code: public static <E extends Enum<E>> StreamableEnumSet<E> allOf (Class<E> elementType)
      {
          StreamableEnumSet<E> set = new StreamableEnumSet<E>(elementType);
          for (E constant : elementType.getEnumConstants()) {
              set.add(constant);
          }
          return set;
      }
docs: Creates a set containing all elements of the specified type.