delayed srtp overload resolution

type Tuple = Tuple with
    static member inline TupleMap (Tuple, (a, b)) = fun f -> (f a, f b)
    static member inline TupleMap (Tuple, (a, b, c)) = fun f -> (f a, f b, f c)
    static member inline TupleMap (Tuple, (a, b, c, d)) = fun f -> (f a, f b, f c, f d)

let inline mapTuple f x =
    let inline map (a: ^a) (b : ^b) = ((^a or ^b) : (static member TupleMap : ^a * ^b -> ^t) (a, b))
    map Tuple x f

mapTuple (fun x -> x * x + 1) (1, 2)
mapTuple string (1, 2, 3)
mapTuple id (1, 2, 3, 4)

type Show =
    static member asString (x: int) : string = string x
    static member asString (x: double) : string = string x

let inline show x =
    let inline resolve (_: ^t) (x: ^x) = ((^t or ^x) : (static member asString: ^x -> string) x)
    resolve Unchecked.defaultof<Show> x

type Show with    
    static member inline asString (x: ^t option) : string =
        match x with
        | Some x -> show x
        | None -> ""

show 1 |> printfn "%s" 
show 2.9 |> printfn "%s"
show "3" |> printfn "%s"
show (Some 5) |> printfn "%s"
show (None: int option) |> printfn "%s"
show (Some 6L) |> printfn "%s" // error
show 1L |> printfn "%s" // error