Extended unit

Hi,

My question is purely theoretical.

I add use in my time in University some software that use "extended
type".
For each variable, we define the mandatory "classic type" as integer,
float, double array of.
And we define an optional "extended type" as the unit in the MKSA
system (Meter, Kilogram, Second, Ampere) or any other unit we would
have previously define (eg. Currency).

This "extended type" was wonderful, because there was warning/error if
"extend type" does not match in any computation: you can not add apple
to orange.

I would appreciate to have such system in PostgreSQL.

Do you think, it is feasible ? unrealistic ?
Any comment ?

Cordialement,
Jean-Gérard Pailloncy