title: object_setClass to bigger class
body: <p>I am changing the class of some objects using <code>object_setClass(id object, Class cls)</code>. I am changing the class to a <strong>subclass</strong> of the original class. Then I set some properties that are only defined on the subclass, and things seem to work fine.</p>
  
  <p>I was a bit surprised that this worked, because <code>object_setClass</code>, as far as I understand, doesn't reallocate the object, it only changes the <code>isa</code> pointer. If the subclass instances are considerably larger (meaning having many more ivars) than the original class instances, I don't see how the object can work as expected.</p>
  
  <p>Does this work only because there is a lot of buffer memory between objects in memory (due to alignment etc)?</p>
  
  <p>Is this robust, or could it crash under some circumstances?</p>