问在go语言中，请问这是什么写法？

type HandlerFun func(http.ResponseWriter, *http.Request)


func (f HandlerFun) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	f(w, r)
}


func main() {
	
	fun := HandlerFun(hellohandler)
	
	fun.ServeHTTP(resq , res)
}
func hellohandler(w http.ResponseWriter, r *http.Request) {

}

fun :=HandlerFun(hellohandler)