c++ - 如何在派生类数据中使用基类进行比较

Question

我在 C++ 中有基类和派生类。
我想使用基类的指针来确定派生类的数据是否相同。
枚举类型

enum class FruitType: int{
    Apple,
    Orange,
};

基类

class Base{
public:
    Base(FruitType t): fruit_type(t){}
    FruitType fruit_type;
};

派生类

class Apple : public Base{
public:
    Apple(int i): Base(FruitType::Apple), foo(i){}
    int foo;
};
class Orange : public Base{
public:
    Orange(float f): Base(FruitType::Orange), bar(f){}
    float bar;
}; 

初始化

// initialize
std::vector<Base*> fruit_list_ = { 
                new Apple(42),
                new Orange(0.f),
                new Apple(1) };

有什么办法可以检查 HasSameData() 吗？

Base* HasSameData(const Base* pCompare){
    for (const auto& list : fruit_list_) 
    {
        if( pCompare->fruit_type == list->fruit_type ){
            // how to check same data...?
            if( /* ... */ ){
                return list;
            }
        }
    }
    return nullptr;
}

int main(){
    // check same data
    Base* pCompare = fruit_list_[2];
    if(HasSameData(pCompare)){
        // I want to return fruit_list_[2] pointer...
    }
}

Answer 1

您可以将抽象方法 sameData() 添加到基本案例

class Base{
public:
    Base(FruitType t): fruit_type(t){}
    FruitType fruit_type;
    virtual bool sameData(const Base& other) const = 0;
};

在派生类中重写:

class Apple : public Base{
public:
    Apple(int i): Base(FruitType::Apple), foo(i){}
    int foo;
    virtual bool sameData(const Base& other) const {
        const Apple* apple = dynamic_cast<const Apple*>(&other);
        return apple && apple->foo == foo;
    }
};

class Orange : public Base{
public:
    Orange(float f): Base(FruitType::Orange), bar(f){}
    float bar;
    virtual bool sameData(const Base& other) const {
        const Orange* orange = dynamic_cast<const Orange*>(&other);
        return orange && orange->bar == bar;
    }
};

并按如下方式使用它:

// how to check same data...?                                       
if( pCompare->sameData(*list) ){