Question

我想知道如何在下面给出的场景中避免代码重复。

（有这个问题：
How do I check if an object's type is a particular subclass in C++?
答案是，它是不可能的，即使是动态演员也无法访问成员，我猜。）

所以我想知道如何避免在不同的方法中使用几乎相同的代码，只有一种方法可以进行一些额外的操作。

class Basic {
    ...
}

class Advanced : public Basic {
    ...
}


AnotherClass::lengthy_method(Basic *basic) {
    // do a lot of processing, access members of basic

    if (*basic is actually of class Advanced)
        // do one or a few specific things with members of Advanced

    // more processing just using Basic

    if (*basic is actually of class Advanced)
        // do one or a few specific things with members of Advanced

    // more processing just using Basic
}

同样从设计角度AnotherClass::lengthy_method不希望在Basic或Advanced中定义，因为它并不真正属于他们中的任何一个。它只是在同类中运作。

我很好奇语言专家知道什么，我希望有一个很好的解决方案，至少可以通过C ++ 11的一些功能。

Answer 1

只要您要访问的dynamic_cast成员被声明为Advanced，或public被声明为AnotherClass，就可以在此处使用

friend } Advanced：

AnotherClass::lengthy_method(Basic *basic) {
    // do a lot of processing, access members of basic

    Advanced *adv = dynamic_cast<Advanced*>(basic);
    if (adv != NULL) {
        // use adv as needed...
    }

    // more processing just using Basic

    if (adv != NULL) {
        // use adv as needed...
    }

    // more processing just using Basic
}

另一种选择是使用多态而不是RTTI。在Basic中展示一些不执行任何操作的其他虚拟方法，然后Advanced覆盖它们：

class Basic {
    ...
    virtual void doSomething1() {}
    virtual void doSomething2() {}
}

class Advanced : public Basic {
    ...
    virtual void doSomething1();
    virtual void doSomething2();
}

void Advanced::doSomething1() {
    ...
}

void Advanced::doSomething2() {
    ...
}    

AnotherClass::lengthy_method(Basic *basic) {
    // do a lot of processing, access members of basic

    // do one or a few specific things with members of Advanced
    basic->doSomething1();

    // more processing just using Basic

    // do one or a few specific things with members of Advanced
    basic->doSomething2();

    // more processing just using Basic
}

以不同方式处理子类/避免代码重复

1 个答案: