@property
    def function(self) -> Callable:
        """
        Getter property for the continuous signal callable.

        Returns
        -------
        Callable
            Continuous signal callable.
        """

        if self._function is None:
            self._create_function()

        return cast(Callable, self._function)

    @property
    def function(self) -> Callable:
        """
        Getter property for the continuous signal callable.

        Returns
        -------
        Callable
            Continuous signal callable.
        """

        if self._function is None:
            if self._domain.size != 0 and self._range.size != 0:
                self._function = self._extrapolator(
                    self._interpolator(
                        self.domain, self.range, **self._interpolator_kwargs
                    ),
                    **self._extrapolator_kwargs,
                )
            else:

                def _undefined_function(*args: Any, **kwargs: Any):
                    """
                    Raise a :class:`ValueError` exception.

                    Other Parameters
                    ----------------
                    args
                        Arguments.
                    kwargs
                        Keywords arguments.

                    Raises
                    ------
                    ValueError
                    """

                    raise ValueError(
                        "Underlying signal interpolator function does not exists, "
                        "please ensure you defined both "
                        '"domain" and "range" variables!'
                    )

                self._function = _undefined_function

        return cast(Callable, self._function)