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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::variant&lt;Types...&gt;::</span>variant</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-variant.html">variant</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> variant<span class="br0">(</span><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></span></div>
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<td>(1)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> variant<span class="br0">(</span> <span class="kw4">const</span> variant<span class="sy3">&amp;</span> other <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> variant<span class="br0">(</span> variant<span class="sy3">&amp;&amp;</span> other <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></span></div>
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<td>(3)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</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 class="kw4">constexpr</span> variant<span class="br0">(</span> T<span class="sy3">&amp;&amp;</span> t <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></span></div>
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<td>(4)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</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="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> <span class="kw1">explicit</span> variant<span class="br0">(</span> <a href="cpp-utility-in_place.html"><span class="kw1083">std::<span class="me2">in_place_type_t</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span>, Args<span class="sy3">&amp;&amp;</span>... <span class="me1">args</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(5)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</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="kw1">class</span> U, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">&gt;</span><br /></span>
<p><span class="kw4">constexpr</span> <span class="kw1">explicit</span> variant<span class="br0">(</span> <a href="cpp-utility-in_place.html"><span class="kw1083">std::<span class="me2">in_place_type_t</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span>,<br /></p>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <a href="cpp-utility-initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1">&lt;</span>U<span class="sy1">&gt;</span> il, Args<span class="sy3">&amp;&amp;</span>... <span class="me1">args</span> <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(6)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> <span class="kw1">explicit</span> variant<span class="br0">(</span> <a href="cpp-utility-in_place.html"><span class="kw1084">std::<span class="me2">in_place_index_t</span></span></a><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span>, Args<span class="sy3">&amp;&amp;</span>... <span class="me1">args</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(7)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> I, <span class="kw1">class</span> U, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">&gt;</span><br /></span>
<p><span class="kw4">constexpr</span> <span class="kw1">explicit</span> variant<span class="br0">(</span> <a href="cpp-utility-in_place.html"><span class="kw1084">std::<span class="me2">in_place_index_t</span></span></a><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span>,<br /></p>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <a href="cpp-utility-initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1">&lt;</span>U<span class="sy1">&gt;</span> il, Args<span class="sy3">&amp;&amp;</span>... <span class="me1">args</span> <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(8)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span></td>
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<p><br />
&#26500;&#36896;&#26032;&#30340; <code>variant</code> &#23545;&#35937;&#12290;</p>
<div class="t-li1"><span class="t-li">1)</span> &#40664;&#35748;&#26500;&#36896;&#20989;&#25968;&#12290;&#26500;&#36896; <code>variant</code> &#65292;&#20445;&#26377;&#39318;&#20010;&#21487;&#36873;&#39033;&#30340;<a href="cpp-language-value_initialization.html">&#20540;&#21021;&#22987;&#21270;</a>&#30340;&#20540;&#65288; <a href="cpp-utility-variant-index.html">index()</a> &#20026;&#38646;&#65289;&#12290;
<ul>
<li>&#24403;&#19988;&#20165;&#24403;&#21487;&#36873;&#39033;&#31867;&#22411; <code>T_0</code> &#30340;&#20540;&#21021;&#22987;&#21270;&#28385;&#36275; <a href="cpp-language-constexpr.html">constexpr &#20989;&#25968;</a>&#30340;&#35201;&#27714;&#65292;&#27492;&#26500;&#36896;&#20989;&#25968;&#25165;&#20026; <code>constexpr</code> &#12290;</li>
<li>&#27492;&#37325;&#36733;&#20165;&#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_default_constructible.html"><span class="kw527">std::<span class="me2">is_default_constructible_v</span></span></a><span class="sy1">&lt;</span>T_0<span class="sy1">&gt;</span></span></span> &#20026; <code>true</code> &#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#12290;</li>
</ul>
</div>
<div class="t-li1"><span class="t-li">2)</span> &#22797;&#21046;&#26500;&#36896;&#20989;&#25968;&#12290;&#33509; <code>other</code> &#38750;<a href="cpp-utility-variant-valueless_by_exception.html">&#22240;&#24322;&#24120;&#26080;&#20540;</a>&#65292;&#21017;&#26500;&#36896;&#19968;&#20010;&#20445;&#26377;&#19982; <code>other</code> &#30456;&#21516;&#21487;&#36873;&#39033;&#30340; <code>variant</code> &#65292;&#24182;&#20197; <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1">&lt;</span>other.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">&gt;</span><span class="br0">(</span>other<span class="br0">)</span></span></span> <a href="cpp-language-direct_initialization.html">&#30452;&#25509;&#21021;&#22987;&#21270;</a>&#25152;&#21547;&#20540;&#12290;&#21542;&#21017;&#65292;&#21021;&#22987;&#21270;&#19968;&#20010;<a href="cpp-utility-variant-valueless_by_exception.html">&#22240;&#24322;&#24120;&#26080;&#20540;</a>&#30340; <code>variant</code> &#12290;
<ul>
<li>&#27492;&#26500;&#36896;&#20989;&#25968;&#23450;&#20041;&#20026;&#34987;&#21024;&#38500;&#65292;&#38500;&#38750; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_copy_constructible.html"><span class="kw533">std::<span class="me2">is_copy_constructible_v</span></span></a><span class="sy1">&lt;</span>T_i<span class="sy1">&gt;</span></span></span> &#23545;&#20110;&#25152;&#26377; <code>Types...</code> &#20013;&#30340; <code>T_i</code> &#20026; <code>true</code> &#12290;</li>
<li>&#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_copy_constructible.html"><span class="kw535">std::<span class="me2">is_trivially_copy_constructible_v</span></span></a><span class="sy1">&lt;</span>T_i<span class="sy1">&gt;</span></span></span> &#23545; <code>Types...</code> &#20013;&#30340;&#25152;&#26377; <code>T_i</code> &#20026; true &#21017;&#23427;&#20026;&#24179;&#20961;&#12290;</li>
</ul>
</div>
<div class="t-li1"><span class="t-li">3)</span> &#31227;&#21160;&#26500;&#36896;&#20989;&#25968;&#12290;&#33509; <code>other</code> &#38750;<a href="cpp-utility-variant-valueless_by_exception.html">&#22240;&#24322;&#24120;&#26080;&#20540;</a>&#65292;&#21017;&#26500;&#36896;&#19968;&#20010;&#20445;&#26377;&#19982; <code>other</code> &#30456;&#21516;&#21487;&#36873;&#39033;&#30340; <code>variant</code> &#24182;&#20197; <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">get</span><span class="sy1">&lt;</span>other.<span class="me1">index</span><span class="br0">(</span><span class="br0">)</span><span class="sy1">&gt;</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>other<span class="br0">)</span><span class="br0">)</span></span></span> <a href="cpp-language-direct_initialization.html">&#30452;&#25509;&#21021;&#22987;&#21270;</a>&#25152;&#21547;&#20540;&#12290;&#21542;&#21017;&#65292;&#21021;&#22987;&#21270;&#19968;&#20010;<a href="cpp-utility-variant-valueless_by_exception.html">&#22240;&#24322;&#24120;&#26080;&#20540;</a>&#30340; <code>variant</code>&#12290;
<ul>
<li>&#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_i<span class="sy1">&gt;</span></span></span> &#23545;&#20110;&#25152;&#26377;<code>Types...</code> &#20013;&#30340; <code>T_i</code> &#20026; <code>true</code> &#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#12290;</li>
<li>&#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_move_constructible.html"><span class="kw541">std::<span class="me2">is_trivially_move_constructible_v</span></span></a><span class="sy1">&lt;</span>T_i<span class="sy1">&gt;</span></span></span> &#23545; <code>Types...</code> &#20013;&#30340;&#25152;&#26377; <code>T_i</code> &#20026; true &#21017;&#23427;&#20026;&#24179;&#20961;&#12290;</li>
</ul>
</div>
<div class="t-li1"><span class="t-li">4)</span> &#36716;&#25442;&#26500;&#36896;&#20989;&#25968;&#12290;&#26500;&#36896;&#20445;&#26377;&#20250;&#34987;&#37325;&#36733;&#20915;&#35758;&#23545;&#34920;&#36798;&#24335; <span class="t-c"><span class="mw-geshi cpp source-cpp">F<span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="br0">(</span>t<span class="br0">)</span><span class="br0">)</span></span></span> &#36873;&#25321;&#30340;&#21487;&#36873;&#39033; <code>T_j</code> &#65292;&#20551;&#35774;&#23545;&#26469;&#33258; <code>Types...</code> &#20013;&#30340;&#27599;&#20010; <code>T_i</code> &#21516;&#26102;&#23384;&#22312;&#19968;&#20010;&#34394;&#26500;&#20989;&#25968; <code>F(T_i)</code> &#30340;&#37325;&#36733;&#65292;&#38500;&#20102;&#65306;
<dl>
<dd>
<ul>
<li>&#20165;&#33509;&#22768;&#26126; <span class="t-c"><span class="mw-geshi cpp source-cpp">T_i x<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="br0">(</span>t<span class="br0">)</span> <span class="br0">}</span><span class="sy4">;</span></span></span> &#23545;&#26576;&#20010;&#34394;&#35774;&#21464;&#37327; <code>x</code> &#25165;&#32771;&#34385; <span class="t-c"><span class="mw-geshi cpp source-cpp">F<span class="br0">(</span>T_i<span class="br0">)</span></span></span> &#65307;</li>
<li>&#33509; <code>T_i</code> &#26159;&#65288;&#21487;&#26377; cv &#38480;&#23450;&#30340;&#65289; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> &#65292;&#21017;&#20165;&#33509; <span class="t-rev-inl t-until-cxx20"><span><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span></span></span></span> <span><span class="t-mark-rev t-until-cxx20">(C++20 &#21069;)</span></span></span><span class="t-rev-inl t-since-cxx20"><span><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span></span></span></span> <span><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></span></span> &#20134;&#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> &#25165;&#32771;&#34385; <span class="t-c"><span class="mw-geshi cpp source-cpp">F<span class="br0">(</span>T_i<span class="br0">)</span></span></span> &#12290;</li>
</ul>
</dd>
</dl>
</div>
<div class="t-li1"><span class="t-li"></span> &#22914;&#21516;&#29992;&#30452;&#25509;&#38750;&#21015;&#34920;&#21021;&#22987;&#21270;&#20174; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="br0">(</span>t<span class="br0">)</span></span></span> <a href="cpp-language-direct_initialization.html">&#30452;&#25509;&#21021;&#22987;&#21270;</a>&#25152;&#21547;&#20540;&#12290;
<ul>
<li>&#27492;&#37325;&#36733;&#20165;&#33509;
<ul>
<li><span class="t-c"><span class="mw-geshi cpp source-cpp">sizeof...<span class="br0">(</span>Types<span class="br0">)</span> <span class="sy1">&gt;</span> <span class="nu0">0</span></span></span> &#65292;</li>
<li><span class="t-rev-inl t-until-cxx20"><span><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1">&lt;</span>U<span class="sy1">&gt;</span></span></span></span> <span><span class="t-mark-rev t-until-cxx20">(C++20 &#21069;)</span></span></span><span class="t-rev-inl t-since-cxx20"><span><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">remove_cvref_t</span><span class="sy1">&lt;</span>U<span class="sy1">&gt;</span></span></span></span> <span><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></span></span> &#26082;&#19981;&#19982; <span class="t-c"><span class="mw-geshi cpp source-cpp">variant</span></span> &#20026;&#21516;&#19968;&#31867;&#22411;&#65292;&#20134;&#38750; <span class="t-lc"><a href="cpp-utility-in_place.html">std::in_place_type_t</a></span> &#25110; <span class="t-lc"><a href="cpp-utility-in_place.html">std::in_place_index_t</a></span> &#30340;&#29305;&#21270;&#65292;</li>
<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_constructible.html"><span class="kw521">std::<span class="me2">is_constructible_v</span></span></a><span class="sy1">&lt;</span>T_j, T<span class="sy1">&gt;</span></span></span> &#20026; <code>true</code> &#65292;</li>
<li>&#19988;&#34920;&#36798;&#24335; <span class="t-c"><span class="mw-geshi cpp source-cpp">F<span class="br0">(</span><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="br0">(</span>t<span class="br0">)</span><span class="br0">)</span></span></span> &#65288;&#20196; <code>F</code> &#20026;&#19978;&#36848;&#34394;&#26500;&#20989;&#25968;&#30340;&#37325;&#36733;&#38598;&#65289;&#20026;&#33391;&#26500;&#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#12290;</li>
</ul>
</li>
<li>&#33509; <code>T_j</code> &#30340;&#34987;&#36873;&#25321;&#26500;&#36896;&#20989;&#25968;&#20026; constexpr &#26500;&#36896;&#20989;&#25968;&#65292;&#21017;&#27492;&#26500;&#36896;&#20989;&#25968;&#20026; constexpr &#26500;&#36896;&#20989;&#25968;&#12290;</li>
</ul>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="cpp source-cpp">
<pre class="de1"><a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</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> v<span class="br0">(</span><span class="st0">&quot;abc&quot;</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK</span>
<a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</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>, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span> w<span class="br0">(</span><span class="st0">&quot;abc&quot;</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// &#35884;&#26500;</span>
<a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</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="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span><span class="sy1">&gt;</span> x<span class="br0">(</span><span class="st0">&quot;abc&quot;</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK &#65306;&#36873;&#25321; const char*</span>
<a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</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="kw4">bool</span><span class="sy1">&gt;</span> y<span class="br0">(</span><span class="st0">&quot;abc&quot;</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// OK &#65306;&#36873;&#25321; string &#65307; bool &#19981;&#26159;&#20505;&#36873;</span>
<a href="cpp-utility-variant.html"><span class="kw1085">std::<span class="me2">variant</span></span></a><span class="sy1">&lt;</span><span class="kw4">float</span>, <span class="kw4">long</span>, <span class="kw4">double</span><span class="sy1">&gt;</span> z <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> <span class="co1">// OK &#65306;&#20445;&#26377; long</span>
<span class="co1">// float &#19982; double &#19981;&#26159;&#20505;&#36873;</span></pre></div>
</div>
</div>
<div class="t-li1"><span class="t-li">5)</span> &#26500;&#36896;&#19968;&#20010;&#26377;&#25351;&#23450;&#21487;&#36873;&#39033;&#31867;&#22411; <code>T</code> &#30340; <code>variant</code> &#24182;&#20197;&#21442;&#25968; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1">&lt;</span>Args<span class="sy1">&gt;</span><span class="br0">(</span>args<span class="br0">)</span>...</span></span> &#21021;&#22987;&#21270;&#25152;&#21547;&#20540;&#12290;
<ul>
<li>&#33509; <code>T</code> &#30340;&#34987;&#36873;&#25321;&#26500;&#36896;&#20989;&#25968;&#26159; constexpr &#26500;&#36896;&#20989;&#25968;&#65292;&#21017;&#27492;&#26500;&#36896;&#20989;&#25968;&#20134;&#20026; constexpr &#26500;&#36896;&#20989;&#25968;&#12290;</li>
<li>&#27492;&#37325;&#36733;&#20165;&#33509; <code>Types...</code> &#20013;&#27491;&#22909;&#20986;&#29616;&#19968;&#27425; <code>T</code> &#19988; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_constructible.html"><span class="kw521">std::<span class="me2">is_constructible_v</span></span></a><span class="sy1">&lt;</span>T, Args...<span class="sy1">&gt;</span></span></span> &#20026; <code>true</code> &#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#12290;</li>
</ul>
</div>
<div class="t-li1"><span class="t-li">6)</span> &#26500;&#36896;&#19968;&#20010;&#26377;&#25351;&#23450;&#21487;&#36873;&#39033;&#31867;&#22411; <code>T</code> &#30340; <code>variant</code> &#24182;&#20197;&#21442;&#25968; <span class="t-c"><span class="mw-geshi cpp source-cpp">il, <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1">&lt;</span>Args<span class="sy1">&gt;</span><span class="br0">(</span>args<span class="br0">)</span>...</span></span> &#21021;&#22987;&#21270;&#25152;&#21547;&#20540;&#12290;
<ul>
<li>&#33509; <code>T</code> &#30340;&#34987;&#36873;&#25321;&#26500;&#36896;&#20989;&#25968;&#26159; constexpr &#26500;&#36896;&#20989;&#25968;&#65292;&#21017;&#27492;&#26500;&#36896;&#20989;&#25968;&#20134;&#20026; constexpr &#26500;&#36896;&#20989;&#25968;&#12290;</li>
<li>&#27492;&#37325;&#36733;&#20165;&#33509; <code>Types...</code> &#20013;&#27491;&#22909;&#20986;&#29616;&#19968;&#27425; <code>T</code> &#19988; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_constructible.html"><span class="kw521">std::<span class="me2">is_constructible_v</span></span></a><span class="sy1">&lt;</span>T, initializer_list<span class="sy1">&lt;</span>U<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, Args...<span class="sy1">&gt;</span></span></span> &#20026; <code>true</code> &#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#12290;</li>
</ul>
</div>
<div class="t-li1"><span class="t-li">7)</span> &#26500;&#36896;&#19968;&#20010;&#26377;&#19979;&#26631; <code>I</code> &#25152;&#25351;&#23450;&#30340;&#21487;&#36873;&#39033;&#31867;&#22411; {{tt|T_i} }&#30340; <code>variant</code> &#24182;&#20197;&#21442;&#25968;<span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1">&lt;</span>Args<span class="sy1">&gt;</span><span class="br0">(</span>args<span class="br0">)</span>...</span></span> &#21021;&#22987;&#21270;&#25152;&#21547;&#20540;&#12290;
<ul>
<li>&#33509; <code>T_i</code> &#30340;&#34987;&#36873;&#25321;&#26500;&#36896;&#20989;&#25968;&#26159; constexpr &#26500;&#36896;&#20989;&#25968;&#65292;&#21017;&#27492;&#26500;&#36896;&#20989;&#25968;&#20134;&#20026; constexpr &#26500;&#36896;&#20989;&#25968;&#12290;</li>
<li>&#27492;&#37325;&#36733;&#20165;&#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp">I <span class="sy1">&lt;</span> sizeof...<span class="br0">(</span>Types<span class="br0">)</span></span></span> &#19982; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_constructible.html"><span class="kw521">std::<span class="me2">is_constructible_v</span></span></a><span class="sy1">&lt;</span>T_i, Args...<span class="sy1">&gt;</span></span></span> &#30342;&#20026; <code>true</code> &#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#12290;</li>
</ul>
</div>
<div class="t-li1"><span class="t-li">8)</span> &#26500;&#36896;&#19968;&#20010;&#26377;&#19979;&#26631; <code>I</code> &#25152;&#25351;&#23450;&#30340;&#21487;&#36873;&#39033;&#31867;&#22411; <code>T_i</code> &#30340; <code>variant</code> &#24182;&#20197;&#21442;&#25968; <span class="t-c"><span class="mw-geshi cpp source-cpp">il, <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1">&lt;</span>Args<span class="sy1">&gt;</span><span class="br0">(</span>args<span class="br0">)</span>...</span></span> &#21021;&#22987;&#21270;&#25152;&#21547;&#20540;&#12290;
<ul>
<li>&#33509; <code>T_i</code> &#30340;&#34987;&#36873;&#25321;&#26500;&#36896;&#20989;&#25968;&#26159; constexpr &#26500;&#36896;&#20989;&#25968;&#65292;&#21017;&#27492;&#26500;&#36896;&#20989;&#25968;&#20134;&#20026; constexpr &#26500;&#36896;&#20989;&#25968;&#12290;</li>
<li>&#27492;&#37325;&#36733;&#20165;&#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp">I <span class="sy1">&lt;</span> sizeof...<span class="br0">(</span>Types<span class="br0">)</span></span></span> &#19982; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-is_constructible.html"><span class="kw521">std::<span class="me2">is_constructible_v</span></span></a><span class="sy1">&lt;</span>T_i, <a href="cpp-utility-initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1">&lt;</span>U<span class="sy1">&gt;</span><span class="sy3">&amp;</span>, Args...<span class="sy1">&gt;</span></span></span> &#30342;&#20026; <code>true</code> &#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#12290;</li>
</ul>
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
<table class="t-par-begin">
<tr class="t-par">
<td>other</td>
<td>-</td>
<td>&#21478;&#19968;&#20010;&#35201;&#22797;&#21046;/&#31227;&#21160;&#20854;&#25152;&#21547;&#20540;&#30340; <code>variant</code> &#23545;&#35937;</td>
</tr>
<tr class="t-par">
<td>t</td>
<td>-</td>
<td>&#29992;&#20197;&#21021;&#22987;&#21270;&#34987;&#25152;&#21547;&#20540;&#30340;&#20540;</td>
</tr>
<tr class="t-par">
<td>args...</td>
<td>-</td>
<td>&#29992;&#20197;&#21021;&#22987;&#21270;&#34987;&#25152;&#21547;&#20540;&#30340;&#21442;&#25968;</td>
</tr>
<tr class="t-par">
<td>il</td>
<td>-</td>
<td>&#29992;&#20197;&#21021;&#22987;&#21270;&#34987;&#25152;&#21547;&#20540;&#30340;&#21021;&#22987;&#21270;&#22120;&#21015;&#34920;</td>
</tr>
<tr class="t-par">
<td>a</td>
<td>-</td>
<td>&#20256;&#36882;&#32473;&#34987;&#25152;&#21547;&#20540;&#30340;&#20998;&#37197;&#22120;</td>
</tr>
</table>
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">&#24322;&#24120;</span></h3>
<div class="t-li1"><span class="t-li">1)</span> &#21487;&#33021;&#25243;&#20986;&#39318;&#20010;&#21487;&#36873;&#39033;&#30340;&#20540;&#21021;&#22987;&#21270;&#25152;&#25243;&#30340;&#20219;&#20309;&#24322;&#24120;&#12290;
<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><a href="cpp-types-is_default_constructible.html"><span class="kw531">std::<span class="me2">is_nothrow_default_constructible_v</span></span></a><span class="sy1">&lt;</span>T_0<span class="sy1">&gt;</span><span class="br0">)</span></span></span></div>
</div>
</div>
<div class="t-li1"><span class="t-li">2)</span> &#21487;&#33021;&#25243;&#20986;&#30452;&#25509;&#21021;&#22987;&#21270;&#20219;&#20309; <code>Types...</code> &#20013;&#30340; <code>T_i</code> &#25152;&#25243;&#30340;&#20219;&#20309;&#24322;&#24120;&#12290;</div>
<div class="t-li1"><span class="t-li">3)</span> &#21487;&#33021;&#25243;&#20986;&#31227;&#21160;&#26500;&#36896;&#20219;&#20309; <code>Types...</code> &#20013;&#30340; <code>T_i</code> &#25152;&#25243;&#30340;&#20219;&#20309;&#24322;&#24120;&#12290;
<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="br0">(</span><a href="cpp-types-is_move_constructible.html"><span class="kw543">std::<span class="me2">is_nothrow_move_constructible_v</span></span></a><span class="sy1">&lt;</span>Types<span class="sy1">&gt;</span> <span class="sy3">&amp;&amp;</span> ...<span class="br0">)</span><span class="br0">)</span></span></span></div>
</div>
</div>
<div class="t-li1"><span class="t-li">4)</span> &#21487;&#33021;&#25243;&#20986;&#21021;&#22987;&#21270;&#25152;&#36873;&#21487;&#36873;&#39033;<code>T_j</code>&#25152;&#25243;&#30340;&#20219;&#20309;&#24322;&#24120;&#12290;
<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><a href="cpp-types-is_constructible.html"><span class="kw525">std::<span class="me2">is_nothrow_constructible_v</span></span></a><span class="sy1">&lt;</span>T_j, T<span class="sy1">&gt;</span><span class="br0">)</span></span></span></div>
</div>
</div>
<div class="t-li1"><span class="t-li">5-8)</span> &#21487;&#33021;&#25243;&#20986;&#35843;&#29992;&#25152;&#36873;&#21487;&#36873;&#39033;&#30340;&#25152;&#36873;&#26500;&#36896;&#20989;&#25968;&#25152;&#25243;&#30340;&#20219;&#20309;&#24322;&#24120;&#12290;</div>
<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>
<table class="dsctable" style="font-size:0.8em">
<tr>
<th>DR</th>
<th>&#24212;&#29992;&#20110;</th>
<th>&#20986;&#29256;&#26102;&#30340;&#34892;&#20026;</th>
<th>&#27491;&#30830;&#34892;&#20026;</th>
</tr>
<tr>
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2901">LWG 2901</a></td>
<td>C++17</td>
<td>&#25552;&#20379;&#20855;&#20998;&#37197;&#22120;&#26500;&#36896;&#20989;&#25968;&#20294; <code>variant</code> &#19981;&#33021;&#27491;&#30830;&#25903;&#25345;&#20998;&#37197;&#22120;</td>
<td>&#31227;&#38500;&#26500;&#36896;&#20989;&#25968;</td>
</tr>
<tr>
<td><a rel="nofollow" class="external text" href="https://wg21.link/p0739r0">P0739R0</a></td>
<td>C++17</td>
<td>&#36716;&#25442;&#26500;&#36896;&#20989;&#25968;&#27169;&#26495;&#19982;&#31867;&#27169;&#26495;&#23454;&#21442;&#25512;&#23548;&#20132;&#20114;&#22256;&#38590;</td>
<td>&#28155;&#21152;&#20102;&#21046;&#32422;</td>
</tr>
<tr>
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3024">LWG 3024</a></td>
<td>C++17</td>
<td>&#33509;&#20219;&#20309;&#25104;&#21592;&#31867;&#22411;&#38750;&#21487;&#22797;&#21046;&#65292;&#21017;&#22797;&#21046;&#26500;&#36896;&#20989;&#25968;&#19981;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;</td>
<td>&#25913;&#20026;&#23450;&#20041;&#20026;&#34987;&#21024;&#38500;</td>
</tr>
<tr>
<td><a rel="nofollow" class="external text" href="https://wg21.link/P0602R4">P0602R4</a></td>
<td>C++17</td>
<td>&#21363;&#20351;&#24213;&#23618;&#26500;&#36896;&#20989;&#25968;&#24179;&#20961;&#65292;&#22797;&#21046;/&#31227;&#21160;&#26500;&#36896;&#20989;&#25968;&#20134;&#21487;&#20026;&#38750;&#24179;&#20961;</td>
<td>&#35201;&#27714;&#20256;&#25773;&#24179;&#20961;&#24615;</td>
</tr>
<tr>
<td><a rel="nofollow" class="external text" href="https://wg21.link/P0608R3">P0608R3</a></td>
<td>C++17</td>
<td>&#36716;&#25442;&#26500;&#36896;&#20989;&#25968;&#30450;&#30446;&#22320;&#32452;&#25104;&#37325;&#36733;&#38598;&#65292;&#23548;&#33268;&#19981;&#24819;&#35201;&#30340;&#36716;&#25442;</td>
<td>&#19981;&#32771;&#34385;&#31364;&#21270;&#19982;&#24067;&#23572;&#36716;&#25442;</td>
</tr>
</table>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
<tr>
<td class="mbox-empty-cell"></td>
<td class="mbox-text" style="">&#26412;&#33410;&#26410;&#23436;&#25104;<br />
&#21407;&#22240;&#65306;&#26242;&#26080;&#31034;&#20363;</td>
</tr>
</table>
</div>
<div class="visualClear"></div>
</div>
</div>
</div>
</body>
</html>
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