Question

This does not work:

def giveArray[T](elem:T):Array[T] = {
    new Array[T](1)
  }

But this does:

  def giveList[T](elem:T):List[T] = {
    List.empty[T]
  }

I am sure this is a pretty basic thing and I know that Arrays can behave a bit unusual in Scala.

Could someone explain to me how to create such an Array and also why it doesn’t work in the first place?

Answer 1

This is due to JVM type erasure. Manifest were introduce to handle this, they cause type information to be attached to the type T. This will compile:

def giveArray[T: Manifest](elem:T):Array[T] = {
  new Array[T](1)
}

There are nearly duplicated questions on this. Let me see if I can dig up.
See http://www.scala-lang.org/docu/files/collections-api/collections_38.html for more details. I quote (replace evenElems with elem in your case)

What’s required here is that you help the compiler out by providing some runtime hint what the actual type parameter of evenElems is

In particular you can also use ClassManifest.

def giveArray[T: ClassManifest](elem:T):Array[T] = {
  new Array[T](1)
}

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