Your code doesn't work... The catch will never be called, and you should never use isset() because it will return false if the value exists but is null. w

Your code doesn't work... The catch will never be called, and you should never use isset() because it will return false if the value exists but is null. whatever->param = null; whatever->param = 123; Both lines will execute here. function __set($k, $v){ if (array_key_exists($k, $this->Properties)){ throw new ReadOnlyException(); }else{ $this->Properties[$k] = $v; } }