继承在C ++中破坏了多态性? [英] Inheritance mucking up polymorphism in C++?

问题描述

也许我对继承和多态性的了解不是我想的那样.谁能给我一些启示?

Perhaps my knowledge of inheritance and polymorphism isn't what I thought it was. Can anyone shed some light?

设置(问题的琐碎化):

Setup (trivialization of problem):

class X {
};

class Y {
};

class Base {
  public:
    void f( X* ) {}
};

class Child: public Base {
  public:
    void f( Y* ) {}
};

问题:这应该起作用，对吧?

Question: This should work, right?

int main( void ) {
  X* x = new X();
  Y* y = new Y();
  Child* c = new Child();
  c->f( x );
  c->f( y );
  return 0;
}

我收到以下错误消息(GCC 4.4):

I get errors (GCC 4.4) to the tune of:

`no matching function for call to 'Child::f(X*&)'`
`note: candidates are: void Child::f(Y*)`

推荐答案

virtual关键字对您没有帮助.

The virtual keyword will not help you here.

您的基类Base::f被派生类型隐藏.您需要执行以下操作:

Your base class Base::f is being hidden by your derived type. You need to do the following:

class Child: public Base {
  public:
    using Base::f;
    void f( Y* ) {}
};

Parashift详细介绍.

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