go语言报错求解

type S struct { v int f float32 } type M struct { s S } func (i *M) GetS() S {return (*i).s} func (p *S) SetV(a int) {(*p).v = a} func main(){ var m M l := m.GetS().SetV(40) fmt.Println(l) } 报错：m.GetS().SetV(40) used as value 求解