将reflect.value转换为reflect.method

I have the fallowing:

func NewMethodDescriptor(typ interface{}) *MethodDescriptor {

    reflectedMethod := reflect.ValueOf(typ)
    methodType := reflectedMethod.Type
    paramCount := methodType.NumIn() - 1
    ...

But when I try:

NewMethodDescriptor(func(){})

I get this compile time error:

methodType.NumIn undefined (type func() reflect.Type has no field or method NumIn)

To be more specific:

You can see a more complete example in "Fun with the reflection package to analyse any function."

func FuncAnalyse(m interface{}) {

    //Reflection type of the underlying data of the interface
    x := reflect.TypeOf(m)

    numIn := x.NumIn()   //Count inbound parameters
    numOut := x.NumOut() //Count outbounding parameters

    fmt.Println("Method:", x.String())
    fmt.Println("Variadic:", x.IsVariadic()) // Used (<type> ...) ?
    fmt.Println("Package:", x.PkgPath())
}