Class casting in PHP (very dirty, not for production)

class_casting.php

<?php

/**
 * Parent class
 */
class mother
{
	protected $myvar;

	function __construct($value)
	{
		$this->myvar = $value;
	}
}

/**
 * Child class
 */
class grandmother extends mother
{
	protected $bval;

	function __construct($value)
	{
		$this->bval = $value;
		$this->myvar = $value / 10;
	}

	function __wakeup()
	{
		if (!isset($this->myvar)) throw new Exception("Illegal unserialize: The original object did not contain a myvar property.");
		$this->bval = $this->myvar * 10;
	}

	function getVal() {
		return $this->bval;
	}
}

/**
 * Cast an object to another class, keeping the properties, but changing the methods
 *
 * @param string $class  Class name
 * @param object $object
 * @return object
 */
function casttoclass($class, $object)
{
	return unserialize(preg_replace('/^O:\d+:"[^"]++"/', 'O:' . strlen($class) . ':"' . $class . '"', serialize($object)));
}

$a = new mother(5);
$z = casttoclass('grandmother', $a);

echo $z->getVal();