}

  @Override
  public boolean equals(@CheckForNull Object object) {
    if (object == this) {
      return true;
    }
    if (object instanceof ByFunctionOrdering) {
      ByFunctionOrdering<?, ?> that = (ByFunctionOrdering<?, ?>) object;
      return this.function.equals(that.function) && this.ordering.equals(that.ordering);
    }
    return false;
  }

  @Override
  public int hashCode() {

   * (you can omit the comparator if it is the natural order).
   */
  @GwtCompatible(serializable = true)
  public <F extends @Nullable Object> Ordering<F> onResultOf(Function<F, ? extends T> function) {
    return new ByFunctionOrdering<>(function, this);
  }

  <T2 extends T> Ordering<Entry<T2, ?>> onKeys() {
    return onResultOf(Maps.<T2>keyFunction());
  }

  /**

   * (you can omit the comparator if it is the natural order).
   */
  @GwtCompatible(serializable = true)
  public <F extends @Nullable Object> Ordering<F> onResultOf(Function<F, ? extends T> function) {
    return new ByFunctionOrdering<>(function, this);
  }

  <T2 extends T> Ordering<Entry<T2, ?>> onKeys() {
    return onResultOf(Maps.<T2>keyFunction());
  }

  /**