Question

Inside a function of mine I construct a result set by filling a new mutable HashMap with data (if there is a better way – I’d appreciate comments). Then I’d like to return the result set as an immutable HashMap. How to derive an immutable from a mutable?

Answer 1

scala> val m = collection.mutable.HashMap(1->2,3->4)
m: scala.collection.mutable.HashMap[Int,Int] = Map(3 -> 4, 1 -> 2)

scala> collection.immutable.HashMap() ++ m
res1: scala.collection.immutable.Map[Int,Int] = Map(1 -> 2, 3 -> 4)

or

scala> collection.immutable.HashMap(m.toSeq:_*)
res2: scala.collection.immutable.HashMap[Int,Int] = Map(1 -> 2, 3 -> 4)