Strip Unit of Measure from array

Question

I am calling external function requiring float[], but my array is float<m>[]. How could I strip the unit of measure from array?

I need something like the function below, but this does not compile. And I would like to avoid any iterating or duplicating of the array, as float<m> and float values are identical...

let demeasure (arr:float<m>[]): float[] = float[] (arr)

Answer 1

I believe that a cast to obj, followed by a dynamic cast to float[] would work, e.g.

(arr :> obj) :?> float[]

because there is no runtime representation.

Possibly see also

F# Units of measure - 'lifting' values to float<something>

How to generically remove F# Units of measure

Answer 2

[<Measure>]type m
let f (arr : float[]) : float = 0.0
let arr = [|1.0<m>|]
f (unbox (box arr))

Answer 3

let demeasure (arr: float<m>[])  = arr |> Array.map (fun i -> float i)

Answer 4

Here's a generic solution for any numeric type, any unit of measure but for Arrays only. If we had Higher Kinds it could be made generic over the container as well:

let inline retype (x: 'T) : 'U = (# "" x: 'U #)

module Array =
    let inline stripUoM (x: '``Num<'M>`` []) =
        let _ = Unchecked.defaultof<'``Num<'M>``> * (LanguagePrimitives.GenericOne : 'Num)
        retype x :'Num []
// Usage

[<Measure>]type m

let x = [|34.0<m>; 9.0<m>; 42.0<m> |] |> Array.stripUoM
// val x : float [] = [|34.0; 9.0; 42.0|]

let y = [|34<m>; 9<m>; 42<m> |] |> Array.stripUoM
// val y : int [] = [|34; 9; 42|]