std::packaged_task::get_future
From cppreference.com
                    
                                        
                    < cpp | thread | packaged task
                    
                                                            
                    | std::future<R> get_future(); | (since C++11) | |
Returns a future which shares the same shared state as *this.
get_future can be called only once for each packaged_task.
[edit] Parameters
(none)
[edit] Return value
A future which shares the same shared state as *this.
[edit] Exceptions
std::future_error on the following error conditions:
-  The shared state has already been retrieved via a call to get_future. The error category is set to future_already_retrieved.
- *this has no shared state. The error category is set to no_state.


