The generator function governs the rule processing for a notification application. 生成器函数控制通知应用程序的规则处理。
Rather than initializing data members when they are defined inside the class definition, classes control initialization through special member functions called constructors. 类不是在类定义里定义数据成员时初始化数据成员，而是通过称为构造函数的特殊成员函数控制初始化。
