class Interpolator {

  public Column<T> backfill() {
    Column<T> result = col.copy();
    T lastVal = null;
    for (int i = col.size() - 1; i >= 0; i--) {
      if (col.isMissing(i)) {
        if (lastVal != null) {
          result.set(i, lastVal);
        }
      } else {
        lastVal = col.get(i);
      }
    }
    return result;
  }

  public  Interpolator(Column<T> column);

}