通过成员函数指向虚函数调用基本成员函数实现

Question

我有一种情况,我想要一个成员函数指针指向虚拟函数,避免动态调度.见下文:

struct Base
{
    virtual int Foo() { return -1; }
};

struct Derived : public Base
{
    virtual int Foo() { return -2; }
};

int main()
{
    Base *x = new Derived;

    // Dynamic dispatch goes to most derived class' implementation    
    std::cout << x->Foo() << std::endl;       // Outputs -2

    // Or I can force calling of the base-class implementation:
    std::cout << x->Base::Foo() << std::endl; // Outputs -1

    // Through a Base function pointer, I also get dynamic dispatch
    // (which ordinarily I would want)
    int (Base::*fooPtr)() = &Base::Foo;
    std::cout << (x->*fooPtr)() << std::endl; // Outputs -2

    // Can I force the calling of the base-class implementation
    // through a member function pointer?
    // ...magic foo here...?

    return 0;
}

对于好奇,我想要的原因是因为派生类实现使用实用程序类来记忆(添加缓存)基类实现.实用程序类采用函数指针,但是,当然,函数指针动态调度到最派生类,我得到无限递归.

是否有一种语法允许我重现我可以x->Base::foo()通过函数指针实现的静态调度行为？

Answer 1

您可以像这样强制切片Base*：

std::cout << (static_cast<Base>(*x).*fooPtr)() << std::endl; // Outputs -1