std::basic_string_view<CharT,Traits>::front
From cppreference.com
                    
                                        
                    < cpp | string | basic string view
                    
                                                            
                    |   constexpr const_reference front() const;  | 
(since C++17) | |
Returns reference to the first character in the view. The behavior is undefined if empty() == true.
Parameters
(none)
Return value
reference to the first character, equivalent to operator[](0).
Complexity
Constant.
See also
|    accesses the last character   (public member function)  | |
|    checks whether the view is empty    (public member function)  |