Opinions on workaround

blahspec.scala

class Blah [@specialized (Int) T:Manifest](a:Array[T]) {
  def map[@specialized (Int) S>:T, @specialized (Int)  W:Manifest](f:S=>W):Blah[W]  = {
    var i = 0
    val newA = new Array[W](a.length)
    while (i < a.length) {
      newA(i) = f(a(i))
      i = i+1
  }
    new Blah(newA)
 }
}