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<title>std::optional&lt;T&gt;::operator-&gt;, std::optional&lt;T&gt;::operator*</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::optional&lt;T&gt;::</span>operator-&gt;, <span style="font-size:0.7em; line-height:130%">std::optional&lt;T&gt;::</span>operator*</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><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">const</span> T<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="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> T<span class="sy2">*</span> operator<span class="sy2">-</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</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> <span class="kw4">const</span> T<span class="sy3">&amp;</span> operator<span class="sy2">*</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy3">&amp;</span> <span class="kw1">noexcept</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> T<span class="sy3">&amp;</span> operator<span class="sy2">*</span><span class="br0">(</span><span class="br0">)</span> <span class="sy3">&amp;</span> <span class="kw1">noexcept</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> <span class="kw4">const</span> T<span class="sy3">&amp;&amp;</span> operator<span class="sy2">*</span><span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy3">&amp;&amp;</span> <span class="kw1">noexcept</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> T<span class="sy3">&amp;&amp;</span> operator<span class="sy2">*</span><span class="br0">(</span><span class="br0">)</span> <span class="sy3">&amp;&amp;</span> <span class="kw1">noexcept</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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<p>&#35775;&#38382;&#25152;&#21547;&#20540;&#12290;</p>
<div class="t-li1"><span class="t-li">1)</span> &#36820;&#22238;&#25351;&#21521;&#25152;&#21547;&#20540;&#30340;&#25351;&#38024;&#12290;</div>
<div class="t-li1"><span class="t-li">2)</span> &#36820;&#22238;&#21040;&#25152;&#21547;&#20540;&#30340;&#24341;&#29992;&#12290;</div>
<p>&#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> &#19981;&#21547;&#20540;&#21017;&#34892;&#20026;&#26410;&#23450;&#20041;&#12290;</p>
<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>
<p>&#25351;&#21521;&#25152;&#21547;&#20540;&#30340;&#25351;&#38024;&#25110;&#21040;&#23427;&#30340;&#24341;&#29992;&#12290;</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">&#27880;&#35299;</span></h3>
<p>&#27492;&#36816;&#31639;&#31526;&#19981;&#26816;&#26597; <code>optional</code> &#26159;&#21542;&#21547;&#20540;&#65281;&#20320;&#33021;&#25163;&#21160;&#29992; <span class="t-lc"><a href="cpp-utility-optional-operator_bool.html">has_value()</a></span> &#25110;&#31616;&#21333;&#22320;&#29992; <span class="t-lc"><a href="cpp-utility-optional-operator_bool.html">operator bool()</a></span> &#20570;&#26816;&#26597;&#12290;&#21478;&#22806;&#65292;&#33509;&#38656;&#35201;&#26377;&#26816;&#26597;&#35775;&#38382;&#65292;&#21487;&#20351;&#29992; <span class="t-lc"><a href="cpp-utility-optional-value.html">value()</a></span> &#25110; <span class="t-lc"><a href="cpp-utility-optional-value_or.html">value_or()</a></span> &#12290;</p>
<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;optional&gt;</span>
<span class="co2">#include &lt;iostream&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>
<span class="kw1">using</span> <span class="kw1">namespace</span> std<span class="sy4">::</span><span class="me2">string_literals</span><span class="sy4">;</span>
<a href="cpp-utility-optional.html"><span class="kw1075">std::<span class="me2">optional</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span> opt1 <span class="sy1">=</span> <span class="nu0">1</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="st0">&quot;opt1: &quot;</span> <span class="sy1">&lt;&lt;</span> <span class="sy2">*</span>opt1 <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="sy2">*</span>opt1 <span class="sy1">=</span> <span class="nu0">2</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="st0">&quot;opt1: &quot;</span> <span class="sy1">&lt;&lt;</span> <span class="sy2">*</span>opt1 <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</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> opt2 <span class="sy1">=</span> <span class="st0">&quot;abc&quot;</span>s<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="st0">&quot;opt2: &quot;</span> <span class="sy1">&lt;&lt;</span> <span class="sy2">*</span>opt2 <span class="sy1">&lt;&lt;</span> <span class="st0">&quot; size: &quot;</span> <span class="sy1">&lt;&lt;</span> opt2<span class="sy2">-</span><span class="sy1">&gt;</span>size<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="co1">// &#20320;&#33021;&#36890;&#36807;&#22312;&#21040; optional &#30340;&#21491;&#20540;&#19978;&#35843;&#29992; operator* &ldquo;&#21462;&rdquo;&#20854;&#25152;&#21547;&#20540;</span>
<span class="kw4">auto</span> taken <span class="sy1">=</span> <span class="sy2">*</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>opt2<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="st0">&quot;taken: &quot;</span> <span class="sy1">&lt;&lt;</span> taken <span class="sy1">&lt;&lt;</span> <span class="st0">&quot; opt2: &quot;</span> <span class="sy1">&lt;&lt;</span> <span class="sy2">*</span>opt2 <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;size: &quot;</span> <span class="sy1">&lt;&lt;</span> opt2<span class="sy2">-</span><span class="sy1">&gt;</span>size<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>&#21487;&#33021;&#30340;&#36755;&#20986;&#65306;</p>
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<pre class="de1">opt1: 1
opt1: 2
opt2: abc size: 3
taken: abc opt2: size: 0</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>
</tr>
<tr>
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2762">LWG 2762</a></td>
<td>C++17</td>
<td><code>operator-&gt;</code> &#19982; <code>operator*</code> &#21487;&#33021;&#20026;&#28508;&#22312;&#25243;&#20986;</td>
<td>&#20351;&#20043;&#20026; noexcept</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-value.html"><span class="t-lines"><span>value</span></span></a></div>
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<td>&#36820;&#22238;&#25152;&#21547;&#20540;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div class="t-dsc-member-div">
<div><a href="cpp-utility-optional-value_or.html"><span class="t-lines"><span>value_or</span></span></a></div>
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</td>
<td>&#33509;&#25152;&#21547;&#20540;&#21487;&#29992;&#21017;&#36820;&#22238;&#23427;&#65292;&#21542;&#21017;&#36820;&#22238;&#21478;&#19968;&#20010;&#20540;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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