}

  /**
   * A helper to create a new {@code ListenableFuture} whose result is generated from a combination
   * of input futures.
   *
   * <p>See {@link #whenAllComplete} and {@link #whenAllSucceed} for how to instantiate this class.
   *
   * <p>Example:
   *
   * <pre>{@code
   * final ListenableFuture<Instant> loginDateFuture =
   *     loginService.findLastLoginDate(username);