`zonal` can't handle mixed type function output

[rafaqz]

We need more sophisticated type promotion.

[asinghvi17]

yeah, maybe some introspection on the Julia end as well?

A call to identity.(vec) always worked for me, otherwise :D but it would be slower for known output types

[rafaqz]

We could do what map does and promote as we go, it's just complicated.

Or use Base.return_type

[asinghvi17]

We'll have to do it at some point, I guess