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CRTP自动注册工厂(静态初始化命令失败)

crtp factory qt c++

1

Moia · 技术社区 · 7 年前

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,而不显式调用register方法。

我的尝试基于 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,它会与segfault崩溃。我错过了什么?

1 回复 | 直到 7 年前

1

2

Moia 7 年前

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

我按照isocpp的建议解决了它。 How do I prevent the âstatic initialization order problemâ for my static data members?

在任何情况下,将x::x_uuu静态数据成员更改为静态成员函数都是可移植和安全的:

所以改变

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;
    }

并更新来自的所有呼叫 map 具有 map() 解决这个问题。

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