from typing import List


def get_instances(ifc_classes: List[str], ifc_model) -> tuple:
    """Gets the instances by their `ifc_classes` of the given `ifc_model`

        Args:
            ifc_classes (List[str]):
                The defined ifc classes of the rule definition.
            ifc_model:
                The model to get the ifc instances by ifc class.

        Returns:
            tuple:
                The ifc instances with appropriate ifc classes in the ifc model.
    """
    ifc_instances = []
    for ifc_class in ifc_classes:
        ifc_instances += ifc_model.by_type(ifc_class)
    return tuple(ifc_instances)