assertFalse(iterator.hasNext());
  }

  public void testTransform() {
    Iterator<String> input = asList("1", "2", "3").iterator();
    Iterator<Integer> result =
        Iterators.transform(
            input,
            new Function<String, Integer>() {
              @Override
              public Integer apply(String from) {

   *
   * @param input the primary input {@code Future}
   * @param exceptionType the exception type that triggers use of {@code fallback}. The exception
   *     type is matched against the input's exception. "The input's exception" means the cause of
   *     the {@link ExecutionException} thrown by {@code input.get()} or, if {@code get()} throws a

            Sets.filter(
                Sets.powerSet(sampleSet),
                new Predicate<Set<Integer>>() {

                  @Override
                  public boolean apply(Set<Integer> input) {
                    return input.size() == size;
                  }
                });
        assertWithMessage("Sets.combinations(%s, %s)", sampleSet, k)
            .that(Sets.combinations(sampleSet, k))

  private static final class PowerSet<E> extends AbstractSet<Set<E>> {
    final ImmutableMap<E, Integer> inputSet;

    PowerSet(Set<E> input) {
      checkArgument(
          input.size() <= 30, "Too many elements to create power set: %s > 30", input.size());
      this.inputSet = Maps.indexMap(input);
    }

    @Override
    public int size() {
      return 1 << inputSet.size();
    }

    @Override

    assertFalse(iterator.hasNext());
  }

  public void testTransform() {
    Iterator<String> input = asList("1", "2", "3").iterator();
    Iterator<Integer> result =
        Iterators.transform(
            input,
            new Function<String, Integer>() {
              @Override
              public Integer apply(String from) {

      Iterator<? extends T>... inputs) {
    for (Iterator<? extends T> input : checkNotNull(inputs)) {
      checkNotNull(input);
    }
    return concat(consumingForArray(inputs));
  }

  /**
   * Divides an iterator into unmodifiable sublists of the given size (the final list may be
   * smaller). For example, partitioning an iterator containing {@code [a, b, c, d, e]} with a

                      fail("Peeker.getDone() should fail for failed inputs");
                    } catch (ExecutionException expected) {
                    }
                    try {
                      peeker.getDone(nonInput);
                      fail("Peeker should not be able to peek into non-input ClosingFuture.");
                    } catch (IllegalArgumentException expected) {
                    }

                      fail("Peeker.getDone() should fail for failed inputs");
                    } catch (ExecutionException expected) {
                    }
                    try {
                      peeker.getDone(nonInput);
                      fail("Peeker should not be able to peek into non-input ClosingFuture.");
                    } catch (IllegalArgumentException expected) {
                    }

 *   if (value < 0) {
 *     throw new IllegalArgumentException("input is negative: " + value);
 *   }
 *   // calculate square root
 * }
 * }</pre>
 *
 * <p>to be replaced with the more compact
 *
 * <pre>{@code
 * public static double sqrt(double value) {
 *   checkArgument(value >= 0, "input is negative: %s", value);
 *   // calculate square root
 * }
 * }</pre>
 *

   * }</pre>
   *
   * ... returns {@code "aaa"}.
   */
  public String retainFrom(CharSequence sequence) {
    return negate().removeFrom(sequence);
  }

  /**
   * Returns a string copy of the input character sequence, with each matching BMP character
   * replaced by a given replacement character. For example:
   *
   * <pre>{@code
   * CharMatcher.is('a').replaceFrom("radar", 'o')
   * }</pre>
   *