class Task(ABC, Generic[T]):
    """Abstract base class for asynchronous tasks in a durable orchestration."""
    _result: T
    _exception: Optional[TaskFailedError]
    _parent: Optional[CompositeTask[T]]

    def __init__(self) -> None:
        super().__init__()
        self._is_complete = False
        self._exception = None
        self._parent = None

    @property
    def is_complete(self) -> bool:
        """Returns True if the task has completed, False otherwise."""
        return self._is_complete

    @property
    def is_failed(self) -> bool:
        """Returns True if the task has failed, False otherwise."""
        return self._exception is not None

    def get_result(self) -> T:
        """Returns the result of the task."""
        if not self._is_complete:
            raise ValueError('The task has not completed.')
        elif self._exception is not None:
            raise self._exception
        return self._result

    def get_exception(self) -> TaskFailedError:
        """Returns the exception that caused the task to fail."""
        if self._exception is None:
            raise ValueError('The task has not failed.')
        return self._exception