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

As far I know from reading this article:

http://www.scala-lang.org/docu/files/collections-api/collections-impl.html

your solution is the simplest one, if you want filter/map/etc. to all return instances of MyList. newBuilder is needed for ops like filter, and the implicit CanBuildFrom for ops like map, which may change the collection type.

What you should maybe do in your CanBuildFrom is this:

def apply(from: MyList) = from.newBuilder // call it on `from'

which ensures that a map on a statically-typed MyList which actually has a dynamic type that is a subtype of MyList will reuse that same dynamic type.

Edit: seems like there is a little something missing, for this map returns an instance of List and not MyList:

val l1: LinearSeq[Int] = new MyList(List(1, 2, 3))
println(l1.map(_ + 1)) // prints List(2, 3, 4)

it looks like this is also the case with the RNA example taken from the linked article. If it has static type IndexedSeq[Base] instead of RNA, a map on it returns a vector.

Edit 2: looks like this is a more general problem, discussed in this question.