parse

# File railties/lib/rails/generators/generated_attribute.rb, line 36
        def parse(column_definition)
          name, type, index_type = column_definition.split(":")

          # if user provided "name:index" instead of "name:string:index"
          # type should be set blank so GeneratedAttribute's constructor
          # could set it to :string
          index_type, type = type, nil if valid_index_type?(type)

          type, attr_options = *parse_type_and_options(type)
          type = type.to_sym if type

          if dangerous_name?(name)
            raise Error, "Could not generate field '#{name}', as it is already defined by Active Record."
          end

          if type && !valid_type?(type)
            raise Error, "Could not generate field '#{name}' with unknown type '#{type}'."
          end

          if index_type && !valid_index_type?(index_type)
            raise Error, "Could not generate field '#{name}' with unknown index '#{index_type}'."
          end

          if type && reference?(type)
            if UNIQ_INDEX_OPTIONS.include?(index_type)
              attr_options[:index] = { unique: true }
            end
          end

          new(name, type, index_type, attr_options)
        end