Observer Pattern in Golang

Observer Pattern is achieved mainly using 2 objects:

Observable : The one who is being observed. He can perform 2 operations:

• Adding observers to observer list [func (o *Observable) addObserver(obs Observer)]. The observers are maintained in a local list.
• Notify all observers when any field value is changed [func (o *Observable) NotifyObservers(value string)]

Observer : One who keeps monitoring other’s activities. He will have a “Update(name string)” method which gets called once the Observable guy sends notification saying “Hey I have a change in my value”. [func (o *Observer) Update(value string)]

Here is how the code looks like:

File: observable.go
Code:

package main
type Observable struct{
 Observers []Observer
}
func (o *Observable) addObserver(obs Observer){
 o.Observers = append(o.Observers, obs)
}
func (o *Observable) NotifyAll(value string){
 for _, ob := range o.Observers {
 ob.Update(value)
 }
}

File: observer.go
Code:

package main
import "fmt"
type Observer interface {
 Update(value string)
}
func createCustomer(name string) *Customer{
 return &Customer{Name:name}
}
type Customer struct {
 Name string
}
func (c *Customer) Update(value string){
 fmt.Printf(“Customer : %s , New value: %s\n”,c.Name, value)
}

File: main.go
Code:

package main
type Item struct{
  Observable
  Name        string
}
func createItem(name string) *Item{
  return &Item{Name:name}
}
func (i *Item) setName(name string){
  i.Name = name
  i.NotifyAll(name)
}
func main(){
  i := createItem("Nike Shoes")
  c1 := createCustomer("Raj")
  c2 := createCustomer("Rohit")
  i.addObserver(c1)
  i.addObserver(c2)
  i.setName("Adidas")
}

Output

$ go run main.go 
Customer : Raj , New value: Adidas
Customer : Rohit , New value: Adidas