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Diffstat (limited to '2023/05/04')
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diff --git a/2023/05/04/C-的-Trait/index.html b/2023/05/04/C-的-Trait/index.html deleted file mode 100644 index e626505f..00000000 --- a/2023/05/04/C-的-Trait/index.html +++ /dev/null @@ -1,294 +0,0 @@ -<!DOCTYPE html> -<html lang="en"> - <head> - <meta charset="UTF-8"> -<meta name="viewport" - content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0"> -<meta http-equiv="X-UA-Compatible" content="ie=edge"> - - <meta name="author" content="韩暮秋"> - - - <meta name="subtitle" content="暮秋小屋"> - - - <meta name="description" content="这里是暮秋小屋，思念和灵感的寄存处"> - - - <meta name="keywords" content="韩暮秋,MuqiuHan,'Muqiu Han', 'muqiu han', muqiuhan"> - - - - -<title>C++ 的 Trait | 暮秋小屋</title> - - - - <link rel="icon" href="/favicon.ico"> - - - -<style> - @import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&family=Noto+Sans+SC:wght@300;400;500;700&family=Roboto+Mono&display=swap'); -</style> - - - - <!-- stylesheets list from _config.yml --> - - <link rel="stylesheet" href="/css/style.css"> - - - - - - <!-- scripts list from _config.yml --> - - <script src="/js/frame.js"></script> - - - - - - <script src="https://polyfill.io/v3/polyfill.min.js?features=es6"></script> - <script id="MathJax-script" async src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"></script> - - - - - - - - <meta name="generator" content="Hexo 6.3.0"></head> - <body> - <div class="mask-border"> - </div> - - <div class="wrapper"> - - <div class="header"> - <div class="flex-container"> - <div class="header-inner"> - <div class="site-brand-container"> - <a href="/"> - - 暮秋小屋 - - </a> - </div> - <div id="menu-btn" class="menu-btn" onclick="toggleMenu()"> - Menu - </div> - <nav class="site-nav"> - <ul class="menu-list"> - - - <li class="menu-item"> - <a href="/">主页</a> - </li> - - - - <li class="menu-item"> - <a href="/categories/gallery/">日记本</a> - </li> - - - - <li class="menu-item"> - <a href="/tags/Medicine/">医学</a> - </li> - - - - <li class="menu-item"> - <a href="/tags/Technique/">计算机科学</a> - </li> - - - - <li class="menu-item"> - <a href="/tags/Life/">生活</a> - </li> - - - - <li class="menu-item"> - <a href="/about">关于</a> - </li> - - - - <li class="menu-item search-btn"> - <a href="#">Search</a> - </li> - - </ul> - </nav> - </div> - </div> -</div> - - - <div class="main"> - <div class="flex-container"> - <article id="post"> - - - <div class="post-head"> - <div class="post-info"> - <div class="tag-list"> - - - <span class="post-tag"> - <a href="/tags/Technique/"> - Technique - </a> - </span> - - <span class="post-tag"> - <a href="/tags/C/"> - C++ - </a> - </span> - - - </div> - <div class="post-title"> - - - C++ 的 Trait - - - </div> - <span class="post-date"> - May 4, 2023 - </span> - </div> - <div class="post-img"> - - <div class="h-line-primary"></div> - - </div> -</div> - <div class="post-content"> - <blockquote> -<p>C++ 的 traits 技术，是一种约定俗称的技术方案，用来为同一类数据（包括自定义数据类型和内置数据类型）提供统一的类型名（traits），这样可以统一的操作函数，例如 advance(), swap(), encode()/decode() 等。</p> -</blockquote> -<p>例如，拥有义类型Foo, Bar，以及编译器自带类型 int, double, string，我们想要为这些不同的类型提供统一的编码函数 decode() 。</p> -<p>除了使用 trait 技术之外，函数重载和模板函数 + 内置字段也可以实现，前者每增加一种数据类型就需要重新实现一个函数，而同一类数据（int, unsinged int）可以使用同样的编码方法。我们想要的是针对同一种数据类型，只编写一个函数。后者对于系统自定义变量 int, double 而言，是无法在其内部定义 type 的。</p> -<p>traits 技术的关键在于，使用另外的模板类 type_traits 来保存不同数据类型的 type，这样就可以兼容自定义数据类型和内置数据类型:</p> -<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 定义数据 type 类</span></span><br><span class="line"><span class="keyword">enum</span> <span class="title class_">Type</span> {</span><br><span class="line"> TYPE_1,</span><br><span class="line"> TYPE_2,</span><br><span class="line"> TYPE_3</span><br><span class="line">}</span><br></pre></td></tr></table></figure> - -<p>对于自定义类型，在类内部定义 type，然后在 traits 类中定义同样的 type:</p> -<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 自定义数据类型</span></span><br><span class="line"><span class="keyword">class</span> <span class="title class_">Foo</span> {</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line"> Type type = TYPE_1;</span><br><span class="line">};</span><br><span class="line"><span class="keyword">class</span> <span class="title class_">Bar</span> {</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line"> Type type = TYPE_2;</span><br><span class="line">};</span><br><span class="line"><span class="keyword">template</span><<span class="keyword">typename</span> T></span><br><span class="line"><span class="keyword">struct</span> <span class="title class_">type_traits</span> {</span><br><span class="line"> Type type = T::type;</span><br><span class="line">}</span><br></pre></td></tr></table></figure> - -<p>对于内置数据类型，使用模板类的特化为自定义类型生成独有的 type_traits:</p> -<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 内置数据类型</span></span><br><span class="line"><span class="keyword">template</span><<span class="keyword">typename</span> <span class="type">int</span>></span><br><span class="line"><span class="keyword">struct</span> <span class="title class_">type_traits</span> {</span><br><span class="line"> Type type = Type::TYPE_1;</span><br><span class="line">}</span><br><span class="line"><span class="keyword">template</span><<span class="keyword">typename</span> <span class="type">double</span>></span><br><span class="line"><span class="keyword">struct</span> <span class="title class_">type_traits</span> {</span><br><span class="line"> Type type = Type::TYPE_3;</span><br><span class="line">}</span><br></pre></td></tr></table></figure> - -<p>这样就可以为不同数据类型生成统一的模板函数</p> -<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// 统一的编码函数</span></span><br><span class="line"><span class="keyword">template</span><<span class="keyword">typename</span> T></span><br><span class="line"><span class="type">void</span> decode<<span class="type">const</span> T& data, <span class="type">char</span>* buf) {</span><br><span class="line"> <span class="keyword">if</span>(type_traits<T>::type == Type::TYPE_1) {</span><br><span class="line"> ...</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">else</span> <span class="keyword">if</span>(type_traits<T>::type == Type::TYPE_2) {</span><br><span class="line"> ...</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure> - -<p>总结</p> -<ul> -<li>traits 技术的关键在于使用第三方模板类 traits，利用模板特化的功能, 实现对自定义数据和编译器内置数据的统一</li> -<li>这个例子使用了枚举变量来表示数据类型，而实际操作中通常使用不同的类来表示不同的类型，这样可以在编写模板函数时更好的优化。</li> -<li>tratis 技术常见于标准库的实现中，但对日常开发中降低代码冗余也有很好的借鉴意义</li> -<li>C++20 提供了Concept 的特性，使用Concept 可以使得实现类似的功能更加方便</li> -</ul> - -</div> - -<script> - window.onload = detectors(); -</script> - <div class="post-footer"> - <div class="h-line-primary"></div> - <nav class="post-nav"> - <div class="prev-item"> - - <div class="icon arrow-left"></div> - <div class="post-link"> - <a href="/2023/05/11/C-vector-%E7%9A%84-push-back-%E5%92%8C-emplace-back/">Prev</a> - </div> - - </div> - <div class="next-item"> - - <div class="icon arrow-right"></div> - <div class="post-link"> - <a href="/2023/05/03/Rust-NewType-%E6%A8%A1%E5%BC%8F/">Next</a> - </div> - - </div> - </nav> -</div> - - - <div class="post-comment"> - - - - - - - -</div> - - -</article> - </div> - </div> - - <div class="footer"> - <div class="flex-container"> - <div class="footer-text"> - - - 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