* @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 void testFromHost() {
    HostAndPort hp = HostAndPort.fromHost("gmail.com");
    assertThat(hp.getHost()).isEqualTo("gmail.com");
    assertFalse(hp.hasPort());

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

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

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

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

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

   */
  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.
   *

   */
  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.
   *