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125 lines
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<title>std::make_any</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>make_any</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</a>‎ | <a href="cpp-utility-any.html">any</a></span></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> T, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<a href="cpp-utility-any.html"><span class="kw1071">std::<span class="me2">any</span></span></a> make_any<span class="br0">(</span> Args<span class="sy3">&&</span>... <span class="me1">args</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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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> T, <span class="kw1">class</span> U, <span class="kw1">class</span>... <span class="me1">Args</span> <span class="sy1">></span><br />
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<a href="cpp-utility-any.html"><span class="kw1071">std::<span class="me2">any</span></span></a> make_any<span class="br0">(</span> <a href="cpp-utility-initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1"><</span>U<span class="sy1">></span> il, Args<span class="sy3">&&</span>... <span class="me1">args</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<p>构造含 <code>T</code> 类型对象的 <code>any</code> 对象，传递提供的参数给 <code>T</code> 的构造函数。</p>
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<div class="t-li1"><span class="t-li">1)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <a href="cpp-utility-any.html"><span class="kw1071">std::<span class="me2">any</span></span></a><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">in_place_type</span><span class="sy1"><</span>T<span class="sy1">></span>, <a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span>args<span class="br0">)</span>...<span class="br0">)</span><span class="sy4">;</span></span></span></div>
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<div class="t-li1"><span class="t-li">2)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <a href="cpp-utility-any.html"><span class="kw1071">std::<span class="me2">any</span></span></a><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">in_place_type</span><span class="sy1"><</span>T<span class="sy1">></span>, il, <a href="cpp-utility-forward.html"><span class="kw1116">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span>args<span class="br0">)</span>...<span class="br0">)</span><span class="sy4">;</span></span></span></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 <any></span>
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<span class="co2">#include <complex></span>
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<span class="co2">#include <functional></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <string></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> a0 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">make_any</span><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="st0">"Hello, std::any!<span class="es1">\n</span>"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">auto</span> a1 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">make_any</span><span class="sy1"><</span><a href="cpp-numeric-complex.html"><span class="kw1471">std::<span class="me2">complex</span></span></a><span class="sy1"><</span><span class="kw4">double</span><span class="sy1">>></span><span class="br0">(</span><span class="nu16">0.1</span>, <span class="nu16">2.3</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-utility-any-any_cast.html"><span class="kw1072">std::<span class="me2">any_cast</span></span></a><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span>a0<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <a href="cpp-utility-any-any_cast.html"><span class="kw1072">std::<span class="me2">any_cast</span></span></a><span class="sy1"><</span><a href="cpp-numeric-complex.html"><span class="kw1471">std::<span class="me2">complex</span></span></a><span class="sy1"><</span><span class="kw4">double</span><span class="sy1">></span><span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span>a1<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">using</span> lambda <span class="sy1">=</span> <a href="cpp-utility-functional-function.html"><span class="kw1059">std::<span class="me2">function</span></span></a><span class="sy1"><</span><span class="kw4">void</span><span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span><span class="sy1">></span><span class="sy4">;</span>
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<span class="co1">// 把 lambda 放入 std::any。尝试 #1 （失败）。</span>
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<a href="cpp-utility-any.html"><span class="kw1071">std::<span class="me2">any</span></span></a> a2 <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Lambda #1.<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"a2.type() = <span class="es1">\"</span>"</span> <span class="sy1"><<</span> a2.<span class="me1">type</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">name</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span><span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="co1">// any_cast 转型到 <void(void)> 但实际类型不是</span>
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<span class="co1">// std::function ……，而是 ~ main::{lambda()#1} ，且它对</span>
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<span class="co1">// 每个 lambda 唯一。所以这会抛出……</span>
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<span class="kw1">try</span> <span class="br0">{</span>
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<a href="cpp-utility-any-any_cast.html"><span class="kw1072">std::<span class="me2">any_cast</span></span></a><span class="sy1"><</span>lambda<span class="sy1">></span><span class="br0">(</span>a2<span class="br0">)</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">catch</span> <span class="br0">(</span><a href="cpp-utility-any-bad_any_cast.html"><span class="kw1073">std::<span class="me2">bad_any_cast</span></span></a> <span class="kw4">const</span><span class="sy3">&</span> ex<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> ex.<span class="me1">what</span><span class="br0">(</span><span class="br0">)</span> <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>
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<span class="co1">// 将 lambda 放入 std::any 中。尝试 #2 （成功）</span>
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<span class="kw4">auto</span> a3 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">make_any</span><span class="sy1"><</span>lambda<span class="sy1">></span><span class="br0">(</span><span class="br0">[</span><span class="br0">]</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Lambda #2.<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"a3.type() = <span class="es1">\"</span>"</span> <span class="sy1"><<</span> a3.<span class="me1">type</span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">name</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span><span class="es1">\n</span>"</span><span class="sy4">;</span>
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<a href="cpp-utility-any-any_cast.html"><span class="kw1072">std::<span class="me2">any_cast</span></span></a><span class="sy1"><</span>lambda<span class="sy1">></span><span class="br0">(</span>a3<span class="br0">)</span><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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</div>
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<p>可能的输出：</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">Hello, std::any!
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(0.1,2.3)
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a2.type() = "Z4mainEUlvE_"
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bad any_cast
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a3.type() = "St8functionIFvvEE"
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Lambda #2.</pre></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 t-dsc-member-nobold-div">
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<div><a href="cpp-utility-any-any.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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</div>
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</td>
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<td>构造 <code>any</code> 对象<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-any-any_cast.html"><span class="t-lines"><span>any_cast</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>对被容纳对象的类型安全访问<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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