Returns a `.Future` that will yield the next available result.

        Note that this `.Future` will not be the same object as any of
        the inputs.

def next(self) -> Future:
        """Returns a `.Future` that will yield the next available result.

        Note that this `.Future` will not be the same object as any of
        the inputs.
        """
        self._running_future = Future()

        if self._finished:
            self._return_result(self._finished.popleft())

        return self._running_future