repos/Callback_05/Callback_05.cpp

#include <iostream>
#include <functional>

using std::cout;
using std::endl;


/**********************************************************************************************
 *
 */
class MyClass
{
public:
    MyClass() {

        private_x = 5;
    };
    
    int public_x = 12;

private:
    int private_x;
};

/**********************************************************************************************
 *
 */
class YourClass
{
public:
    YourClass()
    {
        private_y = 8;
    }

private:
    int private_y;
};

/**********************************************************************************************
 * 
 */
void g(MyClass * a1, YourClass* a2) {

    printf("access both classes\n"); 
    printf("MyClass: %d\n", a1->public_x);
    printf("YourClass: private\n");
}

/**********************************************************************************************
 *
 */
class EventHandler
{
public:

    std::function<void(MyClass*, YourClass*)> cb = nullptr; 

    template<class T1, class T2>
    void addHandler(std::function<void(T1*, T2*)> callback)
    {
        cout << "Handler added..." << endl;
        cb = callback; 
    }

    template<class T1, class T2>
    void call_cb(T1* myCl, T2* yourCl) {
        if(cb != nullptr)
          (cb)(myCl, yourCl);
    }
};

/**********************************************************************************************
 *
 */
int main(int argc, char** argv)
{
    MyClass* myClass = new MyClass();
    YourClass* yourClass = new YourClass();
    EventHandler* handler = new EventHandler();

    /*
     *  Here is the compiler error
     */
    handler->addHandler(g);
    handler->call_cb(myClass, yourClass); 
}