c++ - 如何在 switch 语句中正确初始化不同的派生类？

Question

我有如下代码，有一个基类Base的类层次结构，还有几个派生类Derived1、Derived2、Derived3……等等。

switch(i){
    case 1:{
        Derived1* d1;
        generateD1(d1);
        otherFunc(d1); //function signature is otherFunc(Base*)
        break;
    }
    case 2:{
        Derived2* d2;
        generateD2(d2);
        otherFunc(d2);
        break;
    }
    ...  //goes on for many cases
}

如何使用继承机制来改进上面的代码？

Answer 1

像这样:

class Base
{
    public:
        virtual ~Base() {}

        virtual void generate() = 0 {}

        virtual void other() = 0 {}
};

class Derived1 : public Base
{
    public:
        virtual void generate() override {}

        virtual void other() override {}
};

class Derived2 : public Base
{
    public:
        virtual void generate() override {}

        virtual void other() override {}
};

int main()
{
    int i;
    Base *b;
    switch(i)
    {
        case 1:
            b = new Derived1;
            break;
        case 2:
            b = new Derived2;
            break;
        ...
    }
    b->generate();
    b->other();
    ...
    delete b;
    return 0;
}

---

你可以放弃 generate() 方法而只使用构造函数:

class Base
{
    public:
        virtual ~Base() {}

        virtual void other() = 0 {}
};

class Derived1 : public Base
{
    public:
        Derived1() {}

        virtual void other() override {}
};

class Derived2 : public Base
{
    public:
        Derived2() {}

        virtual void other() override {}
};

int main()
{
    int i;
    Base *b;
    switch(i)
    {
        case 1:
            b = new Derived1;
            break;
        case 2:
            b = new Derived2;
            break;
        ...
    }
    b->other();
    ...
    delete b;
    return 0;
}