问题描述
我只想使用一些并发的 Set(似乎根本不存在).Java 使用 java.util.concurrent.ConcurrentHashMap 来实现该行为.我想在 Scala 中做类似的事情，所以我创建了 Scala HashMap(或 Java ConcurrentHashMap)的实例并尝试添加一些元组:
All I desire is to use some concurrent Set (that appears not to exist at all). Java uses java.util.concurrent.ConcurrentHashMap<K, Void> to achieve that behavior. I'd like to do sth similar in Scala so I created instance of Scala HashMap (or Java ConcurrentHashMap) and tried to add some tuples:
val myMap = new HashMap[String, Unit]()
myMap + (("myStringKey", Unit))
这当然会导致编译过程崩溃，因为 Unit 是抽象的和最终的.
This of course crashed the process of compilation as Unit is abstract and final.
如何做到这一点?我应该改用 Any/AnyRef 吗?我必须确保没有人插入任何值.
How to make this work? Should I use Any/AnyRef instead? I must ensure nobody inserts any value.
感谢您的帮助
推荐答案
你可以使用类型为Unit的():
scala> import scala.collection.mutable.HashMap
import scala.collection.mutable.HashMap
scala> val myMap = new HashMap[String, Unit]()
myMap: scala.collection.mutable.HashMap[String,Unit] = Map()
scala> myMap + ("myStringKey" -> ())
res1: scala.collection.mutable.Map[String,Unit] = Map(myStringKey -> ())
这是来自 Unit.scala:
Unit类型的值只有一个()，在底层运行时系统中不被任何对象表示.
There is only one value of type
Unit,(), and it is not represented by any object in the underlying runtime system.
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