MultiFunctor implementation trouble

Hello all!

I want to implement MultiFunctor class.
Consider the following example:

// MultiFunctor object
MultiFunctor<void (int, string)> mf;
// Type of MultiFunctor's content
typedef Functor<void (int,string)> Func_t;
// Functors
Func_t f1(&some_func);
Func_t f2(some_functor);
Func_t f3(&som_obj, &SomeClass::SomeMemberFunction);
// Add functors
mf+=f1;
mf+=f2;
mf+=f3;
// Call ALL functors
mf(100,"Hello World"); // Calls all functors
// Delete one functor
mf-=f2;
// Call f1 and f3
mf(200,"Only f1 and f3");

It's fine!

But there is a big problem - how to implement operator -=?

template <class T>
MultiFunctor& MultiFunctor::operator -=(const T& functor )
{
  typedef SomeContainer::iterator IT;
  for(IT i = container_.begin(); i!=container_.end();++i)
    {
      if( *i == functor) // !!! Main problem is here !!!
        {
           container_.erase(i);
           break; // Supposing there are not duplicates in container
        }
    }
  return *this;
}

The main question:
Is there a way to compare two functors???

Thanks!

P.S.
I know about another approach:

ID_t id1 = mf.add(f1);
ID_t id2 = mf.add(f2);
ID_t id3 = mf.add(f3);
mf(1000,"Bad solution"); // Calls f1,f2,f3
mf.delete(id2);
mf(1000,"Bad solution"); // Calls f1,f3

But it's a ugly hack :(