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<?php

class Observable implements \SplSubject
{
    private $_observers = array();
    
    public function notify()
    {
        foreach($this->_observers as $observer) {
            $observer->update($this);
        }
    }
    
    public function attach(\SplObserver $observer)
    {
        $this->_observers[] = $observer;
        return $this;
    }
    
    public function detach(\SplObserver $observer)
    {
        foreach($this->_observers as $i => $iteratedObserver) {
            if($observer === $iteratedObserver) {
                unset($this->_observers[$i]);
                break;
            }
        }
        
        return $this;
    }
}

class Observer implements \SplObserver
{
    private $_name;
    
    public function __construct($name)
    {
        $this->_name = $name;
    }
    
    public function update(\SplSubject $subject)
    {
        echo 'Observer ' . $this->_name . ' called' . PHP_EOL;
    }
}

$observable = new Observable;

$observer1 = new Observer('A');
$observable->attach($observer1);

$observer2 = new Observer('B');
$observable->attach($observer2);

$observable->notify();