code: public static Func1<Iterable<Double>, double[]> toDoubles() {
          return new Func1<Iterable<Double>, double[]>() {
              @Override
              public double[] call(Iterable<Double> value) {
                  return new QuickNumberArray(value).toDoubles();
              }
          };
      }
docs: Returns a method that can be used with {@link solid.stream.Stream#collect(Func1)}
  to convert an iterable stream of {@link Number} type into a primitive double[] array.
  
  @return a method that converts an iterable stream of {@link Number} type into a primitive double[] array.