///
// expected - An implementation of std::expected with extensions
// Written in 2017 by Sy Brand (tartanllama@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 1
#define TL_EXPECTED_VERSION_PATCH 0

#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(TL_ASSERT)
// can't have assert in constexpr in C++11 and GCC 4.9 has a compiler bug
#if (__cplusplus > 201103L) && !defined(TL_EXPECTED_GCC49)
#include <cassert>
#define TL_ASSERT(x) assert(x)
#else
#define TL_ASSERT(x)
#endif
#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))
    {
    }

    template <class... Args, typename std::enable_if<std::is_constructible<E, Args&&...>::value>::type* = nullptr>
    constexpr explicit unexpected(Args&&... args)
        : m_val(std::forward<Args>(args)...)
    {
    }
    template <class U, class... Args,
        typename std::enable_if<std::is_constructible<E, std::initializer_list<U>&, Args&&...>::value>::type* = nullptr>
    constexpr explicit unexpected(std::initializer_list<U> l, Args&&... args)
        : m_val(l, std::forward<Args>(args)...)
    {
    }

    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;
};

#ifdef __cpp_deduction_guides
template <class E> unexpected(E) -> unexpected<E>;
#endif

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
        (void)e;
#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> {
#if __GNUC__ <= 5
// no constexpr for GCC 4/5 bug
#else
        TL_EXPECTED_MSVC2015_CONSTEXPR
#endif
        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(std::move(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
#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_error(F&& f) &
    {
        return map_error_impl(*this, std::forward<F>(f));
    }
    template <class F> TL_EXPECTED_11_CONSTEXPR auto transform_error(F&& f) &&
    {
        return map_error_impl(std::move(*this), std::forward<F>(f));
    }
    template <class F> constexpr auto transform_error(F&& f) const&
    {
        return map_error_impl(*this, std::forward<F>(f));
    }
    template <class F> constexpr auto transform_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&&>())) transform_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&&>())) transform_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&&>())) transform_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&&>())) transform_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();
        } else {
            err().~unexpected<E>();
            this->m_has_val = true;
        }
        ::new (valptr()) T(std::forward<Args>(args)...);
    }

    template <class... Args, detail::enable_if_t<!std::is_nothrow_constructible<T, Args&&...>::value>* = nullptr>
    void emplace(Args&&... args)
    {
        if (has_value()) {
            val().~T();
            ::new (valptr()) 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, e_is_nothrow_move_constructible)
    {
        auto temp = std::move(rhs.err());
        rhs.err().~unexpected_type();
#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
        try {
            ::new (rhs.valptr()) T(std::move(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(std::move(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
    {
        TL_ASSERT(has_value());
        return valptr();
    }
    TL_EXPECTED_11_CONSTEXPR T* operator->()
    {
        TL_ASSERT(has_value());
        return valptr();
    }

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

    template <class U> constexpr E error_or(U&& v) const&
    {
        static_assert(std::is_copy_constructible<E>::value && std::is_convertible<U&&, E>::value,
            "E must be copy-constructible and convertible to from U&&");
        return bool(!*this) ? this->error() : static_cast<E>(std::forward<U>(v));
    }
    template <class U> TL_EXPECTED_11_CONSTEXPR T error_or(U&& v) &&
    {
        static_assert(std::is_move_constructible<E>::value && std::is_convertible<U&&, E>::value,
            "E must be move-constructible and convertible to from U&&");
        return bool(!*this) ? std::move(this->error()) : static_cast<E>(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 E, class F> constexpr bool operator==(const expected<void, E>& lhs, const expected<void, F>& rhs)
{
    return (lhs.has_value() != rhs.has_value()) ? false : (!lhs.has_value() ? lhs.error() == rhs.error() : true);
}
template <class E, class F> constexpr bool operator!=(const expected<void, E>& lhs, const expected<void, F>& rhs)
{
    return (lhs.has_value() != rhs.has_value()) ? true : (!lhs.has_value() ? lhs.error() == rhs.error() : 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 : 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