Question

I want to use observer pattern for a logging system.

We have got logObservers and logObservables.

The class that will have to log something will implement iLogObservable and include these methods:

private $logObservers = array();

public function addLogObserver($logObserver) {
    $this->logObservers[] = $logObserver;
}
public function removeLogObserver($logObserver) {
    this->logObservers[] = $logObserver;
}
public function write($type, $message) {
    foreach($this->logObservers as $logObserver) {
        $logObserver->log($level, $message);
    }
}

Then I noticed, that a lot of classes that will use logging will have these methods and I have to copy paste. So isn’t it better to have these methods in a class I call LogObservable or just Log and then use strategy (instantiate this class inside all classes that will have to log). When I change the methods in Log, all logObservables will be affected.

However, I have not seen anyone use observer pattern with strategy pattern yet, but it seems to be very efficient and remove the duplications.

What do you think?

Answer 1

It’s not unusual for an object that supports this functionality to INHERIT from an Observable class, which supports these methods, in languages that support multiple inheritance.

I have never come across a solution that uses aggregation to support this, which is what you are describing, but given PHP doesn’t support multiple-inheritance, it sounds like a reasonable work-around to me.