title: How to increment an Integer variable by X without creating a new object instance
body: <p>How can I increment an Integer variable by X without creating a new object instance?</p>
  
  <p><code>+=</code> does not work because:</p>
  
  <pre><code>ree-1.8.7-2010.02 &gt; x = 1
  1
  ree-1.8.7-2010.02 &gt; x.object_id
  3
  ree-1.8.7-2010.02 &gt; x += 1
  2
  ree-1.8.7-2010.02 &gt; x.object_id
  5
  </code></pre>