boost - C++ boost::shared_ptr和boost::weak_ptr＆dynamic_cast

我有这样的事情:

enum EFood{
    eMeat,
    eFruit
};

class Food{
};

class Meat: public Food{
    void someMeatFunction();
};

class Fruit: public Food{
    void someFruitFunction();
};

class FoodFactory{
    vector<Food*> allTheFood;
    Food* createFood(EFood foodType){
        Food* food=NULL;
        switch(foodType){
            case eMeat:
                food = new Meat();
                break;
            case eFruit:
                food = new Fruit();
                break;
        }
        if(food)
            allTheFood.push_back(food);
        return food;
    }
};

int foo(){
    Fruit* fruit = dynamic_cast<Fruit*>(myFoodFactory->createFood(eFruit));
    if(fruit)
        fruit->someFruitFunction();
}

现在，我想更改我的应用程序以使用boost shared_ptr和weak_ptr，这样我可以在一个地方删除我的food实例。它看起来像这样:

class FoodFactory{
    vector<shared_ptr<Food> > allTheFood;
    weak_ptr<Food> createFood(EFood foodType){
        Food* food=NULL;
        switch(foodType){
            case eMeat:
                food = new Meat();
                break;
            case eFruit:
                food = new Fruit();
                break;
        }

        shared_ptr<Food> ptr(food);
        allTheFood.push_back(ptr);
        return weak_ptr<Food>(ptr);
    }
};

int foo(){
    weak_ptr<Fruit> fruit = dynamic_cast<weak_ptr<Fruit> >(myFoodFactory->createFood(eFruit));
    if(shared_ptr<Fruit> fruitPtr = fruit.lock())
        fruitPtr->someFruitFunction();
}

但问题是dynamic_cast似乎无法与weak_ptr一起使用

如果我知道指向的对象是派生类型，如何从weak_ptr<Fruit>中获取weak_ptr<Food>？

最佳答案

从weak_ptr<A>直接转换为weak_ptr<B>肯定不会起作用，我认为您必须将其转换为shared_ptr，然后使用shared_ptr的转换功能:

weak_ptr<Food> food = myFoodFactory->createFood(eFruit)
weak_ptr<Fruit> fruit = weak_ptr<Fruit>(dynamic_pointer_cast<Fruit>(food.lock());