C++——派生类修改基类成员的访问权限

class A {
	int x, y;
public:
	int getx() {
		return x;
	}
protected:
	int gety() { 
		return y; 
	}
};
class B : private A /* public A */ /* protected A */{
	bool visible;
public:
	using A::getx;
	A::gety;			// deprecated
};

class MyList {
	struct Node
	{
		int v;
		Node* next;
		Node(int v, Node* n) {
			this->v = v;
			next = n;
		}
		~Node() {
			cout << "~Node()\n";
			delete next;
			next = nullptr;
		}
	} *head;
public:
	MyList() {
		head = nullptr;
	}
	~MyList() {
		if (head != nullptr) {
			delete head;
			head = nullptr;
		}
	}
	int insert(int v) {
		head = new Node(v, head);
		if(head) return 1;
		return 0;
	}
	int contain(int v) {
		// 这里要注意，使用局部变量
		// 不要使用 head，会改变整个链表的头指针
		Node* tmp = head;
		while (tmp != nullptr)
		{
			if (tmp->v == v) return 1;
			tmp = tmp->next;
		}
		return 0;
	}
};
class MySet : protected MyList {
	int count;
public:
	MySet() { count = 0; };
	using MyList::contain;
	int insert(int v) {
		if (!contain(v) && MyList::insert(v)) return ++count;
		return 0;
	}
};

int main()
{
	MySet l;
	l.insert(1);
	l.insert(2);
	l.insert(3);
	cout << l.insert(4) << endl;
	cout << l.contain(3) << endl;

	//MyList& list = l;	// 不允许对不可访问的基类 "MyList" 进行转换

	return 0;
}