inline-pi.fs

type Circle<'t when 't : (static member Zero : 't)
                and 't : (static member One : 't)
                and 't : (static member (+) : 't * 't -> 't)
                and 't : (static member (-) : 't * 't -> 't)
                and 't : (static member (*) : 't * 't -> 't)
                and 't : (static member (/) : 't * 't -> 't)
                and 't : (static member (~-) : 't -> 't)
                and 't : (static member op_Explicit : float -> 't) > =
  {
    Radius : 't
  }

#nowarn "77" // op_Explicit

module Circle =

  open System

  let inline area (circle : Circle< ^t>) =
    let castFromFloat (x : float) = (^t : (static member op_Explicit : float -> ^t) (x) )

    castFromFloat Math.PI * circle.Radius * circle.Radius

printfn "%A" <| Circle.area { Radius = 1 }
printfn "%A" <| Circle.area { Radius = 1.0 }
printfn "%A" <| Circle.area { Radius = 1.0f }

(*

3
3.141592654
3.141592741f

*)