span><span class="special">+</span><span class="identifier">b</span><span class="special">);</span>
</pre>
<p>
      Will very likely result in obscure error messages inside the body of <code class="computeroutput"><span class="identifier">my_proc</span></code> - since we've passed it an expression
      template type, and not a number type. Instead we probably need:
    </p>
<pre class="programlisting"><span class="identifier">my_proc</span><span class="special">(</span><span class="identifier">my_number_t