Set 的 Scala Nil 等价物
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Scala Nil equivalent for Set
提问by Rand
Is there an equivalent of Nilfor Setin scala?
是否有一个等同Nil于Set在Scala呢？
I tried using Nilas a value for Set, but I got an error (expected since the type of Nilis List)
我尝试将Nil用作 的值Set，但出现错误（预期是因为类型Nil是List）
Thanks
谢谢
回答by Rex Kerr
Set.emptyis that set; although you can't get at it directly, it turns out that it is just a private object in the Setcompanion object (called, obviously enough, EmptySet). All that Set.emptydoes is return that set with a cast to the correct type.
Set.empty是那一套吗？虽然你不能直接得到它，但事实证明它只是Set伴随对象中的一个私有对象（很明显，它被称为EmptySet）。所有这一切Set.empty确实是返回与集合强制转换为正确的类型。
It is done this way, instead of with Nil, because sets are invariantin their parameters. Nilis List[Nothing](), but you couldn't add anything to a Set[Nothing]().
它是通过这种方式完成的，而不是 with Nil，因为集合的参数是不变的。 Nilis List[Nothing]()，但您不能向 a 添加任何内容Set[Nothing]()。
If you need to specify the type of your empty set, you can use e.g. Set.empty[String].
如果需要指定空集的类型，可以使用 eg Set.empty[String]。
回答by paradigmatic
You can use Set.emptyor simply Set().
您可以使用Set.empty或简单地使用Set().
回答by Chris Shain
I think you are looking for Set.empty
我想你正在寻找 Set.empty
