Is there built in version of the type casting functions that preserves units and if not how would I make them? So for example with this code how would I cast intWithSecondsMeasure to a float without losing the measure or multiplying by 1.0<s>?
[<Measure>] type s
let intWithSecondsMeasure = 1<s>
let justAFloat = float intWithSecondsMeasure
The answer provided by @kvb certainly works, but I'd prefer not to use the unbox operator for this conversion. There's a better, built in way that I think should be compiled as a NOP to IL (I haven't checked but unbox is probably going to end up as a unbox instruction in IL and thus adds a runtime type check).
The preferred way to do unit conversions in F# is LanguagePrimitives.TypeWithMeasure (MSDN).
let inline float32toFloat (x:float32<'u>) : float<'u> =
x |> float |> LanguagePrimitives.FloatWithMeasure