lass="n">Ts</span><span class="o">&gt;</span>
    <span class="kt">int</span> <span class="k">operator</span><span class="p">()(</span><span class="n">Ts</span><span class="o">&amp;&amp;</span><span class="p">...)</span>
    <span class="p">{</span>
        <span class="k">return</span> <span class="n">i</span><span class="o">++</span><span class="p">;</span>
    <span class="p">}</span>
<span class="p">};</span>


<span class="n">counter</span> <span class="n">c</span><span class="p">{};</span>
<span class