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<li class="navelem"><a class="el" href="namespacedmlc.html">dmlc</a></li><li class="navelem"><a class="el" href="classdmlc_1_1optional.html">optional</a></li> </ul>
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<a href="#pub-methods">Public Member Functions</a> &#124;
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<div class="title">dmlc::optional&lt; T &gt; Class Template Reference</div> </div>
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<p>c++17 compatible optional class.
<a href="classdmlc_1_1optional.html#details">More...</a></p>
<p><code>#include &lt;<a class="el" href="optional_8h_source.html">optional.h</a>&gt;</code></p>
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Collaboration diagram for dmlc::optional&lt; T &gt;:</div>
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Public Member Functions</h2></td></tr>
<tr class="memitem:a358bf8befa660e58c07856b06c2e2b41"><td class="memItemLeft" align="right" valign="top">&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#a358bf8befa660e58c07856b06c2e2b41">optional</a> ()</td></tr>
<tr class="memdesc:a358bf8befa660e58c07856b06c2e2b41"><td class="mdescLeft">&#160;</td><td class="mdescRight">construct an optional object that contains no value <a href="#a358bf8befa660e58c07856b06c2e2b41">More...</a><br /></td></tr>
<tr class="separator:a358bf8befa660e58c07856b06c2e2b41"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:ad8d39fd99191c6f232063b60a1b7bb6f"><td class="memItemLeft" align="right" valign="top">&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#ad8d39fd99191c6f232063b60a1b7bb6f">optional</a> (const T &amp;<a class="el" href="classdmlc_1_1optional.html#aaf22cb65a584841e054aa69e4acdd0be">value</a>)</td></tr>
<tr class="memdesc:ad8d39fd99191c6f232063b60a1b7bb6f"><td class="mdescLeft">&#160;</td><td class="mdescRight">construct an optional object with value <a href="#ad8d39fd99191c6f232063b60a1b7bb6f">More...</a><br /></td></tr>
<tr class="separator:ad8d39fd99191c6f232063b60a1b7bb6f"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:a0a0f99e2ba48f2583f164c2286dacc58"><td class="memItemLeft" align="right" valign="top">&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#a0a0f99e2ba48f2583f164c2286dacc58">optional</a> (const <a class="el" href="classdmlc_1_1optional.html">optional</a>&lt; T &gt; &amp;other)</td></tr>
<tr class="memdesc:a0a0f99e2ba48f2583f164c2286dacc58"><td class="mdescLeft">&#160;</td><td class="mdescRight">construct an optional object with another optional object <a href="#a0a0f99e2ba48f2583f164c2286dacc58">More...</a><br /></td></tr>
<tr class="separator:a0a0f99e2ba48f2583f164c2286dacc58"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:aacd056f3191890afa191f8ad50ebf27f"><td class="memItemLeft" align="right" valign="top">&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#aacd056f3191890afa191f8ad50ebf27f">~optional</a> ()</td></tr>
<tr class="memdesc:aacd056f3191890afa191f8ad50ebf27f"><td class="mdescLeft">&#160;</td><td class="mdescRight">deconstructor <a href="#aacd056f3191890afa191f8ad50ebf27f">More...</a><br /></td></tr>
<tr class="separator:aacd056f3191890afa191f8ad50ebf27f"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:aca79e391f4df7aaca345d05ae65a4d16"><td class="memItemLeft" align="right" valign="top">void&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#aca79e391f4df7aaca345d05ae65a4d16">swap</a> (<a class="el" href="classdmlc_1_1optional.html">optional</a>&lt; T &gt; &amp;other)</td></tr>
<tr class="memdesc:aca79e391f4df7aaca345d05ae65a4d16"><td class="mdescLeft">&#160;</td><td class="mdescRight">swap two optional <a href="#aca79e391f4df7aaca345d05ae65a4d16">More...</a><br /></td></tr>
<tr class="separator:aca79e391f4df7aaca345d05ae65a4d16"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:ab7b4fba71d2e988cd5dacb99a5da315e"><td class="memItemLeft" align="right" valign="top"><a class="el" href="classdmlc_1_1optional.html">optional</a>&lt; T &gt; &amp;&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#ab7b4fba71d2e988cd5dacb99a5da315e">operator=</a> (const T &amp;<a class="el" href="classdmlc_1_1optional.html#aaf22cb65a584841e054aa69e4acdd0be">value</a>)</td></tr>
<tr class="memdesc:ab7b4fba71d2e988cd5dacb99a5da315e"><td class="mdescLeft">&#160;</td><td class="mdescRight">set this object to hold value <a href="#ab7b4fba71d2e988cd5dacb99a5da315e">More...</a><br /></td></tr>
<tr class="separator:ab7b4fba71d2e988cd5dacb99a5da315e"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:a535a725a80a78681d96feac82c3f5110"><td class="memItemLeft" align="right" valign="top"><a class="el" href="classdmlc_1_1optional.html">optional</a>&lt; T &gt; &amp;&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#a535a725a80a78681d96feac82c3f5110">operator=</a> (const <a class="el" href="classdmlc_1_1optional.html">optional</a>&lt; T &gt; &amp;other)</td></tr>
<tr class="memdesc:a535a725a80a78681d96feac82c3f5110"><td class="mdescLeft">&#160;</td><td class="mdescRight">set this object to hold the same value with other <a href="#a535a725a80a78681d96feac82c3f5110">More...</a><br /></td></tr>
<tr class="separator:a535a725a80a78681d96feac82c3f5110"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:ad2959fc0d19a5e4affbc9e1cd67e57ae"><td class="memItemLeft" align="right" valign="top"><a class="el" href="classdmlc_1_1optional.html">optional</a>&lt; T &gt; &amp;&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#ad2959fc0d19a5e4affbc9e1cd67e57ae">operator=</a> (<a class="el" href="structdmlc_1_1nullopt__t.html">nullopt_t</a>)</td></tr>
<tr class="memdesc:ad2959fc0d19a5e4affbc9e1cd67e57ae"><td class="mdescLeft">&#160;</td><td class="mdescRight">clear the value this object is holding. optional&lt;T&gt; x = nullopt; <a href="#ad2959fc0d19a5e4affbc9e1cd67e57ae">More...</a><br /></td></tr>
<tr class="separator:ad2959fc0d19a5e4affbc9e1cd67e57ae"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:a5df5732afa850c13c880db0db96c2702"><td class="memItemLeft" align="right" valign="top">T &amp;&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#a5df5732afa850c13c880db0db96c2702">operator*</a> ()</td></tr>
<tr class="memdesc:a5df5732afa850c13c880db0db96c2702"><td class="mdescLeft">&#160;</td><td class="mdescRight">non-const dereference operator <a href="#a5df5732afa850c13c880db0db96c2702">More...</a><br /></td></tr>
<tr class="separator:a5df5732afa850c13c880db0db96c2702"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:a0a8ba8634870786f4c8520b82550f57f"><td class="memItemLeft" align="right" valign="top">const T &amp;&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#a0a8ba8634870786f4c8520b82550f57f">operator*</a> () const</td></tr>
<tr class="memdesc:a0a8ba8634870786f4c8520b82550f57f"><td class="mdescLeft">&#160;</td><td class="mdescRight">const dereference operator <a href="#a0a8ba8634870786f4c8520b82550f57f">More...</a><br /></td></tr>
<tr class="separator:a0a8ba8634870786f4c8520b82550f57f"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:a5c857b9eaf4721c111e3753cc7685cc0"><td class="memItemLeft" align="right" valign="top">bool&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#a5c857b9eaf4721c111e3753cc7685cc0">operator==</a> (const <a class="el" href="classdmlc_1_1optional.html">optional</a>&lt; T &gt; &amp;other) const</td></tr>
<tr class="memdesc:a5c857b9eaf4721c111e3753cc7685cc0"><td class="mdescLeft">&#160;</td><td class="mdescRight">equal comparison <a href="#a5c857b9eaf4721c111e3753cc7685cc0">More...</a><br /></td></tr>
<tr class="separator:a5c857b9eaf4721c111e3753cc7685cc0"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:aaf22cb65a584841e054aa69e4acdd0be"><td class="memItemLeft" align="right" valign="top">const T &amp;&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#aaf22cb65a584841e054aa69e4acdd0be">value</a> () const</td></tr>
<tr class="memdesc:aaf22cb65a584841e054aa69e4acdd0be"><td class="mdescLeft">&#160;</td><td class="mdescRight">return the holded value. throws std::logic_error if holding no value <a href="#aaf22cb65a584841e054aa69e4acdd0be">More...</a><br /></td></tr>
<tr class="separator:aaf22cb65a584841e054aa69e4acdd0be"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:aeac40cbe8bcc4c6a5d582fe7a39bc146"><td class="memItemLeft" align="right" valign="top">&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#aeac40cbe8bcc4c6a5d582fe7a39bc146">operator bool</a> () const</td></tr>
<tr class="memdesc:aeac40cbe8bcc4c6a5d582fe7a39bc146"><td class="mdescLeft">&#160;</td><td class="mdescRight">whether this object is holding a value <a href="#aeac40cbe8bcc4c6a5d582fe7a39bc146">More...</a><br /></td></tr>
<tr class="separator:aeac40cbe8bcc4c6a5d582fe7a39bc146"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:a0c135346d7c6425ce730493a89761c96"><td class="memItemLeft" align="right" valign="top">bool&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="classdmlc_1_1optional.html#a0c135346d7c6425ce730493a89761c96">has_value</a> () const</td></tr>
<tr class="memdesc:a0c135346d7c6425ce730493a89761c96"><td class="mdescLeft">&#160;</td><td class="mdescRight">whether this object is holding a value (alternate form). <a href="#a0c135346d7c6425ce730493a89761c96">More...</a><br /></td></tr>
<tr class="separator:a0c135346d7c6425ce730493a89761c96"><td class="memSeparator" colspan="2">&#160;</td></tr>
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<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><h3>template&lt;typename T&gt;<br />
class dmlc::optional&lt; T &gt;</h3>
<p>c++17 compatible optional class. </p>
<p>At any time an optional&lt;T&gt; instance either hold no value (string representation "None") or hold a value of type T. </p>
</div><h2 class="groupheader">Constructor &amp; Destructor Documentation</h2>
<a id="a358bf8befa660e58c07856b06c2e2b41"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a358bf8befa660e58c07856b06c2e2b41">&#9670;&nbsp;</a></span>optional() <span class="overload">[1/3]</span></h2>
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template&lt;typename T&gt; </div>
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<td class="memname"><a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::<a class="el" href="classdmlc_1_1optional.html">optional</a> </td>
<td>(</td>
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<p>construct an optional object that contains no value </p>
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<a id="ad8d39fd99191c6f232063b60a1b7bb6f"></a>
<h2 class="memtitle"><span class="permalink"><a href="#ad8d39fd99191c6f232063b60a1b7bb6f">&#9670;&nbsp;</a></span>optional() <span class="overload">[2/3]</span></h2>
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template&lt;typename T&gt; </div>
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<td class="memname"><a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::<a class="el" href="classdmlc_1_1optional.html">optional</a> </td>
<td>(</td>
<td class="paramtype">const T &amp;&#160;</td>
<td class="paramname"><em>value</em></td><td>)</td>
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<p>construct an optional object with value </p>
</div>
</div>
<a id="a0a0f99e2ba48f2583f164c2286dacc58"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a0a0f99e2ba48f2583f164c2286dacc58">&#9670;&nbsp;</a></span>optional() <span class="overload">[3/3]</span></h2>
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template&lt;typename T&gt; </div>
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<td class="memname"><a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::<a class="el" href="classdmlc_1_1optional.html">optional</a> </td>
<td>(</td>
<td class="paramtype">const <a class="el" href="classdmlc_1_1optional.html">optional</a>&lt; T &gt; &amp;&#160;</td>
<td class="paramname"><em>other</em></td><td>)</td>
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<p>construct an optional object with another optional object </p>
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<a id="aacd056f3191890afa191f8ad50ebf27f"></a>
<h2 class="memtitle"><span class="permalink"><a href="#aacd056f3191890afa191f8ad50ebf27f">&#9670;&nbsp;</a></span>~optional()</h2>
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template&lt;typename T&gt; </div>
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<td>(</td>
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<p>deconstructor </p>
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<h2 class="groupheader">Member Function Documentation</h2>
<a id="a0c135346d7c6425ce730493a89761c96"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a0c135346d7c6425ce730493a89761c96">&#9670;&nbsp;</a></span>has_value()</h2>
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template&lt;typename T&gt; </div>
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<td class="memname">bool <a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::has_value </td>
<td>(</td>
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<p>whether this object is holding a value (alternate form). </p>
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<a id="aeac40cbe8bcc4c6a5d582fe7a39bc146"></a>
<h2 class="memtitle"><span class="permalink"><a href="#aeac40cbe8bcc4c6a5d582fe7a39bc146">&#9670;&nbsp;</a></span>operator bool()</h2>
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template&lt;typename T&gt; </div>
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<td class="memname"><a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::operator bool </td>
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<td> const</td>
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<p>whether this object is holding a value </p>
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<a id="a5df5732afa850c13c880db0db96c2702"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a5df5732afa850c13c880db0db96c2702">&#9670;&nbsp;</a></span>operator*() <span class="overload">[1/2]</span></h2>
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template&lt;typename T&gt; </div>
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<td class="memname">T&amp; <a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::operator* </td>
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<p>non-const dereference operator </p>
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<td class="memname">const T&amp; <a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::operator* </td>
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<p>const dereference operator </p>
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<h2 class="memtitle"><span class="permalink"><a href="#ab7b4fba71d2e988cd5dacb99a5da315e">&#9670;&nbsp;</a></span>operator=() <span class="overload">[1/3]</span></h2>
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<td class="memname"><a class="el" href="classdmlc_1_1optional.html">optional</a>&lt;T&gt;&amp; <a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::operator= </td>
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<p>set this object to hold value </p>
<dl class="params"><dt>Parameters</dt><dd>
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<tr><td class="paramname">value</td><td>the value to hold </td></tr>
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<dl class="section return"><dt>Returns</dt><dd>return self to support chain assignment </dd></dl>
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<td class="memname"><a class="el" href="classdmlc_1_1optional.html">optional</a>&lt;T&gt;&amp; <a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::operator= </td>
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<p>set this object to hold the same value with other </p>
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<dl class="section return"><dt>Returns</dt><dd>return self to support chain assignment </dd></dl>
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<td class="memname"><a class="el" href="classdmlc_1_1optional.html">optional</a>&lt;T&gt;&amp; <a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::operator= </td>
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<p>clear the value this object is holding. optional&lt;T&gt; x = nullopt; </p>
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<h2 class="memtitle"><span class="permalink"><a href="#a5c857b9eaf4721c111e3753cc7685cc0">&#9670;&nbsp;</a></span>operator==()</h2>
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<td class="memname">bool <a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::operator== </td>
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<td class="paramtype">const <a class="el" href="classdmlc_1_1optional.html">optional</a>&lt; T &gt; &amp;&#160;</td>
<td class="paramname"><em>other</em></td><td>)</td>
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<p>equal comparison </p>
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<h2 class="memtitle"><span class="permalink"><a href="#aca79e391f4df7aaca345d05ae65a4d16">&#9670;&nbsp;</a></span>swap()</h2>
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<td class="memname">void <a class="el" href="classdmlc_1_1optional.html">dmlc::optional</a>&lt; T &gt;::swap </td>
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<td class="paramname"><em>other</em></td><td>)</td>
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<p>swap two optional </p>
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<h2 class="memtitle"><span class="permalink"><a href="#aaf22cb65a584841e054aa69e4acdd0be">&#9670;&nbsp;</a></span>value()</h2>
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<td> const</td>
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<p>return the holded value. throws std::logic_error if holding no value </p>
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<hr/>The documentation for this class was generated from the following file:<ul>
<li>/work/mxnet/3rdparty/dmlc-core/include/dmlc/<a class="el" href="optional_8h_source.html">optional.h</a></li>
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