This snipplet shows how to make use of an index sequence when confined to structs, using the same principle exploited in #untuple.cc

indexSequence.cc

// Author:          Julius Hülsmann
// Email:           juliusHuelsmann [at] gmail.com, julius.huelsmann [at] data-spree.com
// Creation Date:   2020-02-18
// Execution: g++-10.0 -std=c++2a indexSequence.cc

// This snipplet shows how to make use of an index sequence when confined to structs, using the
// same principle exploited in #untuple.cc

#include <cstdint>
#include <tuple>

template <std::size_t s, typename is = decltype(std::make_index_sequence<s>())> struct example;

template <std::size_t s, std::size_t... values> struct example<s, std::index_sequence<values...>> {
  using t = int;// expand the std::size_t  :)
};

int main() {
  example<5>::t k = 2;
}