lass="identifier">string_type</span> <span class="special">&amp;</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">string_type</span> <span class="special">&amp;</span><span class="special">,</span> 
                         <span class="keyword">const</span> <span class="identifier">string_type</span> <span class="special">&amp;</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">string_type</span> <span class="spec