Function DeferNotOk

cpp/src/arrow/util/future.h:718–723

/// holding that error.
template <typename T>
static Future<T> DeferNotOk(Result<Future<T>> maybe_future) {
  if (ARROW_PREDICT_FALSE(!maybe_future.ok())) {
    return Future<T>::MakeFinished(std::move(maybe_future).status());
  }
  return std::move(maybe_future).MoveValueUnsafe();
}

/// \brief Create a Future which completes when all of `futures` complete.
///