Base class of most policy classes defining the narrow observer policies.

1. static void _ub(Impl &&)

   Special function which causes noticeable hard undefined behaviour.

2. static bool _has_value(Impl &&) noexcept

   Returns true if a value is present in the implementation passed in. Constexpr, never throws.

3. static bool _has_error(Impl &&) noexcept

   Returns true if an error is present in the implementation passed in. Constexpr, never throws.

4. static bool _has_exception(Impl &&) noexcept

   Returns true if an exception is present in the implementation passed in. Constexpr, never throws.

5. static bool _has_error_is_errno(Impl &&) noexcept

   Returns true if the error code in the implementation passed in has a domain or category matching that of POSIX errno. Constexpr, never throws.

6. static auto &&_value(Impl &&) noexcept

   Returns a reference to the value in the implementation passed in. Constexpr, never throws.

7. static auto &&_error(Impl &&) noexcept

   Returns a reference to the error in the implementation passed in. Constexpr, never throws.

8. static auto &&_exception(Impl &&) noexcept

   Returns a reference to the exception in the implementation passed in. Constexpr, never throws.

9. static void _set_has_value(Impl &&, bool) noexcept

   Sets whether the implementation has a value. Constexpr, never throws.

10. static void _set_has_error(Impl &&, bool) noexcept

    Sets whether the implementation has an error. Constexpr, never throws.

11. static void _set_has_exception(Impl &&, bool) noexcept

    Sets whether the implementation has an exception. Constexpr, never throws.

12. static void _set_has_exception(Impl &&, bool) noexcept

    Sets whether the implementation’s error code has a domain or category matching that of POSIX errno. Constexpr, never throws.

13. static void narrow_value_check(Impl &&) noexcept

    Observer policy performing hard UB if no value is present. Constexpr, never throws.

14. static void narrow_error_check(Impl &&) noexcept

    Observer policy performing hard UB if no error is present. Constexpr, never throws.

15. static void narrow_exception_check(Impl &&) noexcept

    Observer policy performing hard UB if no exception is present. Constexpr, never throws.

16. static void on_outcome_construction(T *, U &&) noexcept

    (>= Outcome v2.2.0) Hook invoked by the implicit constructors of basic_outcome.

17. static void on_outcome_construction(T *, U &&, V &&) noexcept

    (>= Outcome v2.2.0) Hook invoked by the implicit constructors of basic_outcome.

18. static void on_outcome_copy_construction(T *, U &&) noexcept

    (>= Outcome v2.2.0) Hook invoked by the converting copy constructors of basic_outcome.

19. static void on_outcome_copy_construction(T *, U &&, V &&) noexcept

    (>= Outcome v2.2.0) Hook invoked by the converting copy constructors of basic_outcome.

20. static void on_outcome_in_place_construction(T *, in_place_type_t<U>, Args &&...) noexcept

    (>= Outcome v2.2.0) Hook invoked by the in-place constructors of basic_outcome.

21. static void on_outcome_move_construction(T *, U &&) noexcept

    (>= Outcome v2.2.0) Hook invoked by the converting move constructors of basic_outcome.

22. static void on_outcome_move_construction(T *, U &&, V &&) noexcept

    (>= Outcome v2.2.0) Hook invoked by the converting move constructors of basic_outcome.

23. static void on_result_construction(T *, U &&) noexcept

    (>= Outcome v2.2.0) Hook invoked by the implicit constructors of basic_result.

24. static void on_result_copy_construction(T *, U &&) noexcept

    (>= Outcome v2.2.0) Hook invoked by the converting copy constructors of basic_result.

25. static void on_result_in_place_construction(T *, in_place_type_t<U>, Args &&...) noexcept

    (>= Outcome v2.2.0) Hook invoked by the in-place constructors of basic_result.

26. static void on_result_move_construction(T *, U &&) noexcept

    (>= Outcome v2.2.0) Hook invoked by the converting move constructors of basic_result.

Policy class defining that hard undefined behaviour should occur on incorrect narrow and wide value, error or exception observation. Inherits publicly from base.

Policy class defining that EP ought to be rethrown if possible, then the ADL discovered free function outcome_throw_as_system_error_with_payload() should be called on incorrect wide value observation. Inherits publicly from base. Can only be used with basic_outcome.

Policy class defining that the ADL discovered free function outcome_throw_as_system_error_with_payload() should be called on incorrect wide value observation. Inherits publicly from base. Can only be used with basic_result.

Policy class defining that the ADL discovered free function rethrow_exception() should be called on incorrect wide value observation. Inherits publicly from base. Can only be used with basic_outcome.

Policy class defining that the ADL discovered free function rethrow_exception() should be called on incorrect wide value observation. Inherits publicly from base. Can only be used with basic_result.

Policy class defining that a static assertion should occur upon compilation of the wide value, error or exception observation. Inherits publicly from base.

Policy class defining that std::terminate() should be called on incorrect wide value, error or exception observation. Inherits publicly from base.

Policy class defining that bad_result_access_with<EC> should be thrown on incorrect wide value observation. Inherits publicly from base.