Concept example
In e-commerce websites, products are out of stock from time to time. There may be customers who show interest in specific items out of stock. There are three solutions to this problem:
- Customers view product availability at a certain frequency.
- The e-commerce website sends customers all new products in stock.
- Customers subscribe to only specific items they are interested in and will be notified when the items are available. At the same time, multiple customers can also subscribe to the same product.
Option 3 is the most feasible, which is actually the idea of the observer pattern. The main components of the observer pattern are:
- The subject that publishes the event when anything happens.
- Observer who subscribes to the subject event and receives notification when the event occurs.
:main body
package main
type Subject interface {
register(observer Observer)
deregister(obs Observer)
notifyAll()
}:Specific subject
package main
import (
"fmt"
)
type Item struct {
observerList []Observer // Multiple observers name string
inStock bool // In stock}
func newItem(name string) *Item {
return &Item{
name: name,
inStock: false,
}
}
// Update statusfunc (i *Item) updateAvailability() {
("Item %s is now in stock \n", )
= true // Update status, stock s ()
}
func (i *Item) register(o Observer) {
= append(, o)
}
func (i *Item) deregister(o Observer) {
= removeFromslice(, o)
}
func (i *Item) notifyAll() {
for _, v := range {
()
}
}
func removeFromslice(observerList []Observer, observerToRemove Observer) []Observer {
observerListLength := len(observerList)
for i, observer := range observerList {
if () == () {
observerList[observerListLength-1], observerList[i] = observerList[i], observerList[observerListLength-1]
return observerList[:observerListLength-1]
}
}
return observerList
}:Observer
package main
type Observer interface {
update(string)
getID() string
}:Specific observer
package main
import "fmt"
type Customer struct {
id string
}
func (c *Customer) getID() string {
return
}
func (c *Customer) update(iteName string) {
("Sendint email to customer %s for item %s\n", , iteName)
}:Client code
package main
func main() {
shirtItem := newItem("Nick Shirt")
observerFirst := &Customer{
id: "abc@",
}
observerSecond := &Customer{
id: "def@",
}
(observerFirst)
(observerSecond)
()
}:Execution results
Item Nick Shirt is now in stock
Sendint email to customer abc@ for item Nick Shirt
Sendint email to customer def@ for item Nick Shirt
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