def lookup_class
        ObjectSpace.each_object(Class) do |obj|
          return obj if valid_superclass?(obj) and
                        obj.name.split('::').last == class_name
        end
        raise NameError, "Missing #{class_name} class in #{class_file}"
      end
def lookup_class
        ObjectSpace.each_object(Class) do |obj|
          return obj if valid_superclass?(obj) and
                        obj.name.split('::').last == class_name
        end
        raise NameError, "Missing #{class_name} class in #{class_file}"
      end
Search for the first Class descending from RubiGen::Base
 whose name matches the requested class name.