Strong enum handle example

strong_enum_handle_example

template <typename HandleT, unsigned IndexBits = 24U>
HandleT pack(unsigned index, unsigned version) {
  using T = std::underline_type<HandleT>::type;
  auto result = T(version << IndexBits);
  auto const mask = T(1 << IndexBits) - 1;
  result |= T(index) & mask;
  return HandleT(result);
}

template <typename HandleT>
void unpack(HandleT handle, unsigned& out_index, unsigned& out_version) {
  using T = std::underline_type<HandleT>::type;
  auto const mask = T(1 << IndexBits) - 1;
  out_index = T(handle) & mask;
  out_version = T(handle) >> IndexBits;
}

// --- example ---
enum class TextureId : std::uint32_t { None = 0 };

// make a new texture ID
TextureId tex = pack<TextureId>(my_index, my_version);

// extract the index and version from a texture ID
unsigned index, version;
unpack(tex, index, version);