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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. template < class Count >
  5. struct Counter {
  6. 	using count_type = Count;
  7. 	count_type instances = 0;
  8.  
  9. 	template <Counter& c>
  10. 	struct Counted {
  11. 		using id_type = count_type;
  12. 		id_type id;
  13. 		Counted() : id(c.instances) { ++c.instances; }
  14. 		~Counted() { --c.instances; }
  15.  
  16. 		friend std::ostream& operator<<(std::ostream& os, const Counted& lol) {
  17. 			os << "printing inner " << lol.id;
  18. 			return os;
  19. 		}
  20. 	};
  21. };
  22.  
  23. using SCounter = Counter<std::size_t>;
  24. SCounter sc;
  25. using SCounted = SCounter::Counted<sc>;
  26.  
  27. int main() {
  28. 	// your code goes here
  29. 	SCounted i, j, k; // --> ok, works fine
  30. 	std::cout << j << std::endl;
  31. 	return 0;
  32. }
Success #stdin #stdout 0s 3140KB
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stdin
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Standard input is empty
stdout
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printing inner 1
https://ideone.com/NxlvpH
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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