列表的Scala HashMap：更简单的默认？ [英] Scala HashMap of Lists: simpler default?

问题描述

我需要一个HashMap的列表。通常我这样做：

I need a HashMap of Lists. Normally I do this:

val lists = mutable.HashMap[String,List[Int]]() { 
  override def default(key: String) = {
    val newList = List[Int]()
    this(key) = newList
    newList
  }
}

，这样我就可以简单地写出像

so that I can then simply write things like

lists("dog") ::= 14

不必担心狗列表是否已经初始化。

without having to worry about whether the "dog" List has been initialised yet.

有没有更简单的方法来做到这一点？

Is there a cleaner way to do this? I find myself typing out those five default override lines again and again.

谢谢！

Thanks!

推荐答案

val lists = new mutable.HashMap[String,List[Int]].withDefaultValue(Nil)

lists("dog") ::= 13
lists("cat") ::= 14
lists("dog") ::= 15  //(13, 15)

另见

• 如何使用默认操作实现Map在Scala



See also

• How to implement Map with default operation in Scala

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