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  1. #include <type_traits>
  2. #include <iostream>
  3.  
  4. template<class T>
  5. class has_addition
  6. {
  7.     template <typename C> static std::true_type test( decltype(
  8.     	    std::declval<C>() + std::declval<C>()
  9.     	)* );
  10.     template <typename> static std::false_type test(...);
  11.  
  12. public:
  13.     enum { value = decltype(test<T>(0))::value };
  14. };
  15.  
  16. template<class T>
  17. class X
  18. {
  19. public:
  20.  
  21.     template <typename T1 = T>
  22. 	typename std::enable_if<!has_addition<T1>::value, void>::type use(T1 t)
  23. 	{
  24. 		std::cout << "without addition" << std::endl;
  25. 		T1 tt = t;
  26. 	}
  27.  
  28.     template <typename T1 = T>
  29. 	typename std::enable_if<has_addition<T1>::value, void>::type use(T1 t)
  30. 	{
  31. 		std::cout << "with addition" << std::endl;
  32. 		auto tt = t + t;
  33. 	}
  34.  
  35. };
  36.  
  37. int main()
  38. {
  39. 	X<int> x1; x1.use(1);
  40. 	X<void*> x2; x2.use(nullptr);
  41.     return 0;
  42. }
Success #stdin #stdout 0s 3140KB
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stdin
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Standard input is empty
stdout
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with addition
without addition
https://ideone.com/7GNE3B
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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