Class attributes can be initialized when declared, but if the attribute is initialized with a complex object type ( such as a hash or an array) that attribute becomes analogous to a public static variable in a Java class. 类属性可以在声明时进行初始化,但是如果使用复杂对象类型(例如hash或数组)初始化属性,该属性将类似于Java类中的公共静态变量。
This attribute is a hint to the compiler that the function declared with this attribute and the subsequent functions it calls do not throw an exception. 这个属性可以告诉编译器,使用该属性声明的函数以及它调用的后续函数都不会引发异常。