inheritance - Prevent call to base assignment operator in C++ -

i have these 2 classes in library:

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 class available inherited user. should this:

class user_class : public derived {     void foo() {         this->initialize();     } }; 

but instead, this:

class user_class : public derived {     void foo() {         this->base::operator=(999); // no, broke it!     } }; 

how can prevent call base assignment operator?

when change header this

class derived : private base 

the compiler blocks call operator= "cannot access inaccessible member declared in class 'base'", code calls initialize works normally, because accessible.

however, should override operator= in derived, , have check whether or not has been initialized. don't make client class handle internal bookkeeping.