Consider the asJsExp field defined in BaseMappedField -- it returns JsExp.

Then consider cases where subclasses override this field:

• MappedDateTime
• MappedEnum

Note that in both of these cases, the new type is now a Num. (A JE.Num is a subclass of JsExp.)

The problem is that I can not override a MappedEnum's asJsExp field to return a JsExp (like Str) because the subclass needs to declare an explicit type of JsExp (rather than use inference).

For an enum, I'm interested in returning the enum's string value; and for a date-time, I'm interested in returning an alphanumeric time code (not a long integer).