How Can Channels Be Used to Implement the Observer Pattern in Go?

Go Language Implementation of Observer Pattern

The Observer pattern involves a Publisher object notifying its subscribed Observers upon the occurrence of a specific event. The Go language offers a simple way to implement this pattern using channels.

To understand how this works, let's consider a scenario where multiple objects subscribe to a Publisher. The Publisher can then broadcast notifications to all subscribers through channels.

Here's a sample Go code that demonstrates the Observer pattern:

package main

import "fmt"

// Publisher is an object that can notify subscribers of an event.
type Publisher struct {
    listeners []chan string
}

// Subscriber represents an object that can receive notifications from a Publisher.
type Subscriber struct {
    ID       int
    Channel  chan string
}

// Sub adds a Subscriber to the Publisher's list of listeners.
func (p *Publisher) Sub(sub *Subscriber) {
    p.listeners = append(p.listeners, sub.Channel)
}

// Pub sends a notification to the Publisher's subscribers.
func (p *Publisher) Pub(msg string) {
    for _, c := range p.listeners {
        c <- msg
    }
}

// Run starts a Subscriber listening for notifications from the Publisher.
func (s *Subscriber) Run() {
    for {
        msg := <-s.Channel
        fmt.Printf("Subscriber %d received: %s\n", s.ID, msg)
    }
}

func main() {
    // Initialize Publisher
    publisher := &Publisher{}

    // Create and add Subscribers
    for i := 0; i < 3; i++ {
        subscriber := &Subscriber{ID: i, Channel: make(chan string)}
        publisher.Sub(subscriber)
        go subscriber.Run()
    }

    // Send notifications
    publisher.Pub("Hello 1")
    publisher.Pub("Hello 2")
    publisher.Pub("Hello 3")
}

In this example, the Publisher (Publisher) has a list of channels (listeners) where it broadcasts notifications. Subscribers (Subscriber) have their own channels (Channel) to receive notifications. When the Publisher sends a notification (Pub), it sends it to all subscribers through their channels. Each subscriber then prints the received notification. This demonstrates how the Publisher can broadcast updates to its observers.

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