c++ - CRTP 自动注册工厂(静态初始化顺序失败)

Question

我正在尝试自动注册 CRTP 工厂类。我的目标是不使用宏注册类类型并且不显式调用注册方法。

我尝试基于 this answer :

工厂.h

template<typename Base>
struct Factory{
    static Base* create(const QString& name){
        auto callable = map.value(name);
        return callable();
    }

    template<typename Derived>
    static void subscribe(QString name){
        // insert already-exist-check here
        qDebug() << "registered: " << name;
        map.insert(std::move(name), [](){return new Derived{};});
    }

    static QMap< QString, std::function<Base*(void)> > map;
};

template<typename Base>
QMap< QString, std::function<Base*(void)> > Factory<Base>::map;


template<typename Base, typename Derived>
class Registrable{
protected:
    virtual QString registerName() const = 0;

    Registrable(){
        isRegistered;
    }
    ~Registrable() = default;

    static bool init(){
        Derived t;
        Factory<Base>::template subscribe<Derived>(t.registerName());
        return true;
    }

private:
    static bool isRegistered;
};

template<typename Base, typename Derived>
bool Registrable<Base, Derived>::isRegistered = Registrable<Base, Derived>::init();

主要.cpp

struct MyFactoryBase{
    virtual ~MyFactoryBase() = default;
    virtual void method() const = 0;
};

struct MyFactory1 : public MyFactoryBase, public Registrable<MyFactoryBase, MyFactory1>{
    QString registerName() const override{
        return "Class1";
    }
    void method() const override{ qDebug() << "yay Class1"; }

    MyFactory1() : MyFactoryBase(), Registrable<MyFactoryBase, MyFactory1>(){}
};

struct MyFactory2 : public MyFactoryBase, public Registrable<MyFactoryBase, MyFactory2>{
    QString registerName() const override{
        return "Class2";
    }
    void method() const override{ qDebug() << "yay Class2"; }

    MyFactory2() : MyFactoryBase(), Registrable<MyFactoryBase, MyFactory2>(){}
};

int main(){
//    auto* fac = Factory<MyFactoryBase>::create("Class1");
//    auto* fac2 = Factory<MyFactoryBase>::create("Class2");
}

在第一次订阅期间尝试使用 map.insert() 时，它因段错误而崩溃。我缺少什么？

Answer 1

正如评论中所建议的那样，它是一个 static initialization order fiasco .

我按照 ISOCpp 中的建议解决了它 How do I prevent the “static initialization order problem” for my static data members?

In any event, it’s always portable and safe to change the X::x_ static data member into a static member function:

变化多端

static QMap< QString, std::function<Base*(void)> > map;

到

   static QMap< QString, std::function<Base*()> >& map(){
        static QMap< QString, std::function<Base*()> > map;
        return map;
    }

并使用 map() 更新来自 map 的所有调用解决了这个问题。

int main(){
    auto* fac = Factory<MyFactoryBase>::create("Class1");
    auto* fac2 = Factory<MyFactoryBase>::create("Class2");

    fac->method();
    fac2->method();

    return 0;
}

输出:

registered: Class1
registered: Class2
yay Class1
yay Class2