CODEWITHSUNDEEP
scalascala-2.10
matanox
matanox

Reputation: 13686

Scala getClass ponderings

I have a Scala list for which I derive the following pair of outputs (Scala 2.10):

println(myList.getClass)`
// class scala.collection.immutable.$colon$colon

println(myList) 
// List(1, 2, 3,....)

Could you please explain:

  1. What is the meaning of $colon$colon

  2. Why doesn't the output derived from getClass indicate this is a List, not just some collection?

Upvotes: 0

Views: 71

Answers (1)

sjrd
sjrd

Reputation: 22085

First, $colon$colon is the encoding in a JVM-friendly (but not human-friendly) of the class ::. Recall that an empty list is the singleton Nil, and that a non-empty list is a :: (read "cons") with a head (which is an element) and a tail (which is again a list). A non-empty list is therefore always an instance of this class ::. But the compiler renames it to $colon$colon for the JVM to be happy.

I'm not sure I understand your second question. The output of println(myList) simply redirects to the method toString() of List, which (through a few more indirections), prints the string "List" followed by the elements in parentheses. That's all.

Upvotes: 2

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