def _attribute_default(attribute_name)
      default = self.class.attributes[attribute_name][:default]

      case
      when default.respond_to?(:call) then instance_exec(&default)
      when default.duplicable? then default.dup
      else default
      end
    end
def _attribute_default(attribute_name)
      default = self.class.attributes[attribute_name][:default]

      case
      when default.respond_to?(:call) then instance_exec(&default)
      when default.duplicable? then default.dup
      else default
      end
    end
Calculates an attribute default

 @private
 @since 0.5.0