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  1. #include <iostream>
  2. #include <string>
  3.  
  4. using namespace std;
  5.  
  6. struct NO_INIT {};
  7.  
  8. class Thing {
  9. 	int a;
  10. public:
  11.     Thing(int v = 0): a (v) {}
  12.     Thing(NO_INIT) {} 
  13. 	virtual const char * type_name(){ return "Thing"; }
  14. 	virtual int value() { return a; }
  15. };
  16.  
  17. class OtherThing : public Thing {
  18. public:
  19. 	OtherThing(int v): Thing(v) {}
  20. 	OtherThing(NO_INIT ni): Thing(ni) {}
  21.  
  22. 	virtual const char * type_name() { return "Other Thing"; }
  23. };
  24.  
  25. template <typename TO_T>
  26. inline TO_T* turn_thing_to(Thing* p) 
  27. {
  28.   return ::new(p) TO_T(NO_INIT()); 
  29. }
  30.  
  31. int main() {
  32. 	Thing * thing = new Thing(42);
  33. 	std::cout << thing->type_name() << "\n";
  34. 	std::cout << thing->value() << "\n";
  35.  
  36. 	turn_thing_to<OtherThing>(thing);
  37. 	std::cout << thing->type_name() << "\n";
  38. 	std::cout << thing->value() << "\n";
  39. 	return 0;
  40. }
Success #stdin #stdout 0s 3428KB
comments (?)
stdin 
Standard input is empty
stdout 
Thing
42
Other Thing
42
https://ideone.com/DAulzT
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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