st</span><span class="special">::</span><span class="identifier">system</span><span class="special">::</span><span class="identifier">error_code</span><span class="special">&amp;</span> <span class="identifier">error</span><span class="special">,</span> <span class="comment">// Result of operation.</span>
  <span class="identifier">resolver</span><span class="special">::</span><span class="identifier">iterator</span> <span class="identifier">iterator</span>             <span class="comment">// Forward-only 