 Any octets not consumed will be presented again in a subsequent
                  invocation of the callback. The implementation type-erases the
                  callback without requiring a dynamic allocation. For this reason,
                  the callback object is passed by a non-constant reference.
                </p>
                <p>
                  The function object will be called with this equivalent signature:
                </p>
<pre class="programlisting"><span class="identifier">std</