（1）如何檢測一個值`v`是否實現了接口`Stringer`： ~~~ if v, ok := v.(Stringer); ok { fmt.Printf("implements String(): %s\n", v.String()) } ~~~ （2）如何使用接口實現一個類型分類函數： ~~~ func classifier(items ...interface{}) { for i, x := range items { switch x.(type) { case bool: fmt.Printf("param #%d is a bool\n", i) case float64: fmt.Printf("param #%d is a float64\n", i) case int, int64: fmt.Printf("param #%d is an int\n", i) case nil: fmt.Printf("param #%d is nil\n", i) case string: fmt.Printf("param #%d is a string\n", i) default: fmt.Printf("param #%d’s type is unknown\n", i) } } } ~~~