repack.cc

#include <iostream>
#include <utility>
#include <tuple>
#include <typeinfo>

template<typename, template<typename...>class>
struct repack {

};

template<template<typename...> class Source, template<typename...> class Dest, typename ...Ts>
struct repack<Source<Ts...>, Dest> {
  using type = Dest<Ts...>;
};

int main(int argc, char const* argv[])
{
  using x = std::pair<int, double>;
  using y = repack<x, std::tuple>::type;
  y z;
  std::cout << typeid(z).name() << std::endl;
  return 0;
}