sclass Average {
  gettable double sum;
  gettable double n;
  
  void add aka addSample(double d) {
    ++n;
    sum += d;
  }
  
  void add(double d, double weight) {
    n += weight;
    sum += d*weight;
  }
  
  void remove(double d) {
    add(d, -1);
  }
  
  double get aka avg aka average aka getAverage() {
    ret doubleRatio(sum, n);
  }
  
  bool isEmpty() { ret n == 0; }
  
  toString { ret get() + " (n=" + n + ")"; }
  
  void clear {
    n = 0;
    sum = 0;
  }
  
  double size aka count() { ret n; }
}