title: Instance variables in modules?
body: <p>How is it possible that I can have instance variables in a module even though I cannot create an instance of the module? What would be the purpose of <code>@stack</code> in module <code>Stacklike</code> below?</p>
  
  <pre><code>module Stacklike
    def stack
      @stack ||= []
    end
  end
  </code></pre>