Laravel源码分析：Response

/**
     * Determine(判断) if the given content should be turned into JSON.
     *
     * @param  mixed  $content
     * @return bool
     */
    protected function shouldBeJson($content)
    {
        return $content instanceof Arrayable ||
               $content instanceof Jsonable ||
               $content instanceof ArrayObject ||
               $content instanceof JsonSerializable ||
               is_array($content);
    }

Arrayable

Jsonable

ArrayObject

JsonSerializable

TODO