How do I specify a newBuilder for a scala set?

Question

I am trying to extend a set of integers in Scala. Based on an earlier answer I have decided to use a SetProxy object. I am now trying to implement the newBuilder

Answer 1

Give this a shot:

case class CustomSet(override val self: Set[Int]) extends SetProxy[Int] {
  override def newBuilder = new mutable.SetBuilder[Int, Set[Int]](CustomSet())
}

object CustomSet {
  def apply(values: Int*): CustomSet = CustomSet(HashSet(values.toSeq: _*))
}

When creating the SetBuilder, specifying CustomSet as the second type param did not satisfy the type bound for that param. Switching it to Set[Int] meets that criteria and allows you to still pass in your CustomSet as the constructor arg. Hope this helps.