At the start, i did return Unitful Units, but i run of some problems. for example. in a Antoine implementation:
p = exp(a + b/(c+t))
this would require that the implementation itself strips the numbers,or add units to every constant to make the expression inside the exp adimensional. passing just numbers allows passing the properties to the implementations easier. Also, an Unitful Quantity is a number, not a Real, and had blocked me from using ForwardDiff. by passing numbers, an hypothetical user can do this:
∂p∂t(t) = ForwardDiff.derivative(tt->pressure(model,st(tt)),t) #using variable specifications
this is somewhat alleviated in the fact that when printing an state that is not normalized, the units are shown:
julia> st = state(t=1u"°C",p=2u"atm",normalize_units=false)
ThermodynamicState with 2 properties:
Temperature : 1[°C]
Pressure : 2[atm]