问题描述
scala 中是否有与 Nil 等效的 Set ?
Is there an equivalent of Nil for Set in scala?
我尝试使用 Nil 作为 Set 的值，但出现错误(预期，因为 Nil 的类型是 列表)
I tried using Nil as a value for Set, but I got an error (expected since the type of Nil is List)
谢谢
推荐答案
Set.empty 就是那个集合；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).Set.empty 所做的就是通过强制转换将该集合返回到正确的类型.
Set.empty is that set; although you can't get at it directly, it turns out that it is just a private object in the Set companion object (called, obviously enough, EmptySet). All that Set.empty does is return that set with a cast to the correct type.
以这种方式完成，而不是使用 Nil，因为集合在其参数中不变.Nil 是 List[Nothing]()，但是你不能向 Set[Nothing]() 添加任何东西.
It is done this way, instead of with Nil, because sets are invariant in their parameters. Nil is List[Nothing](), but you couldn't add anything to a Set[Nothing]().
如果您需要指定空集的类型，您可以使用例如Set.empty[String].
If you need to specify the type of your empty set, you can use e.g. Set.empty[String].
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