{"id":331,"date":"2021-06-12T11:38:32","date_gmt":"2021-06-12T03:38:32","guid":{"rendered":"https:\/\/swordofmorning.com\/?p=331"},"modified":"2025-10-09T13:56:04","modified_gmt":"2025-10-09T05:56:04","slug":"design-pattern-09-visitor-pattern","status":"publish","type":"post","link":"https:\/\/swordofmorning.com\/index.php\/2021\/06\/12\/design-pattern-09-visitor-pattern\/","title":{"rendered":"\u8bbe\u8ba1\u6a21\u5f0f 09 \u8bbf\u95ee\u8005\u6a21\u5f0f"},"content":{"rendered":"<p><div class=\"has-toc have-toc\"><\/div><\/p>\n<h2>\u4e00\u3001\u610f\u56fe<\/h2>\n<p>&nbsp;&nbsp;&nbsp;&nbsp;\u8868\u793a\u4e00\u4e2a\u4f5c\u7528\u4e8e\u5bf9\u8c61\u7ed3\u6784\u4f53\u4e2d\u7684\u5404\u5143\u7d20\u64cd\u4f5c\u3002\u5b83\u4f7f\u4f60\u53ef\u4ee5\u518d\u4e0d\u6539\u53d8\u5143\u7d20\u7684\u7c7b\u7684\u60c5\u51b5\u4e0b\u5b9a\u4e49\u4f5c\u7528\u4e8e\u8fd9\u4e9b\u5143\u7d20\u7684\u65b0\u64cd\u4f5c\u3002<br \/>\n&nbsp;&nbsp;&nbsp;&nbsp;\u4eba\u8bdd\uff1a\u5728\u4e0d\u6539\u53d8\u65e2\u6709\u7c7b\u65f6\uff0c\u4e3a\u5176\u589e\u52a0\u65b0\u7684\u529f\u80fd\u3002<\/p>\n<h2>\u4e8c\u3001\u548c\u771f\u5b9e\u4e16\u754c\u7684\u7c7b\u6bd4<\/h2>\n<figure style=\"width: 600px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\"   class=\"lazyload\" data-src=\"https:\/\/cdn.swordofmorning.com\/SwordofMorning\/Article%20Images\/Design%20Pattern\/09\/visitor-comic-1.png\" src=\"https:\/\/cdn.jsdelivr.net\/gh\/moezx\/cdn@3.0.2\/img\/svg\/loader\/trans.ajax-spinner-preloader.svg\" onerror=\"imgError(this)\"  width=\"600\" height=\"300\" alt=\"\u56fe1\" class=\"size-full\" \/ ><figcaption class=\"wp-caption-text\"><noscript><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.swordofmorning.com\/SwordofMorning\/Article%20Images\/Design%20Pattern\/09\/visitor-comic-1.png\" width=\"600\" height=\"300\" alt=\"\u56fe1\" class=\"size-full\" \/><\/noscript> \u56fe1\uff1a\u4f18\u79c0\u7684\u4fdd\u9669\u4ee3\u7406\u4eba\u603b\u80fd\u4e3a\u4e0d\u540c\u7c7b\u578b\u7684\u56e2\u4f53\u63d0\u4f9b\u4e0d\u540c\u7684\u4fdd\u5355<\/figcaption><\/figure>\n<p>&nbsp;&nbsp;&nbsp;&nbsp;\u5047\u5982\u6709\u8fd9\u6837\u4e00\u4f4d\u975e\u5e38\u5e0c\u671b\u8d62\u5f97\u65b0\u5ba2\u6237\u7684\u8d44\u6df1\u4fdd\u9669\u4ee3\u7406\u4eba\u3002\u4ed6\u53ef\u4ee5\u62dc\u8bbf\u8857\u533a\u4e2d\u7684\u6bcf\u680b\u697c\uff0c\u5c1d\u8bd5\u5411\u6bcf\u4e2a\u8def\u4eba\u63a8\u9500\u4fdd\u9669\u3002\u6240\u4ee5\uff0c\u6839\u636e\u5927\u697c\u5185\u7ec4\u7ec7\u7c7b\u578b\u7684\u4e0d\u540c\uff0c\u4ed6\u53ef\u4ee5\u63d0\u4f9b\u4e13\u95e8\u7684\u4fdd\u5355\uff1a<br \/>\n&nbsp;&nbsp;&nbsp;&nbsp;\u5982\u679c\u5efa\u7b51\u662f\u5c45\u6c11\u697c\uff0c\u4ed6\u4f1a\u63a8\u9500\u533b\u7597\u4fdd\u9669\u3002<br \/>\n&nbsp;&nbsp;&nbsp;&nbsp;\u5982\u679c\u5efa\u7b51\u662f\u94f6\u884c\uff0c\u4ed6\u4f1a\u63a8\u9500\u5931\u7a83\u4fdd\u9669\u3002<br \/>\n&nbsp;&nbsp;&nbsp;&nbsp;\u5982\u679c\u5efa\u7b51\u662f\u5496\u5561\u5385\uff0c\u4ed6\u4f1a\u63a8\u9500\u706b\u707e\u548c\u6d2a\u6c34\u4fdd\u9669\u3002<\/p>\n<h2>\u4e09\u3001UML<\/h2>\n<figure style=\"width: 520px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\"   class=\"lazyload\" data-src=\"https:\/\/cdn.swordofmorning.com\/SwordofMorning\/Article%20Images\/Design%20Pattern\/09\/structure-zh.png\" src=\"https:\/\/cdn.jsdelivr.net\/gh\/moezx\/cdn@3.0.2\/img\/svg\/loader\/trans.ajax-spinner-preloader.svg\" onerror=\"imgError(this)\"  width=\"520\" height=\"540\" alt=\"\u56fe2\" class=\"size-full\" \/ ><figcaption class=\"wp-caption-text\"><noscript><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.swordofmorning.com\/SwordofMorning\/Article%20Images\/Design%20Pattern\/09\/structure-zh.png\" width=\"520\" height=\"540\" alt=\"\u56fe2\" class=\"size-full\" \/><\/noscript> \u56fe2\uff1a\u8bbf\u95ee\u8005\u6a21\u5f0f\u7ed3\u6784<\/figcaption><\/figure>\n<h2>\u56db\u3001\u5b9e\u4f8b<\/h2>\n<p>&nbsp;&nbsp;&nbsp;&nbsp;\u5047\u8bbe\u6211\u4eec\u8981\u5bf9\u4e00\u4e2a\u6c7d\u8f66\u96f6\u4ef6\u88c5\u914d\u5382\u7684\u7cfb\u7edf\u91cd\u6784\uff0c\u4ed6\u4eec\u7684\u96f6\u4ef6\u5f88\u5c11\u53d8\u5316\uff0c\u4ef7\u683c\u7ecf\u5e38\u53d8\u5316\uff0c\u4e0b\u9762\u4f7f\u7528\u8bbf\u95ee\u8005\u6a21\u5f0f\u6765\u6539\u8fdb\u4ed6\u4eec\u7684\u7cfb\u7edf\u3002<\/p>\n<figure style=\"width: 868px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\"   class=\"lazyload\" data-src=\"https:\/\/cdn.swordofmorning.com\/SwordofMorning\/Article%20Images\/Design%20Pattern\/09\/DP_EXP2_Q3.png\" src=\"https:\/\/cdn.jsdelivr.net\/gh\/moezx\/cdn@3.0.2\/img\/svg\/loader\/trans.ajax-spinner-preloader.svg\" onerror=\"imgError(this)\"  width=\"868\" height=\"862\" alt=\"\u56fe3\" class=\"size-full\" \/ ><figcaption class=\"wp-caption-text\"><noscript><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.swordofmorning.com\/SwordofMorning\/Article%20Images\/Design%20Pattern\/09\/DP_EXP2_Q3.png\" width=\"868\" height=\"862\" alt=\"\u56fe3\" class=\"size-full\" \/><\/noscript> \u56fe3\uff1a\u7c7b\u56fe<\/figcaption><\/figure>\n<p>&nbsp;&nbsp;&nbsp;&nbsp;\u5728\u8fd9\u4e2a\u6848\u4f8b\u4e2d\uff0c\u6211\u4eec\u67095\u4e2a\u4ea7\u54c1\uff0c\u4e24\u4e2a\u8bbf\u95ee\u8005\u5206\u522b\u8bbf\u95ee\u4ed6\u4eec\u7684\u4ef7\u683c\u548c\u63cf\u8ff0\u3002\u4e0b\u9762\u662f\u4ee3\u7801\uff1a<\/p>\n<pre><code class=\"language-cpp\">#include &lt;iostream&gt;\n#include &lt;string&gt;\n\nclass Crankcase;\nclass Carburetor;\nclass Whell;\nclass HeadlightBulb;\nclass Reflector;\nclass Engine;\nclass Headlight;\n\nclass Visitor\n{\npublic:\n    virtual void visit(const Crankcase* ele) const = 0;\n    virtual void visit(const Carburetor* ele) const = 0;\n    virtual void visit(const Whell* ele) const = 0;\n    virtual void visit(const HeadlightBulb* ele) const = 0;\n    virtual void visit(const Reflector* ele) const = 0;\n    virtual void visit(const Headlight* ele) const = 0;\n    virtual void visit(const Engine* ele) const = 0;\n};\n\nclass CarPart\n{\npublic:\n    virtual std::string getDescription() const = 0;\n    virtual void accept(Visitor* vis) const = 0;\n};\n\nclass Engine : public CarPart\n{\npublic:\n    virtual std::string getDescription() const override\n    {\n        return &quot;Engine&quot;;\n    }\n\n    virtual void accept(Visitor* vis) const override\n    {\n        vis-&gt;visit(this);\n    }\n};\n\nclass Whell : public CarPart\n{\npublic:\n    virtual std::string getDescription() const override\n    {\n        return &quot;Whell&quot;;\n    }\n\n    virtual void accept(Visitor* vis) const override\n    {\n        vis-&gt;visit(this);\n    }\n};\n\nclass Headlight : public CarPart\n{\npublic:\n    virtual std::string getDescription() const override\n    {\n        return &quot;Headlight&quot;;\n    }\n\n    virtual void accept(Visitor* vis) const override\n    {\n        vis-&gt;visit(this);\n    }\n};\n\nclass Crankcase : public Engine\n{\npublic:\n    virtual std::string getDescription() const override\n    {\n        return &quot;Crankcase&quot;;\n    }\n\n    virtual void accept(Visitor* vis) const override\n    {\n        vis-&gt;visit(this);\n    }\n};\n\nclass Carburetor : public Engine\n{\npublic:\n    virtual std::string getDescription() const override\n    {\n        return &quot;Carburetor&quot;;\n    }\n\n    virtual void accept(Visitor* vis) const override\n    {\n        vis-&gt;visit(this);\n    }\n};\n\nclass HeadlightBulb : public Headlight\n{\npublic:\n    virtual std::string getDescription() const override\n    {\n        return &quot;HeadlightBulb&quot;;\n    }\n\n    virtual void accept(Visitor* vis) const override\n    {\n        vis-&gt;visit(this);\n    }\n};\n\nclass Reflector : public Headlight\n{\npublic:\n    virtual std::string getDescription() const override\n    {\n        return &quot;Reflector&quot;;\n    }\n\n    virtual void accept(Visitor* vis) const override\n    {\n        vis-&gt;visit(this);\n    }\n};\n\nclass PriceVisitor : public Visitor\n{\npublic:\n    virtual void visit(const Crankcase* ele) const override\n    {\n        std::cout &lt;&lt; 10 &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const Carburetor* ele) const override\n    {\n        std::cout &lt;&lt; 20 &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const Whell* ele) const override\n    {\n        std::cout &lt;&lt; 30 &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const HeadlightBulb* ele) const override\n    {\n        std::cout &lt;&lt; 40 &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const Reflector* ele) const override\n    {\n        std::cout &lt;&lt; 50 &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const Headlight* ele) const override\n    {\n        std::cout &lt;&lt; 60 &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const Engine* ele) const override\n    {\n        std::cout &lt;&lt; 70 &lt;&lt; std::endl;\n    }\n};\n\nclass DesVisitor : public Visitor\n{\npublic:\n    virtual void visit(const Crankcase* ele) const override\n    {\n        std::cout &lt;&lt; ele-&gt;getDescription() &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const Carburetor* ele) const override\n    {\n        std::cout &lt;&lt; ele-&gt;getDescription() &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const Whell* ele) const override\n    {\n        std::cout &lt;&lt; ele-&gt;getDescription() &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const HeadlightBulb* ele) const override\n    {\n        std::cout &lt;&lt; ele-&gt;getDescription() &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const Reflector* ele) const override\n    {\n        std::cout &lt;&lt; ele-&gt;getDescription() &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const Headlight* ele) const override\n    {\n        std::cout &lt;&lt; ele-&gt;getDescription() &lt;&lt; std::endl;\n    }\n\n    virtual void visit(const Engine* ele) const override\n    {\n        std::cout &lt;&lt; ele-&gt;getDescription() &lt;&lt; std::endl;\n    }\n};\n\nvoid Client(CarPart* carpart, Visitor* vis)\n{\n    carpart-&gt;accept(vis);\n}\n\nint main()\n{\n    Visitor* priceVis = new PriceVisitor();\n    Visitor* desVis = new DesVisitor();\n\n    CarPart* whell = new Whell();\n    Client(whell, priceVis);\n    Client(whell, desVis);\n\n    CarPart* engine = new Engine();\n    Client(engine, priceVis);\n    Client(engine, desVis);\n\n    delete priceVis, desVis, whell, engine;\n\n    return 0;\n}<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"<p>\u4e00\u3001\u610f\u56fe &nbsp;&nbsp;&nbsp;&nbsp;\u8868\u793a\u4e00\u4e2a\u4f5c\u7528\u4e8e\u5bf9\u8c61\u7ed3\u6784\u4f53\u4e2d\u7684\u5404\u5143\u7d20\u64cd\u4f5c\u3002\u5b83\u4f7f\u4f60\u53ef\u4ee5\u518d\u4e0d\u6539\u53d8\u5143\u7d20\u7684\u7c7b\u7684\u60c5\u51b5 &#8230;<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[64],"tags":[],"amp_enabled":true,"_links":{"self":[{"href":"https:\/\/swordofmorning.com\/index.php\/wp-json\/wp\/v2\/posts\/331"}],"collection":[{"href":"https:\/\/swordofmorning.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/swordofmorning.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/swordofmorning.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/swordofmorning.com\/index.php\/wp-json\/wp\/v2\/comments?post=331"}],"version-history":[{"count":1,"href":"https:\/\/swordofmorning.com\/index.php\/wp-json\/wp\/v2\/posts\/331\/revisions"}],"predecessor-version":[{"id":464,"href":"https:\/\/swordofmorning.com\/index.php\/wp-json\/wp\/v2\/posts\/331\/revisions\/464"}],"wp:attachment":[{"href":"https:\/\/swordofmorning.com\/index.php\/wp-json\/wp\/v2\/media?parent=331"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/swordofmorning.com\/index.php\/wp-json\/wp\/v2\/categories?post=331"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/swordofmorning.com\/index.php\/wp-json\/wp\/v2\/tags?post=331"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}