Method operator()

cpp/src/arrow/util/async_util.h:427–444

    };

    Result<Future<>> operator()() {
      Future<> task = Future<>::Make();
      // Consume as many items as we can (those that are already finished)
      // synchronously to avoid recursion / stack overflow.
      while (true) {
        Future<T> next = state_holder->generator();
        if (next.TryAddCallback(
                [&] { return SubmitTaskCallback(std::move(state_holder), task); })) {
          return task;
        }
        ARROW_ASSIGN_OR_RAISE(T item, next.result());
        if (IsIterationEnd(item)) {
          task.MarkFinished();
          return task;
        }
        ARROW_RETURN_NOT_OK(state_holder->visitor(item));
      }
    }

    std::string_view name() const { return state_holder->name; }