json.Unmarshal和interface问题请教

``` func main() { //testMidAndGroup() testI() } type t1 interface { Op() } type t1i struct { I int `json:"i"` } func (t *t1i) Op() { fmt.Println("t1i") } func testI() { var t t1 = &t1i{} b, e := json.Marshal(t) if e != nil { fmt.Println(e) return } var t2 t1 e = json.Unmarshal(b, &t2) if e != nil { fmt.Println(e) } } ``` 如上代码， 会有json: cannot unmarshal object into Go value of type main.t1报错，请问接口如何做反序列化