{"id":3989,"date":"2022-08-21T02:04:12","date_gmt":"2022-08-20T20:34:12","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-how-to-self-register-class-instances-using-the-crtp\/"},"modified":"2022-08-21T02:04:12","modified_gmt":"2022-08-20T20:34:12","slug":"solved-how-to-self-register-class-instances-using-the-crtp","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-how-to-self-register-class-instances-using-the-crtp\/","title":{"rendered":"[Solved] How to self register class instances using the CRTP?"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-44594733\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"44594733\" data-parentid=\"44465134\" data-score=\"0\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<p>I decided to reopen the question and self answer based on Yakk&#8217;s fixes. Seems to be a more common problem (see here for example)<\/p>\n<p>Yakk&#8217;s example solved it:<\/p>\n<pre><code>#include &lt;cstdint&gt;\n\nenum class CommandId : uint16_t {\n    Command1 ,\n    Command2 ,\n};\n\n\n#include &lt;map&gt;\n#include &lt;functional&gt;\n#include &lt;string&gt;\n\n\/\/#include \"CommandId.h\"\n\nclass Registry\n{\npublic:\n    static std::map&lt;CommandId,std::function&lt;void (std::string)&gt;&gt;&amp; \n    GetCommands() {\n        static std::map &lt; CommandId, std::function&lt;void(std::string)&gt;&gt; \n        theFunctionRegistry;\n        return theFunctionRegistry;\n    }\n};\n\n\/\/ #include \"CommandId.h\"\n\/\/ #include \"Registry.h\"\n\n\/\/ The general command execution interface\nstruct ICommand {\n    virtual void Execute(const std::string&amp; data) = 0;\n    virtual ~ICommand() {}\n};\n\ntemplate&lt;typename Derived, CommandId CmdId&gt;\nclass CommandBase : public ICommand\n{\npublic:\n    virtual ~CommandBase() {}\n    void Register() {}\nprotected:\n    \/\/ Dummy function to avoid abstract instantiations, should probably throw\n    void Execute(const std::string&amp; data) override {\n    }\n\n    \/\/ Protected constuctor meant for concrete command classes\n    CommandBase(int&amp; derivedRef) : derivedRef_(&amp;derivedRef) {}\n\n    \/\/ The static member that should perform the registation automagically\n    static CommandBase&lt;Derived, CmdId&gt; registryAdder_;\n\n    \/\/ This constructor is meant to be accessed from the above static member\n    \/\/ instantiation only, and just register the lambda function \n    CommandBase() : derivedRef_(nullptr) {\n        \/\/ Register a lambda function that ususe a concrete Derived instance\n        Registry::GetCommands()[CmdId] = [](const std::string&amp; data) {\n            Derived derivedInstance;\n\n            CommandBase&lt;Derived, CmdId&gt;* der = static_cast&lt;CommandBase&lt;Derived, CmdId&gt;*&gt;(&amp;derivedInstance);\n            \/\/ Manipulate the derived instances data and execute\n            *(der-&gt;derivedRef_) = 42;\n            der-&gt;Execute(data);\n        };\n    }\n\n    \/\/ Provides access to the derived class instances data members and allows manipulation \n    int* derivedRef_;\n};\n\ntemplate&lt;typename Derived, CommandId CmdId&gt;\nCommandBase&lt;Derived, CmdId&gt; CommandBase&lt;Derived, CmdId&gt;::registryAdder_;\n\n\/\/ #include \"CommandBase.h\"\n\nclass Command1 : public CommandBase&lt;Command1, CommandId::Command1&gt;\n{\npublic:\n    typedef CommandBase&lt;Command1, CommandId::Command1&gt; BaseClass;\n    friend class CommandBase&lt;Command1, CommandId::Command1&gt;;\n\npublic:\n    Command1(CommandId) {\n        BaseClass::registryAdder_.Register();\n    }\n    virtual ~Command1() override {}\n\nprivate:\n    Command1() : BaseClass(member_)\n    {\n        BaseClass::registryAdder_.Register();\n    }\n\n    void Execute(const std::string&amp; data) override {\n\n    }\nprivate:\n    int member_;\n};\n\n\/\/ #include \"CommandBase.h\"\n\nclass Command2 : public CommandBase&lt;Command2, CommandId::Command2&gt;\n{\npublic:\n    typedef CommandBase&lt;Command2, CommandId::Command2&gt; BaseClass;\n    friend class CommandBase&lt;Command2, CommandId::Command2&gt;;\n\npublic:\n    Command2(CommandId) {\n        BaseClass::registryAdder_.Register();\n    }\n    virtual ~Command2() override {}\n\nprivate:\n    Command2() : BaseClass(member_)\n    {\n        BaseClass::registryAdder_.Register();\n    }\n\n    void Execute(const std::string&amp; data) override {\n\n    }\nprivate:\n    int member_;\n};\n\n#include &lt;iostream&gt;\n\/\/#include \"Command1.h\"\n\/\/#include \"Command2.h\"\n\/\/#include \"Registry.h\"\n\nint main()\n{\n    std::cout &lt;&lt; \"There are \" &lt;&lt; Registry::GetCommands().size() &lt;&lt; \" registered commands.\" &lt;&lt; std::endl;\n    return 0;\n}\n<\/code><\/pre>\n<p>One needs to make use of these <code>static<\/code> instances in the derived classes.<\/p>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\"><\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved How to self register class instances using the CRTP? <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] I decided to reopen the question and self answer based on Yakk&#8217;s fixes. Seems to be a more common problem (see here for example) Yakk&#8217;s example solved it: #include &lt;cstdint&gt; enum class CommandId : uint16_t { Command1 , Command2 , }; #include &lt;map&gt; #include &lt;functional&gt; #include &lt;string&gt; \/\/#include &#8220;CommandId.h&#8221; class Registry { public: static &#8230; <a title=\"[Solved] How to self register class instances using the CRTP?\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-how-to-self-register-class-instances-using-the-crtp\/\" aria-label=\"More on [Solved] How to self register class instances using the CRTP?\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[324,513,515,514,486],"class_list":["post-3989","post","type-post","status-publish","format-standard","hentry","category-solved","tag-c","tag-c11","tag-crtp","tag-template-meta-programming","tag-visual-studio-2017"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] How to self register class instances using the CRTP? - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-how-to-self-register-class-instances-using-the-crtp\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] How to self register class instances using the CRTP? - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] I decided to reopen the question and self answer based on Yakk&#8217;s fixes. Seems to be a more common problem (see here for example) Yakk&#8217;s example solved it: #include &lt;cstdint&gt; enum class CommandId : uint16_t { Command1 , Command2 , }; #include &lt;map&gt; #include &lt;functional&gt; #include &lt;string&gt; \/\/#include &quot;CommandId.h&quot; class Registry { public: static ... 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Seems to be a more common problem (see here for example) Yakk&#8217;s example solved it: #include &lt;cstdint&gt; enum class CommandId : uint16_t { Command1 , Command2 , }; #include &lt;map&gt; #include &lt;functional&gt; #include &lt;string&gt; \/\/#include \"CommandId.h\" class Registry { public: static ... 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