std::basic_string_view::size, std::basic_string_view::length
From cppreference.com
                    
                                        
                    < cpp | string | basic string view
                    
                                                            
                    | constexpr size_type size() const; | (since C++17) | |
| constexpr size_type length() const; | (since C++17) | |
Returns the number of CharT elements in the view, i.e. std::distance(begin(), end()). 
Parameters
(none)
Return value
The number of CharT elements in the view.
Exceptions
noexcept specification:  
noexcept
  Complexity
Constant.
See also
| checks whether the view is empty (public member function) | |
| returns the maximum number of characters (public member function) |