class VarianceFn extends Combine.CombineFn<T, VarianceAccumulator, T> {

  @Override
  public T extractOutput(VarianceAccumulator accumulator) {
    return decimalConverter.apply(getVariance(accumulator));
  }

  private  VarianceFn(boolean isSample, SerializableFunction<BigDecimal, T> decimalConverter);

}