How to initialize empty map that has been type aliased

Question

Typically I have been declaring a map in this fashion because I need it to be empty

var myMap: mutable.Map[String, ListBuffer[Objects]] = mutable.Map[String, ListBuffer[Objects]]()

The object type signature is long so I am trying to declare my own type alias as such in a package object like below.

type MyMapType = mutable.Map[String, ListBuffer[Objects]]

The problem is when I try to declare my map with the alias it doesn't seem to work.

var myMap: MyMapType = MyMapType()

I get an error saying

Expression of type ListBuffer[Objects] doesn't conform to expected type MyPackageObject.MyMapType

Answer 1

Try this:

import collection.mutable.{Map, ListBuffer}
type MyMapType = Map[String, ListBuffer[Object]]
var myMap: MyMapType = Map()

The reason why this works: Map() is shortcut for Map.apply(). It's a method invocation on an object called Map. It is the companion object of mutable.Map. Its name belongs to a completely separate set of identifiers: the names of types are independent from names of objects. Therefore, the companion object Map is still called Map. Note that you can omit all the type arguments to .apply() because of the type inference.