Relaxing ::Real requirement

[MilesCranmer]

Hi,

I was wondering if the requirement for numeric types to be ::Real could be relaxed to ::Any? Since Julia doesn't have multiple inheritance, this limits the range of types you can use perhaps more than necessary. There are some types which act exactly like a Real in every other way, except they do not inherit from Real, so it would be great if one could use those as well.

My specific use-case is I'm trying to use physical units in a Distributions model, but both Unitful.Quantity and DynamicQuantities.Quantity are <:Number so are incompatible, despite the numerical type being a Real in both cases (base type Float64).

julia> using DynamicQuantities  # or Unitful

julia> Normal(10u"km/s", 1u"km/s")
ERROR: MethodError: no method matching Normal(::Quantity{Float64, Dimensions{…}}, ::Quantity{Float64, Dimensions{…}})
Stacktrace:
 [1] top-level scope
   @ REPL[6]:1
Some type information was truncated. Use `show(err)` to see complete types.

I think that 10 km/s ± 1 km/s is a standard description for a physical measurement so this would be useful to have.

Cheers,
Miles

(copied from TuringLang/Turing.jl#2133 as the same issue arises there)

[MilesCranmer]

Ah, just noticed #1684 and #1691 right after posting. Feel free to close if you wish

Edit 2: also I see #1413. Maybe the fix is to add an extension to DynamicQuantities.jl?