* other words, each input value produces an entry in the map whose key is the result of applying
   * {@code keyFunction} to that value. These entries appear in the same order as the input values.
   * Example usage:
   *
   * <pre>{@code
   * Color red = new Color("red", 255, 0, 0);
   * ...
   * ImmutableSet<Color> allColors = ImmutableSet.of(red, green, blue);
   *