callback

# File activerecord/lib/active_record/callbacks.rb, line 339
      def callback(method)
        notify(method)

        callbacks_for(method).each do |callback|
          result = case callback
            when Symbol
              self.send(callback)
            when String
              eval(callback, binding)
            when Proc, Method
              callback.call(self)
            else
              if callback.respond_to?(method)
                callback.send(method, self)
              else
                raise ActiveRecordError, "Callbacks must be a symbol denoting the method to call, a string to be evaluated, a block to be invoked, or an object responding to the callback method."
              end
          end
          return false if result == false
        end

        result = send(method) if respond_to_without_attributes?(method)

        return result
      end