Thread: Storing functors?

I seem to have hit a bit of a snag again.
I wanted to make it possible to couple (I think that's the right word?) my input class a little more, as to make it the answer itself, as well as the inputter of that answer.
To do that, I wanted to add verification as part of the process, as well as the possibility of a custom conversion std::string -> T.
Basically that would mean taking a functor in the constructor and storing it for later when the ask member function is called. But how would we do this? I cannot store it inside the class if I do not know the type... and to know the type, I would have to include it for the class template, which means explicitly specifying it which defeats the entire purpose...

Code:

template<typename Type, typename CharT = StrType_t,
         template<typename> class ValidateFunctor = ValidateDefault,
         template<typename> class Traits = InputTraits
  > class CInput

The red part highlights the unknown. Taking a class functor is not really what I want. I basically want to make it work with lambda expressions that is coming with C++0x. A sample use of how to use the class would be:

Code:

Stuff::Cinput<int> KeyLength(
    "Enter length of the key", [&]
    {
        cout << "Error. Invalid key.";
    },
    [&] (int Key) -> bool
    {
        return (Key >= 2 && Key <= 5);
    });

An example of how I would like an implementation is:

Code:

		void ask(Type& Answer)
		{
			Answer = m_Converter();
			if (! m_Validater(Answer) )
				m_Error();
		}

I simply lack the know-how.