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  1. #include <iostream>
  2. #include <string>
  3.  
  4. using namespace std;
  5.  
  6. class Thing {
  7. public:
  8. 	virtual const char * type_name()=0;
  9. };
  10.  
  11. class OtherThing : public Thing {
  12. public:
  13. 	OtherThing() {}
  14. 	const char * type_name() { return "test"; }
  15. };
  16.  
  17. class ParameterThing : public Thing {
  18. 	std::string var;
  19. public:
  20. 	ParameterThing(const std::string var_) { var = var_; }
  21. 	const char * type_name() { return var.c_str(); }
  22. };
  23.  
  24. class NotAThing {
  25. public:
  26. };
  27.  
  28. template <typename TO_T, class ...Args>
  29. inline TO_T* turn_thing_to(Thing* p, Args&&... args) 
  30. {
  31.   static_assert(std::is_base_of<Thing, TO_T>::value, "TO_T is not derived from Thing");
  32.   TO_T * newtype = new TO_T(args...); 
  33.   p = newtype;
  34.   return newtype;
  35. }
  36.  
  37. int main() {
  38. 	Thing * thing = 0;
  39. 	thing = turn_thing_to<OtherThing>(thing);
  40. 	//compiler can't assign it to the pointer directory from the function argument, so
  41. 	//I returned it.
  42. 	std::cout << thing->type_name() << "\n";
  43. 	thing  = turn_thing_to<ParameterThing>(thing, "test2");
  44. 	std::cout << thing->type_name();
  45.  
  46. 	/*
  47. 	thing = turn_thing_to<NotAThing>(thing); //gives compile error
  48. 	*/
  49. 	return 0;
  50. }
Success #stdin #stdout 0s 3428KB
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stdin
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Standard input is empty
stdout
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test
test2
https://ideone.com/W3PgMS
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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