You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.go
    path of file: ./repos/learning/golang/source_code/Go语言核心编程代码/chapter11/exercise
    
    the code of the file until where you have to start completion: package main
import "fmt"
type Usb 
    
func main() {
	var stu Stu = Stu{}
	// 错误！ 会报 Stu类型没有实现Usb接口 , 
	// 如果希望通过编译,  var u Usb = &stu
	var u Usb = stu  
	u.Say()
	fmt.Println("here", u)
}