Extending Scala collections

Question

I would like to derive a version of a Scala built-in collection that expands on the functionality for a particular generic type e.g.,

import scala.collection         


        

Answer 1

As Kevin Wright said, + operation will return back HashSet. Type class CanBuildFrom is used to build new collections during operations like map. So if you want + to return Tuple2Set instead of HashSet you should implement CanBuildFrom and make it implicitly available in companion object like this:

object Tuple2Set {
    implicit def canBuildFrom[T1, T2] = 
        new CanBuildFrom[Tuple2Set[T1, T2], (T1, T2), Tuple2Set[T1, T2]] {...}
}