<?php

$p = new Test();
$p['foo']=1;
var_dump($p);

class Test implements ArrayAccess
{
 	public function offsetExists($offset)
 	{
 		return property_exists($this, $offset);
 	}
 	public function offsetGet($offset)
 	{
 		return $this->$offset;
 	}
 	public function offsetSet($offset, $value)
 	{
 		$this->$offset = $value;
 	}
 	public function offsetUnset($offset)
 	{
 		unset($this->$offset);
 	}
}

// => Fatal error: Class 'Test' not found

// ---------------------------------------------------

class Test implements ArrayAccess
{
 	public function offsetExists($offset)
 	{
 		return property_exists($this, $offset);
 	}
 	public function offsetGet($offset)
 	{
 		return $this->$offset;
 	}
 	public function offsetSet($offset, $value)
 	{
 		$this->$offset = $value;
 	}
 	public function offsetUnset($offset)
 	{
 		unset($this->$offset);
 	}
}

$p = new Test();
$p['foo']=1;
var_dump($p);

// => object(Test)#1 (1) { ["foo"]=> int(1) } 

?>