constructor.php

<?php

/**
 * Class Car
 *
 * @property integer fuelType fuel value
 */
class Car {

	private $data = array();

	public function __construct ()
	{
	}

	public function __get ($key)
	{
		return array_key_exists( $key, $this->data) ? $this->data[$key] : false;
	}

	public function __set ($key, $value)
	{
		$this->data[$key] =  $value;
	}
	public function printData ()
	{
		print_r($this->data) . PHP_EOL;
	}
}

$bobCar = new Car();
$bobCar->fuelType = 'Unleaded';
$bobCar->color = 'Red';

$bobCar->printData();

echo 'Got Octane #: ' . $bobCar->octane;
var_dump( $bobCar->foobar );
echo 'Done' . PHP_EOL;