enum to string in modern C++11 / C++14 / C++17 and future C++20

Question

Contrary to all other similar questions, this question is about using the new C++ features.

• 2008 c Is there a simple way to convert C++ enum to string?
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Answer 1

My 3 cents, though this is not a complete match to what the op wants. Here is the relevant reference.

namespace enums
{

template 
struct enums : std::integral_constant
{
  static constexpr char const chars[sizeof...(Chars)]{Chars...};
};

template 
constexpr auto make(std::index_sequence) noexcept
{
  return enums();
}

#define ENUM(s, n) []() noexcept{\
  struct S { char const (&chars)[sizeof(s)]{s}; };\
  return enums::make(\
    std::make_index_sequence());}()

#define ENUM_T(s, n)\
  static constexpr auto s ## _tmp{ENUM(#s, n)};\
  using s ## _enum_t = decltype(s ## _tmp)

template 
inline auto map(char const (&s)[N]) noexcept
{
  constexpr auto invalid(~T{});

  auto r{invalid};

  return
    (
      (
        invalid == r ?
          r = std::strncmp(A::chars, s, N) ? invalid : A{} :
          r
      ),
      ...
    );
}

}

int main()
{
  ENUM_T(echo, 0);
  ENUM_T(cat, 1);
  ENUM_T(ls, 2);

  std::cout << echo_enum_t{} << " " << echo_enum_t::chars << std::endl;

  std::cout << enums::map("ls")) << std::endl;

  return 0;
}

So you generate a type, that you can convert to an integer and/or a string.