PHP - Observer pattern with SPL

php_observer_pattern_spl.php

<?php

abstract class Event
{
    public $name, $code;

    public function __toString()
    {
        return $this->name . ' ' . $this->code;
    }

    public function push(SplSubject $subject)
    {
        $subject->handle($this);
    }
}

class Purchase extends Event
{
    const EVENT_NAME = 'PURCHASE';
    const EVENT_CODE = 1;

    public function __construct()
    {
        $this->name = self::EVENT_NAME;
        $this->code = self::EVENT_CODE;
    }
}

class EventsHandler implements SplSubject
{

    protected $observers = array();
    public $object;

    public function attach(SplObserver $observer)
    {
        $id = spl_object_hash($observer);
        $this->observers[$id] = $observer;
    }

    public function detach(SplObserver $observer)
    {
        $id = spl_object_hash($observer);
        unset($observer[$id]);
    }

    public function notify()
    {
        foreach ($this->observers as $observer) {
            $observer->update($this);
        }
    }

    public function handle($object)
    {
        $this->object = $object;
        $this->notify();
    }
}

class Logger implements SplObserver
{

    public function update(SplSubject $subject)
    {
        error_log("[EVENT] " . (string)$subject->object);
    }
}

class EmailSender implements SplObserver
{

    public function update(SplSubject $subject)
    {
        echo 'Email was sent';
    }
}


$eventHandler = new EventsHandler();
$eventHandler->attach(new Logger());
$eventHandler->attach(new EmailSender());

$purchase = new Purchase();
$purchase->push($eventHandler);

// Output:
/*
[EVENT] PURCHASE 1
Email was sent
*/