type BizCode struct {
	User User
	// ...
}

type User struct {
	Id   int
	Name string
	// ...
}

// WithCode creates and returns a new error code based on given Code.
// The code and message is from given `code`, but the detail if from given `detail`.
func WithCode(code Code, detail interface{}) Code

code := gcode.WithCode(gcode.CodeNotFound, BizCode{
	User: User{
		Id:   1,
		Name: "John",
	},
})
fmt.Println(code)

func ResponseHandler(r *ghttp.Request) {
	r.Middleware.Next()
	// There's custom buffer content, it then exits current handler.
	if r.Response.BufferLength() > 0 {
		return
	}
	var (
		err  = r.GetError()
		res  = r.GetHandlerResponse()
		code = gerror.Code(err)
	)
	if code == gcode.CodeNil && err != nil {
		code = gcode.CodeInternalError
	}
	if detail, ok := code.Detail().(BizCode); ok {
		g.Log().Errorf(r.Context(), `error caused by user "%+v"`, detail.User)
	}
	r.Response.WriteJson(ghttp.DefaultHandlerResponse{
		Code:    gcode.CodeOK.Code(),
		Message: gcode.CodeOK.Message(),
		Data:    res,
	})
}