expectUnchanged();
  }

  @CollectionFeature.Require(absent = SUPPORTS_REMOVE)
  @CollectionSize.Require(ZERO)
  public void testRetainAll_emptyPreviouslyEmptyUnsupported() {
    expectReturnsFalseOrThrows(empty);
    expectUnchanged();
  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)
  public void testRetainAll_emptyPreviouslyNonEmpty() {

    assertOneToOne();
  }

  @CollectionSize.Require(absent = ZERO)
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testSetCount_oneToOne_removeSupported() {
    assertOneToOne();
  }

  @CollectionSize.Require(absent = ZERO)
  @CollectionFeature.Require(absent = {SUPPORTS_ADD, SUPPORTS_REMOVE})
  public void testSetCount_oneToOne_unsupported() {
    try {
      assertOneToOne();

    expectUnchanged();
  }

  @CollectionFeature.Require(absent = SUPPORTS_REMOVE)
  @CollectionSize.Require(ZERO)
  public void testRetainAll_emptyPreviouslyEmptyUnsupported() {
    expectReturnsFalseOrThrows(empty);
    expectUnchanged();
  }

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)
  public void testRetainAll_emptyPreviouslyNonEmpty() {

    Set<Object> absentAsSet = Optional.absent().asSet();
    try {
      absentAsSet.add("foo");
      fail();
    } catch (UnsupportedOperationException expected) {
    }
  }

  public void testTransform_absent() {
    assertEquals(Optional.absent(), Optional.absent().transform(Functions.identity()));
    assertEquals(Optional.absent(), Optional.absent().transform(Functions.toStringFunction()));
  }

    assertOneToOne();
  }

  @CollectionSize.Require(absent = ZERO)
  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testSetCount_oneToOne_removeSupported() {
    assertOneToOne();
  }

  @CollectionSize.Require(absent = ZERO)
  @CollectionFeature.Require(absent = {SUPPORTS_ADD, SUPPORTS_REMOVE})
  public void testSetCount_oneToOne_unsupported() {
    try {
      assertOneToOne();

    nextInBucketVToK[src] = ABSENT;
  }

  @Override
  public void clear() {
    Arrays.fill(keys, 0, size, null);
    Arrays.fill(values, 0, size, null);
    Arrays.fill(hashTableKToV, ABSENT);
    Arrays.fill(hashTableVToK, ABSENT);
    Arrays.fill(nextInBucketKToV, 0, size, ABSENT);
    Arrays.fill(nextInBucketVToK, 0, size, ABSENT);
    Arrays.fill(prevInInsertionOrder, 0, size, ABSENT);

			continue
		case selectSend:
			j = nsends
			nsends++
		case selectRecv:
			nrecvs++
			j = len(cases) - nrecvs
		}

		sel[j] = scase{c: rc.ch, elem: rc.val}
		orig[j] = i
	}

	// Only a default case.
	if nsends+nrecvs == 0 {
		return dflt, false
	}

	// Compact sel and orig if necessary.
	if nsends+nrecvs < len(cases) {
		copy(sel[nsends:], sel[len(cases)-nrecvs:])

   * {@code Optional.empty}.
   */
  public static <T> Optional<T> absent() {
    return Absent.withType();
  }

  /**
   * Returns an {@code Optional} instance containing the given non-null reference. To have {@code
   * null} treated as {@link #absent}, use {@link #fromNullable} instead.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> no differences.
   *

   * {@code Optional.empty}.
   */
  public static <T> Optional<T> absent() {
    return Absent.withType();
  }

  /**
   * Returns an {@code Optional} instance containing the given non-null reference. To have {@code
   * null} treated as {@link #absent}, use {@link #fromNullable} instead.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> no differences.
   *

  @CollectionSize.Require(absent = ZERO)
  public void testSubList_subListRemoveAffectsOriginal() {
    List<E> subList = getList().subList(0, 1);
    subList.remove(0);
    List<E> expected = Arrays.asList(createSamplesArray()).subList(1, getNumElements());
    expectContents(expected);
  }

  @ListFeature.Require(SUPPORTS_REMOVE_WITH_INDEX)
  @CollectionSize.Require(absent = ZERO)