Function get_as_upvalues_using_function

3rdparty/lua/sol/sol.hpp:16469–16488

			template <typename T>
			inline std::pair<T, int> get_as_upvalues_using_function(lua_State* L, int function_index = -1) {
				static const std::size_t data_t_count = (sizeof(T) + (sizeof(void*) - 1)) / sizeof(void*);
				typedef std::array<void*, data_t_count> data_t;
				function_index = lua_absindex(L, function_index);
				int index = 0;
				data_t voiddata { {} };
				for (std::size_t d = 0; d < sizeof(T); d += sizeof(void*)) {
					// first upvalue is nullptr to respect environment shenanigans
					// So +2 instead of +1
					const char* upvalue_name = lua_getupvalue(L, function_index, index + 2);
					if (upvalue_name == nullptr) {
						// We should freak out here...
						break;
					}
					voiddata[index] = lua_touserdata(L, -1);
					++index;
				}
				lua_pop(L, index);
				return std::pair<T, int>(*reinterpret_cast<T*>(static_cast<void*>(voiddata.data())), index);
			}

			template <bool checked, typename Handler, typename Fx, typename... Args>
			static decltype(auto) eval(types<>, std::index_sequence<>, lua_State*, int, Handler&&, record&, Fx&& fx, Args&&... args) {