default void computePricesWithTaxRate(float salesTaxRate)
        {
            setPricesWithSalesTax(this.getPrices().stream()
                    .map(x -> x*(1.0f+salesTaxRate)).collect(Collectors.toList()));
        }
This class illustrates an Immutables object with an interface which the
Modifiable version implements.
value-fixture/src/org/immutables/fixture/modifiable/WithModifiableInterface.java