}
  }

  /**
   * Returns the result of the input {@code Future}, which must have already completed.
   *
   * <p>The benefits of this method are twofold. First, the name "getDone" suggests to readers that
   * the {@code Future} is already done. Second, if buggy code calls {@code getDone} on a {@code
   * Future} that is still pending, the program will throw instead of block. This can be important