def downcast_identifier(super_class, identifier):
    """A decorator function for storing downcast identifiers."""

    def store_key_map(class_reference):
        """Store the downcast map."""
        if not hasattr(super_class, "__deserialize_downcast_map__"):
            setattr(super_class, "__deserialize_downcast_map__", {})

        super_class.__deserialize_downcast_map__[identifier] = class_reference

        return class_reference

    return store_key_map