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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>swap<small>(std::optional)</small></h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-utility.html">utility</a>&lrm; | <a href="cpp-utility-optional.html">optional</a></span></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-optional.html">&lt;optional&gt;</a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> T <span class="sy1">&gt;</span><br /></span>
<p><span class="kw4">void</span> swap<span class="br0">(</span> <a href="cpp-utility-optional.html"><span class="kw1075">std::<span class="me2">optional</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span> lhs,<br /></p>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<a href="cpp-utility-optional.html"><span class="kw1075">std::<span class="me2">optional</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span> rhs <span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* see below */</span><span class="br0">)</span><span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span><br />
<span class="t-mark-rev t-until-cxx20">(C++20 &#21069;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> T <span class="sy1">&gt;</span><br /></span>
<p><span class="kw4">constexpr</span> <span class="kw4">void</span> swap<span class="br0">(</span> <a href="cpp-utility-optional.html"><span class="kw1075">std::<span class="me2">optional</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span> lhs,<br /></p>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<a href="cpp-utility-optional.html"><span class="kw1075">std::<span class="me2">optional</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="sy3">&amp;</span> rhs <span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* see below */</span><span class="br0">)</span><span class="sy4">;</span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<p>&#23545; <span class="t-lc"><a href="cpp-utility-optional.html">std::optional</a></span> &#37325;&#36733; <span class="t-lc"><a href="cpp-algorithm-swap.html">std::swap</a></span> &#31639;&#27861;&#12290;&#20132;&#25442; <code>lhs</code> &#19982; <code>rhs</code> &#30340;&#29366;&#24577;&#12290;&#31561;&#25928;&#22320;&#35843;&#29992; <span class="t-c"><span class="mw-geshi cpp source-cpp">lhs.<span class="me1">swap</span><span class="br0">(</span>rhs<span class="br0">)</span></span></span> &#12290;</p>
<p>&#27492;&#37325;&#36733;&#20165;&#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_move_constructible.html"><span class="kw539">std::<span class="me2">is_move_constructible_v</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span></span></span> &#19982; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_swappable.html"><span class="kw573">std::<span class="me2">is_swappable_v</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span></span></span> &#30342;&#20026;<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
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<td>&#35201;&#20132;&#25442;&#29366;&#24577;&#30340; <code>optional</code> &#23545;&#35937;</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<p>&#65288;&#26080;&#65289;</p>
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">&#24322;&#24120;</span></h3>
<div class="t-noexcept-full"><a href="cpp-language-noexcept_spec.html"><tt>noexcept</tt></a> &#35828;&#26126;&#65306;&nbsp;&nbsp;
<div class="t-noexcept-box"><span class="t-cc"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span><span class="kw1">noexcept</span><span class="br0">(</span>lhs.<span class="me1">swap</span><span class="br0">(</span>rhs<span class="br0">)</span><span class="br0">)</span><span class="br0">)</span></span></span></div>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
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<pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;optional&gt;</span>
<span class="co2">#include &lt;string&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="cpp-utility-optional.html"><span class="kw1075">std::<span class="me2">optional</span></span></a><span class="sy1">&lt;</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span> a<span class="br0">{</span><span class="st0">&quot;&#9608;&#9608;&#9608;&#9608;&#9608;&#9608;&quot;</span><span class="br0">}</span>, b<span class="br0">{</span><span class="st0">&quot;&#9618;&#9618;&#9618;&#9618;&#9618;&#9618;&quot;</span><span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">auto</span> print <span class="sy1">=</span> <span class="br0">[</span><span class="sy3">&amp;</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&amp;</span> s<span class="br0">)</span> <span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a>
<span class="sy1">&lt;&lt;</span> s <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\t</span>&quot;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;a = &quot;</span> <span class="sy1">&lt;&lt;</span> a.<span class="me1">value_or</span><span class="br0">(</span><span class="st0">&quot;(null)&quot;</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot; &quot;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;b = &quot;</span> <span class="sy1">&lt;&lt;</span> b.<span class="me1">value_or</span><span class="br0">(</span><span class="st0">&quot;(null)&quot;</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
print<span class="br0">(</span><span class="st0">&quot;Initially:&quot;</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-algorithm-swap.html"><span class="kw1599">std::<span class="me2">swap</span></span></a><span class="br0">(</span>a, b<span class="br0">)</span><span class="sy4">;</span>
print<span class="br0">(</span><span class="st0">&quot;swap(a, b):&quot;</span><span class="br0">)</span><span class="sy4">;</span>
a.<span class="me1">reset</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
print<span class="br0">(</span><span class="st0">&quot;<span class="es1">\n</span>&quot;</span><span class="st0">&quot;a.reset():&quot;</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-algorithm-swap.html"><span class="kw1599">std::<span class="me2">swap</span></span></a><span class="br0">(</span>a, b<span class="br0">)</span><span class="sy4">;</span>
print<span class="br0">(</span><span class="st0">&quot;swap(a, b):&quot;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">Initially: a = &#9608;&#9608;&#9608;&#9608;&#9608;&#9608; b = &#9618;&#9618;&#9618;&#9618;&#9618;&#9618;
swap(a, b): a = &#9618;&#9618;&#9618;&#9618;&#9618;&#9618; b = &#9608;&#9608;&#9608;&#9608;&#9608;&#9608;
a.reset(): a = (null) b = &#9608;&#9608;&#9608;&#9608;&#9608;&#9608;
swap(a, b): a = &#9608;&#9608;&#9608;&#9608;&#9608;&#9608; b = (null)</pre></div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">&#32570;&#38519;&#25253;&#21578;</span></h3>
<p>&#19979;&#21015;&#26356;&#25913;&#34892;&#20026;&#30340;&#32570;&#38519;&#25253;&#21578;&#36861;&#28335;&#22320;&#24212;&#29992;&#20110;&#20197;&#21069;&#20986;&#29256;&#30340; C++ &#26631;&#20934;&#12290;</p>
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<th>DR</th>
<th>&#24212;&#29992;&#20110;</th>
<th>&#20986;&#29256;&#26102;&#30340;&#34892;&#20026;</th>
<th>&#27491;&#30830;&#34892;&#20026;</th>
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<td><a rel="nofollow" class="external text" href="https://wg21.link/P2231R1">P2231R1</a></td>
<td>C++20</td>
<td><code>swap</code> &#19981;&#26159; constexpr &#32780;&#35201;&#27714;&#30340;&#25805;&#20316;&#22312; C++20 &#20013;&#33021;&#20026; constexpr</td>
<td>&#20351;&#20043;&#20026; constexpr</td>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
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<div><a href="cpp-utility-optional-swap.html"><span class="t-lines"><span>swap</span></span></a></div>
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<td>&#20132;&#25442;&#20869;&#23481;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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