}

  public void testAsSet_present() {
    Set<String> expected = Collections.singleton("a");
    assertEquals(expected, Optional.of("a").asSet());
  }

  public void testAsSet_absent() {
    assertTrue("Returned set should be empty", Optional.absent().asSet().isEmpty());
  }

  public void testAsSet_presentIsImmutable() {
    Set<String> presentAsSet = Optional.of("a").asSet();
    try {
      presentAsSet.add("b");

        supplier.get(), "use Optional.orNull() instead of a Supplier that returns null");
  }

  @Override
  @CheckForNull
  public T orNull() {
    return null;
  }

  @Override
  public Set<T> asSet() {
    return Collections.emptySet();
  }

  @Override
  public <V> Optional<V> transform(Function<? super T, V> function) {
    checkNotNull(function);
    return Optional.absent();
  }

  @Override

        supplier.get(), "use Optional.orNull() instead of a Supplier that returns null");
  }

  @Override
  @CheckForNull
  public T orNull() {
    return null;
  }

  @Override
  public Set<T> asSet() {
    return Collections.emptySet();
  }

  @Override
  public <V> Optional<V> transform(Function<? super T, V> function) {
    checkNotNull(function);
    return Optional.absent();
  }

  @Override

    SerializableTester.reserializeAndAssert(asSet);
  }

  public void testAsSetHeadSet() {
    ImmutableSortedSet<Integer> expectedSet = ImmutableSortedSet.of(2, 3, 4, 8, 9, 16, 17);
    ImmutableSortedSet<Integer> asSet = RANGE_SET_ONE.asSet(DiscreteDomain.integers());

    for (int i = 0; i <= 20; i++) {
      assertEquals(asSet.headSet(i, false), expectedSet.headSet(i, false));

   * {@linkplain RangeSet#contains contained} by this range set.
   *
   * <p><b>Note:</b> {@code a.asSet(d).equals(b.asSet(d))} does not imply {@code a.equals(b)}! For
   * example, {@code a} and {@code b} could be {@code [2..4]} and {@code (1..5)}, or the empty
   * ranges {@code [3..3)} and {@code [4..4)}.
   *
   * <p><b>Warning:</b> Be extremely careful what you do with the {@code asSet} view of a large

   * {@linkplain RangeSet#contains contained} by this range set.
   *
   * <p><b>Note:</b> {@code a.asSet(d).equals(b.asSet(d))} does not imply {@code a.equals(b)}! For
   * example, {@code a} and {@code b} could be {@code [2..4]} and {@code (1..5)}, or the empty
   * ranges {@code [3..3)} and {@code [4..4)}.
   *
   * <p><b>Warning:</b> Be extremely careful what you do with the {@code asSet} view of a large

  }

  public void testAsSet_present() {
    Set<String> expected = Collections.singleton("a");
    assertEquals(expected, Optional.of("a").asSet());
  }

  public void testAsSet_absent() {
    assertTrue("Returned set should be empty", Optional.absent().asSet().isEmpty());
  }

  public void testAsSet_presentIsImmutable() {
    Set<String> presentAsSet = Optional.of("a").asSet();
    try {
      presentAsSet.add("b");

  /**
   * Returns an immutable singleton {@link Set} whose only element is the contained instance if it
   * is present; an empty immutable {@link Set} otherwise.
   *
   * <p><b>Comparison to {@code java.util.Optional}:</b> this method has no equivalent in Java 8's
   * {@code Optional} class. However, this common usage:
   *
   * <pre>{@code
   * for (Foo foo : possibleFoo.asSet()) {
   *   doSomethingWith(foo);
   * }

    SerializableTester.reserializeAndAssert(asSet);
  }

  public void testAsSetHeadSet() {
    ImmutableSortedSet<Integer> expectedSet = ImmutableSortedSet.of(2, 3, 4, 8, 9, 16, 17);
    ImmutableSortedSet<Integer> asSet = RANGE_SET_ONE.asSet(DiscreteDomain.integers());

    for (int i = 0; i <= 20; i++) {
      assertEquals(asSet.headSet(i, false), expectedSet.headSet(i, false));

   *     operation
   */
  void clear();

  /**
   * Adds all of the ranges from the specified range set to this range set (optional operation).
   * After this operation, this range set is the minimal range set that {@linkplain
   * #enclosesAll(RangeSet) encloses} both the original range set and {@code other}.
   *
   * <p>This is equivalent to calling {@link #add} on each of the ranges in {@code other} in turn.
   *