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<div class="identifier-type">concept</div><div class="header"><iterator></div><h1 itemprop="name"><span class="namespace" title="namespace std">std::</span><span class="token">indirectly_writable</span><span class="cpp cpp20" title="C++20で追加">(C++20)</span></h1>
<div itemprop="articleBody"><p><div class="codehilite"><pre><span></span><code><span class="k">namespace</span><span class="w"> </span><span class="nn">std</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">template</span><span class="o"><</span><span class="k">class</span><span class="w"> </span><span class="nc">Out</span><span class="p">,</span><span class="w"> </span><span class="k">class</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="w"> </span><span class="k">concept</span><span class="w"> </span><span class="nc">indirectly_writable</span><span class="w"> </span><span class="o">=</span><span class="w"> </span>
<span class="w"> </span><span class="k">requires</span><span class="p">(</span><span class="n">Out</span><span class="o">&&</span><span class="w"> </span><span class="n">o</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="o">&&</span><span class="w"> </span><span class="n">t</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="o">*</span><span class="n">o</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../utility/forward.html">std::forward</a></span><span class="o"><</span><span class="n">T</span><span class="o">></span><span class="p">(</span><span class="n">t</span><span class="p">);</span>
<span class="w"> </span><span class="o">*</span><span class="n"><a href="../utility/forward.html">std::forward</a></span><span class="o"><</span><span class="n">Out</span><span class="o">></span><span class="p">(</span><span class="n">o</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../utility/forward.html">std::forward</a></span><span class="o"><</span><span class="n">T</span><span class="o">></span><span class="p">(</span><span class="n">t</span><span class="p">);</span>
<span class="w"> </span><span class="k">const_cast</span><span class="o"><</span><span class="k">const</span><span class="w"> </span><span class="n"><a href="iter_reference_t.html">iter_reference_t</a></span><span class="o"><</span><span class="n">Out</span><span class="o">>&&></span><span class="p">(</span><span class="o">*</span><span class="n">o</span><span class="p">)</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../utility/forward.html">std::forward</a></span><span class="o"><</span><span class="n">T</span><span class="o">></span><span class="p">(</span><span class="n">t</span><span class="p">);</span>
<span class="w"> </span><span class="k">const_cast</span><span class="o"><</span><span class="k">const</span><span class="w"> </span><span class="n"><a href="iter_reference_t.html">iter_reference_t</a></span><span class="o"><</span><span class="n">Out</span><span class="o">>&&></span><span class="p">(</span><span class="o">*</span><span class="n"><a href="../utility/forward.html">std::forward</a></span><span class="o"><</span><span class="n">Out</span><span class="o">></span><span class="p">(</span><span class="n">o</span><span class="p">))</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n"><a href="../utility/forward.html">std::forward</a></span><span class="o"><</span><span class="n">T</span><span class="o">></span><span class="p">(</span><span class="n">t</span><span class="p">);</span>
<span class="w"> </span><span class="p">};</span>
<span class="p">}</span>
</code></pre></div>
</p>
<h2>概要</h2>
<p><code>indirectly_writable</code>は、任意の型<code>Out</code>が間接参照演算子(<code>operator*</code>)によって型<code>T</code>の値を書き込み(出力)可能であることを表すコンセプトである。</p>
<p>イテレータ型に限らず、ポインタ型、スマートポインタ型などがこのコンセプトのモデルとなることができる。</p>
<h2>要件</h2>
<p>このコンセプトを構成する4つの制約式は全て、<a href="../concepts.html">等しさを保持</a>することを要求しない。</p>
<h3>制約式について</h3>
<p><code>const_cast</code>を用いる制約式は、非プロキシオブジェクト(値を所有するオブジェクトのことである。<code><a href="../string/basic_string.html">std::string</a></code>などが該当)を弾くために存在する。</p>
<p>まず前提として、非プロキシオブジェクトは<a href="../../lang/cpp11/ref_qualifier_for_this.html">メンバ関数の左辺値/右辺値修飾</a>が追加される以前からの慣習により、<em>prvalue</em>であっても代入が可能である。また、値を所有するために<code>const</code>が付与されれば代入は不可能となる。</p>
<p><div class="yata" id="1ab48aa79fe4cd0db783d1cbc6183d2c4a0e42ce"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../string.html"><string></a></span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span><span class="w"> </span>
<span class="w"> </span><span class="n"><a href="../string/basic_string.html">std::string</a></span><span class="p">()</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"string"</span><span class="p">;</span><span class="w"> </span><span class="c1">// prvalueに代入</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<p>このような非プロキシオブジェクトの<em>prvalue</em>がイテレータの間接参照結果として返された場合、それに書き込んだとしても、その<em>prvalue</em>のオブジェクトが所有する値を書き換えるのみであり、正しく出力されるとは言えない。</p>
<p>一方で、プロキシオブジェクト(所有権を持たず、他のオブジェクトを参照するオブジェクト)がイテレータの間接参照結果として返された場合は、<em>prvalue</em>の場合も代入された値を「参照する先のオブジェクトが所有する値」へ書き込むことによって、正しく出力を完了することが出来る。</p>
<p>更に、プロキシオブジェクトは値を所有しないため「<code>const</code>な参照先」でなければ、プロキシオブジェクトそれ自体が<code>const</code>であっても代入は可能であるべきである。しかしながら、従来のプロキシオブジェクトは<code>const</code>を付与された場合代入が不可能になる実装が殆どであり、変更が必要である。例としては<code><a href="../vector/vector.html">std::vector<bool>::reference</a></code>がある。</p>
<p>プロキシオブジェクトの他にも、参照(右辺値参照/左辺値参照問わず)も正しく出力が可能である。このことから、「<code>const</code>を付与した上でも代入が可能であるようなプロキシオブジェクト」と「参照」を合わせて「プロキシ参照(proxy reference)」と呼称することがある。</p>
<p>以上のことから、<code>const</code>を付与した際にも代入が可能であればプロキシ参照、不可能であれば非プロキシ参照と区別することが可能となる。したがって、間接参照が非プロキシ参照(プロキシオブジェクトでない<em>prvalue</em>など)を返すイテレータ型は本コンセプトのモデルとならず、プロキシ参照を返すイテレータは本コンセプトのモデルとなる事ができる。</p>
<h2>モデル</h2>
<p><code>decltype((E)) == T</code>となるような式<code>E</code>及び<code><a href="dereferenceable.html">dereferenceable</a></code>な型<code>Out</code>のオブジェクト<code>o</code>について次の条件を満たす場合に限って、型<code>Out, T</code>は<code>indirectly_writable</code>のモデルである。</p>
<ul>
<li><code>Out, T</code>が次の制約式のモデルとなる場合、式<code>E</code>を上記(定義内)式のいずれかの形で出力した後で、<code>*o</code>は元の<code>E</code>の値と等値(<em>equal</em>)になる。<ul>
<li>ただし、そのような出力の後で<code>o</code>が間接参照可能である必要はない。</li>
</ul>
</li>
</ul>
<p><div class="codehilite"><pre><span></span><code><span class="n"><a href="indirectly_readable.html">indirectly_readable</a></span><span class="o"><</span><span class="n">Out</span><span class="o">></span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n"><a href="../concepts/same_as.html">same_as</a></span><span class="o"><</span><span class="n"><a href="iter_value_t.html">iter_value_t</a></span><span class="o"><</span><span class="n">Out</span><span class="o">></span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../type_traits/decay.html">decay_t</a></span><span class="o"><</span><span class="n">T</span><span class="o">>></span>
</code></pre></div>
</p>
<p><code>E</code>の値カテゴリが<em>xvalue</em>の場合、上記式による出力後<code>E</code>のオブジェクトは有効だが<a class="cpprefjp-defined-word" data-desc="未規定の動作。事前の断りなく処理系によって異なる動作をする" href="../../implementation-compliance.html#dfn-unspecified-behavior">未規定</a>な状態となる</p>
<h2>備考</h2>
<p><code>indirectly_writable</code>のモデルとなる<code>Out</code>の<code>operator*</code>は出力(上記式による代入文の左辺に来ること)だけが唯一有効な使用法であり、<code><a href="indirectly_readable.html">indirectly_readable</a></code>である必要はない。</p>
<h2>例</h2>
<h3>C++20</h3>
<p><div class="yata" id="a8701f50de90bdec17b995ea312930d647f90a44"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../concepts.html"><concepts></a></span>
<span class="cp">#include <a href="../iterator.html"><iterator></a></span>
<span class="cp">#include <a href="../memory.html"><memory></a></span>
<span class="cp">#include <a href="../vector.html"><vector></a></span>
<span class="cp">#include <a href="../optional.html"><optional></a></span>
<span class="k">template</span><span class="o"><</span><span class="k">typename</span><span class="w"> </span><span class="nc">Out</span><span class="p">,</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="k">requires</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::indirectly_writable</span></span><span class="o"><</span><span class="n">Out</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="o">></span>
<span class="kt">void</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">out</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">t</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">out</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">" is indirectly writable "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="p">}</span>
<span class="k">template</span><span class="o"><</span><span class="k">typename</span><span class="w"> </span><span class="nc">Out</span><span class="p">,</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="kt">void</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">out</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">t</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">out</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">" is not indirectly writable "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="p">}</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">writable</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="kt">int</span><span class="o">&</span><span class="w"> </span><span class="k">operator</span><span class="o">*</span><span class="p">();</span>
<span class="p">};</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">not_writable</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">//prvalueを返す、出力不可能</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="k">operator</span><span class="o">*</span><span class="p">();</span>
<span class="p">};</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="kt">int</span><span class="o">*</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="s">"int*"</span><span class="p">,</span><span class="w"> </span><span class="s">"int"</span><span class="p">);</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="n"><a href="../memory/unique_ptr.html">std::unique_ptr</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">&></span><span class="p">(</span><span class="s">"<a href="../memory/unique_ptr.html">std::unique_ptr</a><int>"</span><span class="p">,</span><span class="w"> </span><span class="s">"int&"</span><span class="p">);</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="n"><a href="../vector/vector.html">std::vector</a></span><span class="o"><</span><span class="kt">int</span><span class="o">>::</span><span class="n">iterator</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">&&></span><span class="p">(</span><span class="s">"<a href="../vector/vector.html">std::vector</a><int>::iterator"</span><span class="p">,</span><span class="w"> </span><span class="s">"int&&"</span><span class="p">);</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="n"><a href="ostream_iterator.html">std::ostream_iterator</a></span><span class="o"><</span><span class="kt">double</span><span class="o">></span><span class="p">,</span><span class="w"> </span><span class="kt">double</span><span class="o">></span><span class="p">(</span><span class="s">"<a href="ostream_iterator.html">std::ostream_iterator</a><double>"</span><span class="p">,</span><span class="w"> </span><span class="s">"double"</span><span class="p">);</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="n">writable</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="s">"writable"</span><span class="p">,</span><span class="w"> </span><span class="s">"int"</span><span class="p">);</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="n"><a href="../vector/vector.html">std::vector</a></span><span class="o"><</span><span class="kt">bool</span><span class="o">>::</span><span class="n">iterator</span><span class="p">,</span><span class="w"> </span><span class="kt">bool</span><span class="o">></span><span class="p">(</span><span class="s">"<a href="../vector/vector.html">std::vector</a><bool>::iterator"</span><span class="p">,</span><span class="w"> </span><span class="s">"bool"</span><span class="p">);</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="n"><a href="../optional/optional.html">std::optional</a></span><span class="o"><</span><span class="kt">int</span><span class="o">></span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="s">"<a href="../optional/optional.html">std::optional</a><int>"</span><span class="p">,</span><span class="w"> </span><span class="s">"int"</span><span class="p">);</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="n">not_writable</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">></span><span class="p">(</span><span class="s">"not_writable"</span><span class="p">,</span><span class="w"> </span><span class="s">"int"</span><span class="p">);</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h4>出力</h4>
<p><pre><code>int* is indirectly writable int
<a href="../memory/unique_ptr.html">std::unique_ptr</a><int> is indirectly writable int&
<a href="../vector/vector.html">std::vector</a><int>::iterator is indirectly writable int&&
<a href="ostream_iterator.html">std::ostream_iterator</a><double> is indirectly writable double
writable is indirectly writable int
<a href="../vector/vector.html">std::vector</a><bool>::iterator is not indirectly writable bool
<a href="../optional/optional.html">std::optional</a><int> is not indirectly writable int
not_writable is not indirectly writable int
</code></pre></p>
<h3>C++23 で満たすようになった型</h3>
<p><div class="yata" id="008faddddf66d08d1708290cc935f810914a3cb9"><div class="codehilite"><pre><span></span><code><span class="cp">#include <a href="../iostream.html"><iostream></a></span>
<span class="cp">#include <a href="../concepts.html"><concepts></a></span>
<span class="cp">#include <a href="../iterator.html"><iterator></a></span>
<span class="cp">#include <a href="../utility.html"><utility></a></span>
<span class="cp">#include <a href="../tuple.html"><tuple></a></span>
<span class="cp">#include <a href="../vector.html"><vector></a></span>
<span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">typename</span><span class="w"> </span><span class="nc">Out</span><span class="p">,</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="k">requires</span><span class="w"> </span><span class="n"><span style="color:#ff0000">std::indirectly_writable</span></span><span class="o"><</span><span class="n">Out</span><span class="p">,</span><span class="w"> </span><span class="n">T</span><span class="o">></span>
<span class="kt">void</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">out</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">t</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">out</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">" is indirectly writable "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="p">}</span>
<span class="k">template</span><span class="w"> </span><span class="o"><</span><span class="k">typename</span><span class="w"> </span><span class="nc">Out</span><span class="p">,</span><span class="w"> </span><span class="k">typename</span><span class="w"> </span><span class="nc">T</span><span class="o">></span>
<span class="kt">void</span><span class="w"> </span><span class="n">f</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">out</span><span class="p">,</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">t</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n"><a href="../iostream/cout.html">std::cout</a></span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">out</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">" is not indirectly writable "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n"><a href="../ostream/endl.html">std::endl</a></span><span class="p">;</span>
<span class="p">}</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">ret_proxy_pair</span>
<span class="p">{</span>
<span class="w"> </span><span class="c1">// 全ての要素がプロキシ参照である <a href="../utility/pair.html">pair</a> はプロキシ参照</span>
<span class="w"> </span><span class="n"><a href="../utility/pair.html">std::pair</a></span><span class="o"><</span><span class="kt">int</span><span class="o">&</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../utility/pair.html">std::pair</a></span><span class="o"><</span><span class="kt">int</span><span class="o">&</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">&>></span><span class="w"> </span><span class="k">operator</span><span class="o">*</span><span class="p">();</span>
<span class="p">};</span>
<span class="k">struct</span><span class="w"> </span><span class="nc">ret_proxy_tuple</span>
<span class="p">{</span>
<span class="w"> </span><span class="c1">// 全ての要素がプロキシ参照である <a href="../tuple/tuple.html">tuple</a> はプロキシ参照</span>
<span class="w"> </span><span class="n"><a href="../tuple/tuple.html">std::tuple</a></span><span class="o"><</span><span class="kt">int</span><span class="o">&</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../tuple/tuple.html">std::tuple</a></span><span class="o"><</span><span class="kt">int</span><span class="o">&>></span><span class="w"> </span><span class="k">operator</span><span class="o">*</span><span class="p">();</span>
<span class="p">};</span>
<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="n"><a href="../vector/vector.html">std::vector</a></span><span class="o"><</span><span class="kt">bool</span><span class="o">>::</span><span class="n">iterator</span><span class="p">,</span><span class="w"> </span><span class="kt">bool</span><span class="o">></span><span class="p">(</span><span class="s">"<a href="../vector/vector.html">std::vector</a><bool>::iterator"</span><span class="p">,</span><span class="w"> </span><span class="s">"bool"</span><span class="p">);</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="n">ret_proxy_pair</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../utility/pair.html">std::pair</a></span><span class="o"><</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../utility/pair.html">std::pair</a></span><span class="o"><</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="kt">int</span><span class="o">>>></span><span class="p">(</span><span class="s">"ret_proxy_pair"</span><span class="p">,</span><span class="w"> </span><span class="s">"<a href="../utility/pair.html">std::pair</a><int, <a href="../utility/pair.html">std::pair</a><int, int>>"</span><span class="p">);</span>
<span class="w"> </span><span class="n">f</span><span class="o"><</span><span class="n">ret_proxy_tuple</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../tuple/tuple.html">std::tuple</a></span><span class="o"><</span><span class="kt">int</span><span class="p">,</span><span class="w"> </span><span class="n"><a href="../tuple/tuple.html">std::tuple</a></span><span class="o"><</span><span class="kt">int</span><span class="o">>>></span><span class="p">(</span><span class="s">"ret_proxy_tuple"</span><span class="p">,</span><span class="w"> </span><span class="s">"<a href="../tuple/tuple.html">std::tuple</a><int, <a href="../tuple/tuple.html">std::tuple</a><int>>"</span><span class="p">);</span>
<span class="p">}</span>
</code></pre></div>
</div></p>
<h4>出力</h4>
<p><pre><code><a href="../vector/vector.html">std::vector</a><bool>::iterator is indirectly writable bool
ret_proxy_pair is indirectly writable <a href="../utility/pair.html">std::pair</a><int, <a href="../utility/pair.html">std::pair</a><int, int>>
ret_proxy_tuple is indirectly writable <a href="../tuple/tuple.html">std::tuple</a><int, <a href="../tuple/tuple.html">std::tuple</a><int>>
</code></pre></p>
<h2>バージョン</h2>
<h3>言語</h3>
<ul>
<li>C++20</li>
</ul>
<h3>処理系</h3>
<ul>
<li><a href="../../implementation.html#clang">Clang</a>: ??</li>
<li><a href="../../implementation.html#gcc">GCC</a>: 10.1 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
<li><a href="../../implementation.html#visual_cpp">Visual C++</a>: 2019 Update 6 <span aria-label="検証済" role="img" title="検証済">✅</span></li>
</ul>
<h2>関連項目</h2>
<ul>
<li><a href="../../lang/cpp20/concepts.html">C++20 コンセプト</a></li>
</ul>
<h2>参照</h2>
<ul>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0896r4.pdf" target="_blank">P0896R4 The One Ranges Proposal (was Merging the Ranges TS)</a></li>
<li><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p2214r0.html#a-tuple-that-is-writable" target="_blank">P2214R0 A Plan for C++23 Ranges</a><ul>
<li><code>const_cast</code>を用いる制約式についての説明がなされている</li>
</ul>
</li>
</ul></div>
</div>
</div>
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