月更 技术博客 CXX优先 Zola 2026-08-17T00:00:00+00:00 https://suchaharcan.github.io/tags/cxx/atom.xml 2026-08-17T00:00:00+00:00 2026-08-17T00:00:00+00:00 Suchaharcan https://suchaharcan.github.io/01Write_blog_CXX20/reflection-annotations-validation/ <p>在探索 C++26 系列的过程中，我之前的文章已经介绍了如何在 Ubuntu 上搭建 C++26 构建环境。之后，我探索了另一个名为模板的特性，并通过一个简单的示例讲解了反射的用法，并进一步学习了如何使用反射进行 JSON 序列化。在本文中，我将解释另一个极其强大的 C++26 特性，它叫做……注释以及它们与反思相结合如何使我们的生活更轻松。</p> <p>首先，让我们来看下面这个假设的MotorConfig班级：</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> MotorConfig</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> MotorConfig</span><span class="z-punctuation">(</span><span class="z-storage z-type">int</span><span class="z-variable z-parameter"> rpm</span><span class="z-punctuation">,</span><span class="z-storage z-type"> double</span><span class="z-variable z-parameter"> maxTemperature</span><span class="z-punctuation">,</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">string</span><span class="z-variable z-parameter"> deviceName</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation"> [[</span><span class="z-source">nodiscard</span><span class="z-punctuation">]]</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> rpm</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-storage z-modifier"> noexcept</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> return</span><span class="z-source"> m_rpm</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation"> [[</span><span class="z-source">nodiscard</span><span class="z-punctuation">]]</span></span> <span class="giallo-l"><span class="z-storage z-type"> double</span><span class="z-entity z-name z-function"> max_temperature</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-storage z-modifier"> noexcept</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> return</span><span class="z-source"> m_maxTemperature</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation"> [[</span><span class="z-source">nodiscard</span><span class="z-punctuation">]]</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">string</span><span class="z-storage z-modifier">&amp;</span><span class="z-entity z-name z-function"> device_name</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-storage z-modifier"> noexcept</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> return</span><span class="z-source"> m_deviceName</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> m_rpm</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> double</span><span class="z-source"> m_maxTemperature</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">string m_deviceName</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre> <p>这个类有一些私有成员m_rpm，m_maxTemperature这些m_deviceName成员在构造函数创建对象时会被初始化为特定的值。现在，假设你不希望类实例创建时使用超出某个范围的值，并且你想确保在构造时进行验证。你有哪些选择呢？你可以在构造函数中执行类似下面的操作：</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-entity z-name">MotorConfig</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">MotorConfig</span><span class="z-punctuation">(</span><span class="z-storage z-type">int</span><span class="z-source"> rpm</span><span class="z-punctuation">,</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-storage z-type"> double</span><span class="z-source"> maxTemperature</span><span class="z-punctuation">,</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">string deviceName</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> : m_rpm</span><span class="z-punctuation">{</span><span class="z-source">rpm</span><span class="z-punctuation">}</span><span class="z-punctuation">,</span></span> <span class="giallo-l"><span class="z-source"> m_maxTemperature</span><span class="z-punctuation">{</span><span class="z-source">maxTemperature</span><span class="z-punctuation">}</span><span class="z-punctuation">,</span></span> <span class="giallo-l"><span class="z-source"> m_deviceName</span><span class="z-punctuation">{</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">move</span><span class="z-punctuation">(</span><span class="z-source">deviceName</span><span class="z-punctuation">)</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-source">m_rpm </span><span class="z-keyword z-operator">&lt;</span><span class="z-constant z-numeric"> 0</span><span class="z-keyword z-operator"> ||</span><span class="z-source"> m_rpm </span><span class="z-keyword z-operator">&gt;</span><span class="z-constant z-numeric"> 10000</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> throw</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">out_of_range</span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation"> &quot;</span><span class="z-string">m_rpm is outside the permitted range [0, 10000]</span><span class="z-punctuation">&quot;</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-source">m_maxTemperature </span><span class="z-keyword z-operator">&lt;</span><span class="z-keyword z-operator"> -</span><span class="z-constant z-numeric">40</span><span class="z-constant z-numeric">.</span><span class="z-constant z-numeric">0</span><span class="z-keyword z-operator"> ||</span><span class="z-source"> m_maxTemperature </span><span class="z-keyword z-operator">&gt;</span><span class="z-constant z-numeric"> 150</span><span class="z-constant z-numeric">.</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> throw</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">out_of_range</span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation"> &quot;</span><span class="z-string">m_maxTemperature is outside the permitted range [-40, 150]</span><span class="z-punctuation">&quot;</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-variable z-other">m_deviceName</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> throw</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">invalid_argument</span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-punctuation"> &quot;</span><span class="z-string">m_deviceName is required</span><span class="z-punctuation">&quot;</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre> <p>太好了！但是，如果向类中添加了另一个类成员，而该成员的值也需要验证，那么您必须在构造函数中手动添加验证代码来处理新成员。手动添加很容易出错。在 C++26 中，我们可以使用注解等特性，并结合反射等特性来自动化此验证过程。</p> <p>使用注释 C++26 引入了注解的概念。注解的一般语法如下：</p> <p>[[=constant-expression]] declaration 这意味着您可以将常量表达式与声明关联起来，然后在编译时检索这些值。我们稍后会详细介绍。此类注解的示例如下所示：</p> <p>[[=42]] int value; 我们还可以使用用户自定义数据类型来定义更个性化的注释。</p> <p>注解的用户自定义类型 您还可以使用已定义的类型作为声明的注解，如下所示：</p> <p>[[=AnnotationType{arguments…}]] declaration 例如，在我们的示例代码中，我们可以声明类型为 <code>and</code> 的注解Range，Required如下所示：</p> <pre class="giallo z-code"><code data-lang="plain"><span class="giallo-l"><span>struct Range</span></span> <span class="giallo-l"><span>{</span></span> <span class="giallo-l"><span> double minimum;</span></span> <span class="giallo-l"><span> double maximum;</span></span> <span class="giallo-l"><span>};</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span>struct Required</span></span> <span class="giallo-l"><span>{</span></span> <span class="giallo-l"><span>};</span></span></code></pre> <p>声明完成后，我们现在可以使用用户定义的类型注解将 MotorConfig 类重写如下：</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> MotorConfig</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> MotorConfig</span><span class="z-punctuation">(</span><span class="z-storage z-type">int</span><span class="z-variable z-parameter"> rpm</span><span class="z-punctuation">,</span><span class="z-storage z-type"> double</span><span class="z-variable z-parameter"> maxTemperature</span><span class="z-punctuation">,</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">string</span><span class="z-variable z-parameter"> deviceName</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation"> [[</span><span class="z-source">nodiscard</span><span class="z-punctuation">]]</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> rpm</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-storage z-modifier"> noexcept</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> return</span><span class="z-source"> m_rpm</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation"> [[</span><span class="z-source">nodiscard</span><span class="z-punctuation">]]</span></span> <span class="giallo-l"><span class="z-storage z-type"> double</span><span class="z-entity z-name z-function"> max_temperature</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-storage z-modifier"> noexcept</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> return</span><span class="z-source"> m_maxTemperature</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-punctuation"> [[</span><span class="z-source">nodiscard</span><span class="z-punctuation">]]</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">string</span><span class="z-storage z-modifier">&amp;</span><span class="z-entity z-name z-function"> device_name</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-storage z-modifier"> noexcept</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> return</span><span class="z-source"> m_deviceName</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-punctuation"> [[</span><span class="z-source">= </span><span class="z-source">Range</span><span class="z-source">{</span><span class="z-constant z-numeric">0</span><span class="z-constant z-numeric">.</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 10000</span><span class="z-constant z-numeric">.</span><span class="z-constant z-numeric">0</span><span class="z-source">}</span><span class="z-punctuation">]]</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> m_rpm</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> [[</span><span class="z-source">= </span><span class="z-source">Range</span><span class="z-source">{-</span><span class="z-constant z-numeric">40</span><span class="z-constant z-numeric">.</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 150</span><span class="z-constant z-numeric">.</span><span class="z-constant z-numeric">0</span><span class="z-source">}</span><span class="z-punctuation">]]</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-storage z-type"> double</span><span class="z-source"> m_maxTemperature</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> [[</span><span class="z-source">= </span><span class="z-source">Required</span><span class="z-source">{}</span><span class="z-punctuation">]]</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">string m_deviceName</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><pre class="giallo z-code"><code data-lang="plain"><span class="giallo-l"><span>仔细阅读声明：</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span>[[= Range{0.0, 10000.0}]] </span></span> <span class="giallo-l"><span>int m_rpm;</span></span> <span class="giallo-l"><span>它表示成员变量的允许取值范围m_rpm为0.00 到10000.01。然而，目前该注解仅提供附加信息，它本身并不强制执行取值范围，除非后续代码强制执行，否则可以忽略。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span>现在反思一下</span></span> <span class="giallo-l"><span>如上文代码所示，一旦注释就位，我们现在就可以利用反射来提取它们并在代码中使用它们。</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span>首先，我们将编写一个循环来遍历类中的所有非静态成员MotorConfig：</span></span> <span class="giallo-l"><span>```C++</span></span> <span class="giallo-l"><span>template for (constexpr std::meta::info member : </span></span> <span class="giallo-l"><span> std::define_static_array(</span></span> <span class="giallo-l"><span> std::meta::nonstatic_data_members_of(^^T,</span></span> <span class="giallo-l"><span> std::meta::access_context::unchecked())))</span></span></code></pre> <p>我在本文template for中详细讨论了这一点。简而言之，它表示类型为的反射，在本例中为。它返回一个包含所有非静态成员反射的向量。但由于该向量使用动态存储，因此不能用作的范围。要将其与一起使用，我们需要将其复制到静态数组中，这可以通过来实现。^^TTMotorConfigstd::meta::nonstatic_data_members_oftemplate fortemplate forstd::define_static_array</p> <p>然后，在每次迭代中，我们提取每个成员的注释：</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-modifier">constexpr</span><span class="z-storage z-type"> auto</span><span class="z-source"> ranges </span><span class="z-keyword z-operator">=</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">define_static_array</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">annotations_of_with_type</span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-source"> member</span><span class="z-punctuation">,</span><span class="z-keyword z-operator"> ^</span><span class="z-keyword z-operator">^</span><span class="z-source">Range</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span></code></pre> <p>该函数std::meta::annotations_of_with_type返回一个向量，其中包含所有类型为 <code>&lt;input&gt;</code> 的注解的反射Range。std::define_static_array它将这些反射复制到一个静态存储的数组中，并返回一个std::span指向该数组的引用。<code>&lt;input&gt;</code> 通常将其元素存储在动态分配的内存中，因此其内容不能直接存储在constexpr变量中ranges。</p> <p>单注与多注 请记住，每种类型中只能有一个注解：</p> <p>[[= Range{0.0, 10000.0}]] int m_rpm; 但是，也可以在一个类型中包含多个注解：</p> <p>[[=Range{0.0, 10000.0}, =Range{1000.0, 8000.0}]] int m_rpm; 你可以用以下任何一种方式表达：</p> <p>[[=Range{0.0, 3000.0}, =Range{7000.0, 10000.0}]] int m_rpm; 或者分别如下：</p> <p>[[=Range{0.0, 3000.0}]] [[=Range{7000.0, 10000.0}]] int m_rpm; 因此，在以下表达式中，ranges表示span引用注解的静态反射数组：</p> <p>constexpr auto ranges = std::define_static_array(std::meta::annotations_of_with_type( member, ^^Range)); 在我们的例子中，我们只有一个注解，其反射可以用 表示ranges[0]。为了提取可用范围，我们可以这样做：</p> <p>constexpr Range range = std::meta::extract<Range>(ranges[0]); 剪接表达 我们即将能够访问每个成员的当前值并将其与允许的范围进行比较。可以使用以下拼接表达式访问成员值：</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">template</span><span class="z-keyword z-control"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-modifier">constexpr</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-source">info member </span><span class="z-punctuation">:</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">define_static_array</span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">nonstatic_data_members_of</span><span class="z-punctuation">(</span><span class="z-keyword z-operator">^</span><span class="z-keyword z-operator">^</span><span class="z-source">T</span><span class="z-punctuation">,</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name">access_context</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">unchecked</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> ...</span></span> <span class="giallo-l"><span class="z-source"> ...</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> constexpr</span><span class="z-storage z-type"> auto</span><span class="z-source"> ranges </span><span class="z-keyword z-operator">=</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">define_static_array</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">annotations_of_with_type</span><span class="z-punctuation">(</span><span class="z-source">member</span><span class="z-punctuation">,</span><span class="z-keyword z-operator"> ^</span><span class="z-keyword z-operator">^</span><span class="z-source">Range</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-storage z-modifier"> constexpr</span><span class="z-punctuation"> (</span><span class="z-keyword z-operator">!</span><span class="z-variable z-other">ranges</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-source"> ...</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-storage z-type"> auto</span><span class="z-keyword z-operator">&amp;</span><span class="z-source"> value </span><span class="z-keyword z-operator">=</span><span class="z-source"> object.</span><span class="z-punctuation">[</span><span class="z-source">:member:</span><span class="z-punctuation">]</span><span class="z-punctuation z-terminator">;</span></span></code></pre> <p>[:member:]这是一个 C++26 拼接表达式。它将反射转换回该反射所代表的实体。因此，在第一次迭代中object.[:member:]，它将给出 的值object.m_rpm，现在我们可以进行如下比较：</p> <p>if (value &lt; range.minimum || value &gt; range.maximum) { throw std::out_of_range(std::string{name} + “ is outside the permitted range [“ + std::to_string(range.minimum) + “, “ + std::to_string(range.maximum) + “]”); } 在下一次迭代中，它将object.[:member:]给出值，object.m_maxTemperature依此类推。以下代码片段实现了所有这些功能：</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">template</span><span class="z-punctuation"> &lt;</span><span class="z-storage z-type">typename</span><span class="z-entity z-name z-type"> T</span><span class="z-punctuation">&gt;</span></span> <span class="giallo-l"><span class="z-storage z-type">void</span><span class="z-entity z-name z-function"> validate_or_throw</span><span class="z-punctuation">(</span><span class="z-storage z-modifier">const</span><span class="z-entity z-name z-type"> T</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> object</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> template</span><span class="z-keyword z-control"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-modifier">constexpr</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-source">info member </span><span class="z-punctuation">:</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">define_static_array</span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">nonstatic_data_members_of</span><span class="z-punctuation">(</span><span class="z-keyword z-operator">^</span><span class="z-keyword z-operator">^</span><span class="z-source">T</span><span class="z-punctuation">,</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name">access_context</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">unchecked</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> constexpr</span><span class="z-storage z-type"> auto</span><span class="z-source"> ranges </span><span class="z-keyword z-operator">=</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">define_static_array</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">annotations_of_with_type</span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-source"> member</span><span class="z-punctuation">,</span><span class="z-keyword z-operator"> ^</span><span class="z-keyword z-operator">^</span><span class="z-source">Range</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-storage z-modifier"> constexpr</span><span class="z-punctuation"> (</span><span class="z-keyword z-operator">!</span><span class="z-variable z-other">ranges</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> constexpr</span><span class="z-source"> Range range </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">extract</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">Range</span><span class="z-punctuation">&gt;</span><span class="z-punctuation">(</span><span class="z-variable z-other">ranges</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">]</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-storage z-type"> auto</span><span class="z-keyword z-operator">&amp;</span><span class="z-source"> value </span><span class="z-keyword z-operator">=</span><span class="z-source"> object.</span><span class="z-punctuation">[</span><span class="z-source">:member:</span><span class="z-punctuation">]</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-source">value </span><span class="z-keyword z-operator">&lt;</span><span class="z-variable z-other"> range</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">minimum</span><span class="z-keyword z-operator"> ||</span><span class="z-source"> value </span><span class="z-keyword z-operator">&gt;</span><span class="z-variable z-other"> range</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">maximum</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> throw</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">out_of_range</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-source">string{name} </span></span> <span class="giallo-l"><span class="z-keyword z-operator"> +</span><span class="z-punctuation"> &quot;</span><span class="z-string"> is outside the permitted range [</span><span class="z-punctuation">&quot;</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> +</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">to_string</span><span class="z-punctuation">(</span><span class="z-variable z-other">range</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">minimum</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> +</span><span class="z-punctuation"> &quot;</span><span class="z-string">, </span><span class="z-punctuation">&quot;</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> +</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">to_string</span><span class="z-punctuation">(</span><span class="z-variable z-other">range</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">maximum</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> +</span><span class="z-punctuation"> &quot;</span><span class="z-string">]</span><span class="z-punctuation">&quot;</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span></code></pre> <p>注解的处理方式Required非常相似，可以大致按如下方式实现：</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-modifier">constexpr</span><span class="z-storage z-type"> auto</span><span class="z-source"> required </span><span class="z-keyword z-operator">=</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">define_static_array</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">annotations_of_with_type</span><span class="z-punctuation">(</span><span class="z-source">member</span><span class="z-punctuation">,</span><span class="z-keyword z-operator"> ^</span><span class="z-keyword z-operator">^</span><span class="z-source">Required</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-control">if</span><span class="z-storage z-modifier"> constexpr</span><span class="z-punctuation"> (</span><span class="z-keyword z-operator">!</span><span class="z-variable z-other">required</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-storage z-type"> auto</span><span class="z-keyword z-operator">&amp;</span><span class="z-source"> value </span><span class="z-keyword z-operator">=</span><span class="z-source"> object.</span><span class="z-punctuation">[</span><span class="z-source">:member:</span><span class="z-punctuation">]</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-storage z-modifier"> constexpr</span><span class="z-punctuation"> (</span><span class="z-source">requires { </span><span class="z-variable z-other">value</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-source"> }</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-variable z-other">value</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> throw</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">invalid_argument</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-source">string{name} </span><span class="z-keyword z-operator">+</span><span class="z-punctuation"> &quot;</span><span class="z-string"> is required</span><span class="z-punctuation">&quot;</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword z-control"> else</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword"> static_assert</span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-source"> requires { </span><span class="z-variable z-other">value</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-source"> }</span><span class="z-punctuation">,</span></span> <span class="giallo-l"><span class="z-punctuation"> &quot;</span><span class="z-string">Required annotation can only be applied to a type </span><span class="z-punctuation">&quot;</span></span> <span class="giallo-l"><span class="z-punctuation"> &quot;</span><span class="z-string">that provides empty()</span><span class="z-punctuation">&quot;</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre> <p>施工阶段验证 验证功能在以下模板函数中实现：</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">template</span><span class="z-punctuation"> &lt;</span><span class="z-storage z-type">typename</span><span class="z-entity z-name z-type"> T</span><span class="z-punctuation">&gt;</span></span> <span class="giallo-l"><span class="z-storage z-type">void</span><span class="z-entity z-name z-function"> validate_or_throw</span><span class="z-punctuation">(</span><span class="z-storage z-modifier">const</span><span class="z-entity z-name z-type"> T</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> object</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-source"> template</span><span class="z-keyword z-control"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-modifier">constexpr</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-source">info member </span><span class="z-punctuation">:</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">define_static_array</span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">nonstatic_data_members_of</span><span class="z-punctuation">(</span><span class="z-keyword z-operator">^</span><span class="z-keyword z-operator">^</span><span class="z-source">T</span><span class="z-punctuation">,</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name">access_context</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">unchecked</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> constexpr</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">string_view name </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">identifier_of</span><span class="z-punctuation">(</span><span class="z-source">member</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation"> &quot;</span><span class="z-string">Validating member: </span><span class="z-punctuation">&quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> name </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation"> &#39;</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation">&#39;</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-modifier"> constexpr</span><span class="z-storage z-type"> auto</span><span class="z-source"> ranges </span><span class="z-keyword z-operator">=</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">define_static_array</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">annotations_of_with_type</span><span class="z-punctuation">(</span><span class="z-source">member</span><span class="z-punctuation">,</span><span class="z-keyword z-operator"> ^</span><span class="z-keyword z-operator">^</span><span class="z-source">Range</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-modifier"> constexpr</span><span class="z-storage z-type"> auto</span><span class="z-source"> range_count </span><span class="z-keyword z-operator">=</span><span class="z-variable z-other"> ranges</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">size</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">cout </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation"> &quot;</span><span class="z-string">Found </span><span class="z-punctuation">&quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> range_count </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation"> &quot;</span><span class="z-string"> range annotations for member: </span><span class="z-punctuation">&quot;</span><span class="z-keyword z-operator"> &lt;&lt;</span><span class="z-source"> name </span><span class="z-keyword z-operator">&lt;&lt;</span><span class="z-punctuation"> &#39;</span><span class="z-constant z-character z-escape">\n</span><span class="z-punctuation">&#39;</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-storage z-modifier"> constexpr</span><span class="z-punctuation"> (</span><span class="z-keyword z-operator">!</span><span class="z-variable z-other">ranges</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> constexpr</span><span class="z-source"> Range range </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">extract</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">Range</span><span class="z-punctuation">&gt;</span><span class="z-punctuation">(</span><span class="z-variable z-other">ranges</span><span class="z-punctuation">[</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">]</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-storage z-type"> auto</span><span class="z-keyword z-operator">&amp;</span><span class="z-source"> value </span><span class="z-keyword z-operator">=</span><span class="z-source"> object.</span><span class="z-punctuation">[</span><span class="z-source">:member:</span><span class="z-punctuation">]</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-source">value </span><span class="z-keyword z-operator">&lt;</span><span class="z-variable z-other"> range</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">minimum</span><span class="z-keyword z-operator"> ||</span><span class="z-source"> value </span><span class="z-keyword z-operator">&gt;</span><span class="z-variable z-other"> range</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">maximum</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> throw</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">out_of_range</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-source">string{name} </span><span class="z-keyword z-operator">+</span><span class="z-punctuation"> &quot;</span><span class="z-string"> is outside the permitted range [</span><span class="z-punctuation">&quot;</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> +</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">to_string</span><span class="z-punctuation">(</span><span class="z-variable z-other">range</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">minimum</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> +</span><span class="z-punctuation"> &quot;</span><span class="z-string">, </span><span class="z-punctuation">&quot;</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> +</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">to_string</span><span class="z-punctuation">(</span><span class="z-variable z-other">range</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">maximum</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> +</span><span class="z-punctuation"> &quot;</span><span class="z-string">]</span><span class="z-punctuation">&quot;</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-modifier"> constexpr</span><span class="z-storage z-type"> auto</span><span class="z-source"> required </span><span class="z-keyword z-operator">=</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">define_static_array</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name">meta</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">annotations_of_with_type</span><span class="z-punctuation">(</span><span class="z-source">member</span><span class="z-punctuation">,</span><span class="z-keyword z-operator"> ^</span><span class="z-keyword z-operator">^</span><span class="z-source">Required</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-storage z-modifier"> constexpr</span><span class="z-punctuation"> (</span><span class="z-keyword z-operator">!</span><span class="z-variable z-other">required</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-storage z-type"> auto</span><span class="z-keyword z-operator">&amp;</span><span class="z-source"> value </span><span class="z-keyword z-operator">=</span><span class="z-source"> object.</span><span class="z-punctuation">[</span><span class="z-source">:member:</span><span class="z-punctuation">]</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-storage z-modifier"> constexpr</span><span class="z-punctuation"> (</span><span class="z-source">requires { </span><span class="z-variable z-other">value</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-source"> }</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-variable z-other">value</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> throw</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">invalid_argument</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-source">string{name} </span><span class="z-keyword z-operator">+</span><span class="z-punctuation"> &quot;</span><span class="z-string"> is required</span><span class="z-punctuation">&quot;</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-keyword z-control"> else</span></span> <span class="giallo-l"><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword"> static_assert</span><span class="z-punctuation">(</span></span> <span class="giallo-l"><span class="z-source"> requires { </span><span class="z-variable z-other">value</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">empty</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-source"> }</span><span class="z-punctuation">,</span></span> <span class="giallo-l"><span class="z-punctuation"> &quot;</span><span class="z-string">Required annotation can only be applied to a type </span><span class="z-punctuation">&quot;</span></span> <span class="giallo-l"><span class="z-punctuation"> &quot;</span><span class="z-string">that provides empty()</span><span class="z-punctuation">&quot;</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre> <p>完整的源代码可在 GitHub 链接中找到。要编译代码，请在命令行中执行以下操作：</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-source">g</span><span class="z-keyword z-operator">++</span><span class="z-keyword z-operator"> -</span><span class="z-source">std</span><span class="z-keyword z-operator">=</span><span class="z-source">c</span><span class="z-keyword z-operator">++</span><span class="z-constant z-numeric">26</span><span class="z-constant z-character z-escape"> \</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> -</span><span class="z-source">freflection </span><span class="z-constant z-character z-escape">\</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> -</span><span class="z-source">Wall </span><span class="z-constant z-character z-escape">\</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> -</span><span class="z-source">Wextra </span><span class="z-constant z-character z-escape">\</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> -</span><span class="z-source">Wpedantic </span><span class="z-constant z-character z-escape">\</span></span> <span class="giallo-l"><span class="z-variable z-other"> reflection_validation</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">cpp</span><span class="z-constant z-character z-escape"> \</span></span> <span class="giallo-l"><span class="z-keyword z-operator"> -</span><span class="z-source">o reflection_validation</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-source">.</span><span class="z-keyword z-operator">/</span><span class="z-source">reflection_validation</span></span> <span class="giallo-l"><span class="z-source">Validating member: m_rpm</span></span> <span class="giallo-l"><span class="z-source">Found </span><span class="z-constant z-numeric">1</span><span class="z-source"> range annotations</span><span class="z-keyword z-control"> for</span><span class="z-source"> member: m_rpm</span></span> <span class="giallo-l"><span class="z-source">Construction failed: m_rpm is outside the permitted range </span><span class="z-punctuation">[</span><span class="z-constant z-numeric">0</span><span class="z-punctuation">,</span><span class="z-constant z-numeric"> 10000</span><span class="z-punctuation">]</span></span> <span class="giallo-l"><span class="z-source">Validating member: m_rpm</span></span> <span class="giallo-l"><span class="z-source">Found </span><span class="z-constant z-numeric">1</span><span class="z-source"> range annotations</span><span class="z-keyword z-control"> for</span><span class="z-source"> member: m_rpm</span></span> <span class="giallo-l"><span class="z-source">Validating member: m_maxTemperature</span></span> <span class="giallo-l"><span class="z-source">Found </span><span class="z-constant z-numeric">1</span><span class="z-source"> range annotations</span><span class="z-keyword z-control"> for</span><span class="z-source"> member: m_maxTemperature</span></span> <span class="giallo-l"><span class="z-source">Validating member: m_deviceName</span></span> <span class="giallo-l"><span class="z-source">Found </span><span class="z-constant z-numeric">0</span><span class="z-source"> range annotations</span><span class="z-keyword z-control"> for</span><span class="z-source"> member: m_deviceName</span></span> <span class="giallo-l"><span class="z-source">Valid configuration created.</span></span> <span class="giallo-l"><span class="z-source">RPM: </span><span class="z-constant z-numeric">5000</span></span> <span class="giallo-l"><span class="z-source">Maximum temperature: </span><span class="z-constant z-numeric">85</span></span> <span class="giallo-l"><span class="z-source">Device name: motor</span><span class="z-keyword z-operator">-</span><span class="z-source">controller</span><span class="z-keyword z-operator">-</span><span class="z-constant z-numeric">1</span></span></code></pre> <p>为了在程序启动时就启用验证，我们可以按如下方式在类validate_or_throw的构造函数中调用验证函数模板：MotorConfig</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-entity z-name">MotorConfig</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">MotorConfig</span><span class="z-punctuation">(</span><span class="z-storage z-type">int</span><span class="z-source"> rpm</span><span class="z-punctuation">,</span><span class="z-storage z-type"> double</span><span class="z-source"> maxTemperature</span><span class="z-punctuation">,</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">string deviceName</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> : m_rpm</span><span class="z-punctuation">{</span><span class="z-source">rpm</span><span class="z-punctuation">}</span><span class="z-punctuation">,</span></span> <span class="giallo-l"><span class="z-source"> m_maxTemperature</span><span class="z-punctuation">{</span><span class="z-source">maxTemperature</span><span class="z-punctuation">}</span><span class="z-punctuation">,</span></span> <span class="giallo-l"><span class="z-source"> m_deviceName</span><span class="z-punctuation">{</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">move</span><span class="z-punctuation">(</span><span class="z-source">deviceName</span><span class="z-punctuation">)</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> validate_or_throw</span><span class="z-punctuation">(</span><span class="z-keyword z-operator">*</span><span class="z-variable z-language">this</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span></span></code></pre> <p>这样可以确保当传递给构造函数的MotorConfig参数值超出允许范围时，构造函数会抛出异常。手动检查传递的参数值的麻烦就此消失了！</p> 2026-08-11T00:00:00+00:00 2026-08-11T00:00:00+00:00 Suchaharcan https://suchaharcan.github.io/01Write_blog_PaperReading/design-patterns-23-cxx/ <h1 id="23-chong-she-ji-mo-shi-c-ban-you-que-dian-yu-ying-yong-chang-jing">23 种设计模式 · C++ 版优缺点与应用场景</h1> <blockquote> <p>GoF《设计模式》23 种，按目的分三类：<strong>创建型（5）· 结构型（7）· 行为型（11）</strong>。本文给出每种模式的意图、C++ 关键代码、优缺点与典型应用场景。</p> </blockquote> <hr /> <h2 id="zong-lan">总览</h2> <table><thead><tr><th>类别</th><th>模式</th><th>一句话</th></tr></thead><tbody> <tr><td>创建型</td><td>单例 Singleton</td><td>全局唯一实例</td></tr> <tr><td>创建型</td><td>工厂方法 Factory Method</td><td>子类决定创建哪个类</td></tr> <tr><td>创建型</td><td>抽象工厂 Abstract Factory</td><td>创建一族相关对象</td></tr> <tr><td>创建型</td><td>建造者 Builder</td><td>分步构建复杂对象</td></tr> <tr><td>创建型</td><td>原型 Prototype</td><td>复制已有对象</td></tr> <tr><td>结构型</td><td>适配器 Adapter</td><td>接口转换</td></tr> <tr><td>结构型</td><td>桥接 Bridge</td><td>抽象与实现分离</td></tr> <tr><td>结构型</td><td>组合 Composite</td><td>树形整体-部分</td></tr> <tr><td>结构型</td><td>装饰 Decorator</td><td>动态附加职责</td></tr> <tr><td>结构型</td><td>外观 Facade</td><td>统一门面接口</td></tr> <tr><td>结构型</td><td>享元 Flyweight</td><td>共享细粒度对象</td></tr> <tr><td>结构型</td><td>代理 Proxy</td><td>替身控制访问</td></tr> <tr><td>行为型</td><td>责任链 Chain of Responsibility</td><td>请求沿链传递</td></tr> <tr><td>行为型</td><td>命令 Command</td><td>请求封装为对象</td></tr> <tr><td>行为型</td><td>解释器 Interpreter</td><td>文法解释</td></tr> <tr><td>行为型</td><td>迭代器 Iterator</td><td>顺序访问集合</td></tr> <tr><td>行为型</td><td>中介者 Mediator</td><td>对象间解耦通信</td></tr> <tr><td>行为型</td><td>备忘录 Memento</td><td>保存/恢复状态</td></tr> <tr><td>行为型</td><td>观察者 Observer</td><td>一对多通知</td></tr> <tr><td>行为型</td><td>状态 State</td><td>状态行为切换</td></tr> <tr><td>行为型</td><td>策略 Strategy</td><td>算法族可替换</td></tr> <tr><td>行为型</td><td>模板方法 Template Method</td><td>骨架固定、步骤可变</td></tr> <tr><td>行为型</td><td>访问者 Visitor</td><td>数据结构与操作分离</td></tr> </tbody></table> <hr /> <h1 id="yi-chuang-jian-xing-mo-shi">一、创建型模式</h1> <h2 id="1-dan-li-singleton">1. 单例 Singleton</h2> <p><strong>意图</strong>：确保一个类只有一个实例，并提供全局访问点。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Logger</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> static</span><span class="z-entity z-name z-type"> Logger</span><span class="z-storage z-modifier">&amp;</span><span class="z-entity z-name z-function"> instance</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> static</span><span class="z-source"> Logger inst</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation z-definition z-comment"> //</span><span class="z-comment"> C++11 线程安全</span></span> <span class="giallo-l"><span class="z-keyword z-control"> return</span><span class="z-source"> inst</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> Logger</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-keyword"> default</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>全局唯一、省资源</td><td>隐藏依赖，难测试</td></tr> <tr><td>延迟初始化</td><td>多线程初始化需注意</td></tr> </tbody></table> <p><strong>场景</strong>：日志系统、配置中心、线程池、连接池。</p> <h2 id="2-gong-han-fang-fa-factory-method">2. 工厂方法 Factory Method</h2> <p><strong>意图</strong>：定义一个创建对象的接口，让子类决定实例化哪个类。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> Product</span><span class="z-punctuation"> {</span><span class="z-storage z-modifier"> virtual</span><span class="z-keyword z-operator"> ~</span><span class="z-entity z-name z-function">Product</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-keyword z-control"> default</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> ConcreteA</span><span class="z-punctuation"> :</span><span class="z-source"> Product </span><span class="z-punctuation">{</span><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Factory</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">unique_ptr</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">Product</span><span class="z-punctuation">&gt;</span><span class="z-entity z-name z-function"> create</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> FactoryA</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Factory</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">unique_ptr</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">Product</span><span class="z-punctuation">&gt;</span><span class="z-entity z-name z-function"> create</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-keyword z-control"> return</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">make_unique</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">ConcreteA</span><span class="z-punctuation">&gt;</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>解耦创建与使用</td><td>每加一个产品需加子类</td></tr> <tr><td>开闭原则友好</td><td>类数量膨胀</td></tr> </tbody></table> <p><strong>场景</strong>：框架中由子类决定对象类型（如游戏单位工厂）。</p> <h2 id="3-chou-xiang-gong-han-abstract-factory">3. 抽象工厂 Abstract Factory</h2> <p><strong>意图</strong>：提供创建<strong>一族</strong>相关对象的接口。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> Button</span><span class="z-punctuation"> {</span><span class="z-storage z-modifier"> virtual</span><span class="z-keyword z-operator"> ~</span><span class="z-entity z-name z-function">Button</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-keyword z-control"> default</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> WinButton</span><span class="z-punctuation"> :</span><span class="z-source"> Button </span><span class="z-punctuation">{</span><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> UIFactory</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">unique_ptr</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">Button</span><span class="z-punctuation">&gt;</span><span class="z-entity z-name z-function"> makeButton</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> WinFactory</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> UIFactory</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">unique_ptr</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">Button</span><span class="z-punctuation">&gt;</span><span class="z-entity z-name z-function"> makeButton</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-keyword z-control"> return</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">make_unique</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">WinButton</span><span class="z-punctuation">&gt;</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>保证产品族一致</td><td>新增产品族类型困难</td></tr> <tr><td>隔离具体类</td><td>新增产品（方法）违反开闭</td></tr> </tbody></table> <p><strong>场景</strong>：跨平台 UI 组件、数据库访问层（不同方言）。</p> <h2 id="4-jian-zao-zhe-builder">4. 建造者 Builder</h2> <p><strong>意图</strong>：分步骤构建复杂对象，步骤可复用于不同表示。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> PizzaBuilder</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> PizzaBuilder</span><span class="z-storage z-modifier">&amp;</span><span class="z-entity z-name z-function"> size</span><span class="z-punctuation">(</span><span class="z-storage z-type">int</span><span class="z-variable z-parameter"> s</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-source"> size_ </span><span class="z-keyword z-operator">=</span><span class="z-source"> s</span><span class="z-punctuation z-terminator">;</span><span class="z-keyword z-control"> return</span><span class="z-keyword z-operator"> *</span><span class="z-variable z-language">this</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> Pizza</span><span class="z-entity z-name z-function"> build</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-keyword z-control"> return</span><span class="z-entity z-name z-function"> Pizza</span><span class="z-punctuation">(</span><span class="z-source">size_</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> size_ </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation z-definition z-comment">//</span><span class="z-comment"> 使用：PizzaBuilder{}.size(12).build();</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>构造参数可读、不可变</td><td>需要额外类</td></tr> <tr><td>复用构建流程</td><td>简单对象反而过度设计</td></tr> </tbody></table> <p><strong>场景</strong>：复杂配置对象、文档/查询构建器。</p> <h2 id="5-yuan-xing-prototype">5. 原型 Prototype</h2> <p><strong>意图</strong>：通过克隆已有对象创建新对象。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> Shape</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-entity z-name z-function"> ~Shape</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-keyword"> default</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">unique_ptr</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">Shape</span><span class="z-punctuation">&gt;</span><span class="z-entity z-name z-function"> clone</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> Circle</span><span class="z-punctuation"> :</span><span class="z-source"> Shape </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">unique_ptr</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">Shape</span><span class="z-punctuation">&gt;</span><span class="z-entity z-name z-function"> clone</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> return</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">make_unique</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">Circle</span><span class="z-punctuation">&gt;</span><span class="z-punctuation">(</span><span class="z-keyword z-operator">*</span><span class="z-variable z-language">this</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>避免重复构造开销</td><td>深拷贝语义易出错</td></tr> <tr><td>动态类型克隆</td><td>含资源成员需自定义拷贝</td></tr> </tbody></table> <p><strong>场景</strong>：编辑器复制图形、游戏单位克隆、配置模板。</p> <hr /> <h1 id="er-jie-gou-xing-mo-shi">二、结构型模式</h1> <h2 id="6-gua-pei-qi-adapter">6. 适配器 Adapter</h2> <p><strong>意图</strong>：将不兼容接口转换为客户端期望的接口。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Target</span><span class="z-punctuation"> {</span><span class="z-storage z-type z-modifier"> public</span><span class="z-punctuation">:</span><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> request</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Adaptee</span><span class="z-punctuation"> {</span><span class="z-storage z-type z-modifier"> public</span><span class="z-punctuation">:</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> specific</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Adapter</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Target</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> request</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-variable z-other"> adaptee_</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">specific</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-source"> Adaptee adaptee_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>复用已有类，不改源码</td><td>过度使用使架构混乱</td></tr> <tr><td>符合开闭原则</td><td>有性能微开销</td></tr> </tbody></table> <p><strong>场景</strong>：接入第三方库、新旧接口桥接。</p> <h2 id="7-qiao-jie-bridge">7. 桥接 Bridge</h2> <p><strong>意图</strong>：将抽象部分与实现部分分离，各自独立变化。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Renderer</span><span class="z-punctuation"> {</span><span class="z-storage z-type z-modifier"> public</span><span class="z-punctuation">:</span><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> draw</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Shape</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> explicit</span><span class="z-entity z-name z-function"> Shape</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">Renderer</span><span class="z-storage z-modifier">*</span><span class="z-variable z-parameter"> r</span><span class="z-punctuation">)</span><span class="z-punctuation"> :</span><span class="z-entity z-name z-function"> r_</span><span class="z-punctuation">(</span><span class="z-source">r</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">protected</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-source"> Renderer</span><span class="z-keyword z-operator">*</span><span class="z-source"> r_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Circle</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Shape</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-keyword"> using</span><span class="z-entity z-name"> Shape</span><span class="z-punctuation">::</span><span class="z-source">Shape</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> draw</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-variable z-other"> r_</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">draw</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>抽象与实现可独立扩展</td><td>增加系统复杂度</td></tr> <tr><td>符合开闭原则</td><td>需提前识别维度</td></tr> </tbody></table> <p><strong>场景</strong>：图形渲染后端（OpenGL/Vulkan）、跨平台设备驱动。</p> <h2 id="8-zu-he-composite">8. 组合 Composite</h2> <p><strong>意图</strong>：将对象组织成树形结构，一致对待叶子与容器。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Component</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> render</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> add</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">Component</span><span class="z-storage z-modifier">*</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Leaf</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Component</span><span class="z-punctuation"> {</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> render</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Composite</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Component</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> add</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">Component</span><span class="z-storage z-modifier">*</span><span class="z-variable z-parameter"> c</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-variable z-other"> children_</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">push_back</span><span class="z-punctuation">(</span><span class="z-source">c</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> render</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-keyword z-control"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">auto</span><span class="z-keyword z-operator">*</span><span class="z-source"> c </span><span class="z-punctuation">:</span><span class="z-source"> children_</span><span class="z-punctuation">)</span><span class="z-variable z-other"> c</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">render</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">vector</span><span class="z-keyword z-operator">&lt;</span><span class="z-source">Component</span><span class="z-keyword z-operator">*</span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> children_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>树形结构统一操作</td><td>叶子与容器接口耦合</td></tr> <tr><td>易扩展新节点</td><td>违反接口隔离</td></tr> </tbody></table> <p><strong>场景</strong>：文件系统、UI 控件树、组织架构。</p> <h2 id="9-zhuang-shi-decorator">9. 装饰 Decorator</h2> <p><strong>意图</strong>：动态给对象添加职责，替代继承。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Stream</span><span class="z-punctuation"> {</span><span class="z-storage z-type z-modifier"> public</span><span class="z-punctuation">:</span><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> write</span><span class="z-punctuation">(</span><span class="z-storage z-modifier">const</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">string</span><span class="z-keyword z-operator">&amp;</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> FileStream</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Stream</span><span class="z-punctuation"> {</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> write</span><span class="z-punctuation">(</span><span class="z-storage z-modifier">const</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">string</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> s</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> EncryptedStream</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Stream</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> explicit</span><span class="z-entity z-name z-function"> EncryptedStream</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">Stream</span><span class="z-storage z-modifier">*</span><span class="z-variable z-parameter"> s</span><span class="z-punctuation">)</span><span class="z-punctuation"> :</span><span class="z-entity z-name z-function"> s_</span><span class="z-punctuation">(</span><span class="z-source">s</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> write</span><span class="z-punctuation">(</span><span class="z-storage z-modifier">const</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">string</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> s</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-variable z-other"> s_</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">write</span><span class="z-punctuation">(</span><span class="z-entity z-name z-function">encrypt</span><span class="z-punctuation">(</span><span class="z-source">s</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-source"> Stream</span><span class="z-keyword z-operator">*</span><span class="z-source"> s_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>组合优于继承，灵活</td><td>层数多时难调试</td></tr> <tr><td>运行时叠加能力</td><td>小对象过多</td></tr> </tbody></table> <p><strong>场景</strong>：IO 流加缓冲/加密/压缩、中间件管道。</p> <h2 id="10-wai-guan-facade">10. 外观 Facade</h2> <p><strong>意图</strong>：为复杂子系统提供统一简化的入口。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> VideoConverter</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> convert</span><span class="z-punctuation">(</span><span class="z-storage z-modifier">const</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">string</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> file</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-variable z-other"> codec_</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">load</span><span class="z-punctuation">(</span><span class="z-source">file</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-variable z-other"> filter_</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">apply</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-variable z-other"> mux_</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">save</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-source"> Codec codec_</span><span class="z-punctuation z-terminator">;</span><span class="z-source"> Filter filter_</span><span class="z-punctuation z-terminator">;</span><span class="z-source"> Muxer mux_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>客户端使用简单</td><td>可能变成“上帝对象“</td></tr> <tr><td>隔离子系统变化</td><td>隐藏了灵活性</td></tr> </tbody></table> <p><strong>场景</strong>：编译模块入口、播放器/转换器统一 API。</p> <h2 id="11-xiang-yuan-flyweight">11. 享元 Flyweight</h2> <p><strong>意图</strong>：共享细粒度对象，减少内存占用。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> CharStyle</span><span class="z-punctuation"> {</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">string font</span><span class="z-punctuation z-terminator">;</span><span class="z-storage z-type"> int</span><span class="z-source"> size</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> StyleCache</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-entity z-name z-type"> CharStyle</span><span class="z-storage z-modifier">&amp;</span><span class="z-entity z-name z-function"> get</span><span class="z-punctuation">(</span><span class="z-storage z-modifier">const</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">string</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> font</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> size</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type"> auto</span><span class="z-source"> key </span><span class="z-keyword z-operator">=</span><span class="z-source"> font </span><span class="z-keyword z-operator">+</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">to_string</span><span class="z-punctuation">(</span><span class="z-source">size</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> auto</span><span class="z-source"> it </span><span class="z-keyword z-operator">=</span><span class="z-variable z-other"> cache_</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">find</span><span class="z-punctuation">(</span><span class="z-source">key</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-source">it </span><span class="z-keyword z-operator">==</span><span class="z-variable z-other"> cache_</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">end</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span></span> <span class="giallo-l"><span class="z-source"> it </span><span class="z-keyword z-operator">=</span><span class="z-variable z-other"> cache_</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">emplace</span><span class="z-punctuation">(</span><span class="z-source">key</span><span class="z-punctuation">,</span><span class="z-source"> CharStyle{font</span><span class="z-punctuation">,</span><span class="z-source"> size}</span><span class="z-punctuation">)</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">first</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-keyword z-control"> return</span><span class="z-variable z-other"> it</span><span class="z-punctuation">-&gt;</span><span class="z-variable z-other z-property">second</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">unordered_map</span><span class="z-keyword z-operator">&lt;</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-source">string</span><span class="z-punctuation">,</span><span class="z-source"> CharStyle</span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> cache_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>大幅减少内存</td><td>外部状态管理复杂</td></tr> <tr><td>提高缓存命中</td><td>引入共享对象并发问题</td></tr> </tbody></table> <p><strong>场景</strong>：文本编辑器字符样式、游戏贴图/粒子模板、连接池。</p> <h2 id="12-dai-li-proxy">12. 代理 Proxy</h2> <p><strong>意图</strong>：提供替身控制对真实对象的访问（延迟/权限/缓存）。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Image</span><span class="z-punctuation"> {</span><span class="z-storage z-type z-modifier"> public</span><span class="z-punctuation">:</span><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> show</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> RealImage</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Image</span><span class="z-punctuation"> {</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> show</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> ImageProxy</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Image</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> show</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-keyword z-operator">!</span><span class="z-source">real_</span><span class="z-punctuation">)</span><span class="z-source"> real_ </span><span class="z-keyword z-operator">=</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-function">make_unique</span><span class="z-punctuation">&lt;</span><span class="z-entity z-name z-type">RealImage</span><span class="z-punctuation">&gt;</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-variable z-other"> real_</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">show</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation z-definition z-comment"> //</span><span class="z-comment"> 延迟加载</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">unique_ptr</span><span class="z-keyword z-operator">&lt;</span><span class="z-source">RealImage</span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> real_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>延迟加载、访问控制、日志</td><td>增加间接层</td></tr> <tr><td>透明代理</td><td>过度代理增加延迟</td></tr> </tbody></table> <p><strong>场景</strong>：懒加载图片、智能指针、远程调用（RPC stub）。</p> <hr /> <h1 id="san-xing-wei-xing-mo-shi">三、行为型模式</h1> <h2 id="13-ze-ren-lian-chain-of-responsibility">13. 责任链 Chain of Responsibility</h2> <p><strong>意图</strong>：多个处理者串成链，请求沿链传递直到被处理。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Handler</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> Handler</span><span class="z-storage z-modifier">*</span><span class="z-entity z-name z-function"> next</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">Handler</span><span class="z-storage z-modifier">*</span><span class="z-variable z-parameter"> n</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-source"> next_ </span><span class="z-keyword z-operator">=</span><span class="z-source"> n</span><span class="z-punctuation z-terminator">;</span><span class="z-keyword z-control"> return</span><span class="z-variable z-language"> this</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> handle</span><span class="z-punctuation">(</span><span class="z-storage z-type">int</span><span class="z-variable z-parameter"> level</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-entity z-name z-function">canHandle</span><span class="z-punctuation">(</span><span class="z-source">level</span><span class="z-punctuation">)</span><span class="z-punctuation">)</span><span class="z-entity z-name z-function"> process</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-keyword z-control"> else</span><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-source">next_</span><span class="z-punctuation">)</span><span class="z-variable z-other"> next_</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">handle</span><span class="z-punctuation">(</span><span class="z-source">level</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> bool</span><span class="z-entity z-name z-function"> canHandle</span><span class="z-punctuation">(</span><span class="z-storage z-type">int</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> process</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-source"> Handler</span><span class="z-keyword z-operator">*</span><span class="z-source"> next_ </span><span class="z-keyword z-operator">=</span><span class="z-constant z-language"> nullptr</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>发送者与处理者解耦</td><td>请求可能无人处理</td></tr> <tr><td>灵活增删处理者</td><td>调试链长时困难</td></tr> </tbody></table> <p><strong>场景</strong>：日志级别过滤、事件冒泡、中间件管道。</p> <h2 id="14-ming-ling-command">14. 命令 Command</h2> <p><strong>意图</strong>：把请求封装成对象，支持参数化、队列、撤销。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Command</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> execute</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> undo</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> CopyCommand</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Command</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> execute</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> undo</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>支持撤销/重做、任务队列</td><td>每个操作一个类</td></tr> <tr><td>请求可参数化延迟执行</td><td>类数量增加</td></tr> </tbody></table> <p><strong>场景</strong>：编辑器撤销栈、事务、宏录制、线程任务。</p> <h2 id="15-jie-shi-qi-interpreter">15. 解释器 Interpreter</h2> <p><strong>意图</strong>：为文法定义解释器，求值表达式。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> Expr</span><span class="z-punctuation"> {</span><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> eval</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> Num</span><span class="z-punctuation"> :</span><span class="z-source"> Expr </span><span class="z-punctuation">{</span><span class="z-storage z-type"> int</span><span class="z-source"> v</span><span class="z-punctuation z-terminator">;</span><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> eval</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-keyword z-control"> return</span><span class="z-source"> v</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> Add</span><span class="z-punctuation"> :</span><span class="z-source"> Expr </span><span class="z-punctuation">{</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> const</span><span class="z-source"> Expr </span><span class="z-keyword z-operator">*</span><span class="z-source">l</span><span class="z-punctuation">,</span><span class="z-keyword z-operator"> *</span><span class="z-source">r</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> eval</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-keyword z-control"> return</span><span class="z-variable z-other"> l</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">eval</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> +</span><span class="z-variable z-other"> r</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">eval</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>文法易扩展</td><td>复杂文法维护困难</td></tr> <tr><td>领域语言表达力强</td><td>性能较低</td></tr> </tbody></table> <p><strong>场景</strong>：SQL/正则/数学表达式引擎、脚本解析。</p> <h2 id="16-die-dai-qi-iterator">16. 迭代器 Iterator</h2> <p><strong>意图</strong>：不暴露内部结构，顺序访问集合元素。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Iter</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> bool</span><span class="z-entity z-name z-function"> hasNext</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> next</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> RangeIter</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Iter</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> cur_</span><span class="z-punctuation">,</span><span class="z-source"> end_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> RangeIter</span><span class="z-punctuation">(</span><span class="z-storage z-type">int</span><span class="z-variable z-parameter"> a</span><span class="z-punctuation">,</span><span class="z-storage z-type"> int</span><span class="z-variable z-parameter"> b</span><span class="z-punctuation">)</span><span class="z-punctuation"> :</span><span class="z-entity z-name z-function"> cur_</span><span class="z-punctuation">(</span><span class="z-source">a</span><span class="z-punctuation">)</span><span class="z-punctuation">,</span><span class="z-entity z-name z-function"> end_</span><span class="z-punctuation">(</span><span class="z-source">b</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-storage z-type"> bool</span><span class="z-entity z-name z-function"> hasNext</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-keyword z-control"> return</span><span class="z-source"> cur_ </span><span class="z-keyword z-operator">&lt;=</span><span class="z-source"> end_</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-entity z-name z-function"> next</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-keyword z-control"> return</span><span class="z-source"> cur_</span><span class="z-keyword z-operator">++</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>集合遍历与结构解耦</td><td>简单集合反而多余</td></tr> <tr><td>支持多种遍历策略</td><td>遍历中修改集合需约定</td></tr> </tbody></table> <p><strong>场景</strong>：STL 迭代器、分页遍历、树遍历。</p> <h2 id="17-zhong-jie-zhe-mediator">17. 中介者 Mediator</h2> <p><strong>意图</strong>：用一个中介对象协调多个对象的交互。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Mediator</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> notify</span><span class="z-punctuation">(</span><span class="z-storage z-modifier">const</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">string</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> from</span><span class="z-punctuation">,</span><span class="z-storage z-modifier"> const</span><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">string</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> msg</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-keyword z-control"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">auto</span><span class="z-keyword z-operator">*</span><span class="z-source"> c </span><span class="z-punctuation">:</span><span class="z-source"> colleagues_</span><span class="z-punctuation">)</span><span class="z-keyword z-control"> if</span><span class="z-punctuation"> (</span><span class="z-variable z-other">c</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">name</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> !=</span><span class="z-source"> from</span><span class="z-punctuation">)</span><span class="z-variable z-other"> c</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">receive</span><span class="z-punctuation">(</span><span class="z-source">msg</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> add</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">Colleague</span><span class="z-storage z-modifier">*</span><span class="z-variable z-parameter"> c</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-variable z-other"> colleagues_</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">push_back</span><span class="z-punctuation">(</span><span class="z-source">c</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">vector</span><span class="z-keyword z-operator">&lt;</span><span class="z-source">Colleague</span><span class="z-keyword z-operator">*</span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> colleagues_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>减少对象间网状依赖</td><td>中介者可能过于庞大</td></tr> <tr><td>交互集中管理</td><td>单点故障</td></tr> </tbody></table> <p><strong>场景</strong>：聊天室、UI 控件协调、航班调度。</p> <h2 id="18-bei-wang-lu-memento">18. 备忘录 Memento</h2> <p><strong>意图</strong>：在不破坏封装的前提下保存并恢复对象状态。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">struct</span><span class="z-entity z-name z-type"> Memento</span><span class="z-punctuation"> {</span><span class="z-storage z-type"> int</span><span class="z-source"> state</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Originator</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name z-type"> Memento</span><span class="z-entity z-name z-function"> save</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> const</span><span class="z-punctuation"> {</span><span class="z-keyword z-control"> return</span><span class="z-punctuation"> {</span><span class="z-source">state_</span><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> restore</span><span class="z-punctuation">(</span><span class="z-storage z-modifier">const</span><span class="z-entity z-name z-type"> Memento</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> m</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-source"> state_ </span><span class="z-keyword z-operator">=</span><span class="z-variable z-other"> m</span><span class="z-punctuation">.</span><span class="z-variable z-other z-property">state</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> int</span><span class="z-source"> state_ </span><span class="z-keyword z-operator">=</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>状态快照与恢复简单</td><td>大对象快照开销高</td></tr> <tr><td>不破坏封装</td><td>历史过多占内存</td></tr> </tbody></table> <p><strong>场景</strong>：编辑器撤销、游戏存档、事务回滚。</p> <h2 id="19-guan-cha-zhe-observer">19. 观察者 Observer</h2> <p><strong>意图</strong>：定义一对多依赖，状态变化自动通知。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Observer</span><span class="z-punctuation"> {</span><span class="z-storage z-type z-modifier"> public</span><span class="z-punctuation">:</span><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> update</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Subject</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> attach</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">Observer</span><span class="z-storage z-modifier">*</span><span class="z-variable z-parameter"> o</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-variable z-other"> obs_</span><span class="z-punctuation">.</span><span class="z-entity z-name z-function">push_back</span><span class="z-punctuation">(</span><span class="z-source">o</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> notify</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-keyword z-control"> for</span><span class="z-punctuation"> (</span><span class="z-storage z-type">auto</span><span class="z-keyword z-operator">*</span><span class="z-source"> o </span><span class="z-punctuation">:</span><span class="z-source"> obs_</span><span class="z-punctuation">)</span><span class="z-variable z-other"> o</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">update</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-entity z-name"> std</span><span class="z-punctuation">::</span><span class="z-source">vector</span><span class="z-keyword z-operator">&lt;</span><span class="z-source">Observer</span><span class="z-keyword z-operator">*</span><span class="z-keyword z-operator">&gt;</span><span class="z-source"> obs_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>主题与观察者解耦</td><td>通知顺序不确定</td></tr> <tr><td>广播机制天然</td><td>级联更新难排查</td></tr> </tbody></table> <p><strong>场景</strong>：事件总线、MVC 视图刷新、发布订阅。</p> <h2 id="20-zhuang-tai-state">20. 状态 State</h2> <p><strong>意图</strong>：对象状态改变时行为随之改变，替代大量 if-else。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> State</span><span class="z-punctuation"> {</span><span class="z-storage z-type z-modifier"> public</span><span class="z-punctuation">:</span><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> handle</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> IdleState</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> State</span><span class="z-punctuation"> {</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> handle</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> RunningState</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> State</span><span class="z-punctuation"> {</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> handle</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>状态行为内聚、可扩展</td><td>状态类数量多</td></tr> <tr><td>消除巨型条件分支</td><td>状态转换逻辑分散</td></tr> </tbody></table> <p><strong>场景</strong>：播放器状态、订单状态机、网络连接状态。</p> <h2 id="21-ce-lue-strategy">21. 策略 Strategy</h2> <p><strong>意图</strong>：定义算法族并封装，运行时切换。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> SortStrategy</span><span class="z-punctuation"> {</span><span class="z-storage z-type z-modifier"> public</span><span class="z-punctuation">:</span><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> sort</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-source">vector</span><span class="z-keyword z-operator">&lt;</span><span class="z-storage z-type">int</span><span class="z-keyword z-operator">&gt;</span><span class="z-keyword z-operator">&amp;</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> QuickSort</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> SortStrategy</span><span class="z-punctuation"> {</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> sort</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> v</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> MergeSort</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> SortStrategy</span><span class="z-punctuation"> {</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> sort</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> v</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span><span class="z-punctuation"> }</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Sorter</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> setStrategy</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">SortStrategy</span><span class="z-storage z-modifier">*</span><span class="z-variable z-parameter"> s</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-source"> s_ </span><span class="z-keyword z-operator">=</span><span class="z-source"> s</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> run</span><span class="z-punctuation">(</span><span class="z-entity z-name">std</span><span class="z-punctuation">::</span><span class="z-entity z-name z-type">vector</span><span class="z-punctuation">&lt;</span><span class="z-storage z-type">int</span><span class="z-punctuation">&gt;</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> v</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-variable z-other"> s_</span><span class="z-punctuation">-&gt;</span><span class="z-entity z-name z-function">sort</span><span class="z-punctuation">(</span><span class="z-source">v</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-source"> SortStrategy</span><span class="z-keyword z-operator">*</span><span class="z-source"> s_</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>算法可替换、开闭原则</td><td>客户端需了解策略差异</td></tr> <tr><td>消除条件分支</td><td>策略对象数量增加</td></tr> </tbody></table> <p><strong>场景</strong>：排序算法选择、压缩/加密算法、价格计算。</p> <h2 id="22-mo-ban-fang-fa-template-method">22. 模板方法 Template Method</h2> <p><strong>意图</strong>：定义算法骨架，子类实现可变步骤。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> DataParser</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> parse</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-punctuation z-definition z-comment"> //</span><span class="z-comment"> 骨架固定</span></span> <span class="giallo-l"><span class="z-entity z-name z-function"> open</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-entity z-name z-function"> read</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-entity z-name z-function"> process</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span><span class="z-entity z-name z-function"> close</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation"> }</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">protected</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> process</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span><span class="z-punctuation z-definition z-comment"> //</span><span class="z-comment"> 可变步骤</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">private</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> open</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> read</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> close</span><span class="z-punctuation">(</span><span class="z-punctuation">)</span><span class="z-punctuation"> {</span><span class="z-punctuation">}</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>复用公共流程</td><td>骨架修改影响全部子类</td></tr> <tr><td>约束子类实现范围</td><td>违反 LSP 风险（子类改变骨架）</td></tr> </tbody></table> <p><strong>场景</strong>：框架生命周期（初始化-运行-清理）、解析器流程。</p> <h2 id="23-fang-wen-zhe-visitor">23. 访问者 Visitor</h2> <p><strong>意图</strong>：在不修改类的前提下，为对象结构增加新操作。</p> <pre class="giallo z-code"><code data-lang="cpp"><span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Visitor</span><span class="z-punctuation z-terminator">;</span><span class="z-source"> </span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Node</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> accept</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">Visitor</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> v</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> TextNode</span><span class="z-punctuation"> :</span><span class="z-storage z-type z-modifier"> public</span><span class="z-entity z-name z-type"> Node</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> accept</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">Visitor</span><span class="z-storage z-modifier">&amp;</span><span class="z-variable z-parameter"> v</span><span class="z-punctuation">)</span><span class="z-storage z-modifier"> override</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-storage z-type">class</span><span class="z-entity z-name z-type"> Visitor</span><span class="z-punctuation"> {</span></span> <span class="giallo-l"><span class="z-storage z-type z-modifier">public</span><span class="z-punctuation">:</span></span> <span class="giallo-l"><span class="z-storage z-modifier"> virtual</span><span class="z-storage z-type"> void</span><span class="z-entity z-name z-function"> visit</span><span class="z-punctuation">(</span><span class="z-entity z-name z-type">TextNode</span><span class="z-storage z-modifier">&amp;</span><span class="z-punctuation">)</span><span class="z-keyword z-operator"> =</span><span class="z-constant z-numeric"> 0</span><span class="z-punctuation z-terminator">;</span></span> <span class="giallo-l"><span class="z-punctuation">}</span><span class="z-punctuation z-terminator">;</span></span></code></pre><table><thead><tr><th>优点</th><th>缺点</th></tr></thead><tbody> <tr><td>数据结构与操作分离，易加操作</td><td>新增节点类型需改所有访问者</td></tr> <tr><td>操作内聚</td><td>破坏封装（需暴露内部）</td></tr> </tbody></table> <p><strong>场景</strong>：AST 编译/解释、对象结构统计与序列化。</p> <hr /> <h2 id="xuan-xing-su-cha">选型速查</h2> <table><thead><tr><th>问题</th><th>推荐模式</th></tr></thead><tbody> <tr><td>全局唯一</td><td>单例</td></tr> <tr><td>创建复杂对象</td><td>建造者 / 工厂 / 抽象工厂</td></tr> <tr><td>接口不兼容</td><td>适配器</td></tr> <tr><td>动态加职责</td><td>装饰</td></tr> <tr><td>树形结构</td><td>组合</td></tr> <tr><td>延迟/控制访问</td><td>代理</td></tr> <tr><td>一对多通知</td><td>观察者</td></tr> <tr><td>运行时换算法</td><td>策略</td></tr> <tr><td>状态行为切换</td><td>状态</td></tr> <tr><td>撤销重做</td><td>命令 + 备忘录</td></tr> <tr><td>为结构加新操作</td><td>访问者</td></tr> </tbody></table> <blockquote> <p>原则提醒：<strong>优先组合而非继承、面向接口而非实现、对扩展开放对修改关闭</strong>。模式是工具，不要为模式而模式。</p> </blockquote>