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  1. #include <iostream>
  2.  
  3. using namespace std;
  4.  
  5. struct EventReceiverBase {
  6.     virtual ~EventReceiverBase() { }
  7. };
  8.  
  9. template<typename T>
  10. struct EventReceiver : public virtual EventReceiverBase {
  11.     virtual void receiveEvent(T* pSender) = 0;
  12. };
  13.  
  14. struct EventSender {
  15.     EventReceiverBase* pReceiver;
  16.  
  17.     template<typename T>
  18.     void sendEvent(T* pSender) {
  19.         EventReceiver<T>* pCastedReceiver =
  20.             dynamic_cast<EventReceiver<T>*>(pReceiver);
  21.         // HERE IS THE PROBLEM
  22.         // pCastedReceiver is null. T is BaseSender. The pointer
  23.         // being casted is really of type EventReceiver<DerivedSender>*,
  24.         // but it tries to cast to EventReceiver<BaseSender>*, and that
  25.         // fails.
  26.         pCastedReceiver->receiveEvent(pSender);
  27.     }
  28. };
  29.  
  30. struct BaseSender : public virtual EventSender {
  31. };
  32. struct DerivedSender : public BaseSender {
  33.     void f() {
  34.         sendEvent(this);
  35.     }
  36. };
  37.  
  38. struct MyClass : public virtual EventReceiver<DerivedSender> {
  39.     void receiveEvent(DerivedSender* pSender) { }
  40. };
  41.  
  42. int main() {
  43.     MyClass my;
  44.     DerivedSender derivedSender;
  45.     derivedSender.pReceiver = &my;
  46.     derivedSender.f();
  47.     return 0;
  48. }
Success #stdin #stdout 0.02s 2720KB
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https://ideone.com/LpM1d9
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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