std::is_error_condition_enum<std::future_errc>
From cppreference.com
                    
                                        
                    < cpp | thread | future errc
                    
                                                            
                    |   Defined in header <future>
   | 
||
|   template<> struct is_error_condition_enum<std::future_errc> : std::true_type;  | 
(since C++11) | |
Specifies that std::future_errc is an error condition enum. This enables std::error_code and std::error_condition automatic conversions.
[edit] See also
|    (C++11)  | 
   identifies an enumeration as an std::error_condition  (class template)  |