* in encounter order will appear in the result.
   *
   * @since 21.0
   */
  public static <E> Collector<E, ?, ImmutableSortedSet<E>> toImmutableSortedSet(
      Comparator<? super E> comparator) {
    return CollectCollectors.toImmutableSortedSet(comparator);
  }

  static <E> RegularImmutableSortedSet<E> emptySet(Comparator<? super E> comparator) {
    if (Ordering.natural().equals(comparator)) {

      Collector<T, ?, M> toMultiset(
          Function<? super T, E> elementFunction,
          ToIntFunction<? super T> countFunction,
          Supplier<M> multisetSupplier) {
    return CollectCollectors.toMultiset(elementFunction, countFunction, multisetSupplier);
  }

  /**
   * Returns an unmodifiable view of the specified multiset. Query operations on the returned

          java.util.function.Function<? super T, ? extends K> keyFunction,
          java.util.function.Function<? super T, ? extends V> valueFunction,
          java.util.function.Supplier<M> multimapSupplier) {
    return CollectCollectors.<T, K, V, M>toMultimap(keyFunction, valueFunction, multimapSupplier);
  }

  /**
   * Returns a {@code Collector} accumulating entries into a {@code Multimap} generated from the

          java.util.function.Function<? super T, ? extends K> keyFunction,
          java.util.function.Function<? super T, ? extends V> valueFunction,
          java.util.function.Supplier<M> multimapSupplier) {
    return CollectCollectors.<T, K, V, M>toMultimap(keyFunction, valueFunction, multimapSupplier);
  }

  /**
   * Returns a {@code Collector} accumulating entries into a {@code Multimap} generated from the

   *
   * @since 21.0
   */
  public static <E extends Enum<E>> Collector<E, ?, ImmutableSet<E>> toImmutableEnumSet() {
    return CollectCollectors.toImmutableEnumSet();
  }

  /**
   * Returns a new, <i>mutable</i> {@code EnumSet} instance containing the given elements in their

  @IgnoreJRERequirement // Users will use this only if they're already using streams.
  public static <E extends Enum<E>> Collector<E, ?, ImmutableSet<E>> toImmutableEnumSet() {
    return CollectCollectors.toImmutableEnumSet();
  }

  /**
   * Returns a new, <i>mutable</i> {@code EnumSet} instance containing the given elements in their

          java.util.function.Function<? super T, ? extends K> keyFunction,
          java.util.function.Function<? super T, ? extends V> valueFunction) {
    return CollectCollectors.toImmutableEnumMap(keyFunction, valueFunction);
  }

  /**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableMap} whose keys

          java.util.function.Function<? super T, ? extends K> keyFunction,
          java.util.function.Function<? super T, ? extends V> valueFunction) {
    return CollectCollectors.toImmutableEnumMap(keyFunction, valueFunction);
  }

  /**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableMap} whose keys