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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::common_iterator&lt;I,S&gt;::</span>operator*,-&gt;</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-iterator.html">iterator</a>&lrm; | <a href="cpp-iterator-common_iterator.html">common iterator</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> decltype<span class="br0">(</span><span class="kw4">auto</span><span class="br0">)</span> operator<span class="sy2">*</span><span class="br0">(</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-cxx20">(C++20 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> decltype<span class="br0">(</span><span class="kw4">auto</span><span class="br0">)</span> operator<span class="sy2">*</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><br />
&nbsp; &nbsp; requires <span class="coMULTI">/*dereferenceable*/</span><span class="sy1">&lt;</span><span class="kw4">const</span> I<span class="sy1">&gt;</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> decltype<span class="br0">(</span><span class="kw4">auto</span><span class="br0">)</span> operator<span class="sy2">-</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><br />
&nbsp; &nbsp; requires <span class="coMULTI">/* see description */</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<div>&#36741;&#21161;&#31867;&#22411;</div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> <span class="coMULTI">/*proxy*/</span> <span class="br0">{</span> &nbsp; &nbsp;<span class="co1">// &#20165;&#29992;&#20110;&#38416;&#37322;</span><br /></span>
<p>&nbsp; &nbsp; std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span> keep_<span class="sy4">;</span><br />
&nbsp; &nbsp; <span class="kw4">constexpr</span> proxy<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span><span class="sy3">&amp;&amp;</span> x<span class="br0">)</span><br />
&nbsp; &nbsp; &nbsp; <span class="sy4">:</span> keep_<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>x<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span><br />
<span class="kw1">public</span><span class="sy4">:</span><br />
&nbsp; &nbsp; <span class="kw4">constexpr</span> <span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span><span class="sy2">*</span> operator<span class="sy2">-</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span> <span class="br0">{</span><br />
&nbsp; &nbsp; &nbsp; &nbsp; <span class="kw1">return</span> <a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>keep_<span class="br0">)</span><span class="sy4">;</span><br />
&nbsp; &nbsp; <span class="br0">}</span><br /></p>
<span class="br0">}</span><span class="sy4">;</span></div>
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<td>(4)</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<p>&#36820;&#22238;&#25351;&#21521;&#24403;&#21069;&#20803;&#32032;&#30340;&#25351;&#38024;&#25110;&#24341;&#29992;&#65292;&#25110;&#20445;&#26377;&#23427;&#30340;&#20195;&#29702;&#12290;</p>
<p>&#33509;&#24213;&#23618; <span class="t-lc"><a href="cpp-utility-variant.html">std::variant</a></span> &#25104;&#21592;&#23545;&#35937; <code><i>var</i></code> &#19981;&#20445;&#26377; <code>I</code> &#31867;&#22411;&#23545;&#35937;&#65292;&#21363; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-variant-holds_alternative.html"><span class="kw1087">std::<span class="me2">holds_alternative</span></span></a><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span><span class="br0">(</span>var<span class="br0">)</span></span></span> &#31561;&#20110; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> &#21017;&#34892;&#20026;&#26410;&#23450;&#20041;&#12290;</p>
<p>&#20196; <code>it</code> &#20195;&#34920; <code><i>var</i></code> &#25152;&#20445;&#26377;&#30340; <code>I</code> &#31867;&#22411;&#36845;&#20195;&#22120;&#65292;&#21363; <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>I<span class="sy1">&gt;</span><span class="br0">(</span>var<span class="br0">)</span></span></span> &#12290;</p>
<div class="t-li1"><span class="t-li">1-2)</span> &#36820;&#22238;&#35299;&#24341;&#29992; <code>it</code> &#30340;&#32467;&#26524;&#12290;</div>
<div class="t-li1"><span class="t-li">3)</span> &#36820;&#22238;&#25351;&#21521;&#24403;&#21069;&#20803;&#32032;&#30340;&#25351;&#38024;&#25110;&#24213;&#23618;&#36845;&#20195;&#22120;&#65292;&#25110;&#20445;&#26377;&#23427;&#30340;&#20195;&#29702;&#65306;
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<li>&#31561;&#20215;&#20110; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> it<span class="sy4">;</span></span></span> &#65292;&#33509; <code>I</code> &#20026;&#25351;&#38024;&#31867;&#22411;&#25110;&#33509;&#34920;&#36798;&#24335; <span class="t-c"><span class="mw-geshi cpp source-cpp">it.<span class="me1">operator</span><span class="sy2">-</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span></span></span> &#20026;&#33391;&#26500;&#65292;</li>
<li>&#21542;&#21017;&#31561;&#20215;&#20110; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">auto</span><span class="sy3">&amp;&amp;</span> tmp <span class="sy1">=</span> <span class="sy2">*</span>it<span class="sy4">;</span> <span class="kw1">return</span> <a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>tmp<span class="br0">)</span><span class="sy4">;</span></span></span> &#65292;&#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span></span></span> &#20026;&#24341;&#29992;&#31867;&#22411;&#65292;</li>
<li>&#21542;&#21017;&#31561;&#20215;&#20110; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> proxy<span class="br0">(</span><span class="sy2">*</span>it<span class="br0">)</span><span class="sy4">;</span></span></span> &#65292;&#20854;&#20013; <code><i>proxy</i></code> &#20026;&#20165;&#29992;&#20110;&#38416;&#37322;&#30340;&#31867; <span class="t-v">(4)</span> &#12290;</li>
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<div class="t-li1"><span class="t-li"></span> <code>requires</code> &#23376;&#21477;&#20013;&#30340;&#34920;&#36798;&#24335;&#31561;&#20215;&#20110;<br />
<span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">indirectly_readable</span><span class="sy1">&lt;</span><span class="kw4">const</span> I<span class="sy1">&gt;</span> <span class="sy3">&amp;&amp;</span> <span class="br0">(</span><br /></span></span>
<p>&nbsp; &nbsp; requires<span class="br0">(</span><span class="kw4">const</span> I<span class="sy3">&amp;</span> i<span class="br0">)</span> <span class="br0">{</span> i.<span class="me1">operator</span><span class="sy2">-</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span> <span class="sy3">||</span><br />
&nbsp; &nbsp; <a href="cpp-types-is_reference.html"><span class="kw481">std::<span class="me2">is_reference_v</span></span></a><span class="sy1">&lt;</span>std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;&gt;</span> <span class="sy3">||</span><br />
&nbsp; &nbsp; std<span class="sy4">::</span><span class="me2">constructible_from</span><span class="sy1">&lt;</span>std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span>, std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;&gt;</span><br /></p>
<span class="br0">)</span>.</div>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
<p>&#65288;&#26080;&#65289;</p>
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<div class="t-li1"><span class="t-li">1-2)</span> &#21040;&#24403;&#21069;&#20803;&#32032;&#30340;&#24341;&#29992;&#25110;&#32431;&#21491;&#20540;&#20020;&#26102;&#37327;&#12290;&#31561;&#20215;&#20110; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>it</span></span> &#12290;</div>
<div class="t-li1"><span class="t-li">3)</span> &#21069;&#36848;&#30340;&#25351;&#21521;&#24403;&#21069;&#20803;&#32032;&#30340;&#25351;&#38024;&#25110;&#36845;&#20195;&#22120;&#65292;&#25110;&#20445;&#26377;&#23427;&#30340;&#20195;&#29702;&#12290;</div>
<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;algorithm&gt;</span>
<span class="co2">#include &lt;complex&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;iterator&gt;</span>
<span class="co2">#include &lt;initializer_list&gt;</span>
<span class="kw1">using</span> std<span class="sy4">::</span><span class="me2">complex_literals</span><span class="sy4">::</span><span class="me2">operator</span><span class="st0">&quot;&quot;</span>i<span class="sy4">;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
<span class="kw4">const</span> <span class="kw4">auto</span> il <span class="sy1">=</span> <span class="br0">{</span>1i,<span class="nu16">3.14</span><span class="sy2">+</span>2i,3i,4i,5i<span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">using</span> CI <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">common_iterator</span><span class="sy1">&lt;</span>
std<span class="sy4">::</span><span class="me2">counted_iterator</span><span class="sy1">&lt;</span>decltype<span class="br0">(</span>il<span class="br0">)</span><span class="sy4">::</span><span class="me2">iterator</span><span class="sy1">&gt;</span>,
std<span class="sy4">::</span><span class="me2">default_sentinel_t</span><span class="sy1">&gt;</span><span class="sy4">;</span>
CI ci <span class="br0">{</span> std<span class="sy4">::</span><span class="me2">counted_iterator</span><span class="br0">{</span>
<a href="cpp-iterator-next.html"><span class="kw674">std::<span class="me2">next</span></span></a><span class="br0">(</span>begin<span class="br0">(</span>il<span class="br0">)</span>, <span class="nu0">1</span><span class="br0">)</span>, ssize<span class="br0">(</span>il<span class="br0">)</span> <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="sy2">*</span>ci <span class="sy1">&lt;&lt;</span> <span class="st0">&#39; &#39;</span> <span class="sy1">&lt;&lt;</span> ci<span class="sy2">-</span><span class="sy1">&gt;</span>real<span class="br0">(</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></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">(3.14,2) 3.14</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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<tr>
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3574">LWG 3574</a></td>
<td>C++20</td>
<td><code>variant</code> &#20026;&#23436;&#20840; constexpr (P2231R1) &#20294; <code>common_iterator</code> &#19981;&#26159;</td>
<td>&#20134;&#20351;&#20043;&#20026; constexpr</td>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3595">LWG 3595</a></td>
<td>C++20</td>
<td>&#20195;&#29702;&#31867;&#22411;&#30340;&#20989;&#25968;&#32570;&#23569; constexpr &#19982; noexcept</td>
<td>&#24050;&#28155;&#21152;</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-iterator-common_iterator-common_iterator.html"><span class="t-lines"><span>(&#26500;&#36896;&#20989;&#25968;)</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
</div>
</td>
<td>&#26500;&#36896;&#26032;&#30340;&#36845;&#20195;&#22120;&#36866;&#37197;&#22120;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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