implemented the SyncTopic

sync.go

@@ -0,0 +1,44 @@
+package gubgub
+
+import "sync"
+
+// SyncTopic allows any message T to be broadcast to subscribers. Publishing and Subscribing
+// happens synchronously (block).
+type SyncTopic[T any] struct {
+	mu          sync.Mutex
+	subscribers []Subscriber[T]
+}
+
+// NewSyncTopic creates a zero SyncTopic and return a pointer to it.
+func NewSyncTopic[T any]() *SyncTopic[T] {
+	return &SyncTopic[T]{}
+}
+
+// Publish broadcasts a message to all subscribers.
+func (t *SyncTopic[T]) Publish(msg T) error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	keepers := make([]Subscriber[T], 0, len(t.subscribers))
+
+	for _, callback := range t.subscribers {
+		keep := callback(msg)
+		if keep {
+			keepers = append(keepers, callback)
+		}
+	}
+
+	t.subscribers = keepers
+
+	return nil
+}
+
+// Subscribe adds a Subscriber func that will consume future published messages.
+func (t *SyncTopic[T]) Subscribe(fn Subscriber[T]) error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	t.subscribers = append(t.subscribers, fn)
+
+	return nil
+}