constexpr enum constants from string constants at compile time

to_int_constant.cpp

/***
 * @brief Convert a string literal to a compile-time integer constant.
 * @tparam IntT The integer type to return.
 * @tparam CharT The character type of the string literal.
 * @tparam NameLength  The length of the string literal.
 * @tparam NameIndex  The current index of the string literal.
 * @tparam TBytes  The number of bytes in the integer type.
 * @param name  The string literal to convert.
 * @return  The integer constant.
 */
template<typename IntT, typename CharT, int NameLength, int NameIndex = 0>
requires std::integral<IntT>
constexpr IntT to_int_constant(const CharT(&name)[NameLength]) noexcept {
    constexpr int n_bytes = sizeof(IntT);
    if constexpr (NameIndex >= NameLength || NameIndex >= n_bytes) {
        return 0;
    } else {
        auto c = static_cast<IntT>(static_cast<unsigned char>(name[NameIndex]));
        return (c << (8 * sizeof(CharT) * (std::min(NameLength,n_bytes) - NameIndex - 1))) |
                to_int_constant<IntT, CharT, NameLength, NameIndex + 1>(name);
    }
}

/**
 * @brief Convert a string literal to a compile-time uint64_t constant.
 * @tparam NameLength the length of the string literal.
 * @tparam CharT the character type of the string literal.
 * @param s the string literal to convert.
 * @return  the integer constant.
 */
template<int NameLength, typename CharT>
constexpr uint64_t to_uint64(const CharT (&s)[NameLength]) noexcept {
    return to_int_constant<uint64_t>(s);
}

enum class Ok : uint64_t {
    ABCD = to_uint64("ABCD"),
    DEADBEEF = to_uint64("DEADBEEF"),
    VERY_LONG_CONSTANT_FOR_INFORMATION = to_uint64("very long constant for information")
};