[Project] Add expected library

1 files changed, 2326 insertions, 0 deletions

diff --git a/contrib/expected/expected.hpp b/contrib/expected/expected.hpp
new file mode 100644
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+++ b/contrib/expected/expected.hpp
@@ -0,0 +1,2326 @@
+///
+// expected - An implementation of std::expected with extensions
+// Written in 2017 by Simon Brand (simonrbrand@gmail.com, @TartanLlama)
+//
+// Documentation available at http://tl.tartanllama.xyz/
+//
+// To the extent possible under law, the author(s) have dedicated all
+// copyright and related and neighboring rights to this software to the
+// public domain worldwide. This software is distributed without any warranty.
+//
+// You should have received a copy of the CC0 Public Domain Dedication
+// along with this software. If not, see
+// <http://creativecommons.org/publicdomain/zero/1.0/>.
+///
+
+#ifndef TL_EXPECTED_HPP
+#define TL_EXPECTED_HPP
+
+#define TL_EXPECTED_VERSION_MAJOR 1
+#define TL_EXPECTED_VERSION_MINOR 0
+#define TL_EXPECTED_VERSION_PATCH 1
+
+#include <exception>
+#include <functional>
+#include <type_traits>
+#include <utility>
+
+#if defined(__EXCEPTIONS) || defined(_CPPUNWIND)
+#define TL_EXPECTED_EXCEPTIONS_ENABLED
+#endif
+
+#if (defined(_MSC_VER) && _MSC_VER == 1900)
+#define TL_EXPECTED_MSVC2015
+#define TL_EXPECTED_MSVC2015_CONSTEXPR
+#else
+#define TL_EXPECTED_MSVC2015_CONSTEXPR constexpr
+#endif
+
+#if (defined(__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ <= 9 &&              \
+     !defined(__clang__))
+#define TL_EXPECTED_GCC49
+#endif
+
+#if (defined(__GNUC__) && __GNUC__ == 5 && __GNUC_MINOR__ <= 4 &&              \
+     !defined(__clang__))
+#define TL_EXPECTED_GCC54
+#endif
+
+#if (defined(__GNUC__) && __GNUC__ == 5 && __GNUC_MINOR__ <= 5 &&              \
+     !defined(__clang__))
+#define TL_EXPECTED_GCC55
+#endif
+
+#if (defined(__GNUC__) && __GNUC__ == 4 && __GNUC_MINOR__ <= 9 &&              \
+     !defined(__clang__))
+// GCC < 5 doesn't support overloading on const&& for member functions
+
+#define TL_EXPECTED_NO_CONSTRR
+// GCC < 5 doesn't support some standard C++11 type traits
+#define TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T)                         \
+  std::has_trivial_copy_constructor<T>
+#define TL_EXPECTED_IS_TRIVIALLY_COPY_ASSIGNABLE(T)                            \
+  std::has_trivial_copy_assign<T>
+
+// This one will be different for GCC 5.7 if it's ever supported
+#define TL_EXPECTED_IS_TRIVIALLY_DESTRUCTIBLE(T)                               \
+  std::is_trivially_destructible<T>
+
+// GCC 5 < v < 8 has a bug in is_trivially_copy_constructible which breaks std::vector
+// for non-copyable types
+#elif (defined(__GNUC__) && __GNUC__ < 8 &&                                                \
+     !defined(__clang__))
+#ifndef TL_GCC_LESS_8_TRIVIALLY_COPY_CONSTRUCTIBLE_MUTEX
+#define TL_GCC_LESS_8_TRIVIALLY_COPY_CONSTRUCTIBLE_MUTEX
+namespace tl {
+  namespace detail {
+      template<class T>
+      struct is_trivially_copy_constructible : std::is_trivially_copy_constructible<T>{};
+#ifdef _GLIBCXX_VECTOR
+      template<class T, class A>
+      struct is_trivially_copy_constructible<std::vector<T,A>>
+          : std::false_type{};
+#endif
+  }
+}
+#endif
+
+#define TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T)                                     \
+  tl::detail::is_trivially_copy_constructible<T>
+#define TL_EXPECTED_IS_TRIVIALLY_COPY_ASSIGNABLE(T)                                        \
+  std::is_trivially_copy_assignable<T>
+#define TL_EXPECTED_IS_TRIVIALLY_DESTRUCTIBLE(T) std::is_trivially_destructible<T>
+#else
+#define TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T)                         \
+  std::is_trivially_copy_constructible<T>
+#define TL_EXPECTED_IS_TRIVIALLY_COPY_ASSIGNABLE(T)                            \
+  std::is_trivially_copy_assignable<T>
+#define TL_EXPECTED_IS_TRIVIALLY_DESTRUCTIBLE(T)                               \
+  std::is_trivially_destructible<T>
+#endif
+
+#if __cplusplus > 201103L
+#define TL_EXPECTED_CXX14
+#endif
+
+#ifdef TL_EXPECTED_GCC49
+#define TL_EXPECTED_GCC49_CONSTEXPR
+#else
+#define TL_EXPECTED_GCC49_CONSTEXPR constexpr
+#endif
+
+#if (__cplusplus == 201103L || defined(TL_EXPECTED_MSVC2015) ||                \
+     defined(TL_EXPECTED_GCC49))
+#define TL_EXPECTED_11_CONSTEXPR
+#else
+#define TL_EXPECTED_11_CONSTEXPR constexpr
+#endif
+
+namespace tl {
+template <class T, class E> class expected;
+
+#ifndef TL_MONOSTATE_INPLACE_MUTEX
+#define TL_MONOSTATE_INPLACE_MUTEX
+class monostate {};
+
+struct in_place_t {
+  explicit in_place_t() = default;
+};
+static constexpr in_place_t in_place{};
+#endif
+
+template <class E> class unexpected {
+public:
+  static_assert(!std::is_same<E, void>::value, "E must not be void");
+
+  unexpected() = delete;
+  constexpr explicit unexpected(const E &e) : m_val(e) {}
+
+  constexpr explicit unexpected(E &&e) : m_val(std::move(e)) {}
+
+  constexpr const E &value() const & { return m_val; }
+  TL_EXPECTED_11_CONSTEXPR E &value() & { return m_val; }
+  TL_EXPECTED_11_CONSTEXPR E &&value() && { return std::move(m_val); }
+  constexpr const E &&value() const && { return std::move(m_val); }
+
+private:
+  E m_val;
+};
+
+template <class E>
+constexpr bool operator==(const unexpected<E> &lhs, const unexpected<E> &rhs) {
+  return lhs.value() == rhs.value();
+}
+template <class E>
+constexpr bool operator!=(const unexpected<E> &lhs, const unexpected<E> &rhs) {
+  return lhs.value() != rhs.value();
+}
+template <class E>
+constexpr bool operator<(const unexpected<E> &lhs, const unexpected<E> &rhs) {
+  return lhs.value() < rhs.value();
+}
+template <class E>
+constexpr bool operator<=(const unexpected<E> &lhs, const unexpected<E> &rhs) {
+  return lhs.value() <= rhs.value();
+}
+template <class E>
+constexpr bool operator>(const unexpected<E> &lhs, const unexpected<E> &rhs) {
+  return lhs.value() > rhs.value();
+}
+template <class E>
+constexpr bool operator>=(const unexpected<E> &lhs, const unexpected<E> &rhs) {
+  return lhs.value() >= rhs.value();
+}
+
+template <class E>
+unexpected<typename std::decay<E>::type> make_unexpected(E &&e) {
+  return unexpected<typename std::decay<E>::type>(std::forward<E>(e));
+}
+
+struct unexpect_t {
+  unexpect_t() = default;
+};
+static constexpr unexpect_t unexpect{};
+
+namespace detail {
+template<typename E>
+[[noreturn]] TL_EXPECTED_11_CONSTEXPR void throw_exception(E &&e) {
+#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
+    throw std::forward<E>(e);
+#else
+  #ifdef _MSC_VER
+    __assume(0);
+  #else
+    __builtin_unreachable();
+  #endif
+#endif
+}
+
+#ifndef TL_TRAITS_MUTEX
+#define TL_TRAITS_MUTEX
+// C++14-style aliases for brevity
+template <class T> using remove_const_t = typename std::remove_const<T>::type;
+template <class T>
+using remove_reference_t = typename std::remove_reference<T>::type;
+template <class T> using decay_t = typename std::decay<T>::type;
+template <bool E, class T = void>
+using enable_if_t = typename std::enable_if<E, T>::type;
+template <bool B, class T, class F>
+using conditional_t = typename std::conditional<B, T, F>::type;
+
+// std::conjunction from C++17
+template <class...> struct conjunction : std::true_type {};
+template <class B> struct conjunction<B> : B {};
+template <class B, class... Bs>
+struct conjunction<B, Bs...>
+  : std::conditional<bool(B::value), conjunction<Bs...>, B>::type {};
+
+#if defined(_LIBCPP_VERSION) && __cplusplus == 201103L
+#define TL_TRAITS_LIBCXX_MEM_FN_WORKAROUND
+#endif
+
+// In C++11 mode, there's an issue in libc++'s std::mem_fn
+// which results in a hard-error when using it in a noexcept expression
+// in some cases. This is a check to workaround the common failing case.
+#ifdef TL_TRAITS_LIBCXX_MEM_FN_WORKAROUND
+template <class T> struct is_pointer_to_non_const_member_func : std::false_type {};
+template <class T, class Ret, class... Args>
+struct is_pointer_to_non_const_member_func<Ret(T::*) (Args...)> : std::true_type {};
+template <class T, class Ret, class... Args>
+struct is_pointer_to_non_const_member_func<Ret(T::*) (Args...)&> : std::true_type {};
+template <class T, class Ret, class... Args>
+struct is_pointer_to_non_const_member_func<Ret(T::*) (Args...) &&> : std::true_type {};
+template <class T, class Ret, class... Args>
+struct is_pointer_to_non_const_member_func<Ret(T::*) (Args...) volatile> : std::true_type {};
+template <class T, class Ret, class... Args>
+struct is_pointer_to_non_const_member_func<Ret(T::*) (Args...) volatile &> : std::true_type {};
+template <class T, class Ret, class... Args>
+struct is_pointer_to_non_const_member_func<Ret(T::*) (Args...) volatile &&> : std::true_type {};
+
+template <class T> struct is_const_or_const_ref : std::false_type {};
+template <class T> struct is_const_or_const_ref<T const&> : std::true_type {};
+template <class T> struct is_const_or_const_ref<T const> : std::true_type {};
+#endif
+
+// std::invoke from C++17
+// https://stackoverflow.com/questions/38288042/c11-14-invoke-workaround
+template <typename Fn, typename... Args,
+#ifdef TL_TRAITS_LIBCXX_MEM_FN_WORKAROUND
+  typename = enable_if_t<!(is_pointer_to_non_const_member_func<Fn>::value
+    && is_const_or_const_ref<Args...>::value)>,
+#endif
+  typename = enable_if_t<std::is_member_pointer<decay_t<Fn>>::value>,
+  int = 0>
+  constexpr auto invoke(Fn && f, Args && ... args) noexcept(
+    noexcept(std::mem_fn(f)(std::forward<Args>(args)...)))
+  -> decltype(std::mem_fn(f)(std::forward<Args>(args)...)) {
+  return std::mem_fn(f)(std::forward<Args>(args)...);
+}
+
+template <typename Fn, typename... Args,
+  typename = enable_if_t<!std::is_member_pointer<decay_t<Fn>>::value>>
+  constexpr auto invoke(Fn && f, Args && ... args) noexcept(
+    noexcept(std::forward<Fn>(f)(std::forward<Args>(args)...)))
+  -> decltype(std::forward<Fn>(f)(std::forward<Args>(args)...)) {
+  return std::forward<Fn>(f)(std::forward<Args>(args)...);
+}
+
+// std::invoke_result from C++17
+template <class F, class, class... Us> struct invoke_result_impl;
+
+template <class F, class... Us>
+struct invoke_result_impl<
+  F, decltype(detail::invoke(std::declval<F>(), std::declval<Us>()...), void()),
+  Us...> {
+  using type = decltype(detail::invoke(std::declval<F>(), std::declval<Us>()...));
+};
+
+template <class F, class... Us>
+using invoke_result = invoke_result_impl<F, void, Us...>;
+
+template <class F, class... Us>
+using invoke_result_t = typename invoke_result<F, Us...>::type;
+
+#if defined(_MSC_VER) && _MSC_VER <= 1900
+// TODO make a version which works with MSVC 2015
+template <class T, class U = T> struct is_swappable : std::true_type {};
+
+template <class T, class U = T> struct is_nothrow_swappable : std::true_type {};
+#else
+// https://stackoverflow.com/questions/26744589/what-is-a-proper-way-to-implement-is-swappable-to-test-for-the-swappable-concept
+namespace swap_adl_tests {
+  // if swap ADL finds this then it would call std::swap otherwise (same
+  // signature)
+  struct tag {};
+
+  template <class T> tag swap(T&, T&);
+  template <class T, std::size_t N> tag swap(T(&a)[N], T(&b)[N]);
+
+  // helper functions to test if an unqualified swap is possible, and if it
+  // becomes std::swap
+  template <class, class> std::false_type can_swap(...) noexcept(false);
+  template <class T, class U,
+    class = decltype(swap(std::declval<T&>(), std::declval<U&>()))>
+    std::true_type can_swap(int) noexcept(noexcept(swap(std::declval<T&>(),
+      std::declval<U&>())));
+
+  template <class, class> std::false_type uses_std(...);
+  template <class T, class U>
+  std::is_same<decltype(swap(std::declval<T&>(), std::declval<U&>())), tag>
+    uses_std(int);
+
+  template <class T>
+  struct is_std_swap_noexcept
+    : std::integral_constant<bool,
+    std::is_nothrow_move_constructible<T>::value&&
+    std::is_nothrow_move_assignable<T>::value> {};
+
+  template <class T, std::size_t N>
+  struct is_std_swap_noexcept<T[N]> : is_std_swap_noexcept<T> {};
+
+  template <class T, class U>
+  struct is_adl_swap_noexcept
+    : std::integral_constant<bool, noexcept(can_swap<T, U>(0))> {};
+} // namespace swap_adl_tests
+
+template <class T, class U = T>
+struct is_swappable
+  : std::integral_constant<
+  bool,
+  decltype(detail::swap_adl_tests::can_swap<T, U>(0))::value &&
+  (!decltype(detail::swap_adl_tests::uses_std<T, U>(0))::value ||
+  (std::is_move_assignable<T>::value &&
+    std::is_move_constructible<T>::value))> {};
+
+template <class T, std::size_t N>
+struct is_swappable<T[N], T[N]>
+  : std::integral_constant<
+  bool,
+  decltype(detail::swap_adl_tests::can_swap<T[N], T[N]>(0))::value &&
+  (!decltype(
+    detail::swap_adl_tests::uses_std<T[N], T[N]>(0))::value ||
+    is_swappable<T, T>::value)> {};
+
+template <class T, class U = T>
+struct is_nothrow_swappable
+  : std::integral_constant<
+  bool,
+  is_swappable<T, U>::value &&
+  ((decltype(detail::swap_adl_tests::uses_std<T, U>(0))::value
+    && detail::swap_adl_tests::is_std_swap_noexcept<T>::value) ||
+    (!decltype(detail::swap_adl_tests::uses_std<T, U>(0))::value &&
+      detail::swap_adl_tests::is_adl_swap_noexcept<T,
+      U>::value))> {
+};
+#endif
+#endif
+
+// Trait for checking if a type is a tl::expected
+template <class T> struct is_expected_impl : std::false_type {};
+template <class T, class E>
+struct is_expected_impl<expected<T, E>> : std::true_type {};
+template <class T> using is_expected = is_expected_impl<decay_t<T>>;
+
+template <class T, class E, class U>
+using expected_enable_forward_value = detail::enable_if_t<
+    std::is_constructible<T, U &&>::value &&
+    !std::is_same<detail::decay_t<U>, in_place_t>::value &&
+    !std::is_same<expected<T, E>, detail::decay_t<U>>::value &&
+    !std::is_same<unexpected<E>, detail::decay_t<U>>::value>;
+
+template <class T, class E, class U, class G, class UR, class GR>
+using expected_enable_from_other = detail::enable_if_t<
+    std::is_constructible<T, UR>::value &&
+    std::is_constructible<E, GR>::value &&
+    !std::is_constructible<T, expected<U, G> &>::value &&
+    !std::is_constructible<T, expected<U, G> &&>::value &&
+    !std::is_constructible<T, const expected<U, G> &>::value &&
+    !std::is_constructible<T, const expected<U, G> &&>::value &&
+    !std::is_convertible<expected<U, G> &, T>::value &&
+    !std::is_convertible<expected<U, G> &&, T>::value &&
+    !std::is_convertible<const expected<U, G> &, T>::value &&
+    !std::is_convertible<const expected<U, G> &&, T>::value>;
+
+template <class T, class U>
+using is_void_or = conditional_t<std::is_void<T>::value, std::true_type, U>;
+
+template <class T>
+using is_copy_constructible_or_void =
+    is_void_or<T, std::is_copy_constructible<T>>;
+
+template <class T>
+using is_move_constructible_or_void =
+    is_void_or<T, std::is_move_constructible<T>>;
+
+template <class T>
+using is_copy_assignable_or_void =
+    is_void_or<T, std::is_copy_assignable<T>>;
+
+
+template <class T>
+using is_move_assignable_or_void =
+    is_void_or<T, std::is_move_assignable<T>>;
+    
+
+} // namespace detail
+
+namespace detail {
+struct no_init_t {};
+static constexpr no_init_t no_init{};
+
+// Implements the storage of the values, and ensures that the destructor is
+// trivial if it can be.
+//
+// This specialization is for where neither `T` or `E` is trivially
+// destructible, so the destructors must be called on destruction of the
+// `expected`
+template <class T, class E, bool = std::is_trivially_destructible<T>::value,
+          bool = std::is_trivially_destructible<E>::value>
+struct expected_storage_base {
+  constexpr expected_storage_base() : m_val(T{}), m_has_val(true) {}
+  constexpr expected_storage_base(no_init_t) : m_no_init(), m_has_val(false) {}
+
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<T, Args &&...>::value> * =
+                nullptr>
+  constexpr expected_storage_base(in_place_t, Args &&... args)
+      : m_val(std::forward<Args>(args)...), m_has_val(true) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                T, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr expected_storage_base(in_place_t, std::initializer_list<U> il,
+                                  Args &&... args)
+      : m_val(il, std::forward<Args>(args)...), m_has_val(true) {}
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<E, Args &&...>::value> * =
+                nullptr>
+  constexpr explicit expected_storage_base(unexpect_t, Args &&... args)
+      : m_unexpect(std::forward<Args>(args)...), m_has_val(false) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                E, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr explicit expected_storage_base(unexpect_t,
+                                           std::initializer_list<U> il,
+                                           Args &&... args)
+      : m_unexpect(il, std::forward<Args>(args)...), m_has_val(false) {}
+
+  ~expected_storage_base() {
+    if (m_has_val) {
+      m_val.~T();
+    } else {
+      m_unexpect.~unexpected<E>();
+    }
+  }
+  union {
+    T m_val;
+    unexpected<E> m_unexpect;
+    char m_no_init;
+  };
+  bool m_has_val;
+};
+
+// This specialization is for when both `T` and `E` are trivially-destructible,
+// so the destructor of the `expected` can be trivial.
+template <class T, class E> struct expected_storage_base<T, E, true, true> {
+  constexpr expected_storage_base() : m_val(T{}), m_has_val(true) {}
+  constexpr expected_storage_base(no_init_t) : m_no_init(), m_has_val(false) {}
+
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<T, Args &&...>::value> * =
+                nullptr>
+  constexpr expected_storage_base(in_place_t, Args &&... args)
+      : m_val(std::forward<Args>(args)...), m_has_val(true) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                T, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr expected_storage_base(in_place_t, std::initializer_list<U> il,
+                                  Args &&... args)
+      : m_val(il, std::forward<Args>(args)...), m_has_val(true) {}
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<E, Args &&...>::value> * =
+                nullptr>
+  constexpr explicit expected_storage_base(unexpect_t, Args &&... args)
+      : m_unexpect(std::forward<Args>(args)...), m_has_val(false) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                E, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr explicit expected_storage_base(unexpect_t,
+                                           std::initializer_list<U> il,
+                                           Args &&... args)
+      : m_unexpect(il, std::forward<Args>(args)...), m_has_val(false) {}
+
+  ~expected_storage_base() = default;
+  union {
+    T m_val;
+    unexpected<E> m_unexpect;
+    char m_no_init;
+  };
+  bool m_has_val;
+};
+
+// T is trivial, E is not.
+template <class T, class E> struct expected_storage_base<T, E, true, false> {
+  constexpr expected_storage_base() : m_val(T{}), m_has_val(true) {}
+  TL_EXPECTED_MSVC2015_CONSTEXPR expected_storage_base(no_init_t)
+      : m_no_init(), m_has_val(false) {}
+
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<T, Args &&...>::value> * =
+                nullptr>
+  constexpr expected_storage_base(in_place_t, Args &&... args)
+      : m_val(std::forward<Args>(args)...), m_has_val(true) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                T, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr expected_storage_base(in_place_t, std::initializer_list<U> il,
+                                  Args &&... args)
+      : m_val(il, std::forward<Args>(args)...), m_has_val(true) {}
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<E, Args &&...>::value> * =
+                nullptr>
+  constexpr explicit expected_storage_base(unexpect_t, Args &&... args)
+      : m_unexpect(std::forward<Args>(args)...), m_has_val(false) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                E, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr explicit expected_storage_base(unexpect_t,
+                                           std::initializer_list<U> il,
+                                           Args &&... args)
+      : m_unexpect(il, std::forward<Args>(args)...), m_has_val(false) {}
+
+  ~expected_storage_base() {
+    if (!m_has_val) {
+      m_unexpect.~unexpected<E>();
+    }
+  }
+
+  union {
+    T m_val;
+    unexpected<E> m_unexpect;
+    char m_no_init;
+  };
+  bool m_has_val;
+};
+
+// E is trivial, T is not.
+template <class T, class E> struct expected_storage_base<T, E, false, true> {
+  constexpr expected_storage_base() : m_val(T{}), m_has_val(true) {}
+  constexpr expected_storage_base(no_init_t) : m_no_init(), m_has_val(false) {}
+
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<T, Args &&...>::value> * =
+                nullptr>
+  constexpr expected_storage_base(in_place_t, Args &&... args)
+      : m_val(std::forward<Args>(args)...), m_has_val(true) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                T, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr expected_storage_base(in_place_t, std::initializer_list<U> il,
+                                  Args &&... args)
+      : m_val(il, std::forward<Args>(args)...), m_has_val(true) {}
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<E, Args &&...>::value> * =
+                nullptr>
+  constexpr explicit expected_storage_base(unexpect_t, Args &&... args)
+      : m_unexpect(std::forward<Args>(args)...), m_has_val(false) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                E, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr explicit expected_storage_base(unexpect_t,
+                                           std::initializer_list<U> il,
+                                           Args &&... args)
+      : m_unexpect(il, std::forward<Args>(args)...), m_has_val(false) {}
+
+  ~expected_storage_base() {
+    if (m_has_val) {
+      m_val.~T();
+    }
+  }
+  union {
+    T m_val;
+    unexpected<E> m_unexpect;
+    char m_no_init;
+  };
+  bool m_has_val;
+};
+
+// `T` is `void`, `E` is trivially-destructible
+template <class E> struct expected_storage_base<void, E, false, true> {
+  TL_EXPECTED_MSVC2015_CONSTEXPR expected_storage_base() : m_has_val(true) {}
+  constexpr expected_storage_base(no_init_t) : m_val(), m_has_val(false) {}
+
+  constexpr expected_storage_base(in_place_t) : m_has_val(true) {}
+
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<E, Args &&...>::value> * =
+                nullptr>
+  constexpr explicit expected_storage_base(unexpect_t, Args &&... args)
+      : m_unexpect(std::forward<Args>(args)...), m_has_val(false) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                E, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr explicit expected_storage_base(unexpect_t,
+                                           std::initializer_list<U> il,
+                                           Args &&... args)
+      : m_unexpect(il, std::forward<Args>(args)...), m_has_val(false) {}
+
+  ~expected_storage_base() = default;
+  struct dummy {};
+  union {
+    unexpected<E> m_unexpect;
+    dummy m_val;
+  };
+  bool m_has_val;
+};
+
+// `T` is `void`, `E` is not trivially-destructible
+template <class E> struct expected_storage_base<void, E, false, false> {
+  constexpr expected_storage_base() : m_dummy(), m_has_val(true) {}
+  constexpr expected_storage_base(no_init_t) : m_dummy(), m_has_val(false) {}
+
+  constexpr expected_storage_base(in_place_t) : m_dummy(), m_has_val(true) {}
+
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<E, Args &&...>::value> * =
+                nullptr>
+  constexpr explicit expected_storage_base(unexpect_t, Args &&... args)
+      : m_unexpect(std::forward<Args>(args)...), m_has_val(false) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                E, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr explicit expected_storage_base(unexpect_t,
+                                           std::initializer_list<U> il,
+                                           Args &&... args)
+      : m_unexpect(il, std::forward<Args>(args)...), m_has_val(false) {}
+
+  ~expected_storage_base() {
+    if (!m_has_val) {
+      m_unexpect.~unexpected<E>();
+    }
+  }
+
+  union {
+    unexpected<E> m_unexpect;
+    char m_dummy;
+  };
+  bool m_has_val;
+};
+
+// This base class provides some handy member functions which can be used in
+// further derived classes
+template <class T, class E>
+struct expected_operations_base : expected_storage_base<T, E> {
+  using expected_storage_base<T, E>::expected_storage_base;
+
+  template <class... Args> void construct(Args &&... args) noexcept {
+    new (std::addressof(this->m_val)) T(std::forward<Args>(args)...);
+    this->m_has_val = true;
+  }
+
+  template <class Rhs> void construct_with(Rhs &&rhs) noexcept {
+    new (std::addressof(this->m_val)) T(std::forward<Rhs>(rhs).get());
+    this->m_has_val = true;
+  }
+
+  template <class... Args> void construct_error(Args &&... args) noexcept {
+    new (std::addressof(this->m_unexpect))
+        unexpected<E>(std::forward<Args>(args)...);
+    this->m_has_val = false;
+  }
+
+  #ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
+
+  // These assign overloads ensure that the most efficient assignment
+  // implementation is used while maintaining the strong exception guarantee.
+  // The problematic case is where rhs has a value, but *this does not.
+  //
+  // This overload handles the case where we can just copy-construct `T`
+  // directly into place without throwing.
+  template <class U = T,
+            detail::enable_if_t<std::is_nothrow_copy_constructible<U>::value>
+                * = nullptr>
+  void assign(const expected_operations_base &rhs) noexcept {
+    if (!this->m_has_val && rhs.m_has_val) {
+      geterr().~unexpected<E>();
+      construct(rhs.get());
+    } else {
+      assign_common(rhs);
+    }
+  }
+
+  // This overload handles the case where we can attempt to create a copy of
+  // `T`, then no-throw move it into place if the copy was successful.
+  template <class U = T,
+            detail::enable_if_t<!std::is_nothrow_copy_constructible<U>::value &&
+                                std::is_nothrow_move_constructible<U>::value>
+                * = nullptr>
+  void assign(const expected_operations_base &rhs) noexcept {
+    if (!this->m_has_val && rhs.m_has_val) {
+      T tmp = rhs.get();
+      geterr().~unexpected<E>();
+      construct(std::move(tmp));
+    } else {
+      assign_common(rhs);
+    }
+  }
+
+  // This overload is the worst-case, where we have to move-construct the
+  // unexpected value into temporary storage, then try to copy the T into place.
+  // If the construction succeeds, then everything is fine, but if it throws,
+  // then we move the old unexpected value back into place before rethrowing the
+  // exception.
+  template <class U = T,
+            detail::enable_if_t<!std::is_nothrow_copy_constructible<U>::value &&
+                                !std::is_nothrow_move_constructible<U>::value>
+                * = nullptr>
+  void assign(const expected_operations_base &rhs) {
+    if (!this->m_has_val && rhs.m_has_val) {
+      auto tmp = std::move(geterr());
+      geterr().~unexpected<E>();
+
+#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
+      try {
+        construct(rhs.get());
+      } catch (...) {
+        geterr() = std::move(tmp);
+        throw;
+      }
+#else
+      construct(rhs.get());
+#endif
+    } else {
+      assign_common(rhs);
+    }
+  }
+
+  // These overloads do the same as above, but for rvalues
+  template <class U = T,
+            detail::enable_if_t<std::is_nothrow_move_constructible<U>::value>
+                * = nullptr>
+  void assign(expected_operations_base &&rhs) noexcept {
+    if (!this->m_has_val && rhs.m_has_val) {
+      geterr().~unexpected<E>();
+      construct(std::move(rhs).get());
+    } else {
+      assign_common(std::move(rhs));
+    }
+  }
+
+  template <class U = T,
+            detail::enable_if_t<!std::is_nothrow_move_constructible<U>::value>
+                * = nullptr>
+  void assign(expected_operations_base &&rhs) {
+    if (!this->m_has_val && rhs.m_has_val) {
+      auto tmp = std::move(geterr());
+      geterr().~unexpected<E>();
+#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
+      try {
+        construct(std::move(rhs).get());
+      } catch (...) {
+        geterr() = std::move(tmp);
+        throw;
+      }
+#else
+      construct(std::move(rhs).get());
+#endif
+    } else {
+      assign_common(std::move(rhs));
+    }
+  }
+
+  #else
+
+  // If exceptions are disabled then we can just copy-construct
+  void assign(const expected_operations_base &rhs) noexcept {
+    if (!this->m_has_val && rhs.m_has_val) {
+      geterr().~unexpected<E>();
+      construct(rhs.get());
+    } else {
+      assign_common(rhs);
+    }
+  }
+
+  void assign(expected_operations_base &&rhs) noexcept {
+    if (!this->m_has_val && rhs.m_has_val) {
+      geterr().~unexpected<E>();
+      construct(std::move(rhs).get());
+    } else {
+      assign_common(rhs);
+    }
+  }
+
+  #endif
+
+  // The common part of move/copy assigning
+  template <class Rhs> void assign_common(Rhs &&rhs) {
+    if (this->m_has_val) {
+      if (rhs.m_has_val) {
+        get() = std::forward<Rhs>(rhs).get();
+      } else {
+		destroy_val();
+        construct_error(std::forward<Rhs>(rhs).geterr());
+      }
+    } else {
+      if (!rhs.m_has_val) {
+        geterr() = std::forward<Rhs>(rhs).geterr();
+      }
+    }
+  }
+
+  bool has_value() const { return this->m_has_val; }
+
+  TL_EXPECTED_11_CONSTEXPR T &get() & { return this->m_val; }
+  constexpr const T &get() const & { return this->m_val; }
+  TL_EXPECTED_11_CONSTEXPR T &&get() && { return std::move(this->m_val); }
+#ifndef TL_EXPECTED_NO_CONSTRR
+  constexpr const T &&get() const && { return std::move(this->m_val); }
+#endif
+
+  TL_EXPECTED_11_CONSTEXPR unexpected<E> &geterr() & {
+    return this->m_unexpect;
+  }
+  constexpr const unexpected<E> &geterr() const & { return this->m_unexpect; }
+  TL_EXPECTED_11_CONSTEXPR unexpected<E> &&geterr() && {
+    return std::move(this->m_unexpect);
+  }
+#ifndef TL_EXPECTED_NO_CONSTRR
+  constexpr const unexpected<E> &&geterr() const && {
+    return std::move(this->m_unexpect);
+  }
+#endif
+
+  TL_EXPECTED_11_CONSTEXPR void destroy_val() {
+	get().~T();
+  }
+};
+
+// This base class provides some handy member functions which can be used in
+// further derived classes
+template <class E>
+struct expected_operations_base<void, E> : expected_storage_base<void, E> {
+  using expected_storage_base<void, E>::expected_storage_base;
+
+  template <class... Args> void construct() noexcept { this->m_has_val = true; }
+
+  // This function doesn't use its argument, but needs it so that code in
+  // levels above this can work independently of whether T is void
+  template <class Rhs> void construct_with(Rhs &&) noexcept {
+    this->m_has_val = true;
+  }
+
+  template <class... Args> void construct_error(Args &&... args) noexcept {
+    new (std::addressof(this->m_unexpect))
+        unexpected<E>(std::forward<Args>(args)...);
+    this->m_has_val = false;
+  }
+
+  template <class Rhs> void assign(Rhs &&rhs) noexcept {
+    if (!this->m_has_val) {
+      if (rhs.m_has_val) {
+        geterr().~unexpected<E>();
+        construct();
+      } else {
+        geterr() = std::forward<Rhs>(rhs).geterr();
+      }
+    } else {
+      if (!rhs.m_has_val) {
+        construct_error(std::forward<Rhs>(rhs).geterr());
+      }
+    }
+  }
+
+  bool has_value() const { return this->m_has_val; }
+
+  TL_EXPECTED_11_CONSTEXPR unexpected<E> &geterr() & {
+    return this->m_unexpect;
+  }
+  constexpr const unexpected<E> &geterr() const & { return this->m_unexpect; }
+  TL_EXPECTED_11_CONSTEXPR unexpected<E> &&geterr() && {
+    return std::move(this->m_unexpect);
+  }
+#ifndef TL_EXPECTED_NO_CONSTRR
+  constexpr const unexpected<E> &&geterr() const && {
+    return std::move(this->m_unexpect);
+  }
+#endif
+
+  TL_EXPECTED_11_CONSTEXPR void destroy_val() {
+	  //no-op
+  }
+};
+
+// This class manages conditionally having a trivial copy constructor
+// This specialization is for when T and E are trivially copy constructible
+template <class T, class E,
+          bool = is_void_or<T, TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T)>::
+              value &&TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(E)::value>
+struct expected_copy_base : expected_operations_base<T, E> {
+  using expected_operations_base<T, E>::expected_operations_base;
+};
+
+// This specialization is for when T or E are not trivially copy constructible
+template <class T, class E>
+struct expected_copy_base<T, E, false> : expected_operations_base<T, E> {
+  using expected_operations_base<T, E>::expected_operations_base;
+
+  expected_copy_base() = default;
+  expected_copy_base(const expected_copy_base &rhs)
+      : expected_operations_base<T, E>(no_init) {
+    if (rhs.has_value()) {
+      this->construct_with(rhs);
+    } else {
+      this->construct_error(rhs.geterr());
+    }
+  }
+
+  expected_copy_base(expected_copy_base &&rhs) = default;
+  expected_copy_base &operator=(const expected_copy_base &rhs) = default;
+  expected_copy_base &operator=(expected_copy_base &&rhs) = default;
+};
+
+// This class manages conditionally having a trivial move constructor
+// Unfortunately there's no way to achieve this in GCC < 5 AFAIK, since it
+// doesn't implement an analogue to std::is_trivially_move_constructible. We
+// have to make do with a non-trivial move constructor even if T is trivially
+// move constructible
+#ifndef TL_EXPECTED_GCC49
+template <class T, class E,
+          bool = is_void_or<T, std::is_trivially_move_constructible<T>>::value
+              &&std::is_trivially_move_constructible<E>::value>
+struct expected_move_base : expected_copy_base<T, E> {
+  using expected_copy_base<T, E>::expected_copy_base;
+};
+#else
+template <class T, class E, bool = false> struct expected_move_base;
+#endif
+template <class T, class E>
+struct expected_move_base<T, E, false> : expected_copy_base<T, E> {
+  using expected_copy_base<T, E>::expected_copy_base;
+
+  expected_move_base() = default;
+  expected_move_base(const expected_move_base &rhs) = default;
+
+  expected_move_base(expected_move_base &&rhs) noexcept(
+      std::is_nothrow_move_constructible<T>::value)
+      : expected_copy_base<T, E>(no_init) {
+    if (rhs.has_value()) {
+      this->construct_with(std::move(rhs));
+    } else {
+      this->construct_error(std::move(rhs.geterr()));
+    }
+  }
+  expected_move_base &operator=(const expected_move_base &rhs) = default;
+  expected_move_base &operator=(expected_move_base &&rhs) = default;
+};
+
+// This class manages conditionally having a trivial copy assignment operator
+template <class T, class E,
+          bool = is_void_or<
+              T, conjunction<TL_EXPECTED_IS_TRIVIALLY_COPY_ASSIGNABLE(T),
+                             TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(T),
+                             TL_EXPECTED_IS_TRIVIALLY_DESTRUCTIBLE(T)>>::value
+              &&TL_EXPECTED_IS_TRIVIALLY_COPY_ASSIGNABLE(E)::value
+                  &&TL_EXPECTED_IS_TRIVIALLY_COPY_CONSTRUCTIBLE(E)::value
+                      &&TL_EXPECTED_IS_TRIVIALLY_DESTRUCTIBLE(E)::value>
+struct expected_copy_assign_base : expected_move_base<T, E> {
+  using expected_move_base<T, E>::expected_move_base;
+};
+
+template <class T, class E>
+struct expected_copy_assign_base<T, E, false> : expected_move_base<T, E> {
+  using expected_move_base<T, E>::expected_move_base;
+
+  expected_copy_assign_base() = default;
+  expected_copy_assign_base(const expected_copy_assign_base &rhs) = default;
+
+  expected_copy_assign_base(expected_copy_assign_base &&rhs) = default;
+  expected_copy_assign_base &operator=(const expected_copy_assign_base &rhs) {
+    this->assign(rhs);
+    return *this;
+  }
+  expected_copy_assign_base &
+  operator=(expected_copy_assign_base &&rhs) = default;
+};
+
+// This class manages conditionally having a trivial move assignment operator
+// Unfortunately there's no way to achieve this in GCC < 5 AFAIK, since it
+// doesn't implement an analogue to std::is_trivially_move_assignable. We have
+// to make do with a non-trivial move assignment operator even if T is trivially
+// move assignable
+#ifndef TL_EXPECTED_GCC49
+template <class T, class E,
+          bool =
+              is_void_or<T, conjunction<std::is_trivially_destructible<T>,
+                                        std::is_trivially_move_constructible<T>,
+                                        std::is_trivially_move_assignable<T>>>::
+                  value &&std::is_trivially_destructible<E>::value
+                      &&std::is_trivially_move_constructible<E>::value
+                          &&std::is_trivially_move_assignable<E>::value>
+struct expected_move_assign_base : expected_copy_assign_base<T, E> {
+  using expected_copy_assign_base<T, E>::expected_copy_assign_base;
+};
+#else
+template <class T, class E, bool = false> struct expected_move_assign_base;
+#endif
+
+template <class T, class E>
+struct expected_move_assign_base<T, E, false>
+    : expected_copy_assign_base<T, E> {
+  using expected_copy_assign_base<T, E>::expected_copy_assign_base;
+
+  expected_move_assign_base() = default;
+  expected_move_assign_base(const expected_move_assign_base &rhs) = default;
+
+  expected_move_assign_base(expected_move_assign_base &&rhs) = default;
+
+  expected_move_assign_base &
+  operator=(const expected_move_assign_base &rhs) = default;
+
+  expected_move_assign_base &
+  operator=(expected_move_assign_base &&rhs) noexcept(
+      std::is_nothrow_move_constructible<T>::value
+          &&std::is_nothrow_move_assignable<T>::value) {
+    this->assign(std::move(rhs));
+    return *this;
+  }
+};
+
+// expected_delete_ctor_base will conditionally delete copy and move
+// constructors depending on whether T is copy/move constructible
+template <class T, class E,
+          bool EnableCopy = (is_copy_constructible_or_void<T>::value &&
+                             std::is_copy_constructible<E>::value),
+          bool EnableMove = (is_move_constructible_or_void<T>::value &&
+                             std::is_move_constructible<E>::value)>
+struct expected_delete_ctor_base {
+  expected_delete_ctor_base() = default;
+  expected_delete_ctor_base(const expected_delete_ctor_base &) = default;
+  expected_delete_ctor_base(expected_delete_ctor_base &&) noexcept = default;
+  expected_delete_ctor_base &
+  operator=(const expected_delete_ctor_base &) = default;
+  expected_delete_ctor_base &
+  operator=(expected_delete_ctor_base &&) noexcept = default;
+};
+
+template <class T, class E>
+struct expected_delete_ctor_base<T, E, true, false> {
+  expected_delete_ctor_base() = default;
+  expected_delete_ctor_base(const expected_delete_ctor_base &) = default;
+  expected_delete_ctor_base(expected_delete_ctor_base &&) noexcept = delete;
+  expected_delete_ctor_base &
+  operator=(const expected_delete_ctor_base &) = default;
+  expected_delete_ctor_base &
+  operator=(expected_delete_ctor_base &&) noexcept = default;
+};
+
+template <class T, class E>
+struct expected_delete_ctor_base<T, E, false, true> {
+  expected_delete_ctor_base() = default;
+  expected_delete_ctor_base(const expected_delete_ctor_base &) = delete;
+  expected_delete_ctor_base(expected_delete_ctor_base &&) noexcept = default;
+  expected_delete_ctor_base &
+  operator=(const expected_delete_ctor_base &) = default;
+  expected_delete_ctor_base &
+  operator=(expected_delete_ctor_base &&) noexcept = default;
+};
+
+template <class T, class E>
+struct expected_delete_ctor_base<T, E, false, false> {
+  expected_delete_ctor_base() = default;
+  expected_delete_ctor_base(const expected_delete_ctor_base &) = delete;
+  expected_delete_ctor_base(expected_delete_ctor_base &&) noexcept = delete;
+  expected_delete_ctor_base &
+  operator=(const expected_delete_ctor_base &) = default;
+  expected_delete_ctor_base &
+  operator=(expected_delete_ctor_base &&) noexcept = default;
+};
+
+// expected_delete_assign_base will conditionally delete copy and move
+// constructors depending on whether T and E are copy/move constructible +
+// assignable
+template <class T, class E,
+          bool EnableCopy = (is_copy_constructible_or_void<T>::value &&
+                             std::is_copy_constructible<E>::value &&
+                             is_copy_assignable_or_void<T>::value &&
+                             std::is_copy_assignable<E>::value),
+          bool EnableMove = (is_move_constructible_or_void<T>::value &&
+                             std::is_move_constructible<E>::value &&
+                             is_move_assignable_or_void<T>::value &&
+                             std::is_move_assignable<E>::value)>
+struct expected_delete_assign_base {
+  expected_delete_assign_base() = default;
+  expected_delete_assign_base(const expected_delete_assign_base &) = default;
+  expected_delete_assign_base(expected_delete_assign_base &&) noexcept =
+      default;
+  expected_delete_assign_base &
+  operator=(const expected_delete_assign_base &) = default;
+  expected_delete_assign_base &
+  operator=(expected_delete_assign_base &&) noexcept = default;
+};
+
+template <class T, class E>
+struct expected_delete_assign_base<T, E, true, false> {
+  expected_delete_assign_base() = default;
+  expected_delete_assign_base(const expected_delete_assign_base &) = default;
+  expected_delete_assign_base(expected_delete_assign_base &&) noexcept =
+      default;
+  expected_delete_assign_base &
+  operator=(const expected_delete_assign_base &) = default;
+  expected_delete_assign_base &
+  operator=(expected_delete_assign_base &&) noexcept = delete;
+};
+
+template <class T, class E>
+struct expected_delete_assign_base<T, E, false, true> {
+  expected_delete_assign_base() = default;
+  expected_delete_assign_base(const expected_delete_assign_base &) = default;
+  expected_delete_assign_base(expected_delete_assign_base &&) noexcept =
+      default;
+  expected_delete_assign_base &
+  operator=(const expected_delete_assign_base &) = delete;
+  expected_delete_assign_base &
+  operator=(expected_delete_assign_base &&) noexcept = default;
+};
+
+template <class T, class E>
+struct expected_delete_assign_base<T, E, false, false> {
+  expected_delete_assign_base() = default;
+  expected_delete_assign_base(const expected_delete_assign_base &) = default;
+  expected_delete_assign_base(expected_delete_assign_base &&) noexcept =
+      default;
+  expected_delete_assign_base &
+  operator=(const expected_delete_assign_base &) = delete;
+  expected_delete_assign_base &
+  operator=(expected_delete_assign_base &&) noexcept = delete;
+};
+
+// This is needed to be able to construct the expected_default_ctor_base which
+// follows, while still conditionally deleting the default constructor.
+struct default_constructor_tag {
+  explicit constexpr default_constructor_tag() = default;
+};
+
+// expected_default_ctor_base will ensure that expected has a deleted default
+// consturctor if T is not default constructible.
+// This specialization is for when T is default constructible
+template <class T, class E,
+          bool Enable =
+              std::is_default_constructible<T>::value || std::is_void<T>::value>
+struct expected_default_ctor_base {
+  constexpr expected_default_ctor_base() noexcept = default;
+  constexpr expected_default_ctor_base(
+      expected_default_ctor_base const &) noexcept = default;
+  constexpr expected_default_ctor_base(expected_default_ctor_base &&) noexcept =
+      default;
+  expected_default_ctor_base &
+  operator=(expected_default_ctor_base const &) noexcept = default;
+  expected_default_ctor_base &
+  operator=(expected_default_ctor_base &&) noexcept = default;
+
+  constexpr explicit expected_default_ctor_base(default_constructor_tag) {}
+};
+
+// This specialization is for when T is not default constructible
+template <class T, class E> struct expected_default_ctor_base<T, E, false> {
+  constexpr expected_default_ctor_base() noexcept = delete;
+  constexpr expected_default_ctor_base(
+      expected_default_ctor_base const &) noexcept = default;
+  constexpr expected_default_ctor_base(expected_default_ctor_base &&) noexcept =
+      default;
+  expected_default_ctor_base &
+  operator=(expected_default_ctor_base const &) noexcept = default;
+  expected_default_ctor_base &
+  operator=(expected_default_ctor_base &&) noexcept = default;
+
+  constexpr explicit expected_default_ctor_base(default_constructor_tag) {}
+};
+} // namespace detail
+
+template <class E> class bad_expected_access : public std::exception {
+public:
+  explicit bad_expected_access(E e) : m_val(std::move(e)) {}
+
+  virtual const char *what() const noexcept override {
+    return "Bad expected access";
+  }
+
+  const E &error() const & { return m_val; }
+  E &error() & { return m_val; }
+  const E &&error() const && { return std::move(m_val); }
+  E &&error() && { return std::move(m_val); }
+
+private:
+  E m_val;
+};
+
+/// An `expected<T, E>` object is an object that contains the storage for
+/// another object and manages the lifetime of this contained object `T`.
+/// Alternatively it could contain the storage for another unexpected object
+/// `E`. The contained object may not be initialized after the expected object
+/// has been initialized, and may not be destroyed before the expected object
+/// has been destroyed. The initialization state of the contained object is
+/// tracked by the expected object.
+template <class T, class E>
+class expected : private detail::expected_move_assign_base<T, E>,
+                 private detail::expected_delete_ctor_base<T, E>,
+                 private detail::expected_delete_assign_base<T, E>,
+                 private detail::expected_default_ctor_base<T, E> {
+  static_assert(!std::is_reference<T>::value, "T must not be a reference");
+  static_assert(!std::is_same<T, std::remove_cv<in_place_t>>::value,
+                "T must not be in_place_t");
+  static_assert(!std::is_same<T, std::remove_cv<unexpect_t>>::value,
+                "T must not be unexpect_t");
+  static_assert(!std::is_same<T, std::remove_cv<unexpected<E>>>::value,
+                "T must not be unexpected<E>");
+  static_assert(!std::is_reference<E>::value, "E must not be a reference");
+
+  T *valptr() { return std::addressof(this->m_val); }
+  const T *valptr() const { return std::addressof(this->m_val); }    
+  unexpected<E> *errptr() { return std::addressof(this->m_unexpect); }
+  const unexpected<E> *errptr() const { return std::addressof(this->m_unexpect); }    
+
+  template <class U = T,
+            detail::enable_if_t<!std::is_void<U>::value> * = nullptr>
+  TL_EXPECTED_11_CONSTEXPR U &val() {
+    return this->m_val;
+  }
+  TL_EXPECTED_11_CONSTEXPR unexpected<E> &err() { return this->m_unexpect; }
+
+  template <class U = T,
+            detail::enable_if_t<!std::is_void<U>::value> * = nullptr>
+  constexpr const U &val() const {
+    return this->m_val;
+  }
+  constexpr const unexpected<E> &err() const { return this->m_unexpect; }
+
+  using impl_base = detail::expected_move_assign_base<T, E>;
+  using ctor_base = detail::expected_default_ctor_base<T, E>;
+
+public:
+  typedef T value_type;
+  typedef E error_type;
+  typedef unexpected<E> unexpected_type;
+
+#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) &&               \
+    !defined(TL_EXPECTED_GCC54) && !defined(TL_EXPECTED_GCC55)
+  template <class F> TL_EXPECTED_11_CONSTEXPR auto and_then(F &&f) & {
+    return and_then_impl(*this, std::forward<F>(f));
+  }
+  template <class F> TL_EXPECTED_11_CONSTEXPR auto and_then(F &&f) && {
+    return and_then_impl(std::move(*this), std::forward<F>(f));
+  }
+  template <class F> constexpr auto and_then(F &&f) const & {
+    return and_then_impl(*this, std::forward<F>(f));
+  }
+
+#ifndef TL_EXPECTED_NO_CONSTRR
+  template <class F> constexpr auto and_then(F &&f) const && {
+    return and_then_impl(std::move(*this), std::forward<F>(f));
+  }
+#endif
+
+#else
+  template <class F>
+  TL_EXPECTED_11_CONSTEXPR auto
+  and_then(F &&f) & -> decltype(and_then_impl(std::declval<expected&>(), std::forward<F>(f))) {
+    return and_then_impl(*this, std::forward<F>(f));
+  }
+  template <class F>
+  TL_EXPECTED_11_CONSTEXPR auto and_then(F &&f) && -> decltype(
+      and_then_impl(std::declval<expected&&>(), std::forward<F>(f))) {
+    return and_then_impl(std::move(*this), std::forward<F>(f));
+  }
+  template <class F>
+  constexpr auto and_then(F &&f) const & -> decltype(
+      and_then_impl(std::declval<expected const&>(), std::forward<F>(f))) {
+    return and_then_impl(*this, std::forward<F>(f));
+  }
+
+#ifndef TL_EXPECTED_NO_CONSTRR
+  template <class F>
+  constexpr auto and_then(F &&f) const && -> decltype(
+      and_then_impl(std::declval<expected const&&>(), std::forward<F>(f))) {
+    return and_then_impl(std::move(*this), std::forward<F>(f));
+  }
+#endif
+#endif
+
+#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) &&               \
+    !defined(TL_EXPECTED_GCC54) && !defined(TL_EXPECTED_GCC55)
+    template <class F> TL_EXPECTED_11_CONSTEXPR auto map(F &&f) & {
+    return expected_map_impl(*this, std::forward<F>(f));
+  }
+  template <class F> TL_EXPECTED_11_CONSTEXPR auto map(F &&f) && {
+    return expected_map_impl(std::move(*this), std::forward<F>(f));
+  }
+  template <class F> constexpr auto map(F &&f) const & {
+    return expected_map_impl(*this, std::forward<F>(f));
+  }
+  template <class F> constexpr auto map(F &&f) const && {
+    return expected_map_impl(std::move(*this), std::forward<F>(f));
+  }
+#else
+  template <class F>
+  TL_EXPECTED_11_CONSTEXPR decltype(
+      expected_map_impl(std::declval<expected &>(), std::declval<F &&>()))
+  map(F &&f) & {
+    return expected_map_impl(*this, std::forward<F>(f));
+  }
+  template <class F>
+  TL_EXPECTED_11_CONSTEXPR decltype(
+      expected_map_impl(std::declval<expected>(), std::declval<F &&>()))
+  map(F &&f) && {
+    return expected_map_impl(std::move(*this), std::forward<F>(f));
+  }
+  template <class F>
+  constexpr decltype(expected_map_impl(std::declval<const expected &>(),
+                                       std::declval<F &&>()))
+  map(F &&f) const & {
+    return expected_map_impl(*this, std::forward<F>(f));
+  }
+
+#ifndef TL_EXPECTED_NO_CONSTRR
+  template <class F>
+  constexpr decltype(expected_map_impl(std::declval<const expected &&>(),
+                                       std::declval<F &&>()))
+  map(F &&f) const && {
+    return expected_map_impl(std::move(*this), std::forward<F>(f));
+  }
+#endif
+#endif
+
+#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) &&               \
+    !defined(TL_EXPECTED_GCC54) && !defined(TL_EXPECTED_GCC55)
+    template <class F> TL_EXPECTED_11_CONSTEXPR auto transform(F &&f) & {
+    return expected_map_impl(*this, std::forward<F>(f));
+  }
+  template <class F> TL_EXPECTED_11_CONSTEXPR auto transform(F &&f) && {
+    return expected_map_impl(std::move(*this), std::forward<F>(f));
+  }
+  template <class F> constexpr auto transform(F &&f) const & {
+    return expected_map_impl(*this, std::forward<F>(f));
+  }
+  template <class F> constexpr auto transform(F &&f) const && {
+    return expected_map_impl(std::move(*this), std::forward<F>(f));
+  }
+#else
+    template <class F>
+  TL_EXPECTED_11_CONSTEXPR decltype(
+      expected_map_impl(std::declval<expected &>(), std::declval<F &&>()))
+  transform(F &&f) & {
+    return expected_map_impl(*this, std::forward<F>(f));
+  }
+  template <class F>
+  TL_EXPECTED_11_CONSTEXPR decltype(
+      expected_map_impl(std::declval<expected>(), std::declval<F &&>()))
+  transform(F &&f) && {
+    return expected_map_impl(std::move(*this), std::forward<F>(f));
+  }
+  template <class F>
+  constexpr decltype(expected_map_impl(std::declval<const expected &>(),
+                                       std::declval<F &&>()))
+  transform(F &&f) const & {
+    return expected_map_impl(*this, std::forward<F>(f));
+  }
+
+#ifndef TL_EXPECTED_NO_CONSTRR
+  template <class F>
+  constexpr decltype(expected_map_impl(std::declval<const expected &&>(),
+                                       std::declval<F &&>()))
+  transform(F &&f) const && {
+    return expected_map_impl(std::move(*this), std::forward<F>(f));
+  }
+#endif
+#endif
+
+#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) &&               \
+    !defined(TL_EXPECTED_GCC54) && !defined(TL_EXPECTED_GCC55)
+  template <class F> TL_EXPECTED_11_CONSTEXPR auto map_error(F &&f) & {
+    return map_error_impl(*this, std::forward<F>(f));
+  }
+  template <class F> TL_EXPECTED_11_CONSTEXPR auto map_error(F &&f) && {
+    return map_error_impl(std::move(*this), std::forward<F>(f));
+  }
+  template <class F> constexpr auto map_error(F &&f) const & {
+    return map_error_impl(*this, std::forward<F>(f));
+  }
+  template <class F> constexpr auto map_error(F &&f) const && {
+    return map_error_impl(std::move(*this), std::forward<F>(f));
+  }
+#else
+  template <class F>
+  TL_EXPECTED_11_CONSTEXPR decltype(map_error_impl(std::declval<expected &>(),
+                                                   std::declval<F &&>()))
+  map_error(F &&f) & {
+    return map_error_impl(*this, std::forward<F>(f));
+  }
+  template <class F>
+  TL_EXPECTED_11_CONSTEXPR decltype(map_error_impl(std::declval<expected &&>(),
+                                                   std::declval<F &&>()))
+  map_error(F &&f) && {
+    return map_error_impl(std::move(*this), std::forward<F>(f));
+  }
+  template <class F>
+  constexpr decltype(map_error_impl(std::declval<const expected &>(),
+                                    std::declval<F &&>()))
+  map_error(F &&f) const & {
+    return map_error_impl(*this, std::forward<F>(f));
+  }
+
+#ifndef TL_EXPECTED_NO_CONSTRR
+  template <class F>
+  constexpr decltype(map_error_impl(std::declval<const expected &&>(),
+                                    std::declval<F &&>()))
+  map_error(F &&f) const && {
+    return map_error_impl(std::move(*this), std::forward<F>(f));
+  }
+#endif
+#endif
+  template <class F> expected TL_EXPECTED_11_CONSTEXPR or_else(F &&f) & {
+    return or_else_impl(*this, std::forward<F>(f));
+  }
+
+  template <class F> expected TL_EXPECTED_11_CONSTEXPR or_else(F &&f) && {
+    return or_else_impl(std::move(*this), std::forward<F>(f));
+  }
+
+  template <class F> expected constexpr or_else(F &&f) const & {
+    return or_else_impl(*this, std::forward<F>(f));
+  }
+
+#ifndef TL_EXPECTED_NO_CONSTRR
+  template <class F> expected constexpr or_else(F &&f) const && {
+    return or_else_impl(std::move(*this), std::forward<F>(f));
+  }
+#endif
+  constexpr expected() = default;
+  constexpr expected(const expected &rhs) = default;
+  constexpr expected(expected &&rhs) = default;
+  expected &operator=(const expected &rhs) = default;
+  expected &operator=(expected &&rhs) = default;
+
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<T, Args &&...>::value> * =
+                nullptr>
+  constexpr expected(in_place_t, Args &&... args)
+      : impl_base(in_place, std::forward<Args>(args)...),
+        ctor_base(detail::default_constructor_tag{}) {}
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                T, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr expected(in_place_t, std::initializer_list<U> il, Args &&... args)
+      : impl_base(in_place, il, std::forward<Args>(args)...),
+        ctor_base(detail::default_constructor_tag{}) {}
+
+  template <class G = E,
+            detail::enable_if_t<std::is_constructible<E, const G &>::value> * =
+                nullptr,
+            detail::enable_if_t<!std::is_convertible<const G &, E>::value> * =
+                nullptr>
+  explicit constexpr expected(const unexpected<G> &e)
+      : impl_base(unexpect, e.value()),
+        ctor_base(detail::default_constructor_tag{}) {}
+
+    template <
+      class G = E,
+      detail::enable_if_t<std::is_constructible<E, const G &>::value> * =
+          nullptr,
+      detail::enable_if_t<std::is_convertible<const G &, E>::value> * = nullptr>
+  constexpr expected(unexpected<G> const &e)
+      : impl_base(unexpect, e.value()),
+        ctor_base(detail::default_constructor_tag{}) {}
+
+  template <
+      class G = E,
+      detail::enable_if_t<std::is_constructible<E, G &&>::value> * = nullptr,
+      detail::enable_if_t<!std::is_convertible<G &&, E>::value> * = nullptr>
+  explicit constexpr expected(unexpected<G> &&e) noexcept(
+      std::is_nothrow_constructible<E, G &&>::value)
+      : impl_base(unexpect, std::move(e.value())),
+        ctor_base(detail::default_constructor_tag{}) {}
+
+    template <
+      class G = E,
+      detail::enable_if_t<std::is_constructible<E, G &&>::value> * = nullptr,
+      detail::enable_if_t<std::is_convertible<G &&, E>::value> * = nullptr>
+  constexpr expected(unexpected<G> &&e) noexcept(
+      std::is_nothrow_constructible<E, G &&>::value)
+      : impl_base(unexpect, std::move(e.value())),
+        ctor_base(detail::default_constructor_tag{}) {}
+
+  template <class... Args,
+            detail::enable_if_t<std::is_constructible<E, Args &&...>::value> * =
+                nullptr>
+  constexpr explicit expected(unexpect_t, Args &&... args)
+      : impl_base(unexpect, std::forward<Args>(args)...),
+        ctor_base(detail::default_constructor_tag{}) {}
+
+    template <class U, class... Args,
+            detail::enable_if_t<std::is_constructible<
+                E, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  constexpr explicit expected(unexpect_t, std::initializer_list<U> il,
+                              Args &&... args)
+      : impl_base(unexpect, il, std::forward<Args>(args)...),
+        ctor_base(detail::default_constructor_tag{}) {}
+
+  template <class U, class G,
+            detail::enable_if_t<!(std::is_convertible<U const &, T>::value &&
+                                  std::is_convertible<G const &, E>::value)> * =
+                nullptr,
+            detail::expected_enable_from_other<T, E, U, G, const U &, const G &>
+                * = nullptr>
+  explicit TL_EXPECTED_11_CONSTEXPR expected(const expected<U, G> &rhs)
+      : ctor_base(detail::default_constructor_tag{}) {
+    if (rhs.has_value()) {
+      this->construct(*rhs);
+    } else {
+      this->construct_error(rhs.error());        
+    }
+  }
+
+    template <class U, class G,
+            detail::enable_if_t<(std::is_convertible<U const &, T>::value &&
+                                 std::is_convertible<G const &, E>::value)> * =
+                nullptr,
+            detail::expected_enable_from_other<T, E, U, G, const U &, const G &>
+                * = nullptr>
+  TL_EXPECTED_11_CONSTEXPR expected(const expected<U, G> &rhs)
+      : ctor_base(detail::default_constructor_tag{}) {
+    if (rhs.has_value()) {
+      this->construct(*rhs);
+    } else {
+      this->construct_error(rhs.error());        
+    }      
+  }
+
+  template <
+      class U, class G,
+      detail::enable_if_t<!(std::is_convertible<U &&, T>::value &&
+                            std::is_convertible<G &&, E>::value)> * = nullptr,
+      detail::expected_enable_from_other<T, E, U, G, U &&, G &&> * = nullptr>
+  explicit TL_EXPECTED_11_CONSTEXPR expected(expected<U, G> &&rhs)
+      : ctor_base(detail::default_constructor_tag{}) {
+    if (rhs.has_value()) {
+      this->construct(std::move(*rhs));
+    } else {
+      this->construct_error(std::move(rhs.error()));        
+    }            
+  }
+
+    template <
+      class U, class G,
+      detail::enable_if_t<(std::is_convertible<U &&, T>::value &&
+                           std::is_convertible<G &&, E>::value)> * = nullptr,
+      detail::expected_enable_from_other<T, E, U, G, U &&, G &&> * = nullptr>
+  TL_EXPECTED_11_CONSTEXPR expected(expected<U, G> &&rhs)
+      : ctor_base(detail::default_constructor_tag{}) {
+    if (rhs.has_value()) {
+      this->construct(std::move(*rhs));
+    } else {
+      this->construct_error(std::move(rhs.error()));        
+    }                  
+  }
+
+  template <
+      class U = T,
+      detail::enable_if_t<!std::is_convertible<U &&, T>::value> * = nullptr,
+      detail::expected_enable_forward_value<T, E, U> * = nullptr>
+  explicit TL_EXPECTED_MSVC2015_CONSTEXPR expected(U &&v)
+      : expected(in_place, std::forward<U>(v)) {}
+
+    template <
+      class U = T,
+      detail::enable_if_t<std::is_convertible<U &&, T>::value> * = nullptr,
+      detail::expected_enable_forward_value<T, E, U> * = nullptr>
+  TL_EXPECTED_MSVC2015_CONSTEXPR expected(U &&v)
+      : expected(in_place, std::forward<U>(v)) {}
+
+  template <
+      class U = T, class G = T,
+      detail::enable_if_t<std::is_nothrow_constructible<T, U &&>::value> * =
+          nullptr,
+      detail::enable_if_t<!std::is_void<G>::value> * = nullptr,
+      detail::enable_if_t<
+          (!std::is_same<expected<T, E>, detail::decay_t<U>>::value &&
+           !detail::conjunction<std::is_scalar<T>,
+                                std::is_same<T, detail::decay_t<U>>>::value &&
+           std::is_constructible<T, U>::value &&
+           std::is_assignable<G &, U>::value &&
+           std::is_nothrow_move_constructible<E>::value)> * = nullptr>
+  expected &operator=(U &&v) {
+    if (has_value()) {
+      val() = std::forward<U>(v);
+    } else {
+      err().~unexpected<E>();
+      ::new (valptr()) T(std::forward<U>(v));
+      this->m_has_val = true;
+    }
+
+    return *this;
+  }
+
+    template <
+      class U = T, class G = T,
+      detail::enable_if_t<!std::is_nothrow_constructible<T, U &&>::value> * =
+          nullptr,
+      detail::enable_if_t<!std::is_void<U>::value> * = nullptr,
+      detail::enable_if_t<
+          (!std::is_same<expected<T, E>, detail::decay_t<U>>::value &&
+           !detail::conjunction<std::is_scalar<T>,
+                                std::is_same<T, detail::decay_t<U>>>::value &&
+           std::is_constructible<T, U>::value &&
+           std::is_assignable<G &, U>::value &&
+           std::is_nothrow_move_constructible<E>::value)> * = nullptr>
+  expected &operator=(U &&v) {
+    if (has_value()) {
+      val() = std::forward<U>(v);
+    } else {
+      auto tmp = std::move(err());
+      err().~unexpected<E>();
+
+      #ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
+      try {
+        ::new (valptr()) T(std::forward<U>(v));
+        this->m_has_val = true;
+      } catch (...) {
+        err() = std::move(tmp);
+        throw;
+      }
+      #else
+        ::new (valptr()) T(std::forward<U>(v));
+        this->m_has_val = true;
+      #endif
+    }
+
+    return *this;
+  }
+
+  template <class G = E,
+            detail::enable_if_t<std::is_nothrow_copy_constructible<G>::value &&
+                                std::is_assignable<G &, G>::value> * = nullptr>
+  expected &operator=(const unexpected<G> &rhs) {
+    if (!has_value()) {
+      err() = rhs;
+    } else {
+      this->destroy_val();
+      ::new (errptr()) unexpected<E>(rhs);
+      this->m_has_val = false;
+    }
+
+    return *this;
+  }
+
+  template <class G = E,
+            detail::enable_if_t<std::is_nothrow_move_constructible<G>::value &&
+                                std::is_move_assignable<G>::value> * = nullptr>
+  expected &operator=(unexpected<G> &&rhs) noexcept {
+    if (!has_value()) {
+      err() = std::move(rhs);
+    } else {
+      this->destroy_val();
+      ::new (errptr()) unexpected<E>(std::move(rhs));
+      this->m_has_val = false;
+    }
+
+    return *this;
+  }
+
+  template <class... Args, detail::enable_if_t<std::is_nothrow_constructible<
+                               T, Args &&...>::value> * = nullptr>
+  void emplace(Args &&... args) {
+    if (has_value()) {
+      val() = T(std::forward<Args>(args)...);
+    } else {
+      err().~unexpected<E>();
+      ::new (valptr()) T(std::forward<Args>(args)...);
+      this->m_has_val = true;
+    }
+  }
+
+    template <class... Args, detail::enable_if_t<!std::is_nothrow_constructible<
+                               T, Args &&...>::value> * = nullptr>
+  void emplace(Args &&... args) {
+    if (has_value()) {
+      val() = T(std::forward<Args>(args)...);
+    } else {
+      auto tmp = std::move(err());
+      err().~unexpected<E>();
+
+      #ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
+      try {
+        ::new (valptr()) T(std::forward<Args>(args)...);
+        this->m_has_val = true;
+      } catch (...) {
+        err() = std::move(tmp);
+        throw;
+      }
+      #else
+      ::new (valptr()) T(std::forward<Args>(args)...);
+      this->m_has_val = true;
+      #endif
+    }
+  }
+
+  template <class U, class... Args,
+            detail::enable_if_t<std::is_nothrow_constructible<
+                T, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  void emplace(std::initializer_list<U> il, Args &&... args) {
+    if (has_value()) {
+      T t(il, std::forward<Args>(args)...);
+      val() = std::move(t);
+    } else {
+      err().~unexpected<E>();
+      ::new (valptr()) T(il, std::forward<Args>(args)...);
+      this->m_has_val = true;
+    }
+  }
+
+    template <class U, class... Args,
+            detail::enable_if_t<!std::is_nothrow_constructible<
+                T, std::initializer_list<U> &, Args &&...>::value> * = nullptr>
+  void emplace(std::initializer_list<U> il, Args &&... args) {
+    if (has_value()) {
+      T t(il, std::forward<Args>(args)...);
+      val() = std::move(t);
+    } else {
+      auto tmp = std::move(err());
+      err().~unexpected<E>();
+
+      #ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
+      try {
+        ::new (valptr()) T(il, std::forward<Args>(args)...);
+        this->m_has_val = true;
+      } catch (...) {
+        err() = std::move(tmp);
+        throw;
+      }
+      #else
+      ::new (valptr()) T(il, std::forward<Args>(args)...);
+      this->m_has_val = true;
+      #endif
+    }
+  }
+
+private:
+  using t_is_void = std::true_type;
+  using t_is_not_void = std::false_type;
+  using t_is_nothrow_move_constructible = std::true_type;
+  using move_constructing_t_can_throw = std::false_type;
+  using e_is_nothrow_move_constructible = std::true_type;
+  using move_constructing_e_can_throw = std::false_type;
+
+  void swap_where_both_have_value(expected &/*rhs*/ , t_is_void) noexcept {
+    // swapping void is a no-op
+  }
+
+  void swap_where_both_have_value(expected &rhs, t_is_not_void) {
+    using std::swap;
+    swap(val(), rhs.val());
+  }
+
+  void swap_where_only_one_has_value(expected &rhs, t_is_void) noexcept(
+      std::is_nothrow_move_constructible<E>::value) {
+    ::new (errptr()) unexpected_type(std::move(rhs.err()));
+    rhs.err().~unexpected_type();
+    std::swap(this->m_has_val, rhs.m_has_val);
+  }
+
+  void swap_where_only_one_has_value(expected &rhs, t_is_not_void) {
+    swap_where_only_one_has_value_and_t_is_not_void(
+        rhs, typename std::is_nothrow_move_constructible<T>::type{},
+        typename std::is_nothrow_move_constructible<E>::type{});
+  }
+
+  void swap_where_only_one_has_value_and_t_is_not_void(
+      expected &rhs, t_is_nothrow_move_constructible,
+      e_is_nothrow_move_constructible) noexcept {
+    auto temp = std::move(val());
+    val().~T();
+    ::new (errptr()) unexpected_type(std::move(rhs.err()));
+    rhs.err().~unexpected_type();
+    ::new (rhs.valptr()) T(std::move(temp));
+    std::swap(this->m_has_val, rhs.m_has_val);
+  }
+
+  void swap_where_only_one_has_value_and_t_is_not_void(
+      expected &rhs, t_is_nothrow_move_constructible,
+      move_constructing_e_can_throw) {
+    auto temp = std::move(val());
+    val().~T();
+#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
+    try {
+      ::new (errptr()) unexpected_type(std::move(rhs.err()));
+      rhs.err().~unexpected_type();
+      ::new (rhs.valptr()) T(std::move(temp));
+      std::swap(this->m_has_val, rhs.m_has_val);
+    } catch (...) {
+      val() = std::move(temp);
+      throw;
+    }
+#else
+    ::new (errptr()) unexpected_type(std::move(rhs.err()));
+    rhs.err().~unexpected_type();
+    ::new (rhs.valptr()) T(std::move(temp));
+    std::swap(this->m_has_val, rhs.m_has_val);
+#endif
+  }
+
+  void swap_where_only_one_has_value_and_t_is_not_void(
+      expected &rhs, move_constructing_t_can_throw,
+      t_is_nothrow_move_constructible) {
+    auto temp = std::move(rhs.err());
+    rhs.err().~unexpected_type();
+#ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
+    try {
+      ::new (rhs.valptr()) T(val());
+      val().~T();
+      ::new (errptr()) unexpected_type(std::move(temp));
+      std::swap(this->m_has_val, rhs.m_has_val);
+    } catch (...) {
+      rhs.err() = std::move(temp);
+      throw;
+    }
+#else
+    ::new (rhs.valptr()) T(val());
+    val().~T();
+    ::new (errptr()) unexpected_type(std::move(temp));
+    std::swap(this->m_has_val, rhs.m_has_val);
+#endif
+  }
+
+public:
+  template <class OT = T, class OE = E>
+  detail::enable_if_t<detail::is_swappable<OT>::value &&
+                      detail::is_swappable<OE>::value &&
+                      (std::is_nothrow_move_constructible<OT>::value ||
+                       std::is_nothrow_move_constructible<OE>::value)>
+  swap(expected &rhs) noexcept(
+      std::is_nothrow_move_constructible<T>::value
+          &&detail::is_nothrow_swappable<T>::value
+              &&std::is_nothrow_move_constructible<E>::value
+                  &&detail::is_nothrow_swappable<E>::value) {
+    if (has_value() && rhs.has_value()) {
+      swap_where_both_have_value(rhs, typename std::is_void<T>::type{});
+    } else if (!has_value() && rhs.has_value()) {
+      rhs.swap(*this);
+    } else if (has_value()) {
+      swap_where_only_one_has_value(rhs, typename std::is_void<T>::type{});
+    } else {
+      using std::swap;
+      swap(err(), rhs.err());
+    }
+  }
+
+  constexpr const T *operator->() const { return valptr(); }
+  TL_EXPECTED_11_CONSTEXPR T *operator->() { return valptr(); }
+
+  template <class U = T,
+            detail::enable_if_t<!std::is_void<U>::value> * = nullptr>
+  constexpr const U &operator*() const & {
+    return val();
+  }
+  template <class U = T,
+            detail::enable_if_t<!std::is_void<U>::value> * = nullptr>
+  TL_EXPECTED_11_CONSTEXPR U &operator*() & {
+    return val();
+  }
+  template <class U = T,
+            detail::enable_if_t<!std::is_void<U>::value> * = nullptr>
+  constexpr const U &&operator*() const && {
+    return std::move(val());
+  }
+  template <class U = T,
+            detail::enable_if_t<!std::is_void<U>::value> * = nullptr>
+  TL_EXPECTED_11_CONSTEXPR U &&operator*() && {
+    return std::move(val());
+  }
+
+  constexpr bool has_value() const noexcept { return this->m_has_val; }
+  constexpr explicit operator bool() const noexcept { return this->m_has_val; }
+
+  template <class U = T,
+            detail::enable_if_t<!std::is_void<U>::value> * = nullptr>
+  TL_EXPECTED_11_CONSTEXPR const U &value() const & {
+    if (!has_value())
+      detail::throw_exception(bad_expected_access<E>(err().value()));
+    return val();
+  }
+  template <class U = T,
+            detail::enable_if_t<!std::is_void<U>::value> * = nullptr>
+  TL_EXPECTED_11_CONSTEXPR U &value() & {
+    if (!has_value())
+      detail::throw_exception(bad_expected_access<E>(err().value()));
+    return val();
+  }
+  template <class U = T,
+            detail::enable_if_t<!std::is_void<U>::value> * = nullptr>
+  TL_EXPECTED_11_CONSTEXPR const U &&value() const && {
+    if (!has_value())
+      detail::throw_exception(bad_expected_access<E>(std::move(err()).value()));
+    return std::move(val());
+  }
+  template <class U = T,
+            detail::enable_if_t<!std::is_void<U>::value> * = nullptr>
+  TL_EXPECTED_11_CONSTEXPR U &&value() && {
+    if (!has_value())
+      detail::throw_exception(bad_expected_access<E>(std::move(err()).value()));
+    return std::move(val());
+  }
+
+  constexpr const E &error() const & { return err().value(); }
+  TL_EXPECTED_11_CONSTEXPR E &error() & { return err().value(); }
+  constexpr const E &&error() const && { return std::move(err().value()); }
+  TL_EXPECTED_11_CONSTEXPR E &&error() && { return std::move(err().value()); }
+
+  template <class U> constexpr T value_or(U &&v) const & {
+    static_assert(std::is_copy_constructible<T>::value &&
+                      std::is_convertible<U &&, T>::value,
+                  "T must be copy-constructible and convertible to from U&&");
+    return bool(*this) ? **this : static_cast<T>(std::forward<U>(v));
+  }
+  template <class U> TL_EXPECTED_11_CONSTEXPR T value_or(U &&v) && {
+    static_assert(std::is_move_constructible<T>::value &&
+                      std::is_convertible<U &&, T>::value,
+                  "T must be move-constructible and convertible to from U&&");
+    return bool(*this) ? std::move(**this) : static_cast<T>(std::forward<U>(v));
+  }
+};
+
+namespace detail {
+template <class Exp> using exp_t = typename detail::decay_t<Exp>::value_type;
+template <class Exp> using err_t = typename detail::decay_t<Exp>::error_type;
+template <class Exp, class Ret> using ret_t = expected<Ret, err_t<Exp>>;
+
+#ifdef TL_EXPECTED_CXX14
+template <class Exp, class F,
+          detail::enable_if_t<!std::is_void<exp_t<Exp>>::value> * = nullptr,
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              *std::declval<Exp>()))>
+constexpr auto and_then_impl(Exp &&exp, F &&f) {
+  static_assert(detail::is_expected<Ret>::value, "F must return an expected");
+
+  return exp.has_value()
+             ? detail::invoke(std::forward<F>(f), *std::forward<Exp>(exp))
+             : Ret(unexpect, std::forward<Exp>(exp).error());
+}
+
+template <class Exp, class F,
+          detail::enable_if_t<std::is_void<exp_t<Exp>>::value> * = nullptr,
+          class Ret = decltype(detail::invoke(std::declval<F>()))>
+constexpr auto and_then_impl(Exp &&exp, F &&f) {
+  static_assert(detail::is_expected<Ret>::value, "F must return an expected");
+
+  return exp.has_value() ? detail::invoke(std::forward<F>(f))
+                         : Ret(unexpect, std::forward<Exp>(exp).error());
+}
+#else
+template <class> struct TC;
+template <class Exp, class F,
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              *std::declval<Exp>())),
+          detail::enable_if_t<!std::is_void<exp_t<Exp>>::value> * = nullptr>
+auto and_then_impl(Exp &&exp, F &&f) -> Ret {
+  static_assert(detail::is_expected<Ret>::value, "F must return an expected");
+
+  return exp.has_value()
+             ? detail::invoke(std::forward<F>(f), *std::forward<Exp>(exp))
+             : Ret(unexpect, std::forward<Exp>(exp).error());
+}
+
+template <class Exp, class F,
+          class Ret = decltype(detail::invoke(std::declval<F>())),
+          detail::enable_if_t<std::is_void<exp_t<Exp>>::value> * = nullptr>
+constexpr auto and_then_impl(Exp &&exp, F &&f) -> Ret {
+  static_assert(detail::is_expected<Ret>::value, "F must return an expected");
+
+  return exp.has_value() ? detail::invoke(std::forward<F>(f))
+                         : Ret(unexpect, std::forward<Exp>(exp).error());
+}
+#endif
+
+#ifdef TL_EXPECTED_CXX14
+template <class Exp, class F,
+          detail::enable_if_t<!std::is_void<exp_t<Exp>>::value> * = nullptr,          
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              *std::declval<Exp>())),
+          detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
+constexpr auto expected_map_impl(Exp &&exp, F &&f) {
+  using result = ret_t<Exp, detail::decay_t<Ret>>;
+  return exp.has_value() ? result(detail::invoke(std::forward<F>(f),
+                                                 *std::forward<Exp>(exp)))
+                         : result(unexpect, std::forward<Exp>(exp).error());
+}
+
+template <class Exp, class F,
+          detail::enable_if_t<!std::is_void<exp_t<Exp>>::value> * = nullptr,          
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              *std::declval<Exp>())),
+          detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
+auto expected_map_impl(Exp &&exp, F &&f) {
+  using result = expected<void, err_t<Exp>>;
+  if (exp.has_value()) {
+    detail::invoke(std::forward<F>(f), *std::forward<Exp>(exp));
+    return result();
+  }
+
+  return result(unexpect, std::forward<Exp>(exp).error());
+}
+
+template <class Exp, class F,
+          detail::enable_if_t<std::is_void<exp_t<Exp>>::value> * = nullptr,
+          class Ret = decltype(detail::invoke(std::declval<F>())),
+          detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
+constexpr auto expected_map_impl(Exp &&exp, F &&f) {
+  using result = ret_t<Exp, detail::decay_t<Ret>>;
+  return exp.has_value() ? result(detail::invoke(std::forward<F>(f)))
+                         : result(unexpect, std::forward<Exp>(exp).error());
+}
+
+template <class Exp, class F,
+          detail::enable_if_t<std::is_void<exp_t<Exp>>::value> * = nullptr,          
+          class Ret = decltype(detail::invoke(std::declval<F>())),
+          detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
+auto expected_map_impl(Exp &&exp, F &&f) {
+  using result = expected<void, err_t<Exp>>;
+  if (exp.has_value()) {
+    detail::invoke(std::forward<F>(f));
+    return result();
+  }
+
+  return result(unexpect, std::forward<Exp>(exp).error());
+}    
+#else
+template <class Exp, class F,
+          detail::enable_if_t<!std::is_void<exp_t<Exp>>::value> * = nullptr,          
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              *std::declval<Exp>())),
+          detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
+
+constexpr auto expected_map_impl(Exp &&exp, F &&f)
+    -> ret_t<Exp, detail::decay_t<Ret>> {
+  using result = ret_t<Exp, detail::decay_t<Ret>>;
+
+  return exp.has_value() ? result(detail::invoke(std::forward<F>(f),
+                                                 *std::forward<Exp>(exp)))
+                         : result(unexpect, std::forward<Exp>(exp).error());
+}
+
+template <class Exp, class F,
+          detail::enable_if_t<!std::is_void<exp_t<Exp>>::value> * = nullptr,                    
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              *std::declval<Exp>())),
+          detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
+
+auto expected_map_impl(Exp &&exp, F &&f) -> expected<void, err_t<Exp>> {
+  if (exp.has_value()) {
+    detail::invoke(std::forward<F>(f), *std::forward<Exp>(exp));
+    return {};
+  }
+
+  return unexpected<err_t<Exp>>(std::forward<Exp>(exp).error());
+}
+
+template <class Exp, class F,
+          detail::enable_if_t<std::is_void<exp_t<Exp>>::value> * = nullptr,                              
+          class Ret = decltype(detail::invoke(std::declval<F>())),
+          detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
+
+constexpr auto expected_map_impl(Exp &&exp, F &&f)
+    -> ret_t<Exp, detail::decay_t<Ret>> {
+  using result = ret_t<Exp, detail::decay_t<Ret>>;
+
+  return exp.has_value() ? result(detail::invoke(std::forward<F>(f)))
+                         : result(unexpect, std::forward<Exp>(exp).error());
+}
+
+template <class Exp, class F,
+          detail::enable_if_t<std::is_void<exp_t<Exp>>::value> * = nullptr,                                        
+          class Ret = decltype(detail::invoke(std::declval<F>())),
+          detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
+
+auto expected_map_impl(Exp &&exp, F &&f) -> expected<void, err_t<Exp>> {
+  if (exp.has_value()) {
+    detail::invoke(std::forward<F>(f));
+    return {};
+  }
+
+  return unexpected<err_t<Exp>>(std::forward<Exp>(exp).error());
+}    
+#endif
+
+#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) &&               \
+    !defined(TL_EXPECTED_GCC54) && !defined(TL_EXPECTED_GCC55)
+template <class Exp, class F,
+          detail::enable_if_t<!std::is_void<exp_t<Exp>>::value> * = nullptr,          
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+          detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
+constexpr auto map_error_impl(Exp &&exp, F &&f) {
+  using result = expected<exp_t<Exp>, detail::decay_t<Ret>>;
+  return exp.has_value()
+             ? result(*std::forward<Exp>(exp))
+             : result(unexpect, detail::invoke(std::forward<F>(f),
+                                               std::forward<Exp>(exp).error()));
+}
+template <class Exp, class F,
+          detail::enable_if_t<!std::is_void<exp_t<Exp>>::value> * = nullptr,                    
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+          detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
+auto map_error_impl(Exp &&exp, F &&f) {
+  using result = expected<exp_t<Exp>, monostate>;
+  if (exp.has_value()) {
+    return result(*std::forward<Exp>(exp));
+  }
+
+  detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
+  return result(unexpect, monostate{});
+}
+template <class Exp, class F,
+          detail::enable_if_t<std::is_void<exp_t<Exp>>::value> * = nullptr,          
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+          detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
+constexpr auto map_error_impl(Exp &&exp, F &&f) {
+  using result = expected<exp_t<Exp>, detail::decay_t<Ret>>;
+  return exp.has_value()
+             ? result()
+             : result(unexpect, detail::invoke(std::forward<F>(f),
+                                               std::forward<Exp>(exp).error()));
+}
+template <class Exp, class F,
+          detail::enable_if_t<std::is_void<exp_t<Exp>>::value> * = nullptr,                    
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+          detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
+auto map_error_impl(Exp &&exp, F &&f) {
+  using result = expected<exp_t<Exp>, monostate>;
+  if (exp.has_value()) {
+    return result();
+  }
+
+  detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
+  return result(unexpect, monostate{});
+}    
+#else
+template <class Exp, class F,
+          detail::enable_if_t<!std::is_void<exp_t<Exp>>::value> * = nullptr,                              
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+          detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
+constexpr auto map_error_impl(Exp &&exp, F &&f)
+    -> expected<exp_t<Exp>, detail::decay_t<Ret>> {
+  using result = expected<exp_t<Exp>, detail::decay_t<Ret>>;
+
+  return exp.has_value()
+             ? result(*std::forward<Exp>(exp))
+             : result(unexpect, detail::invoke(std::forward<F>(f),
+                                               std::forward<Exp>(exp).error()));
+}
+
+template <class Exp, class F,
+          detail::enable_if_t<!std::is_void<exp_t<Exp>>::value> * = nullptr,                                        
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+          detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
+auto map_error_impl(Exp &&exp, F &&f) -> expected<exp_t<Exp>, monostate> {
+  using result = expected<exp_t<Exp>, monostate>;
+  if (exp.has_value()) {
+    return result(*std::forward<Exp>(exp));
+  }
+
+  detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
+  return result(unexpect, monostate{});
+}
+
+template <class Exp, class F,
+          detail::enable_if_t<std::is_void<exp_t<Exp>>::value> * = nullptr,                              
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+          detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
+constexpr auto map_error_impl(Exp &&exp, F &&f)
+    -> expected<exp_t<Exp>, detail::decay_t<Ret>> {
+  using result = expected<exp_t<Exp>, detail::decay_t<Ret>>;
+
+  return exp.has_value()
+             ? result()
+             : result(unexpect, detail::invoke(std::forward<F>(f),
+                                               std::forward<Exp>(exp).error()));
+}
+
+template <class Exp, class F,
+          detail::enable_if_t<std::is_void<exp_t<Exp>>::value> * = nullptr,                                        
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+          detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
+auto map_error_impl(Exp &&exp, F &&f) -> expected<exp_t<Exp>, monostate> {
+  using result = expected<exp_t<Exp>, monostate>;
+  if (exp.has_value()) {
+    return result();
+  }
+
+  detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
+  return result(unexpect, monostate{});
+}    
+#endif
+
+#ifdef TL_EXPECTED_CXX14
+template <class Exp, class F,
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+          detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
+constexpr auto or_else_impl(Exp &&exp, F &&f) {
+  static_assert(detail::is_expected<Ret>::value, "F must return an expected");
+  return exp.has_value()
+  ? std::forward<Exp>(exp)
+  : detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
+}
+
+template <class Exp, class F,
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+          detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
+detail::decay_t<Exp> or_else_impl(Exp &&exp, F &&f) {
+  return exp.has_value()
+  ? std::forward<Exp>(exp)
+  : (detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error()),
+    std::forward<Exp>(exp));
+}
+#else
+template <class Exp, class F,
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+  detail::enable_if_t<!std::is_void<Ret>::value> * = nullptr>
+auto or_else_impl(Exp &&exp, F &&f) -> Ret {
+  static_assert(detail::is_expected<Ret>::value, "F must return an expected");
+  return exp.has_value()
+         ? std::forward<Exp>(exp)
+         : detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error());
+}
+
+template <class Exp, class F,
+          class Ret = decltype(detail::invoke(std::declval<F>(),
+                                              std::declval<Exp>().error())),
+  detail::enable_if_t<std::is_void<Ret>::value> * = nullptr>
+detail::decay_t<Exp> or_else_impl(Exp &&exp, F &&f) {
+  return exp.has_value()
+         ? std::forward<Exp>(exp)
+         : (detail::invoke(std::forward<F>(f), std::forward<Exp>(exp).error()),
+            std::forward<Exp>(exp));
+}
+#endif
+} // namespace detail
+
+template <class T, class E, class U, class F>
+constexpr bool operator==(const expected<T, E> &lhs,
+                          const expected<U, F> &rhs) {
+  return (lhs.has_value() != rhs.has_value())
+             ? false
+             : (!lhs.has_value() ? lhs.error() == rhs.error() : *lhs == *rhs);
+}
+template <class T, class E, class U, class F>
+constexpr bool operator!=(const expected<T, E> &lhs,
+                          const expected<U, F> &rhs) {
+  return (lhs.has_value() != rhs.has_value())
+             ? true
+             : (!lhs.has_value() ? lhs.error() != rhs.error() : *lhs != *rhs);
+}
+
+template <class T, class E, class U>
+constexpr bool operator==(const expected<T, E> &x, const U &v) {
+  return x.has_value() ? *x == v : false;
+}
+template <class T, class E, class U>
+constexpr bool operator==(const U &v, const expected<T, E> &x) {
+  return x.has_value() ? *x == v : false;
+}
+template <class T, class E, class U>
+constexpr bool operator!=(const expected<T, E> &x, const U &v) {
+  return x.has_value() ? *x != v : true;
+}
+template <class T, class E, class U>
+constexpr bool operator!=(const U &v, const expected<T, E> &x) {
+  return x.has_value() ? *x != v : true;
+}
+
+template <class T, class E>
+constexpr bool operator==(const expected<T, E> &x, const unexpected<E> &e) {
+  return x.has_value() ? false : x.error() == e.value();
+}
+template <class T, class E>
+constexpr bool operator==(const unexpected<E> &e, const expected<T, E> &x) {
+  return x.has_value() ? false : x.error() == e.value();
+}
+template <class T, class E>
+constexpr bool operator!=(const expected<T, E> &x, const unexpected<E> &e) {
+  return x.has_value() ? true : x.error() != e.value();
+}
+template <class T, class E>
+constexpr bool operator!=(const unexpected<E> &e, const expected<T, E> &x) {
+  return x.has_value() ? true : x.error() != e.value();
+}
+
+template <class T, class E,
+          detail::enable_if_t<(std::is_void<T>::value ||
+                               std::is_move_constructible<T>::value) &&
+                              detail::is_swappable<T>::value &&
+                              std::is_move_constructible<E>::value &&
+                              detail::is_swappable<E>::value> * = nullptr>
+void swap(expected<T, E> &lhs,
+          expected<T, E> &rhs) noexcept(noexcept(lhs.swap(rhs))) {
+  lhs.swap(rhs);
+}
+} // namespace tl
+
+#endif