将对象声明为"最终"有什么意义？

Question

我只是注意到可以final在Scala中声明对象:

final object O

这样做有什么意义？无论如何,无法继承对象:

object A
object B extends A // not found: type A

Answer 1

不是有人这样做,但是:

$ scala -Yoverride-objects
Welcome to Scala version 2.11.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_11).
Type in expressions to have them evaluated.
Type :help for more information.

scala> trait A { object O } ; trait B extends A { override object O }
defined trait A
defined trait B

scala> trait A { final object O } ; trait B extends A { override object O }
<console>:8: error: overriding object O in trait A;
 object O cannot override final member
       trait A { final object O } ; trait B extends A { override object O }
                                                                        ^

有时人们可能想要这样做.(例如.)

Answer 2

没什么区别; 对象定义总是最终的.该语言规范明确提到这5.4修改器:

final 对象定义是多余的.