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| author | nsfisis <nsfisis@gmail.com> | 2025-06-27 23:39:31 +0900 |
|---|---|---|
| committer | nsfisis <nsfisis@gmail.com> | 2025-06-27 23:39:31 +0900 |
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diff --git a/services/blog/public/posts/2021-10-02/cpp-you-can-use-keywords-in-attributes/index.html b/services/blog/public/posts/2021-10-02/cpp-you-can-use-keywords-in-attributes/index.html new file mode 100644 index 00000000..53bd4c70 --- /dev/null +++ b/services/blog/public/posts/2021-10-02/cpp-you-can-use-keywords-in-attributes/index.html @@ -0,0 +1,193 @@ +<!DOCTYPE html> +<html lang="ja-JP"> + <head> + <meta charset="UTF-8"> + <meta name="viewport" content="width=device-width, initial-scale=1.0"> + <meta name="author" content="nsfisis"> + <meta name="copyright" content="© 2021 nsfisis"> + <meta name="description" content="C++ の属性構文の属性名には、キーワードが使える。ネタ記事。"> + <meta name="keywords" content="C++,C++ 17"> + <meta property="og:type" content="article"> + <meta property="og:title" content="【C++】 属性構文の属性名にはキーワードが使える｜REPL: Rest-Eat-Program Loop"> + <meta property="og:description" content="C++ の属性構文の属性名には、キーワードが使える。ネタ記事。"> + <meta property="og:site_name" content="REPL: Rest-Eat-Program Loop"> + <meta property="og:locale" content="ja_JP"> + <link rel="icon" type="image/svg+xml" href="/favicon.svg"> + <title>【C++】 属性構文の属性名にはキーワードが使える｜REPL: Rest-Eat-Program Loop</title> + <link rel="stylesheet" href="/style.css?h=9513229b52eb2041b99ba1b959305633"> + </head> + <body class="single"> + <header class="header"> + <div class="site-logo"> + <a href="/">REPL: Rest-Eat-Program Loop</a> + </div> + <nav class="nav"> + <ul> + <li> + <a href="/about/">About</a> + </li> + <li> + <a href="/posts/">Posts</a> + </li> + <li> + <a href="/slides/">Slides</a> + </li> + <li> + <a href="/tags/">Tags</a> + </li> + </ul> + </nav> + </header> + <main class="main"> + <article class="post-single"> + <header class="post-header"> + <h1 class="post-title">【C++】 属性構文の属性名にはキーワードが使える</h1> + <ul class="post-tags"> + <li class="tag"> + <a href="/tags/cpp/">C++</a> + </li> + <li class="tag"> + <a href="/tags/cpp17/">C++ 17</a> + </li> + </ul> + </header> + <div class="post-content"> + <section id="changelog"> + <h2><a href="#changelog">更新履歴</a></h2> + <ol> + <li class="revision"> + <time datetime="2021-10-02">2021-10-02</time>: Qiita から移植 + </li> + </ol> + </section> + <div class="admonition"> + <div class="admonition-label"> + NOTE + </div> + <div class="admonition-content"> + <p> + この記事は Qiita から移植してきたものです。元 URL: <a href="https://qiita.com/nsfisis/items/94090937bcf860cfa93b" rel="noreferrer" target="_blank">https://qiita.com/nsfisis/items/94090937bcf860cfa93b</a> + </p> + </div> + </div> + <p> + タイトル落ち。まずはこのコードを見て欲しい。 + </p> + <div class="codeblock"> + <pre class="shiki github-light" style="background-color:#f5f5f5;color:#24292e" tabindex="0"><code><span class="line"><span style="color:#D73A49">#include</span><span style="color:#032F62"> <iostream></span></span> +<span class="line"></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">alignas</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">alignof</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">and</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">and_eq</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">asm</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">auto</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">bitand</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">bitor</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">bool</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">break</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">case</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">catch</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">char</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">char16_t</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">char32_t</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">class</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">compl</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">const</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">const_cast</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">constexpr</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">continue</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">decltype</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">default</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">delete</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">do</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">double</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">dynamic_cast</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">else</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">enum</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">explicit</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">export</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">extern</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">false</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">final</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">float</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">for</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">friend</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">goto</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">if</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">inline</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">int</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">long</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">mutable</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">namespace</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">new</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">noexcept</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">not</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">not_eq</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">nullptr</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">operator</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">or</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">or_eq</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">override</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">private</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">protected</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">public</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">register</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">reinterpret_cast</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">return</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">short</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">signed</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">sizeof</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">static</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">static_assert</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">static_cast</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">struct</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">switch</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">template</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">this</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">thread_local</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">throw</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">true</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">try</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">typedef</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">typeid</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">typename</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">union</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">unsigned</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#6F42C1">virtual</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">void</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">volatile</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">wchar_t</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">while</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">xor</span><span style="color:#005CC5">]]</span><span style="color:#005CC5"> [[</span><span style="color:#6F42C1">xor_eq</span><span style="color:#005CC5">]]</span></span> +<span class="line"><span style="color:#6A737D">// [[using]]</span></span> +<span class="line"><span style="color:#D73A49">int</span><span style="color:#6F42C1"> main</span><span style="color:#24292E">() {</span></span> +<span class="line"><span style="color:#6F42C1"> std</span><span style="color:#24292E">::cout </span><span style="color:#D73A49"><<</span><span style="color:#032F62"> "Hello, World!"</span><span style="color:#D73A49"> <<</span><span style="color:#6F42C1"> std</span><span style="color:#24292E">::endl;</span></span> +<span class="line"><span style="color:#24292E">}</span></span></code></pre> + </div> + <p> + コンパイラのバージョン + </p> + <div class="codeblock"> + <pre class="shiki github-light" style="background-color:#f5f5f5;color:#24292e" tabindex="0"><code><span class="line"><span>$ clang++ –version Apple clang version 11.0.0</span></span> +<span class="line"><span>(clang-1100.0.33.8) Target: x86_64-apple-darwin19.6.0 Thread model:</span></span> +<span class="line"><span>posix InstalledDir:</span></span> +<span class="line"><span>/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin</span></span></code></pre> + </div> + <p> + コンパイルコマンド (C17指定) + </p> + <div class="codeblock"> + <pre class="shiki github-light" style="background-color:#f5f5f5;color:#24292e" tabindex="0"><code><span class="line"><span>$ clang –std=c++17 hoge.cpp</span></span></code></pre> + </div> + <p> + この記事から得られるものはこれ以上ないので以下は蛇足になる。 + </p> + <p> + 別件で <a href="https://en.cppreference.com/w/cpp/language/identifiers" rel="noreferrer" target="_blank">cppreference.com の identifier のページ</a>を読んでいた時、次の文が目に止まった。 + </p> + <blockquote> + <ul> + <li> + the identifiers that are keywords cannot be used for other purposes; + <ul> + <li> + The only place they can be used as non-keywords is in an attribute-token. (e.g. [[private]] is a valid attribute) (since C++11) + </li> + </ul> + </li> + </ul> + </blockquote> + <p> + キーワードでも属性として指定する場合は非キーワードとして使えるらしい。実際にやってみる。 + </p> + <p> + 同サイトの <a href="https://en.cppreference.com/w/cpp/keyword" rel="noreferrer" target="_blank">keywords のページ</a> から一覧を拝借し、上のコードが出来上がった (C++17 においてキーワードでないものなど、一部省いている)。 大量の警告 (unknown attribute `〇〇’ ignored) がコンパイラから出力されるが、コンパイルできる。 + </p> + <p> + 上のコードでは <code>[[using]]</code> をコメントアウトしているが、これは <code>using</code> キーワードのみ属性構文の中で意味を持つからであり、このコメントアウトを外すとコンパイルに失敗する。 + </p> + <div class="codeblock"> + <pre class="shiki github-light" style="background-color:#f5f5f5;color:#24292e" tabindex="0"><code><span class="line"><span style="color:#6A737D">// using の例</span></span> +<span class="line"><span style="color:#005CC5">[[</span><span style="color:#D73A49">using</span><span style="color:#6F42C1"> foo</span><span style="color:#005CC5">: </span><span style="color:#6F42C1">attr1</span><span style="color:#005CC5">, </span><span style="color:#6F42C1">attr2</span><span style="color:#005CC5">]]</span><span style="color:#D73A49"> int</span><span style="color:#24292E"> x;</span><span style="color:#6A737D"> // [[foo::attr1, foo::attr2]] の糖衣構文</span></span></code></pre> + </div> + <p> + C++17 の仕様も見てみる (正確には標準化前のドラフト)。 + </p> + <p> + 引用元: <a href="https://timsong-cpp.github.io/cppwp/n4659/dcl.attr#grammar-4" rel="noreferrer" target="_blank">https://timsong-cpp.github.io/cppwp/n4659/dcl.attr#grammar-4</a> + </p> + <blockquote> + <p> + If a keyword or an alternative token that satisfies the syntactic requirements of an identifier is contained in an attribute-token, it is considered an identifier. + </p> + </blockquote> + <p> + 「<code>identifier</code> の構文上の要件を満たすキーワードまたは代替トークンが <code>attribute-token</code> に含まれている場合、<code>identifier</code> とみなされる」とある。どうやら間違いないようだ。 + </p> + <p> + ところで、代替トークン (alternative token) とは <code>and</code> (<code>&</code>) や <code>bitor</code> (<code>|</code>) などのことだが、<code>identifier</code> の構文上の要件を満たさないような代替トークンなどあるのか？ 疑問に思って調べたところ、代替トークンという語にはダイグラフも含まれるらしい (参考: <a href="https://timsong-cpp.github.io/cppwp/n4659/lex.digraph" rel="noreferrer" target="_blank">同ドラフト</a> ) + </p> + <ul> + <li> + <code><%</code> → <code>{</code> + </li> + <li> + <code>%></code> → <code>}</code> + </li> + <li> + <code><:</code> → <code>[</code> + </li> + <li> + <code>:></code> → <code>]</code> + </li> + <li> + <code>%:</code> → <code>#</code> + </li> + <li> + <code>%:%:</code> → <code>##</code> + </li> + </ul> + <p> + 「<code>identifier</code> の構文上の要件を満たさないような代替トークン」はこれらが当てはまると思われる。 + </p> + <p> + 調べた感想: 字句解析器か構文解析器が辛そう + </p> + </div> + </article> + </main> + <footer class="footer"> + © 2021 nsfisis + </footer> + </body> +</html> |