* Color red = new Color("red", 255, 0, 0);
   * ...
   * Iterator<Color> allColors = ImmutableSet.of(red, green, blue).iterator();
   *
   * Map<String, Color> colorForName = uniqueIndex(allColors, toStringFunction());
   * assertThat(colorForName).containsEntry("red", red);
   * }
   *
   * <p>If your index may associate multiple values with each key, use {@link
   * Multimaps#index(Iterator, Function) Multimaps.index}.

   * string forms, in a case-insensitive manner, use:
   *
   * {@snippet :
   * Ordering.from(String.CASE_INSENSITIVE_ORDER).onResultOf(Functions.toStringFunction())
   * }
   *
   * <p><b>Java 8+ users:</b> Use {@code Comparator.comparing(function, thisComparator)} instead
   * (you can omit the comparator if it is the natural order).
   */