s="link" href="variable_value.html" title="Class variable_value">variable_value</a> <span class="special">&amp;</span> <a class="link" href="variables_map.html#id-1_3_31_9_11_1_1_4_4_1-bb"><span class="keyword">operator</span><span class="special">[</span><span class="special">]</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">&amp;</span><span class="speci