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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>empty</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> <span class="kw4">bool</span> empty<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> <span class="kw4">bool</span> empty<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> 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>empty</code> &#25104;&#21592;&#20989;&#25968;&#30340;&#40664;&#35748;&#23454;&#29616;&#26816;&#26597;&#36215;&#22987;&#36845;&#20195;&#22120;&#19982;&#21736;&#20301;&#26159;&#21542;&#27604;&#36739;&#30456;&#31561;&#12290;</p>
<div class="t-li1"><span class="t-li">1)</span> &#20196; <code>derived</code> &#20026;&#32465;&#23450;&#21040; <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> &#30340;&#24341;&#29992;&#12290;&#31561;&#20215;&#20110; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>derived<span class="br0">)</span> <span class="sy1">==</span> ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>derived<span class="br0">)</span><span class="sy4">;</span></span></span> &#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>&#33509;&#27966;&#29983;&#31867;&#22411;&#23545;&#35937;&#30340;&#36215;&#22987;&#36845;&#20195;&#22120;&#19982;&#21736;&#20301;&#27604;&#36739;&#30456;&#31561;&#21017;&#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#65292;&#21542;&#21017;&#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> &#12290;</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">&#27880;&#35299;</span></h3>
<p>&#19979;&#21015;&#27966;&#29983;&#31867;&#22411;&#21487;&#20351;&#29992; <code>empty</code> &#30340;&#40664;&#35748;&#23454;&#29616;&#65306;</p>
<ul>
<li><span class="t-lc">std::ranges::common_view</span></li>
<li><span class="t-lc">std::ranges::drop_view</span></li>
<li><span class="t-lc">std::ranges::drop_while_view</span></li>
<li><span class="t-lc">std::ranges::elements_view</span></li>
<li><span class="t-lc">std::ranges::filter_view</span></li>
<li><span class="t-lc">std::ranges::iota_view</span></li>
<li><span class="t-lc">std::ranges::join_view</span></li>
<li><span class="t-lc">std::ranges::reverse_view</span></li>
<li><span class="t-lc">std::ranges::single_view</span></li>
<li><span class="t-lc">std::ranges::split_view</span></li>
<li><span class="t-lc">std::ranges::take_view</span></li>
<li><span class="t-lc">std::ranges::take_while_view</span></li>
<li><span class="t-lc">std::ranges::transform_view</span></li>
</ul>
<p>&#23613;&#31649; <span class="t-lc">std::ranges::basic_istream_view</span> &#32487;&#25215;&#33258; <span class="t-lc">std::ranges::view_interface</span> &#24182;&#19988;&#19981;&#22768;&#26126; <code>empty</code> &#25104;&#21592;&#20989;&#25968;&#65292;&#23427;&#20173;&#26080;&#27861;&#20351;&#29992;&#40664;&#35748;&#23454;&#29616;&#65292;&#22240;&#20026;&#23427;&#20915;&#19981;&#28385;&#36275; <span class="t-lc">std::ranges::forward_range</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;array&gt;</span>
<span class="co2">#include &lt;ranges&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
<span class="kw4">constexpr</span> <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a> a <span class="br0">{</span><span class="nu0">0</span>, <span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">3</span>, <span class="nu0">4</span><span class="br0">}</span><span class="sy4">;</span>
static_assert<span class="br0">(</span> <span class="sy3">!</span> std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">single_view</span><span class="br0">(</span>a<span class="br0">)</span>.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span>
static_assert<span class="br0">(</span> <span class="br0">(</span>a <span class="sy3">|</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">take</span><span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span><span class="br0">)</span>.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span>
static_assert<span class="br0">(</span> <span class="sy3">!</span> <span class="br0">(</span>a <span class="sy3">|</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">take</span><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span><span class="br0">)</span>.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span>
static_assert<span class="br0">(</span> <span class="br0">(</span>a <span class="sy3">|</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">drop</span><span class="br0">(</span><span class="nu0">9</span><span class="br0">)</span><span class="br0">)</span>.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span>
static_assert<span class="br0">(</span> <span class="sy3">!</span> <span class="br0">(</span>a <span class="sy3">|</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">drop</span><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span><span class="br0">)</span>.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span>
static_assert<span class="br0">(</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">iota</span><span class="br0">(</span><span class="nu0">0</span>,<span class="nu0">0</span><span class="br0">)</span>.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span>
static_assert<span class="br0">(</span> <span class="sy3">!</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">iota</span><span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span>.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
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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-empty.html"><span class="t-lines"><span>empty</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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<td>&#26816;&#26597;&#23481;&#22120;&#26159;&#21542;&#20026;&#31354;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
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<div><a href="cpp-ranges-empty.html"><span class="t-lines"><span>ranges::empty</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>&#26816;&#26597;&#33539;&#22260;&#26159;&#21542;&#20026;&#31354;<br />
<span class="t-mark">(&#23450;&#21046;&#28857;&#23545;&#35937;)</span></td>
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