Base constructor calls derived constructor depending on input - Choose object sub-type at runtime

Question

Let's say I have a Human class:

class Human {
public:
    bool isFemale;
    double height;
    Human(bool isFemale, double height) {
        this->isFemale = isFemale;
        this->height = height;
    }
};

and derived classes, such as Female and Male, which implement their own methods. Do I have a way, in C++11, to determine at runtime, depending on the inputs into the Human constructor, which "sub-type" (Male or Female) Human should be? I am putting different behaviour for Male and Female in their respective classes. What I am trying to do is determine at runtime whether Human is of type Female or of type Male, depending on constructor input, so I can (afterwards) apply appropriate behaviour based on its type. The ideal would be to always call the Human constructor, and the appropriate sub-type to be chosen at runtime, depending on the parameters one enters in the constructor. If that is possible, I guess one should twist the "Human" constructor, but I'm unsure how...

Answer 1

通过调用Human的构造函数，您只能创建一个Human对象。

据我了解，您希望根据在运行时获得的性别输入创建一个Male或Female对象。然后，您可能应该考虑使用工厂函数来实现这一点。

例如，如果您将Male和定义Female为：

struct Male: public Human {
   Male(double height): Human(false, height) {}
   // ...
};

struct Female: public Human {
   Female(double height): Human(true, height) {}
   // ...
};

然后，您可以使用以下工厂函数make_human()：

std::unique_ptr<Human> make_human(bool isFemale, double height) { 
   if (isFemale)
      return std::make_unique<Female>(height);
   return std::make_unique<Male>(height);
}

它在运行时根据传递给参数的参数决定是创建一个对象Female还是一个Male对象isFemale。

请记住 makeHuman的析构函数，virtual因为Male和Female类都公开继承自Human.