is it possible to get the Region and ID of the row of a column in a UDF?

Question

I want to get the row key and Region of the column that is being "operated" on after calling getChildren().get(0);

public boolean evaluate(Tuple tuple, ImmutableBytesWritable ptr) {

    Expression arg = getChildren().get(0);
    if (!arg.evaluate(tuple, ptr)) {
        return false;
    }
}