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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ranges::view_interface&lt;D&gt;::</span>front</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-ranges.html">ranges</a>&lrm; | <a href="cpp-ranges-view_interface.html">view interface</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> front<span class="br0">(</span><span class="br0">)</span> requires ranges<span class="sy4">::</span><span class="me2">forward_range</span><span class="sy1">&lt;</span>D<span class="sy1">&gt;</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> front<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><br />
&nbsp; &nbsp; requires ranges<span class="sy4">::</span><span class="me2">forward_range</span><span class="sy1">&lt;</span><span class="kw4">const</span> D<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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<p><code>front</code> &#25104;&#21592;&#20989;&#25968;&#30340;&#40664;&#35748;&#23454;&#29616;&#36820;&#22238;&#27966;&#29983;&#31867;&#22411;&#30340;&#35270;&#22270;&#20013;&#30340;&#39318;&#20010;&#20803;&#32032;&#12290;&#20803;&#32032;&#26159;&#25353;&#20540;&#36824;&#26159;&#25353;&#24341;&#29992;&#36820;&#22238;&#21462;&#20915;&#20110;&#36845;&#20195;&#22120;&#31867;&#22411;&#30340; <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy2">*</span></span></span> &#12290;</p>
<div class="t-li1"><span class="t-li">1)</span> &#20196; <code>derived</code> &#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1">&lt;</span>D<span class="sy3">&amp;</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span></span></span> &#12290;&#31561;&#20215;&#20110; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <span class="sy2">*</span>ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>derived<span class="br0">)</span><span class="sy4">;</span></span></span> &#12290;&#33509; <a href="cpp-ranges-view_interface-empty.html"><code>empty()</code></a> &#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#65288;&#21363;&#36215;&#22987;&#36845;&#20195;&#22120;&#27604;&#36739;&#31561;&#20110;&#21736;&#20301;&#65289;&#21017;&#34892;&#20026;&#26410;&#23450;&#20041;&#65292;&#21363;&#20351;&#20197;&#21516;&#26679;&#26041;&#24335;&#33719;&#24471;&#30340;&#36845;&#20195;&#22120;&#21487;&#35299;&#24341;&#29992;&#12290;</div>
<div class="t-li1"><span class="t-li">2)</span> &#21516; <span class="t-v">(1)</span> &#65292;&#38500;&#20102; <code>derived</code> &#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1">&lt;</span><span class="kw4">const</span> D<span class="sy3">&amp;</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span></span></span> &#12290;</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>
<p>&#35270;&#22270;&#20013;&#30340;&#39318;&#20010;&#20803;&#32032;&#12290;</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">&#27880;&#35299;</span></h3>
<p>C++20 &#20013;&#65292;&#26631;&#20934;&#24211;&#26080;&#27966;&#29983;&#33258; <span class="t-lc">std::ranges::view_interface</span> &#30340;&#31867;&#22411;&#25552;&#20379;&#20854;&#33258;&#36523;&#30340; <code>front</code> &#25104;&#21592;&#20989;&#25968;&#12290;&#20960;&#20046;&#25152;&#26377;&#36825;&#20123;&#31867;&#22411;&#37117;&#20351;&#29992;&#40664;&#35748;&#23454;&#29616;&#12290;</p>
<p>&#19968;&#20010;&#20540;&#24471;&#27880;&#24847;&#30340;&#20363;&#22806;&#26159; <span class="t-lc">std::ranges::basic_istream_view</span> &#12290;&#30001;&#20110;&#23427;&#20915;&#19981;&#28385;&#36275; <a href="cpp-ranges-forward_range.html"><code>forward_range</code></a> &#65292;&#35813;&#35270;&#22270;&#26080;&#27861;&#20351;&#29992;&#32487;&#25215;&#30340; <code>front</code> &#12290;</p>
<p>&#32487;&#25215;&#30340; <code>front</code> &#25104;&#21592;&#20989;&#25968;&#23545; <span class="t-lc">std::ranges::empty_view</span> &#21487;&#29992;&#65292;&#20294;&#23545;&#23427;&#30340;&#35843;&#29992;&#22987;&#32456;&#23548;&#33268;&#26410;&#23450;&#20041;&#34892;&#20026;&#12290;</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
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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-begin.html"><span class="t-lines"><span>begin</span><span>cbegin</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx14">(C++14)</span></span></span></div>
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<td>&#36820;&#22238;&#25351;&#21521;&#23481;&#22120;&#25110;&#25968;&#32452;&#36215;&#22987;&#30340;&#36845;&#20195;&#22120;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
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<div><a href="cpp-ranges-begin.html"><span class="t-lines"><span>ranges::begin</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>&#36820;&#22238;&#25351;&#21521;&#33539;&#22260;&#36215;&#22987;&#30340;&#36845;&#20195;&#22120;<br />
<span class="t-mark">(&#23450;&#21046;&#28857;&#23545;&#35937;)</span></td>
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<div><a href="cpp-ranges-cbegin.html"><span class="t-lines"><span>ranges::cbegin</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>&#36820;&#22238;&#25351;&#21521;&#21482;&#35835;&#33539;&#22260;&#36215;&#22987;&#30340;&#36845;&#20195;&#22120;<br />
<span class="t-mark">(&#23450;&#21046;&#28857;&#23545;&#35937;)</span></td>
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