summaryrefslogtreecommitdiff
path: root/2024/05/04/C-的-Trait/index.html
diff options
context:
space:
mode:
Diffstat (limited to '2024/05/04/C-的-Trait/index.html')
-rw-r--r--2024/05/04/C-的-Trait/index.html257
1 files changed, 257 insertions, 0 deletions
diff --git a/2024/05/04/C-的-Trait/index.html b/2024/05/04/C-的-Trait/index.html
new file mode 100644
index 00000000..7145bdec
--- /dev/null
+++ b/2024/05/04/C-的-Trait/index.html
@@ -0,0 +1,257 @@
+<!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">
+
+
+
+
+<title>C++ 的 Trait | 暮秋小屋</title>
+
+
+
+
+
+<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>
+
+
+
+ </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, 2024
+ </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()&#x2F;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> &#123;</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">&#125;</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> &#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line"> Type type = TYPE_1;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">class</span> <span class="title class_">Bar</span> &#123;</span><br><span class="line"><span class="keyword">public</span>:</span><br><span class="line"> Type type = TYPE_2;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">template</span>&lt;<span class="keyword">typename</span> T&gt;</span><br><span class="line"><span class="keyword">struct</span> <span class="title class_">type_traits</span> &#123;</span><br><span class="line"> Type type = T::type;</span><br><span class="line">&#125;</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>&lt;<span class="keyword">typename</span> <span class="type">int</span>&gt;</span><br><span class="line"><span class="keyword">struct</span> <span class="title class_">type_traits</span> &#123;</span><br><span class="line"> Type type = Type::TYPE_1;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">template</span>&lt;<span class="keyword">typename</span> <span class="type">double</span>&gt;</span><br><span class="line"><span class="keyword">struct</span> <span class="title class_">type_traits</span> &#123;</span><br><span class="line"> Type type = Type::TYPE_3;</span><br><span class="line">&#125;</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>&lt;<span class="keyword">typename</span> T&gt;</span><br><span class="line"><span class="type">void</span> decode&lt;<span class="type">const</span> T&amp; data, <span class="type">char</span>* buf) &#123;</span><br><span class="line"> <span class="keyword">if</span>(type_traits&lt;T&gt;::type == Type::TYPE_1) &#123;</span><br><span class="line"> ...</span><br><span class="line"> &#125;</span><br><span class="line"> <span class="keyword">else</span> <span class="keyword">if</span>(type_traits&lt;T&gt;::type == Type::TYPE_2) &#123;</span><br><span class="line"> ...</span><br><span class="line"> &#125;</span><br><span class="line">&#125;</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="/2024/05/07/%E4%BA%8C%E3%80%87%E4%BA%8C%E5%9B%9B%E5%B9%B4%E4%BA%94%E6%9C%88%E4%B8%83%E6%97%A5/">Prev</a>
+ </div>
+
+ </div>
+ <div class="next-item">
+
+ <div class="icon arrow-right"></div>
+ <div class="post-link">
+ <a href="/2024/05/03/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">
+
+
+ |
+
+
+ 希望路过的人可以添点柴火让这里暖和点
+
+ </div>
+ </div>
+</div>
+
+ </div>
+
+
+
+
+ </body>
+</html>
generated by cgit v1.2.3 (git 2.39.1) at 2026-10-04 17:21:45 +0000