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  1. #include <iostream>
  2. #include <unordered_set>
  3. #include <memory>
  4.  
  5. template < typename T, typename TAG = void  > struct magic
  6. {
  7.     // ...
  8.     /* private: */ static std::unordered_set<T*> objects ;
  9. };
  10.  
  11. template < typename T, typename TAG > std::unordered_set<T*> magic<T,TAG>::objects ;
  12.  
  13. template < typename T, typename TAG = void > struct tracked
  14.                                               : T, magic< tracked<T,TAG>, TAG >
  15. {
  16.     template < typename ... ARGS > tracked( ARGS... args ) : T(args...) {}
  17. };
  18.  
  19. struct A { /* ... */ };
  20.  
  21. template < int N > struct use_case {} ;
  22.  
  23. int main()
  24. {
  25.     std::cout << std::addressof( tracked<A>::objects ) << '\n' ;
  26.     std::cout << std::addressof( tracked< A, use_case<1> >::objects ) << '\n' ;
  27.     std::cout << std::addressof( tracked< A, use_case<2> >::objects ) << '\n' ;
  28.     std::cout << std::addressof( tracked< A, use_case<3> >::objects ) << '\n' ;
  29.     std::cout << std::addressof( tracked< A, use_case<4> >::objects ) << '\n' ;
  30.     std::cout << std::addressof( tracked< A, use_case<5> >::objects ) << '\n' ;
  31. }
  32.  
Success #stdin #stdout 0s 2992KB
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0x804b700
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https://ideone.com/1M0VDy
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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