I changed the names of the local variables in commit 77afb5d8c6d2.

Thanks for your imporvments.

Now I should have addressed all your issues. It is now only possible to write one header line before data into the csv file.

template <typename... Ts>
template <size_t... S0>
void DeluxeTuple<Ts...>::dump(std::ostream &OS, Seq<S0...>) const noexcept {
  STATIC_ASSERT(sizeof...(S0) == sizeof...(Ts), "inconsistent type arguments");
  OS << "{";
  (OS << ... << (" " + std::to_string(std::get<S0>(*this))));
  OS << " }";
}

Will this also work if the type of S0 is already std::string??

Resolved issues of code review.