How to create a wrapper of List with a specific type

Question

I am trying to create a wrapper of List with a specific type (e.g. List[Int]) such that methods that take an implicit CanBuildFrom par

Answer 1

Regarding my follow-up question how to mixin the wrapper logic via classes or traits, this is what I came up with:

import scala.collection._

trait ListWrapper[Elem, Repr <: ListWrapper[Elem, Repr]]
    extends immutable.LinearSeq[Elem]
    with LinearSeqLike[Elem, Repr]
    with generic.SeqForwarder[Elem] { self: Repr =>

  def wrapperCompanion: ListWrapperCompanion[Elem, Repr]

  override def newBuilder: mutable.Builder[Elem, Repr] =
    wrapperCompanion.newBuilder
}

trait ListWrapperCompanion[Elem, Repr <: ListWrapper[Elem, Repr]] {
  def apply(elems: TraversableOnce[Elem]): Repr

  def newBuilder: mutable.Builder[Elem, Repr] =
    new mutable.ListBuffer[Elem].mapResult(apply)

  def canBuildFromWrapper: generic.CanBuildFrom[Repr, Elem, Repr] = {
    new generic.CanBuildFrom[Repr, Elem, Repr] {
      def apply(from: Repr) = from.newBuilder
      def apply() = newBuilder
    }
  }
}

Now MyList can be implemented by:

class MyList(val underlying: List[Int]) extends ListWrapper[Int, MyList] {
  def wrapperCompanion = MyList
}

object MyList extends ListWrapperCompanion[Int, MyList] {
  def apply(elems: TraversableOnce[Int]) = new MyList(elems.toList)

  implicit def canBuildFrom = canBuildFromWrapper
}

This is definitely better than having all the boilerplate code in MyList's definition, but it is still a lot to write for making MyList just a wrapper for List.