/**
   * A builder of a {@link ClosingFuture} step that is derived from more than one input step.
   *
   * <p>See {@link #whenAllComplete(Iterable)} and {@link #whenAllSucceed(Iterable)} for how to
   * instantiate this class.
   *
   * <p>Example:
   *
   * {@snippet :
   * ClosingFuture<BufferedReader> file1ReaderFuture = ...;
   * ClosingFuture<BufferedReader> file2ReaderFuture = ...;