parse

# File railties/lib/rails/generators/generated_attribute.rb, line 16
        def parse(column_definition)
          name, type, has_index = 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
          has_index, type = type, nil if INDEX_OPTIONS.include?(type)

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

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

          new(name, type, has_index, attr_options)
        end