Scala Map foreach

Question

given:

val m = Map[String, Int]("a" -> 1, "b" -> 2, "c" -> 3) m.foreach((key: String, value: Int) => println(">>> key=" + key + ", value=" + value)) 

why does the compiler complain

error: type mismatch found   : (String, Int) => Unit required: (String, Int) => ? 

Answer 1

I'm not sure about the error, but you can achieve what you want as follows:

m.foreach(p => println(">>> key=" + p._1 + ", value=" + p._2)) 

That is, foreach takes a function that takes a pair and returns Unit, not a function that takes two arguments: here, p has type (String, Int).

Another way to write it is:

m.foreach { case (key, value) => println(">>> key=" + key + ", value=" + value) } 

In this case, the { case ... } block is a partial function.

Answer 2

oops, read the doco wrong, map.foreach expects a function literal with a tuple argument!

so

m.foreach((e: (String, Int)) => println(e._1 + "=" + e._2)) 

works