有没有办法专门

Question

我有两个专门的对象继承对象的一般方法：

class Food {}; 
class Fruit : public Food {}; 
class Vegetable : public Food {}; 

然后我将继承父类：

class Parent 
{ 
    virtual void say(Food* obj) { std::cout << "The object is food" << std::endl; } 
}; 

而且继承来自父母的课程。

class Child : public Parent 
{ 
    virtual void say(Fruit* obj) { std::cout << "The object is a fruit" << std::endl; } 
    virtual void say(Vegetable* obj) { std::cout << "The object is a vegetable" << std::endl; } 
}; 

我做的：

std::vector<Food*> basket; 
Fruit fruit = Fruit(); 
Vegetable vegetable = Vegetable(); 
basket.push_back(&fruit); 
basket.push_back(&vegetable); 

Child child = Child(); 

for (Food* food : basket) 
{ 
    child.say(food); 
} 

我想它打印“的对象是一种水果”，然后“的对象是蔬菜”，但它不工作： 我得到错误消息：参数1从'Food *'到'Fruit *'没有已知的转换。

有没有办法做到这一点，如果可能的话，不使用typeid，因为我听到它会导致开销。这里是一个在线编辑器代码：cpp.sh/27ekc

Answer 1

我认为合适的解决方案，这是以下几点：

class Food 
{ 
public: 
    virtual ~Food() = default; 
    virtual void say() const; 
}; 
class Fruit : public Food 
{ 
public: 
    void say() const override { std::cout << "The object is a fruit" << std::endl; } 
}; 
class Vegetable : public Food 
{ 
public: 
    void say() const override { std::cout << "The object is a vegetable" << std::endl; } 
}; 

class Parent 
{ 
public: 
    virtual ~Parent() = default; 
    virtual void say(const Food& obj) const { obj.say(); } 
}; 

class Child : public Parent {}; 

int main() 
{ 
    std::vector<Food*> basket; 
    Fruit fruit = Fruit(); 
    Vegetable vegetable = Vegetable(); 
    basket.push_back(&fruit); 
    basket.push_back(&vegetable); 

    Child child = Child(); 

    for (const Food* food : basket) 
    { 
     child.say(*food); 
    } 
} 

编辑： 按您的评论，它是根据你所说的健康是什么。 我把它解释为这些方针的东西：

class Food 
{ 
public: 
    virtual ~Food() = default; 
    virtual void say() const; 
    virtual int health() const; 
}; 
class Fruit : public Food 
{ 
public: 
    void say() const override { std::cout << "The object is a fruit" << std::endl; } 
    int health() const override { return 5; } 
}; 
class Vegetable : public Food 
{ 
public: 
    void say() const override { std::cout << "The object is a vegetable" << std::endl; } 
    int health() const override { return 10; } 
}; 

class Parent 
{ 
public: 
    virtual ~Parent() = default; 
    virtual void say(const Food& obj) const { obj.say(); } 
}; 

class Child : public Parent 
{ 
    int health; 

public: 
    void eat(const Food& obj) { health += obj.health(); } 
}; 

int main() 
{ 
    std::vector<Food*> basket; 
    Fruit fruit = Fruit(); 
    Vegetable vegetable = Vegetable(); 
    basket.push_back(&fruit); 
    basket.push_back(&vegetable); 

    Child child = Child(); 

    for (const Food* food : basket) 
    { 
     child.say(*food); 
     child.eat(*food); 
    } 
} 

有很多不同的方式来实现这一目标。