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  1. #include <iostream>
  2. #include <type_traits>
  3.  
  4. class SubType {};
  5.  
  6. class A : SubType {
  7.   // things
  8. };
  9.  
  10. class B : public A {
  11.   // more things
  12. };
  13.  
  14. class SubBase {
  15. 	/* default impl. */
  16. 	public:
  17. 	    virtual A* get() = 0;
  18.  
  19. };
  20.  
  21. template <typename T>
  22. class Base : public SubBase {
  23. 	public:
  24. 		Base(SubType* subinst) :instance((void*)subinst) {}
  25. 		Base(void* inst) :instance(inst) {}
  26. 		Base(T* t) :Base(dynamic_cast<A*>(t)) {}
  27. 	public:
  28. 		void* instance;
  29.  
  30. };
  31.  
  32. template <typename T, typename = typename std::is_base_of<T, A>::type>
  33. class Wrapper : public Base<T> {
  34. 	public:
  35. 		Wrapper(T* t) :Base<T>(static_cast<void*>(t)) {}
  36. 	    virtual T* get() { return (T*)Base<T>::instance; }
  37. };
  38.  
  39. class Worker {
  40. 	public:
  41. 	  void work(Wrapper<A>* wa){
  42.     	A* a = wa->get();
  43.     	//do stuff with a.
  44.   	  }
  45. };
  46.  
  47. int main() {
  48. 	B b;
  49. 	Worker worker;
  50. 	Wrapper<B> wrapped_b(&b);
  51. 	worker.work((Wrapper<A>*)&wrapped_b);
  52. }
Success #stdin #stdout 0s 15240KB
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https://ideone.com/mGrGA1
CRTP-ish Example
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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