title: Singleton class and instance variables
body: <p>Why does the <code>instance_variables</code> method not show <code>@var_one</code> against the variable <code>a</code>?</p>
  
  <pre><code>a = Object.new
  
  def a.my_eval; yield end
  
  a.my_eval { @var_one = 1 }
  a.instance_variables
  # =&gt; []
  instance_variables
  # =&gt; [@var_one]
  </code></pre>