Practical Template Programming - Learn C++ for Game Development - page 197

template <typename T>
friend void AttachEvent(EventID eventId, T* eventHandler);
template <typename T>
friend void DetachEvent(EventID eventId, T* eventHandler);
private:
using EventMap = std::unordered_map<EventID, Event*>;
using EventMapIterator = EventMap::iterator;
EventMap m_eventMap;
void SendEvent(EventID eventId);
void SendEventToHandler(EventID eventId, EventHandler& eventHandler);
bool RegisterEvent(EventID eventId);
void AttachEvent(EventID eventId, EventHandler& eventHandler);
void DetachEvent(EventID eventId, EventHandler& eventHandler);
public:
virtual ~EventManager();
};
The EventManager class has an interesting design. The Event objects are stored in an unordered_map
using the EventID as a key. There are also private member methods that contain the behavior of the
class: SendEvent , SendEventToHandler , RegisterEvent , AttachEvent , and DetachEvent . There are also
public friend methods that are used to wrap these function calls and use template code. I'll show
you the code for the private methods first then talk you through how and why the public friend
functions are used. Listing 21-10 contains the code for the RegisterEvent method.
Listing 21-10. EventManager::RegisterEvent
bool EventManager::RegisterEvent(EventID eventId)
{
bool added = false;
EventMapIterator result = m_eventMap.find(eventId);
if (result == m_eventMap.end())
{
Event* pNewEvent = new Event(eventId);
if (pNewEvent)
{
std::pair<EventID, Event*> newEvent(eventId, pNewEvent);
auto addedIter = m_eventMap.insert(newEvent);
added = addedIter.second;
}
}
assert(added);
return added;
}