title: operator T&() or operator T()?
body: <p>In defining a conversion operator, is there any advantage of defining</p>
  
  <pre><code>operator T() const;
  </code></pre>
  
  <p>over</p>
  
  <pre><code>operator T&amp;();
  operator const T&amp;() const;
  </code></pre>
  
  <p>Assuming that I'm not concerned in potential performance gain in returning a value instead of a reference.</p>