我正在使用Go内置的http服务器，并拍拍来响应一些URL：

mux.Get("/products", http.HandlerFunc(index))

func index(w http.ResponseWriter, r *http.Request) {
    // Do something.
}

我需要向该处理函数传递一个额外的参数-一个接口。

func (api Api) Attach(resourceManager interface{}, route string) {
    // Apply typical REST actions to Mux.
    // ie: Product - to /products
    mux.Get(route, http.HandlerFunc(index(resourceManager)))

    // ie: Product ID: 1 - to /products/1
    mux.Get(route+"/:id", http.HandlerFunc(show(resourceManager)))
}

func index(w http.ResponseWriter, r *http.Request, resourceManager interface{}) {
    managerType := string(reflect.TypeOf(resourceManager).String())
    w.Write([]byte(fmt.Sprintf("%v", managerType)))
}

func show(w http.ResponseWriter, r *http.Request, resourceManager interface{}) {
    managerType := string(reflect.TypeOf(resourceManager).String())
    w.Write([]byte(fmt.Sprintf("%v", managerType)))
}

如何向处理程序函数发送额外的参数？