C++类名称数组

Question

我正在构建一个可以通过添加新类来扩展的c ++框架

我想找到一种简化新​​类扩展的方法.

我目前的代码如下:

class Base {
public:
    virtual void doxxx() {...}
};

class X: public Base {
public:
    static bool isMe(int i) { return i == 1; }
};

class Y: public Base {
public:
    static bool isMe(int i) { return i == 2; }
};

class Factory {
public:
    static std::unique_ptr<Base> getObject(int i) {
        if (X::isMe(i)) return std::make_unique<X>();
        if (Y::isMe(i)) return std::make_unique<Y>();

        throw ....
    }
};

此外,对于每个新类,都必须添加新的if语句.

现在我想找到一种方法来重写我的Factory类(使用元编程),可以通过调用add方法来完成添加新类,并且工厂类看起来像跟随伪代码:

class Factory
{
public:
    static std::unique_ptr<Base> getObject(int i) {
        for X in classNames:
            if (X::isMe(i)) return std::make_unique<X>();

        throw ....
    }

    static void add() {...}

    static classNames[];...
};

Factory::add(X);
Factory::add(Y);

..

有可能吗？提前谢谢了

Answer 1

您可能会执行以下操作:

template <typename ... Ts>
class Factory {
public:
    static std::unique_ptr<Base> createObject(int i) {
        if (i < sizeof...(Ts)) {
            static const std::function<std::unique_ptr<Base>()> fs[] = {
                [](){ return std::make_unique<Ts>();}...
            };
            return fs[i]();
        }
        throw std::runtime_error("Invalid arg");
    }

};

用法是:

using MyFactory = Factory<X, Y /*, ...*/>;

auto x = MyFactory::createObject(0);
auto y = MyFactory::createObject(1);

如果您想要运行时注册,则可以改为:

class Factory {
public:
    static std::unique_ptr<Base> createObject(int i) {
        auto it = builders.find(i);
        if (it == builders.end()) {
            throw std::runtime_error("Invalid arg");
        }
        return it->second();
    }

template <typename T>
void Register()
{
    builders.emplace(T::Id, [](){ return std::make_unique<T>();});
}

private:
    std::map<int, std::function<std::unique_ptr<Base>()>> builders;
};

用法是:

class X: public Base {
public:
    static constexpr int id = 1;
};

class Y: public Base {
public:
    static constexpr int id = 2;
};

和

Factory factory;
factory.register<X>();
factory.register<Y>();

auto x = factory.createObject(1);
auto y = factory.createObject(Y::id);