With a warning, yes. You should avoid warnings though 
Otherwise it is not clear to me what you are trying to do. I see no reason for element_types/2 to be exported. Can you share the code you want to write?
With a warning, yes. You should avoid warnings though Otherwise it is not clear to me what you are trying to do. I see no reason for element_types/2 to be exported. Can you share the code you want to write?