* accepts non-{@code Collection} iterables and empty iterables.
   */
  public static <E extends Enum<E>> EnumSet<E> newEnumSet(
      Iterable<E> iterable, Class<E> elementType) {
    EnumSet<E> set = EnumSet.noneOf(elementType);
    Iterables.addAll(set, iterable);
    return set;
  }

  // HashSet

  /**
   * Creates a <i>mutable</i>, initially empty {@code HashSet} instance.
   *

   * entries in the same order as the original iterable.
   *
   * @throws IllegalArgumentException if two keys have the same value or two values have the same
   *     key
   * @throws NullPointerException if any key, value, or entry is null
   * @since 19.0
   */
  public static <K, V> ImmutableBiMap<K, V> copyOf(
      Iterable<? extends Entry<? extends K, ? extends V>> entries) {

   *     original iterable.
   * @throws NullPointerException if the specified iterable is null or has any null elements.
   * @since 12.0
   */
  public static <E extends Comparable<? super E>> Collection<List<E>> orderedPermutations(
      Iterable<E> elements) {
    return orderedPermutations(elements, Ordering.natural());
  }

  /**
   * Returns a {@link Collection} of all the permutations of the specified {@link Iterable} using

   * over keys in the order they were first encountered in the input, and the values for each key
   * are iterated in the order they were encountered.
   *
   * @throws NullPointerException if any key, value, or entry is null
   * @since 19.0
   */
  public static <K, V> ImmutableMultimap<K, V> copyOf(
      Iterable<? extends Entry<? extends K, ? extends V>> entries) {

   * over keys in the order they were first encountered in the input, and the values for each key
   * are iterated in the order they were encountered.
   *
   * @throws NullPointerException if any key, value, or entry is null
   * @since 19.0
   */
  public static <K, V> ImmutableMultimap<K, V> copyOf(
      Iterable<? extends Entry<? extends K, ? extends V>> entries) {

     * @since 19.0
     */
    @CanIgnoreReturnValue
    @Override
    public Builder<K, V> putAll(Iterable<? extends Entry<? extends K, ? extends V>> entries) {
      super.putAll(entries);
      return this;
    }

    @CanIgnoreReturnValue
    @Override
    public Builder<K, V> putAll(K key, Iterable<? extends V> values) {
      super.putAll(key, values);
      return this;
    }

    } catch (UnsupportedOperationException expected) {
    }
  }

  /**
   * Verifies that an Iterator is unmodifiable.
   *
   * <p>This test only works with iterators that iterate over a finite set.
   */
  public static void assertIteratorIsUnmodifiable(Iterator<?> iterator) {
    while (iterator.hasNext()) {
      iterator.next();
      try {
        iterator.remove();

  public void testSize0() {
    Iterable<String> iterable = Collections.emptySet();
    assertEquals(0, Iterables.size(iterable));
  }

  public void testSize1Collection() {
    Iterable<String> iterable = Collections.singleton("a");
    assertEquals(1, Iterables.size(iterable));
  }

  public void testSize2NonCollection() {
    Iterable<Integer> iterable =
        new Iterable<Integer>() {
          @Override

      Comparator<? super E> comparator, Collection<? extends E> elements) {
    return copyOf(comparator, (Iterable<? extends E>) elements);
  }

  /**
   * Returns an immutable sorted set containing the elements of a sorted set, sorted by the same
   * {@code Comparator}. That behavior differs from {@link #copyOf(Iterable)}, which always uses the
   * natural ordering of the elements.
   *

  private static final Iterable<Integer> ITERABLE_ = Arrays.<Integer>asList();
  private static final Iterable<Integer> ITERABLE_1 = Arrays.asList(1);
  private static final Iterable<Integer> ITERABLE_12 = Arrays.asList(1, 2);
  private static final Iterable<Integer> ITERABLE_123 = Arrays.asList(1, 2, 3);
  private static final Iterable<@Nullable Integer> ITERABLE_NULL = Arrays.asList((Integer) null);