}

  public void testFromHost() {
    HostAndPort hp = HostAndPort.fromHost("gmail.com");
    assertEquals("gmail.com", hp.getHost());
    assertFalse(hp.hasPort());

    hp = HostAndPort.fromHost("[::1]");
    assertEquals("::1", hp.getHost());
    assertFalse(hp.hasPort());

    assertThrows(IllegalArgumentException.class, () -> HostAndPort.fromHost("gmail.com:80"));

   * @return if parsing was successful, a populated HostAndPort object.
   * @throws IllegalArgumentException if {@code host} contains a port number.
   * @since 17.0
   */
  public static HostAndPort fromHost(String host) {
    HostAndPort parsedHost = fromString(host);
    checkArgument(!parsedHost.hasPort(), "Host has a port: %s", host);
    return parsedHost;
  }

  /**

   */
  public static <F extends @Nullable Object, T extends @Nullable Object> List<T> transform(
      List<F> fromList, Function<? super F, ? extends T> function) {
    return (fromList instanceof RandomAccess)
        ? new TransformingRandomAccessList<>(fromList, function)
        : new TransformingSequentialList<>(fromList, function);
  }

  /**
   * Implementation of a sequential transforming list.
   *

    /* fromList modifications reflected in toList */
    fromList.set(0, 5);
    assertEquals(asList(4, 3, 2, 5), toList);
    fromList.add(6);
    assertEquals(asList(6, 4, 3, 2, 5), toList);
    fromList.add(2, 9);
    assertEquals(asList(6, 4, 3, 9, 2, 5), toList);
    fromList.remove(Integer.valueOf(2));
    assertEquals(asList(6, 4, 3, 9, 5), toList);
    fromList.remove(3);

    /* fromList modifications reflected in toList */
    fromList.set(0, 5);
    assertEquals(asList(4, 3, 2, 5), toList);
    fromList.add(6);
    assertEquals(asList(6, 4, 3, 2, 5), toList);
    fromList.add(2, 9);
    assertEquals(asList(6, 4, 3, 9, 2, 5), toList);
    fromList.remove(Integer.valueOf(2));
    assertEquals(asList(6, 4, 3, 9, 5), toList);
    fromList.remove(3);