class Person implements ArrayAccess
{
    private $age;
   
    public function offsetSet($property, $value) {   
        // Validation code here
        $this->$property = $value;
    }   
   
    public function offsetExists($property) {   
        return isset($this->$property);
    }   
   
    public function offsetUnset($property) {
        $this->$property = NULL;
    }   
   
    public function offsetGet($property) {
        return $this->$property;
    }   
           
}
   
$john = new Person();
$john['age'] = 30;
echo $john['age'];