120 lines
13 KiB
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120 lines
13 KiB
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<title>std::experimental::make_array</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_experimental_make_array skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::experimental::</span>make_array</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-experimental.html">experimental</a></span></div>
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<div>定义于头文件 <code><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/header/experimental/array&action=edit&redlink=1" class="new" title="cpp/header/experimental/array（页面不存在）"><experimental/array></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">class</span> D <span class="sy1">=</span> <span class="kw4">void</span>, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span><br />
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<span class="kw4">constexpr</span> <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span>VT <span class="coMULTI">/* see below */</span>, sizeof...<span class="br0">(</span>Types<span class="br0">)</span><span class="sy1">></span> make_array<span class="br0">(</span>Types<span class="sy3">&&</span>... <span class="me1">t</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-libfund-ts-2 t-mark-ts">(库基础 TS v2)</span></td>
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<p>创建一个 <span class="t-lc"><a href="cpp-container-array.html">std::array</a></span> ，其大小等于参数数量，且其元素从对应参数初始化。返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span>VT, sizeof...<span class="br0">(</span>Types<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"><</span>Types<span class="sy1">></span><span class="br0">(</span>t<span class="br0">)</span>...<span class="br0">}</span></span></span></p>
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<p>若 <code>D</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> ，则推出的类型 <code>VT</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-common_type.html"><span class="kw636">std::<span class="me2">common_type_t</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span></span></span> 。否则，类型为 <code>D</code> 。</p>
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<p>若 <code>D</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> ，且 <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"><</span>Types<span class="sy1">></span>...</span></span> 中任意一者是 <span class="t-lc"><a href="cpp-utility-functional-reference_wrapper.html">std::reference_wrapper</a></span> 的特化，则程序为谬构。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p><code>make_array</code> 在库基础 TS v3 中被移除，因为 <code>std::array</code> 的<a href="cpp-container-array-deduction_guides.html">推导指引</a>与 <a href="cpp-container-array-to_array.html"><tt>std::to_array</tt></a> 已在 C++20 中。</p>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">可能的实现</span></h3>
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<div class="cpp source-cpp">
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<pre class="de1"><span class="kw1">namespace</span> details <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span><span class="sy1">></span> <span class="kw1">struct</span> is_ref_wrapper <span class="sy4">:</span> <a href="cpp-types-integral_constant.html"><span class="kw650">std::<span class="me2">false_type</span></span></a> <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span> <span class="kw1">struct</span> is_ref_wrapper<span class="sy1"><</span><a href="cpp-utility-functional-reference_wrapper.html"><span class="kw1068">std::<span class="me2">reference_wrapper</span></span></a><span class="sy1"><</span>T<span class="sy1">>></span> <span class="sy4">:</span> <a href="cpp-types-integral_constant.html"><span class="kw649">std::<span class="me2">true_type</span></span></a> <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span>
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<span class="kw1">using</span> not_ref_wrapper <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">experimental</span><span class="sy4">::</span><span class="me2">negation</span><span class="sy1"><</span>is_ref_wrapper<span class="sy1"><</span><a href="cpp-types-decay.html"><span class="kw629">std::<span class="me2">decay_t</span></span></a><span class="sy1"><</span>T<span class="sy1">>>></span><span class="sy4">;</span>
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<span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">class</span> D, <span class="kw1">class</span>...<span class="sy1">></span> <span class="kw1">struct</span> return_type_helper <span class="br0">{</span> <span class="kw1">using</span> type <span class="sy1">=</span> D<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw1">struct</span> return_type_helper<span class="sy1"><</span><span class="kw4">void</span>, Types...<span class="sy1">></span> <span class="sy4">:</span> <a href="cpp-types-common_type.html"><span class="kw635">std::<span class="me2">common_type</span></span></a><span class="sy1"><</span>Types...<span class="sy1">></span> <span class="br0">{</span>
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static_assert<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">experimental</span><span class="sy4">::</span><span class="me2">conjunction_v</span><span class="sy1"><</span>not_ref_wrapper<span class="sy1"><</span>Types<span class="sy1">></span>...<span class="sy1">></span>,
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<span class="st0">"Types cannot contain reference_wrappers when D is void"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">class</span> D, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw1">using</span> return_type <span class="sy1">=</span> <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span><span class="kw1">typename</span> return_type_helper<span class="sy1"><</span>D, Types...<span class="sy1">></span><span class="sy4">::</span><span class="me2">type</span>,
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sizeof...<span class="br0">(</span>Types<span class="br0">)</span><span class="sy1">></span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">template</span> <span class="sy1"><</span> <span class="kw1">class</span> D <span class="sy1">=</span> <span class="kw4">void</span>, <span class="kw1">class</span>... <span class="me1">Types</span><span class="sy1">></span>
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<span class="kw4">constexpr</span> details<span class="sy4">::</span><span class="me2">return_type</span><span class="sy1"><</span>D, Types...<span class="sy1">></span> make_array<span class="br0">(</span>Types<span class="sy3">&&</span>... <span class="me1">t</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">return</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"><</span>Types<span class="sy1">></span><span class="br0">(</span>t<span class="br0">)</span>... <span class="br0">}</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <experimental/array></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <type_traits></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">auto</span> arr <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">experimental</span><span class="sy4">::</span><span class="me2">make_array</span><span class="br0">(</span><span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">3</span>, <span class="nu0">4</span>, <span class="nu0">5</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">bool</span> is_array_of_5_ints <span class="sy1">=</span> <a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>decltype<span class="br0">(</span>arr<span class="br0">)</span>, <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <span class="nu0">5</span><span class="sy1">>></span><span class="sy4">::</span><span class="me2">value</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Returns an array of five ints? "</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-io-manip-boolalpha.html"><span class="kw1764">std::<span class="me2">boolalpha</span></span></a> <span class="sy1"><<</span> is_array_of_5_ints <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">Returns an array of five ints? true</pre></div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<div class="t-dsc-member-div">
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<div><a href="cpp-experimental-to_array.html"><span class="t-lines"><span>to_array</span></span></a></div>
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</div>
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</td>
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<td>从内建数组创建 <span class="t-lc"><a href="cpp-container-array.html">std::array</a></span> 对象<br />
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<span class="t-mark">(函数模板)</span></td>
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<div class="visualClear"></div>
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