Method uniqueIndex

guava/src/com/google/common/collect/Maps.java:1324–1339

Returns a map with the given {@code values}, indexed by keys derived from those values. In 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: {@s

(
      Iterable<V> values, Function<? super V, K> keyFunction)

   *     keyFunction} produces {@code null} for any value
   */
  @CanIgnoreReturnValue
  public static <K, V> ImmutableMap<K, V> uniqueIndex(
      Iterable<V> values, Function<? super V, K> keyFunction) {
    class="cm">// We can provide a hint to the builder to preallocate the correct size when the iterable is
    class="cm">// either a List (which likely has a fast size() implementation), or an ImmutableCollection
    class="cm">// (which definitely has a fast size() implementation). While Collection also has a size()
    class="cm">// implementation, it _may_ require iteration over the entire collection (e.g., a
    class="cm">// FilteredCollection), which we want to avoid.
    if (values instanceof List || values instanceof ImmutableCollection) {
      return uniqueIndex(
          values.iterator(),
          keyFunction,
          ImmutableMap.builderWithExpectedSize(((Collection<?>) values).size()));
    }
    return uniqueIndex(values.iterator(), keyFunction);
  }

  /**
   * Returns a map with the given {@code values}, indexed by keys derived from those values. In