> A physical value is two things:

I would argue it is actually three things: a scalar, a unit, and an indication of error – which is at least another scalar, but there are multiple ways of expressing error, so it might require more than just a single scalar (such as an interval and the probability the actual value lies within that interval.)

> If the type system of your programming language does not allow you to define units, this should at least be a structure with a scalar and an enum

Ideally more than just an enum – Newton = kg*m*s^-2 (equivalently kg^1*m^1*s^-2) – which suggests a set of pairs (unit and exponent).