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  1. #include <type_traits>
  2.  
  3. template<class F, class S>
  4. struct pair_base {
  5. 	template<bool true_ = true
  6. 	        ,typename std::enable_if
  7. 	         <   std::is_default_constructible<F>::value
  8. 	          && std::is_default_constructible<S>::value
  9. 	          && true_
  10. 	         , int
  11. 	         >::type = 0
  12. 	        >
  13. 	pair_base() : first(), second() {}
  14. 	F first;
  15. 	S second;
  16. };
  17.  
  18. template<class F, class S>
  19. struct pair : private pair_base<F,S> {
  20. 	using pair_base<F,S>::first;
  21. 	using pair_base<F,S>::second;
  22. };
  23.  
  24. static_assert(std::is_default_constructible<pair<int,int>>::value, "");
  25. static_assert(!std::is_default_constructible<pair<int&,int&>>::value, "");
  26.  
  27. int main() {}
  28.  
Success #stdin #stdout 0s 3092KB
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https://ideone.com/YBKPMp
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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