lass="toggle-link" data-toggle="collapse" href="#comment-func-next">mutating func next()</a>
        
<div class="comment collapse" id="comment-func-next"><div class="p">
    <p>Advance to the next element and return it, or <code>nil</code> if no next
element exists.</p>

<p>Requires: <code>next()</code> has not been applied to a copy of <code>self</code>
since the copy was made, and no preceding call to <code>self.next()</code>
has returned <code>nil</code>.</p>

    <h4>Declaration</h4>    
    <code clas