Variadic Templates and aliases?

I was given this code yesterday:

#ifndef _MEMOIZE_H_
#define _MEMOIZE_H_

#include <tuple>
#include <map>

template < typename T > struct Memoize
{
     template <typename... Args> static auto Func(Args... args)
                           -> decltype(T::Func(std::forward<Args>(args)...))
     {
         using INPUT = std::tuple<Args...>;

         using RESULT = decltype(T::Func(std::forward<Args>(args)...));

         static std::map< INPUT, RESULT > repository;

         auto key = std::make_tuple(std::forward<Args>(args)...);

         auto it = repository.find(key);

         if (it != repository.end())
         {
             return it->second;
         }

         else
         {
             auto result = T::Func(std::forward<Args>(args)...);

             repository[key] = result;

             return result;
         }
     }
};

#endif // _MEMOIZE_H_

Now, can someone point me to a good tutorial or book on variadic
templates and the "using SOMETHING = " semantics. Is this just an alias?