将对象声明为“最终”的重点是什么？ [英] What's the point of declaring an object as "final"?

问题描述

我刚注意到可以在Scala中将对象声明为 final ：

I just noticed that it's possible to declare objects as final in Scala:

final object O

这样做有什么意义？无论如何都不能从对象继承：

What's the point of doing that? One cannot inherit from objects anyway:

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

推荐答案

并非所有人都这样做，但是：

Not that anyone does this, but:

$ 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。）

Possibly sometimes people want to do it. (For instance.)

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