Question

Suppose I have the following code:

case class Foo(x: SortedSet[String]) {
  def bar: Set[String] = x
}

(This is a simplification of the actual code I have.) If I try to run this, I get the following error:

error: type mismatch;
found   : scala.collection.SortedSet[String]
required: Set[String]
   def bar: Set[String] = x

Why do I get this error? Isn’t SortedSet[String] a subtrait of Set[String]?

Answer 1

Set is immutable.Set.

scala>  import scala.collection.immutable.SortedSet
import scala.collection.immutable.SortedSet

scala> :paste
// Entering paste mode (ctrl-D to finish)

case class Foo(x: SortedSet[String]) {
  def bar: Set[String] = x
}

// Exiting paste mode, now interpreting.

defined class Foo