c++ - 如何禁止 C++ 派生类从基类派生，但允许从另一个派生类派生

Question

鉴于这种情况:

class GrandParent {};
class Parent : public GrandParent {};
class Child : public Parent {}; /// Ok
class Child : public GrandParent {}; /// Is it possible to force a compilation error? 

Answer 1

将 GrandParent 构造函数设为私有(private)，将 Parent 设为好友。

class GrandParent
{
   friend class Parent;
   private:
   GrandParent() {}
   // ...
};

或者，您可以通过将析构函数设为私有(private)来权衡 GrandParents 的多态破坏:

class GrandParent
{
   friend class Parent;
   private:
   virtual ~GrandParent() {}
};

// Invalid Destruction:
GrandParent* p = new Parent;
...
delete p;