// Select stuff - templates that define selection in the general case (4ed, page 792).
// Uses variadic templates (4ed, 809). C++11.

// select - declared, but never instantiated. The specialization below will be instantiated
template<unsigned int N, typename... Types>
struct select;


// Specialization that just recurses in the base type:
template <unsigned int N, typename T, typename... Types>   
struct select<N, T, Types...>: select<N-1, Types...>{
};

// Specialization that represent the base case of the recursion.
// Defines what type stands for: 
template<typename T, typename... Types>
struct select<0, T, Types...>{
  using type = T;
};


// A using alias Select that embellish the use of select - as before:
template <unsigned int N, typename... Types>
using Select = typename select<N, Types...>::type;