title: Ruby difference between send and instance_eval?
body: <p>I know send takes string or symbol with arguments while instance_eval takes string or block, and their difference could be apparent given receivers. </p>
  
  <p>My question is what the '<strong>under the hood</strong>' difference is for the example below?</p>
  
  <pre><code>1234.send 'to_s'               # '1234'
  1234.instance_eval 'to_s'      # '1234'
  </code></pre>