sclass RatioAccumulator {
  double numerator, denominator;
  
  void add(double numerator, double denominator) {
    this.numerator += numerator;
    this.denominator += denominator;
  }
  
  // by default we return the initial state (undefined ratio) as 0
  public double get() {
    ret doubleRatio(numerator, denominator);
  }
  
  bool valid() { ret denominator != 0; }
  
  // ...but you can also get it as null
  public Double getOrNull() {
    ret valid() ? get() : null;
  }
  
  // ...or NaN (my least preferred method)
  public Double getOrNaN() {
    ret valid() ? get() : Double.NaN;
  }
}