sclass LearnDoubleRange {
  double min = positiveInfinity(), max = negativeInfinity();
  
  void add(Number n) {
    if (n != null) {
      double d = toDouble(n);
      min = min(min, d);
      max = max(max, d);
    }
  }
  
  bool empty() { ret min > max; }
  
  DoubleRange range() { ret empty() ? null : DoubleRange(min, max); }
}