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

Issue

I am trying to update an immutable Map in an immutable Map, but that gives me an error:

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)

ERROR:

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))

How can I replace the immutable Map value by a new one in the m without making m mutable?

Solution

As @Luis Miguel Mejía Suárez noted in the comments, using updated and updatedWith methods solved the problem. Example: https://scastie.scala-lang.org/BalmungSan/kdlqN3t5SGiQ26oDPyy0jg/2

Answered By - LinkCoder