std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>
auto
map_error_impl(Exp&& exp, F&& f)
{
  using result = expected<exp_t<Exp>, monostate>;
  if (exp.has_value()) {
    return result(*std::forward<Exp>(exp));
  }

  detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
  return result(unexpect, monostate{});
}
template<class Exp,
         class F,
         detail::enable_if_t<std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>
constexpr auto
map_error_impl(Exp&& exp, F&& f)
{
  using result = expected<exp_t<Exp>, detail::decay_t<Ret>>;
  return exp.has_value()
           ? result()
           : result(unexpect, detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error()));
}
template<class Exp,
         class F,
         detail::enable_if_t<std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>
auto
map_error_impl(Exp&& exp, F&& f)
{
  using result = expected<exp_t<Exp>, monostate>;
  if (exp.has_value()) {
    return result();
  }

  detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
  return result(unexpect, monostate{});
}
#else
template<class Exp,
         class F,
         detail::enable_if_t<!std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>
constexpr auto
map_error_impl(Exp&& exp, F&& f) -> expected<exp_t<Exp>, detail::decay_t<Ret>>
{
  using result = expected<exp_t<Exp>, detail::decay_t<Ret>>;

  return exp.has_value()
           ? result(*std::forward<Exp>(exp))
           : result(unexpect, detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error()));
}

template<class Exp,
         class F,
         detail::enable_if_t<!std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>
auto
map_error_impl(Exp&& exp, F&& f) -> expected<exp_t<Exp>, monostate>
{
  using result = expected<exp_t<Exp>, monostate>;
  if (exp.has_value()) {
    return result(*std::forward<Exp>(exp));
  }

  detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
  return result(unexpect, monostate{});
}

template<class Exp,
         class F,
         detail::enable_if_t<std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>
constexpr auto
map_error_impl(Exp&& exp, F&& f) -> expected<exp_t<Exp>, detail::decay_t<Ret>>
{
  using result = expected<exp_t<Exp>, detail::decay_t<Ret>>;

  return exp.has_value()
           ? result()
           : result(unexpect, detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error()));
}

template<class Exp,
         class F,
         detail::enable_if_t<std::is_void<exp_t<Exp>>::value>* = nullptr,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>
auto
map_error_impl(Exp&& exp, F&& f) -> expected<exp_t<Exp>, monostate>
{
  using result = expected<exp_t<Exp>, monostate>;
  if (exp.has_value()) {
    return result();
  }

  detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
  return result(unexpect, monostate{});
}
#endif

#ifdef TL_EXPECTED_CXX14
template<class Exp,
         class F,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>
constexpr auto
or_else_impl(Exp&& exp, F&& f)
{
  static_assert(detail::is_expected<Ret>::value, "F must return an expected");
  return exp.has_value() ? std::forward<Exp>(exp)
                         : detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
}

template<class Exp,
         class F,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>
detail::decay_t<Exp>
or_else_impl(Exp&& exp, F&& f)
{
  return exp.has_value() ? std::forward<Exp>(exp)
                         : (detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error()),
                            std::forward<Exp>(exp));
}
#else
template<class Exp,
         class F,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<!std::is_void<Ret>::value>* = nullptr>
auto
or_else_impl(Exp&& exp, F&& f) -> Ret
{
  static_assert(detail::is_expected<Ret>::value, "F must return an expected");
  return exp.has_value() ? std::forward<Exp>(exp)
                         : detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
}

template<class Exp,
         class F,
         class Ret = decltype(detail::invoke(std::declval<F>(), std::declval<Exp>().error())),
         detail::enable_if_t<std::is_void<Ret>::value>* = nullptr>
detail::decay_t<Exp>
or_else_impl(Exp&& exp, F&& f)
{
  return exp.has_value() ? std::forward<Exp>(exp)
                         : (detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error()),
                            std::forward<Exp>(exp));
}
#endif
} // namespace detail

template<class T, class E, class U, class F>
constexpr bool
operator==(const expected<T, E>& lhs, const expected<U, F>& rhs)
{
  return (lhs.has_value() != rhs.has_value())
           ? false
           : (!lhs.has_value() ? lhs.error() == rhs.error() : *lhs == *rhs);
}
template<class T, class E, class U, class F>
constexpr bool
operator!=(const expected<T, E>& lhs, const expected<U, F>& rhs)
{
  return (lhs.has_value() != rhs.has_value())
           ? true
           : (!lhs.has_value() ? lhs.error() != rhs.error() : *lhs != *rhs);
}

template<class T, class E, class U>
constexpr bool
operator==(const expected<T, E>& x, const U& v)
{
  return x.has_value() ? *x == v : false;
}
template<class T, class E, class U>
constexpr bool
operator==(const U& v, const expected<T, E>& x)
{
  return x.has_value() ? *x == v : false;
}
template<class T, class E, class U>
constexpr bool
operator!=(const expected<T, E>& x, const U& v)
{
  return x.has_value() ? *x != v : true;
}
template<class T, class E, class U>
constexpr bool
operator!=(const U& v, const expected<T, E>& x)
{
  return x.has_value() ? *x != v : true;
}

template<class T, class E>
constexpr bool
operator==(const expected<T, E>& x, const unexpected<E>& e)
{
  return x.has_value() ? false : x.error() == e.value();
}
template<class T, class E>
constexpr bool
operator==(const unexpected<E>& e, const expected<T, E>& x)
{
  return x.has_value() ? false : x.error() == e.value();
}
template<class T, class E>
constexpr bool
operator!=(const expected<T, E>& x, const unexpected<E>& e)
{
  return x.has_value() ? true : x.error() != e.value();
}
template<class T, class E>
constexpr bool
operator!=(const unexpected<E>& e, const expected<T, E>& x)
{
  return x.has_value() ? true : x.error() != e.value();
}

template<
  class T,
  class E,
  detail::enable_if_t<(std::is_void<T>::value || std::is_move_constructible<T>::value) &&
                      detail::is_swappable<T>::value && std::is_move_constructible<E>::value &&
                      detail::is_swappable<E>::value>* = nullptr>
void
swap(expected<T, E>& lhs, expected<T, E>& rhs) noexcept(noexcept(lhs.swap(rhs)))
{
  lhs.swap(rhs);
}
} // namespace tl

#endif