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