I am trying to practice the Observer design pattern in Golang, here is my code. I would be pleased to receive your comments, improvements, etc.

package observer

import (

//interface that receive updates
type Observer interface{
    Update(s *Subject)

// interface that manage notifying
type Subject struct{
    observers *list.List
    status int

func NewSubject() *Subject {
    //this can be categorized from database etc
    return &Subject{observers:new(list.List)}

func (s *Subject) Attach(o Observer){

func (s *Subject) DeAttach(o Observer){
    for obs := s.observers.Front(); obs != nil; obs = obs.Next() {
        if obs.Value.(Observer) == o {

func (s *Subject) notify(){
    for obs := s.observers.Front(); obs != nil; obs = obs.Next() {
        observer := obs.Value.(Observer)

// some business logic function to notify
func (s *Subject) ScanData() {

    // just generate random number for status
    // this can be a business logic in real world to calculate or fetch status for a specific source or logic
    s.status = rand.Intn(1000)

//Concrete class A for Observer
type ConcreteNotifierA struct{

func NewConcreteNotifierA() *ConcreteNotifierA {
    return &ConcreteNotifierA{

func (a *ConcreteNotifierA) Update(s *Subject) {
    if s.status > 500 {
        fmt.Printf("Status is bigger than 500: %v \n", s.status)

//Concrete class B for Observer
type ConcreteNotifierB struct{

func NewConcreteNotifierB() *ConcreteNotifierB {
    return &ConcreteNotifierB{

func (b *ConcreteNotifierB) Update(s *Subject) {
    if s.status < 501 {
        fmt.Printf("Status is less than 500: %v \n", s.status)

And here is testing:

subject := observer.NewSubject()
concreteObserverA := observer.NewConcreteNotifierA()
concreteObserverA1 := observer.NewConcreteNotifierA()
concreteObserverB := observer.NewConcreteNotifierB()
concreteObserverB1 := observer.NewConcreteNotifierB()


fmt.Printf("First Scan\n")


fmt.Printf("Second Scan\n")

EDIT: Let's say the goal is on different type of "Status", different type of subscribers will be notified.

  • 1
    \$\begingroup\$ What's that code supposed to do in practice? Elaborate please. \$\endgroup\$ Oct 27, 2019 at 17:18
  • \$\begingroup\$ Let's say the goal is on different type of "Status", different type of subscribers will be notified. \$\endgroup\$
    – Mazdak
    Oct 27, 2019 at 17:42
  • 1
    \$\begingroup\$ Your code looks quite hypothetical. Please post real code here for review. \$\endgroup\$ Oct 27, 2019 at 17:45
  • \$\begingroup\$ Typo: Detach, not DeAttach. \$\endgroup\$
    – Eyal
    Dec 10, 2019 at 14:58


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