std::basic_string_view::empty
From cppreference.com
                    
                                        
                    < cpp | string | basic string view
                    
                                                            
                    | constexpr bool empty() const; | (since C++17) | |
Checks if the view has no characters, i.e. whether size() == 0.
Parameters
(none)
Return value
true if the view is empty, false otherwise
Exceptions
noexcept specification:  
noexcept
  Complexity
Constant.
See also
| returns the number of characters (public member function) | |
| returns the maximum number of characters (public member function) |