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<title>&#23454;&#39564;&#24615;&#24211;&#22836;&#25991;&#20214; &lt;experimental/optional&gt;</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">&#23454;&#39564;&#24615;&#24211;&#22836;&#25991;&#20214;</span> &lt;experimental/optional&gt;</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-header.html">header</a>&lrm; | <a href="cpp-header-experimental.html">experimental</a></span></div>
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
<p>&#27492;&#22836;&#25991;&#20214;&#26159;&#24211;&#22522;&#30784; TS (<a href="cpp-experimental-lib_extensions.html">v1</a>, <a href="cpp-experimental-lib_extensions_2.html">v2</a>) &#30340;&#19968;&#37096;&#20998;&#12290;</p>
<h3><span class="mw-headline" id=".E7.B1.BB">&#31867;</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc-hitem">
<td>&#21517;&#23383;</td>
<td>&#35828;&#26126;</td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/optional&amp;action=edit&amp;redlink=1" class="new" title="cpp/experimental/optional&#65288;&#39029;&#38754;&#19981;&#23384;&#22312;&#65289;"><span class="t-lines"><span>optional</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-libfund-ts t-mark-ts">(&#24211;&#22522;&#30784; TS)</span></span></span></div>
</div>
</td>
<td>&#21487;&#33021;&#25110;&#21487;&#33021;&#19981;&#20445;&#26377;&#19968;&#20010;&#23545;&#35937;&#30340;&#21253;&#35013;&#22120;<br />
<span class="t-mark">(&#31867;&#27169;&#26495;)</span></td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/optional/bad_optional_access&amp;action=edit&amp;redlink=1" class="new" title="cpp/experimental/optional/bad optional access&#65288;&#39029;&#38754;&#19981;&#23384;&#22312;&#65289;"><span class="t-lines"><span>bad_optional_access</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-libfund-ts t-mark-ts">(&#24211;&#22522;&#30784; TS)</span></span></span></div>
</div>
</td>
<td>&#25351;&#31034;&#36827;&#34892;&#20102;&#21040;&#19981;&#21547;&#20540;&#30340; <code>optional</code> &#30340;&#26377;&#26816;&#26597;&#35775;&#38382;&#30340;&#24322;&#24120;<br />
<span class="t-mark">(&#31867;)</span></td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/optional/in_place_t&amp;action=edit&amp;redlink=1" class="new" title="cpp/experimental/optional/in place t&#65288;&#39029;&#38754;&#19981;&#23384;&#22312;&#65289;"><span class="t-lines"><span>in_place_t</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-libfund-ts t-mark-ts">(&#24211;&#22522;&#30784; TS)</span></span></span></div>
</div>
</td>
<td>&#29992;&#20110; optional &#31867;&#22411;&#30340;&#23601;&#22320;&#26500;&#36896;&#30340;&#28040;&#27495;&#20041;&#26631;&#31614;&#31867;&#22411;<br />
<span class="t-mark">(&#31867;)</span></td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/optional/hash&amp;action=edit&amp;redlink=1" class="new" title="cpp/experimental/optional/hash&#65288;&#39029;&#38754;&#19981;&#23384;&#22312;&#65289;"><span class="t-lines"><span>std::hash<span class="t-dsc-small">&lt;std::experimental::optional&gt;</span></span></span></a></div>
</div>
</td>
<td>&#29305;&#21270; <span class="t-lc"><a href="cpp-utility-hash.html">std::hash</a></span> &#31639;&#27861;<br />
<span class="t-mark">(&#31867;&#27169;&#26495;&#29305;&#21270;)</span></td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/optional/nullopt_t&amp;action=edit&amp;redlink=1" class="new" title="cpp/experimental/optional/nullopt t&#65288;&#39029;&#38754;&#19981;&#23384;&#22312;&#65289;"><span class="t-lines"><span>nullopt_t</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-libfund-ts t-mark-ts">(&#24211;&#22522;&#30784; TS)</span></span></span></div>
</div>
</td>
<td>&#24102;&#26410;&#21021;&#22987;&#21270;&#29366;&#24577;&#30340; <code>optional</code> &#31867;&#22411;&#30340;&#25351;&#31034;&#22120;<br />
<span class="t-mark">(&#31867;)</span></td>
</tr>
</table>
<h3><span class="mw-headline" id=".E5.87.BD.E6.95.B0">&#20989;&#25968;</span></h3>
<table class="t-dsc-begin">
<tr>
<td colspan="2">
<h5><span class="mw-headline" id=".E6.AF.94.E8.BE.83">&#27604;&#36739;</span></h5>
</td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/optional/operator_cmp&amp;action=edit&amp;redlink=1" class="new" title="cpp/experimental/optional/operator cmp&#65288;&#39029;&#38754;&#19981;&#23384;&#22312;&#65289;"><span class="t-lines"><span>operator==</span><span>operator!=</span><span>operator&lt;</span><span>operator&lt;=</span><span>operator&gt;</span><span>operator&gt;=</span></span></a></div>
</div>
</td>
<td>&#27604;&#36739; <code>optional</code> &#23545;&#35937;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
</tr>
<tr>
<td colspan="2">
<h5><span class="mw-headline" id=".E7.89.B9.E5.8C.96.E7.9A.84.E7.AE.97.E6.B3.95">&#29305;&#21270;&#30340;&#31639;&#27861;</span></h5>
</td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/optional/swap2&amp;action=edit&amp;redlink=1" class="new" title="cpp/experimental/optional/swap2&#65288;&#39029;&#38754;&#19981;&#23384;&#22312;&#65289;"><span class="t-lines"><span>std::swap<span class="t-dsc-small">(std::experimental::optional)</span></span></span></a></div>
</div>
</td>
<td>&#29305;&#21270; <span class="t-lc"><a href="cpp-algorithm-swap.html">std::swap</a></span> &#31639;&#27861;<br />
<span class="t-mark">(&#20989;&#25968;)</span></td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/optional/make_optional&amp;action=edit&amp;redlink=1" class="new" title="cpp/experimental/optional/make optional&#65288;&#39029;&#38754;&#19981;&#23384;&#22312;&#65289;"><span class="t-lines"><span>make_optional</span></span></a></div>
</div>
</td>
<td>&#21019;&#24314;&#19968;&#20010; <code>optional</code> &#23545;&#35937;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
</tr>
<tr>
<td colspan="2">
<h5><span class="mw-headline" id=".E6.95.A3.E5.88.97.E6.94.AF.E6.8C.81">&#25955;&#21015;&#25903;&#25345;</span></h5>
</td>
</tr>
</table>
<h3><span class="mw-headline" id=".E6.A6.82.E8.A6.81">&#27010;&#35201;</span></h3>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="cpp source-cpp">
<pre class="de1"><span class="kw1">namespace</span> std <span class="br0">{</span>
<span class="kw1">namespace</span> experimental <span class="br0">{</span>
<span class="kw1">inline</span> <span class="kw1">namespace</span> fundamentals_v1 <span class="br0">{</span>
<span class="co1">// 5.4&#65292;&#29992;&#20110;&#23545;&#35937;&#31867;&#22411;&#30340; optional</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw1">class</span> optional<span class="sy4">;</span>
<span class="co1">// 5.5&#65292;&#23601;&#22320;&#26500;&#36896;</span>
<span class="kw1">struct</span> in_place_t<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">constexpr</span> in_place_t in_place<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
<span class="co1">// 5.6&#65292;&#26080;&#20540;&#29366;&#24577;&#25351;&#31034;&#22120;</span>
<span class="kw1">struct</span> nullopt_t<span class="br0">{</span>see below<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">constexpr</span> nullopt_t nullopt<span class="br0">(</span>unspecified<span class="br0">)</span><span class="sy4">;</span>
<span class="co1">// 5.7&#65292;&#31867; bad_optional_access</span>
<span class="kw1">class</span> bad_optional_access<span class="sy4">;</span>
<span class="co1">// 5.8&#65292;&#20851;&#31995;&#36816;&#31639;&#31526;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&lt;</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&gt;</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&lt;=</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&gt;=</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="co1">// 5.9&#65292;&#19982; nullopt &#27604;&#36739;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, nullopt_t<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span>nullopt_t, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, nullopt_t<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span>nullopt_t, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&lt;</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, nullopt_t<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&lt;</span><span class="br0">(</span>nullopt_t, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&lt;=</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, nullopt_t<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&lt;=</span><span class="br0">(</span>nullopt_t, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&gt;</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, nullopt_t<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&gt;</span><span class="br0">(</span>nullopt_t, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&gt;=</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, nullopt_t<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&gt;=</span><span class="br0">(</span>nullopt_t, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span>
<span class="co1">// 5.10&#65292;&#19982; T &#27604;&#36739;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> T<span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span><span class="kw4">const</span> T<span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> T<span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy3">!</span><span class="sy1">=</span><span class="br0">(</span><span class="kw4">const</span> T<span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&lt;</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> T<span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&lt;</span><span class="br0">(</span><span class="kw4">const</span> T<span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&lt;=</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> T<span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&lt;=</span><span class="br0">(</span><span class="kw4">const</span> T<span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&gt;</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> T<span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&gt;</span><span class="br0">(</span><span class="kw4">const</span> T<span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&gt;=</span><span class="br0">(</span><span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, <span class="kw4">const</span> T<span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> operator<span class="sy1">&gt;=</span><span class="br0">(</span><span class="kw4">const</span> T<span class="sy3">&amp;</span>, <span class="kw4">const</span> optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="co1">// 5.11&#65292;&#29305;&#21270;&#30340;&#31639;&#27861;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">void</span> swap<span class="br0">(</span>optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, optional<span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span>see below<span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw4">constexpr</span> optional<span class="sy1">&lt;</span>see below<span class="sy1">&gt;</span> make_optional<span class="br0">(</span>T<span class="sy3">&amp;&amp;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span> <span class="co1">// namespace fundamentals_v1</span>
<span class="br0">}</span> <span class="co1">// namespace experimental</span>
<span class="co1">// 5.12&#65292;&#25955;&#21015;&#25903;&#25345;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw1">struct</span> hash<span class="sy4">;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span> <span class="kw1">struct</span> hash<span class="sy1">&lt;</span>experimental<span class="sy4">::</span><span class="me2">optional</span><span class="sy1">&lt;</span>T<span class="sy1">&gt;&gt;</span><span class="sy4">;</span>
<span class="br0">}</span> <span class="co1">// namespace std</span></pre></div>
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