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  1. #include <iostream>
  2. #include <type_traits>
  3.  
  4. #define IS_MEMBER(T1, M) 	\
  5. struct {		\
  6. 	struct verystrangename1 { bool M; }; 	\
  7. 	template<typename T> struct verystrangename2 : verystrangename1, public T { };	\
  8. 	\
  9. 	enum return_t { not_member, is_object, is_function }; \
  10. 	template<typename T, typename = decltype(verystrangename2<T>::M)> constexpr return_t what_member() { return not_member;  } 	\
  11. 	template<typename T> typename std::enable_if<std::is_member_object_pointer<decltype(&T::M)>::value, return_t>::type constexpr what_member() { return is_object; }	\
  12. 	template<typename T> typename std::enable_if<std::is_member_function_pointer<decltype(&T::M)>::value, return_t>::type constexpr what_member() { return is_function; }	\
  13. 	constexpr operator return_t() { return what_member<T1>(); }	\
  14. }
  15.  
  16. struct t {
  17. 	int aaa;
  18. 	float bbb;
  19. 	void func() {}
  20. };
  21.  
  22. // Can't be in function
  23. IS_MEMBER(t, aaa) is_aaa_member_of_t;
  24. IS_MEMBER(t, ccc) is_ccc_member_of_t;
  25. IS_MEMBER(t, func) is_func_member_of_t;
  26.  
  27. // known at compile time
  28. enum { const_is_aaa_member_of_t = (int)is_aaa_member_of_t };
  29. static constexpr int const_is_func_member_of_t = is_func_member_of_t;
  30.  
  31.  
  32. int main() {
  33.  
  34. 	std::cout << std::boolalpha << 
  35. 		"0 - not_member, 1 - is_object, 2 - is_function \n\n" <<
  36. 		"is aaa member of t = " << is_aaa_member_of_t << std::endl << 
  37. 		"is ccc member of t = " << is_ccc_member_of_t << std::endl << 
  38. 		"is func member of t = " << is_func_member_of_t << std::endl << 
  39. 		std::endl;
  40.  
  41. 	return 0;
  42. }
Success #stdin #stdout 0s 3412KB
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Standard input is empty
stdout
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0 - not_member, 1 - is_object, 2 - is_function 

is aaa member of t = 1
is ccc member of t = 0
is func member of t = 2
https://ideone.com/Fjm9u5
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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