#include <iostream>
#include <functional>
using namespace std;
 
// 2 unrelated classes
class A
{
public:
    void func() { cout << "in A::func\n"; }
};
 
class B
{
public:
    void func() { cout << "in B::func\n"; }
};
 
int main()
{
    A a;
    B b;
 
    function<void()> f;  // a generic function that returns void and takes no params
 
    f = bind(&A::func, &a);
    f(); // <- calls A::func
 
 
    f = bind(&B::func, &b);
    f(); // <- calls B::func
}

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