Returning same collection type, differently parameterised

Question

Daniel Sobral showed how we can create a method that returns the same collection type upon which it was called in his answer to this question: Returning original collection

Answer 1

Extending Daniel's answer to the linked question:

def foo[A,T[X] <: TraversableLike[X,T[X]]](xs: T[A])(implicit cbf: CanBuildFrom[T[A],String,T[String]]):  T[String] = xs.map(_.toString)

Note that the map method defined in TraversableLike takes an implicit CanBuildFrom parameter. This is used to create a builder for the desired collection type so it has to be parameterized the way it is in the code (i.e., based on a collection of type T[A], build a T[String] from String elements).