C++ TMP - Non-working skeleton for Fibonacci that contains lazy evaluation using integral constant types.

Cpp_Fibonacci_NonWorkingSkeleton.cpp

#include <iostream>
using namespace std;

template <class CValueOne, class CValueTwo> struct Sum;

template <int N1, int N2>
struct Sum<std::integral_constant<int, N1>, std::integral_constant<int, N2>>
{
	typedef std::integral_constant<int, N1+N2> type;
};

template <class CValueOne, class CValueTwo> struct Equals;

template <int N1, int N2>
struct Equals<std::integral_constant<int, N1>, std::integral_constant<int, N2>>
	: std::false_type
{};

template <int N1>
struct Equals<std::integral_constant<int, N1>, std::integral_constant<int, N1>>
	: std::true_type
{};

template <bool Cond, class EvalIfTrue, class EvalIfFalse>
struct ConditionalEval;

template <class EvalIfTrue, class EvalIfFalse>
struct ConditionalEval<false, EvalIfTrue, EvalIfFalse>
{
	typedef typename EvalIfFalse::type type;
};

template <class EvalIfTrue, class EvalIfFalse>
struct ConditionalEval<true, EvalIfTrue, EvalIfFalse>
{
	typedef typename EvalIfTrue::type type;
};

template <class CIndex>
struct Fibonacci
{
	struct details
	{
		typedef std::integral_constant<int, 0> N0;
		typedef std::integral_constant<int, 1> N1;
		typedef std::integral_constant<int, 2> N2;
		typedef std::integral_constant<int, 42> Nuniverse;
	};
	typedef typename ConditionalEval<
		Equals<CIndex, typename details::N0>::value,
		typename details::N1,
		typename ConditionalEval<
			Equals<CIndex, typename details::N1>::value,
			typename details::N1,
			typename details::Nuniverse
			>::type
		>::type type;
};

int main() 
{
	typedef std::integral_constant<int, 0> N0;
	typedef std::integral_constant<int, 1> N1;
	typedef std::integral_constant<int, 2> N2;
	typedef std::integral_constant<int, 3> N3;
	typedef std::integral_constant<int, 4> N4;
	std::cout << Fibonacci<N2>::type::value << std::endl;
	return 0;
}