如何更新在 Scala 中也是 Map 的 Map 值？

Question

我正在尝试更新不可变映射中的不可变映射，但这给了我一个错误：

var m: immutable.Map[Int, immutable.Map[String, Int]] = Map[Int, immutable.Map[String, Int]]()

val item = Map[String, Int]("Test" -> 0)
m += (1, item)

val newVal: Int = m(1)("Test") + 1
val newValMap = Map[String, Int]("Test"-> newVal)
// This gives an error
m += (1, newValMap)

错误：

value += is not a member of scala.collection.immutable.Map[Int,scala.collection.immutable.Map[String,Int]]
  Expression does not convert to assignment because:
    type mismatch;
     found   : Int
     required: (Int, scala.collection.immutable.Map[String,Int])
    type mismatch;
     found   : (String, Int)
     required: (Int, scala.collection.immutable.Map[String,Int])
    expansion: TestClass.this.m = TestClass.this.m.+(<1: error>, "Test".$minus$greater(1))
        m += (1, ("Test" -> 1))

如何在不使 m 可变的情况下用 m 中的新值替换不可变的 Map 值？

Answer 1

正如@Luis Miguel Mejía Suárez 在评论中指出的那样，使用 updated 和 updatedWith 方法解决了问题。示例：https://scastie.scala-lang.org/BalmungSan/kdlqN3t5SGiQ26oDPyy0jg/2

如何更新在 Scala 中也是 Map 的 Map 值？

How to update Map value that is also a Map in Scala?

java

dictionary

scala