阻止在 C++ 中调用基本分配运算符

问：

我的库里有这两个类：

class Base {
    int _handler;
protected:
    Base() = default;

    Base& operator=(int h) {
        this->_handler = h;
        return *this;
    }
};

class Derived : public Base {
protected:
    Derived() = default;

    void initialize() {
        this->Base::operator=(12345); // internal stuff
    }
};

Derived类可由用户继承。他应该这样做：

class User_Class : public Derived {
    void foo() {
        this->initialize();
    }
};

但相反，他这样做了：

class User_Class : public Derived {
    void foo() {
        this->Base::operator=(999); // no, you broke it!
    }
};

如何防止对分配操作员的呼叫？Base