value_type_wrap operator[](difference_type _Off) const
 
        Iterator index operator. 
        If _Off not in a valid range, the returned value will be invalid. Note that you should use a value_type_wrap type to hold the returned value. 
        
          
          
            
            The valid index relative to this iterator. 
           
         
        
          
          Return the element which is at position *this + _Off, which is an ElementRef<T> object if T is a class type or an ElementHolder<T> object if T is a C++ primitive data type. The returned value can be used to read or update its referenced element.