Method map_error

src/include/expected.hpp:1426–1428

#if defined(TL_EXPECTED_CXX14) && !defined(TL_EXPECTED_GCC49) &&               \
    !defined(TL_EXPECTED_GCC54) && !defined(TL_EXPECTED_GCC55)
  template <class F> TL_EXPECTED_11_CONSTEXPR auto map_error(F &&f) & {
    return map_error_impl(*this, std::forward<F>(f));
  }
  template <class F> TL_EXPECTED_11_CONSTEXPR auto map_error(F &&f) && {
    return map_error_impl(std::move(*this), std::forward<F>(f));
  }