F#3.1:为什么我不能使用具有显式通用成员方法的管道运算符？

给出以下代码:

type MyDU =
| B of bool
| I of int
| S of string

type Ops () =
    static member myFn<'T> x =
        let v =
            match x with
            | B b -> box b
            | I i -> box i
            | S s -> box s

        match v with
        | :? 'T as y -> Some y
        | _ -> None

......以下产品error FS0717: Unexpected type arguments:

I 7 |> Ops.myFn

Ops.myFn <| I 7

但是,这很好用:

Ops.myFn (I 7)

另外,如果我myFn在模块中定义,我没有错误:

let myFn<'T> x =
    let v =
        match x with
        | B b -> box b
        | I i -> box i
        | S s -> box s

    match v with
    | :? 'T as y -> Some y
    | _ -> None

I 7 |> myFn  // Works fine

说明？