Events and Signals

typedef unsigned short QSignal;
struct QEvent
{
  QSignal sig;                        // signal of the event instance
  unsigned char poolId;        // pool this event instance comes from
  unsigned char useNum;         // # of times it has been used so far
};

• Unsigned short limits signal types to 2¹⁶ (less four for system = 65,532 client-specifiable signals)
• Event type includes signal and parameters (defined in derived type)
• struct without constructors and virtual methods enables re-use of event instances in event queue
• General use pattern:
1. State handler method receives generic QEvent * e
2. Handler accesses e->sig
3. Attribute sig must map uniquely to derived event type
4. Handler accesses data after specific down cast to concrete event
• Another example from QCalc[7]