Improving the Event Manager class

Having different states in a game will, without a shadow of a doubt, create situations where the same key or event will be needed by at least two of the states. Let's say we have a menu, where navigation is done by pressing the arrow keys. That's all fine, but what if the game-play state also registers the use of arrow keys and sets up its own callbacks? The very best case scenario is that callbacks from all states will be invoked at the same time and create weird behavior. Things get worse, however, when you have function pointers to methods that are no longer in memory, especially since nobody likes application crashes. A simple way of dealing with this problem is grouping the callbacks together by state and only invoking them if the current state is that of a callback. This obviously means some re-definition of the types being dealt with:

using CallbackContainer = std::unordered_map<std::string, std::function<void(EventDetails*)>>;
enum class...