#include <boost/function.hpp> 
#include <iostream> 

struct world 
{ 
  void hello(std::ostream &os) 
  { 
    os << "Hello, world!" << std::endl; 
  } 
}; 

int main() 
{ 
  boost::function<void (world*, std::ostream&)> f = &world::hello; 
  world w; 
  f(&w, boost::ref(std::cout)); 
}