return new FunctionBasedConverter<>(forwardFunction, backwardFunction);
  }

  private static final class FunctionBasedConverter<A, B> extends Converter<A, B>
      implements Serializable {
    private final Function<? super A, ? extends B> forwardFunction;
    private final Function<? super B, ? extends A> backwardFunction;

    private FunctionBasedConverter(

    return new FunctionBasedConverter<>(forwardFunction, backwardFunction);
  }

  private static final class FunctionBasedConverter<A, B> extends Converter<A, B>
      implements Serializable {
    private final Function<? super A, ? extends B> forwardFunction;
    private final Function<? super B, ? extends A> backwardFunction;

    private FunctionBasedConverter(