in core/src/main/scala/com/spotify/featran/CrossingFeatureBuilder.scala [107:119]
override def add[M[_]](names: Iterable[String], values: M[Double])(implicit
ev: M[Double] => Seq[Double]
): Unit = {
if (xEnabled) {
val i = names.iterator
val j = ev(values).iterator
while (i.hasNext && j.hasNext) {
xQueue.enqueue(CrossValue(i.next(), xOffset, j.next()))
xOffset += 1
}
}
fb.add(names, values)
}