IsIterableOnce

Type class witnessing that a collection representation type Repr has elements of type A and has a conversion to IterableOnce[A].

This type enables simple enrichment of IterableOnces with extension methods which can make full use of the mechanics of the Scala collections framework in their implementation.

Example usage,

class FilterMapImpl[Repr, I <: IsIterableOnce[Repr]](coll: Repr, it: I) {
  final def filterMap[B, That](f: it.A => Option[B])(implicit bf: BuildFrom[Repr, B, That]): That = {
    val b = bf.newBuilder(coll)
    for(e <- it(coll).iterator) f(e) foreach (b +=)
    b.result()
  }
}
implicit def filterMap[Repr](coll: Repr)(implicit it: IsIterableOnce[Repr]): FilterMapImpl[Repr, it.type] =
  new FilterMapImpl(coll, it)

List(1, 2, 3, 4, 5) filterMap (i => if(i % 2 == 0) Some(i) else None)
// == List(2, 4)