i_pass::swap()</span>
        <span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span><span class="identifier">unique</span><span class="special">&amp;);</span>

        <span class="comment">// get_input is called whenever the next input character/token</span>
        <span class="comment">// should be fetched. </span>
        <span class="comment">//</span>
        <span class="comment">//   mp:    is a reference to the whole multi_pass instance</span>
        <