Bug: in Lec 12: Subscriber can't handle multiple channels correctly (always uses the first channel)

[anurag2204-k]

Summary

The current Observer example lets the same Subscriber subscribe to multiple Channel instances, but Subscriber::update() always uses only the first Channel* passed at construction time. This causes incorrect behavior when a single subscriber is attached to multiple channels.

Steps to Reproduce

Channel ch1("CoderArmy");
Channel ch2("TechArmy");

Subscriber s1("Varun", &ch1); // stores ch1 internally
ch1.subscribe(&s1);
ch2.subscribe(&s1);

ch1.uploadVideo("Observer Pattern Tutorial");  // OK
ch2.uploadVideo("Decorator Pattern Tutorial"); // ❌ prints video from ch1 instead of ch2.

Actual Behavior

Varun receives a message for ch2, but the message text uses ch1's latestVideo.

Expected Behavior

When a Channel notifies subscribers, the Subscriber should know which channel triggered the notification and display the correct video's title.

Suggested Fix

Change the update() method to accept a pointer/reference to the notifying Channel. For example:

-class ISubscriber {
-public:
-    virtual void update() = 0;
+class ISubscriber {
+public:
+    virtual void update(IChannel* source) = 0;

And in Channel::notifySubscribers:

-    for (ISubscriber* sub : snapshot) {
-        if (sub) sub->update();
-    }
+    for (ISubscriber* sub : snapshot) {
+        if (sub) sub->update(this);
+    }

Then Subscriber::update() can use source->getVideoData() instead of always using its stored Channel*. This allows the same Subscriber instance to receive updates from multiple channels correctly.