ass="special">)</span>
            <span class="special">&lt;&lt;</span> <span class="string">" Message: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">expr</span><span class="special">::</span><span class="identifier">message</span>
    <span class="special">);</span>

    <span class="comment">// You can also manage backend in a thread-safe manner</span>
    <span class="special">{</span>
        <span class="identifier">sink_t</span><span class="special">::</span><span class="ide