="2">&#160;</td></tr>
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Variables</h2></td></tr>
<tr class="memitem:ga38cf78e1e3e262f7f1c71ddd9ca70cd9"><td class="memTemplParams" colspan="2">template&lt;typename Tag , typename optional_T &gt; </td></tr>
<tr class="memitem:ga38cf78e1e3e262f7f1c71ddd9ca70cd9"><td class="memTemplItemLeft" align="right" valign="top">constexpr auto&#160;</td><td class="memTemplItemRight" valign="bottom"><a 