std::is_error_code_enum<std::future_errc>
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                    < cpp | thread | future errc
                    
                                                            
                    |   Defined in header  <future>
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|   template<> struct is_error_code_enum<std::future_errc> : std::true_type;  | 
(since C++11) | |
Specifies that std::future_errc is an error code enum. This enables std::error_code automatic conversions.
See also
|    (C++11)  | 
  identifies a class as an error_code enumeration (class template)  |