#include "ns3/callback.h"

#include <cassert>

#include <iostream>

using namespace ns3;

static double 

CbOne (double a, double b)

{

    std::cout << "invoke cbOne a=" << a << ", b=" << b << std::endl;

    return a;

}

class MyCb {

public:

    int CbTwo (double a) {

        std::cout << "invoke cbTwo a=" << a << std::endl;

        return -5;

    }

};

int main (int argc, char *argv[])

{

    // return type: double

    // first arg type: double

    // second arg type: double

    Callback<double, double, double> one;

    // build callback instance which points to cbOne function

    one = MakeCallback (&CbOne);

    // this is not a null callback

    assert (!one.IsNull ());

    // invoke cbOne function through callback instance

    double retOne;

    retOne = one (10.0, 20.0);

    // return type: int

    // first arg type: double

    Callback<int, double> two;

    MyCb cb;

    // build callback instance which points to MyCb::cbTwo

    two = MakeCallback (&MyCb::CbTwo, &cb);

    // this is not a null callback

    assert (!two.IsNull ());

    // invoke MyCb::cbTwo through callback instance

    int retTwo;

    retTwo = two (10.0);    

    two = MakeNullCallback<int, double> ();

    // invoking a null callback is just like

    // invoking a null function pointer:

    // it will crash.

    //int retTwoNull = two (20.0);

    assert (two.IsNull ());

    return 0;

}