title: Why's that? Can't convert into String: I do have a to_s method!
body: <p>I don't understand why the following raises an exception:</p>
  
  <pre><code>class X
    def to_s
      "x"
    end
  end
  
  s = ""
  s &lt;&lt; X.new
  # --&gt; TypeError: can't convert X into String
  </code></pre>
  
  <p>After all 'to_s' is supposed to convert X into a String. </p>