struct GraphUpdate_Success {};
struct GraphUpdate_NoWorkToDo {};
struct GraphUpdate_UnsatisfiedDependencies {
	struct Elm { size_t Idx; int FulfilleDependencies; };
	std::vector<Elm> UnsatisfiedNodes;
};
struct GraphUpdate_UnreachableNodes {
	std::vector<size_t> UnreachableNodes;
};

std::variant<
	GraphUpdate_Success,
	GraphUpdate_NoWorkToDo,
	GraphUpdate_UnsatisfiedDependencies,
	GraphUpdate_UnreachableNodes>
UpdateGraph();