A Map is an Iterable consisting of pairs of keys and values (also named mappings or associations). Scala’s Predef object offers an implicit conversion that lets you write key -> value as an alternate syntax for the pair (key, value). For instance Map("x" -> 24, "y" -> 25, "z" -> 26) means exactly the same as Map(("x", 24), ("y", 25), ("z", 26)), but reads better.
This is a companion discussion topic for the original entry at http://docs.scala-lang.org//overviews/collections/maps.html