std::shared_lock::operator bool
From cppreference.com
                    
                                        
                    < cpp | thread | shared lock
                    
                                                            
                    | explicit operator bool() const; | (since C++14) | |
Checks whether *this owns a locked mutex or not. Effectively calls owns_lock().
| Contents | 
[edit] Parameters
(none)
[edit] Return value
true if *this has an associated mutex and has acquired shared ownership of it, false otherwise.
[edit] Exceptions
noexcept specification:  
noexcept
  [edit] See also
| tests whether the lock owns its associated mutex (public member function) | 


