C++17 Tuple Hash

tuple_hash.hpp

template <typename T, typename... Ts>
constexpr void hash_combine(size_t &seed, const T &t, const Ts &...ts) {
  seed ^= std::hash<T>{}(t) + 0x9e3779b97f4a7c15 + (seed << 6) + (seed >> 2);

  if constexpr (sizeof...(ts) > 0) {
    hash_combine(seed, ts...);
  }
}

template <typename T>
struct tuple_hash {
  size_t operator()(const T &t) const {
    size_t seed{0};
    std::apply([&](const auto &...ts) {
      (hash_combine(seed, ts), ...);
    }, t);
    return seed;
  }
};