subscribe method
Implementation
SubscriptionKey subscribe(Iterable<String> match,
void Function(String? ref, Map<T?,T?> data) onData, {String? key})
{
final subscriptionKey = SubscriptionKey(key ?? _uuid.v4(), match);
if(!_listeners.containsKey(subscriptionKey))
{
_listeners[subscriptionKey] =_controller.stream
.where((event)=>subscriptionKey.regexp
.where((reg)=>reg.hasMatch(event.ref!)).isNotEmpty)
.listen((NukeEvent event)=>
onData(event.ref, event.data as Map<T?,T?>));
}
return subscriptionKey;
}