n><span class="special">;</span>
  <a class="link" href="basic_environment/const_entry_type.html" title="Struct template const_entry_type">const_entry_type</a> <a class="link" href="basic_environment.html#idp51508272-bb"><span class="identifier">at</span></a><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="special">;</span>
  <a class="li