(PHP 5 >= 5.1.0)
Serializable::serialize — String representation of object
Should return the string representation of the object.
Note: This method acts as the destructor of the object. The __destruct() method will not be called after this method.
이 함수는 인수가 없습니다.
Returns the string representation of the object or NULL
Throws Exception when returning other types then strings and NULL