Casting allowed for unpivot operator?

[antonio-olleros]

Issue Description

According to VTL Manual row 7183, for unpitvo operator: All the measures of op must be defined on the same Value Domain.
The question is: What happens if we have two measures with different types, but for which implicit casting is allowed (E.g., number and integer)?

Proposed Solution

Whatever solution should be documented in the manual

[vpinna80]

I tend to favor raising an error in this case to avoid surprising results, like numbers converted to strings or vice versa

[antonio-olleros]

I tend to agree, but only because of the implicit conversion to string... Actually, I was thinking that maybe what we should do is to forbid the implicit conversion to string, because it can only cause silent errors... If you want to do a cast, you just need to do it explictly, except when it is a case from a subtype to the supertype. What do you think about this option? I can open an issue