Hidden Interface Implementation on C++

HiddenInterface.cpp

#include <iostream> // std::cout

class Interface {
public:
    class HiddenInterface;
    
    static inline Interface* of(Interface::HiddenInterface* hInterface);
    static inline Interface& of(Interface::HiddenInterface& hInterface);
	
	virtual void show(char const* const msg) const =0;
    
	virtual ~Interface() {}
};

class Interface::HiddenInterface: private Interface
{
public:	
    friend Interface* Interface::of(Interface::HiddenInterface* hInterface);
    friend Interface& Interface::of(Interface::HiddenInterface& hInterface);
    
	virtual ~HiddenInterface(){}
};

Interface* Interface::of(Interface::HiddenInterface* hInterface)
{
    return hInterface;
}

Interface& Interface::of(Interface::HiddenInterface& hInterface)
{
    return hInterface;
}

class ObjClass: public Interface::HiddenInterface {
    void show(char const* const msg) const {
        std::cout << msg << std::endl;
    }
    
public:
    virtual ~ObjClass() {}
    
    // Implement public methods
};

int main()
{
    ObjClass object;
    
    Interface::of(object).show("Hello, world!");
}