Class unexpected

test-app/runtime/src/main/cpp/ada/ada.h:1749–1776

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>