title: Add a callback function to a Ruby array to do something when an element is added
body: <p>I'd like to add something like a callback function to a Ruby array, so that when elements are added to that array, this function is called.
  One thing I can think of is to override all methods (like &lt;&lt;, =, insert, ...) and call that callback from there.</p>
  
  <p>Is there an easier solution?</p>