更改派生类中的函数访问模式

问题描述

考虑以下片段:

struct Base
{
  virtual ~Base() {}

  virtual void Foo() const = 0; // Public
};

class Child : public Base
{
  virtual void Foo() const {} // Private
};

int main()
{
  Child child;

  child.Foo(); // Won't work. Foo is private in this context.

  static_cast<Base&> (child).Foo(); // Okay. Foo is public in this context.
}

这是合法的 C++ 吗?this"正在改变派生类中虚函数的访问模式.

Is this legal C++? "This" being changing the virtual function's access mode in the derived class.

推荐答案

是的，在派生类中改变访问模式是合法的.

Yes, changing the access mode in derived classes is legal.

这在形式上相似，但在意图上与 习惯用法.此处给出了一些理由:

This is similar in form but different in intent to the Non-Virtual Interface idiom. Some rationale is given here:

关键是存在允许定制的虚函数；除非它们还需要从派生类的代码中直接调用，否则除了私有之外，没有必要将它们设为任何东西.

至于为什么您实际上会在基础中制作public，而在没有private 或protected 的派生中制作private继承超出了我的范围.

As to why you would actually make something public in base but private in derived without private or protected inheritance is beyond me.

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