std::future_category
From cppreference.com
                    
                                        
                    
                    
                                                            
                    |   Defined in header  <future>
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|   const std::error_category& future_category() noexcept;  | 
(since C++11) | |
Obtains a reference to the static error category object for the errors related to futures and promises. The object is required to override the virtual function error_category::name() to return a pointer to the string "future". It is used to identify error codes provided in the exceptions of type std::future_error.
Parameters
(none)
Return value
A reference to the static object of unspecified runtime type, derived from std::error_category.
Example
| This section is incomplete Reason: no example  | 
See also
|    (C++11)  | 
   identifies the future error codes  (enum)  | 
|    (C++11)  | 
   reports an error related to futures or promises   (class)  | 
|    (C++11)  | 
   base class for error categories   (class)  |