#define constexpr_toupper(text) detail::toupper<text>()

namespace detail {

inline static constexpr char toupper(char c) {
	return (c >= 'a' && c <= 'z') ? (c - 'a' + 'A') : c;
}

template <size_t size>
struct CopyUppercase {
	inline constexpr Copy(const char (&text)[size]) {
		std::copy_n(text, size, _data.begin());
		std::transform(_data.begin(), _data.end(), _data.begin(), [](char c) {
			return toupper(c);
		});
	}
	std::array<char, size> _data;
};

template <CopyUppercase text>
inline static constexpr const char* toupper() {
	return text._data.data();
}

} // namespace detail

// C++14

#define constexpr_toupper(text) detail::toupper(detail::Split<text>)

namespace detail {

template <size_t size>
struct Copy {
	inline constexpr Copy(const char (&text)[size]) {
		std::copy_n(text, size, _data.begin());
	}
	std::array<char, size> _data;
};

template <char... c>
struct Join {
	inline static constexpr char value[] = { c... };
};

template <Copy copy>
inline static constexpr auto Split = ([]<size_t... i>(std::index_sequence<i...>) {
	return Join<copy._data[i]...>();
})(std::make_index_sequence<copy._data.size()>());

inline static constexpr char toupper(char c) {
	return (c >= 'a' && c <= 'z') ? (c - 'a' + 'A') : c;
}

template <char... c>
inline static constexpr std::string_view toupper(Join<c...>) {
	return std::string_view(Join<toupper(c)...>::value);
}

} // namespace detail