Observer

class Memory implements SplSubject
{
	const READ_OPERATION  = 0 ;
	const WRITE_OPERATION = 1 ;
 
	private $data           = array() ;
	private $observers      = array() ;
	private $last_operation = null ;
	private $address        = null ;
	private $value          = null ;
 
	public function getLastOperation()
	{
		return $this->last_operation ;
	}
 
	public function getAddress()
	{
		return $this->address ;
	}
 
	public function getValue()
	{
		return $this->value ;
	}
 
	public function read($address)
	{
		$this->last_operation = self::READ_OPERATION ;
		$this->address        = $address ;
		$this->value          = isset($this->data[$address]) ? $this->data[$address] : 0 ;
 
		$this->notify() ;
		return $this->value ;
	}
 
	public function write($address, $value)
	{
		$this->last_operation = self::WRITE_OPERATION ;
		$this->address        = $address ;
		$this->value          = $value ;
 
		$this->data[$address] = $value ;
		$this->notify() ;
	}
 
	public function attach(SplObserver $observer)
	{
		if(in_array($observer, $this->observers))
			return ;
 
		$this->observers[] = $observer ;
	}
 
	public function detach(SplObserver $observer)
	{
		$key = array_search($observer, $this->observers) ;
		if(is_null($key))
			return ;
 
		unset($this->observers[$key]) ;
	}
 
	public function notify()
	{
		foreach($this->observers as $obs)
		{
			$obs->update($this) ;
		}
	}
}
 
class MemoryLog implements SplObserver
{
	private $filename = '' ;
 
	public function __construct($filename)
	{
		$this->filename = $filename ;
	}
 
	public function update(SplSubject $subject)
	{
		file_put_contents(
			$this->filename,
			'Last operation: ' . $subject->getLastOperation() .
			' - address: ' . $subject->getAddress() .
			' - value: ' . $subject->getValue() .
			"\r\n",
			FILE_APPEND
		) ;
	}
}
 
class MemoryDisplayEvents implements SplObserver
{
	public function update(SplSubject $subject)
	{
		echo $subject->getLastOperation() == Memory::READ_OPERATION ? 'read' : 'write' ;
		echo ' at ', $subject->getAddress(), ' : ', $subject->getValue(), '<br />' ;
	}
}
 
 
 
$mem = new Memory() ;
$mem->attach(new MemoryLog('C:/mem.log')) ;
$mem->attach(new MemoryDisplayEvents()) ;
 
for($i = 0 ; $i < 50 ; $i++)
{
	$address = rand(0,10) ;
	if(rand() % 2)
	{
		$mem->read($address) ;
	}
	else
	{
		$value = rand(0,255) ;
		$mem->write($address, $value) ;
	}
}