#include <iostream>
#include <functional>

using namespace std;
using namespace std::placeholders;

// there are a few way of declaring "callable objects"

// as a non-static method
class A {
public:
	int f0(int i) {
		return v+i;
	}
	int v;
};

// as a function:
int f1(A *a, int i) {
	return a->v+i;
}

// as a functor
class F2 {
public:
	int operator()(A *a, int i) const {
		return a->v + i;
	}
};

F2 f2;

// as a lambda expression
auto f3 = [](A *a, int i) { return a->v + i; };

int main(int arg, char **argv) {
	// std::function (from #include <functional>) can hold all of them...
	std::function<int(A*,int)> f = nullptr;
	if (!f) cout << "not yet initialized (1)" << endl;
	f = f1;
	if (!f) cout << "not yet initialized (2)" << endl;
	f = f2;
	f = f3;
	f = std::bind(&A::f0,_1,_2); // have to use bind to get a non-static
			// member method
			
	// cannot compare f to anything except to check if it is nullptr
	// std::bind can be used on all these things
}