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  1. #include <iostream>
  2. #include <iomanip>
  3. #include <utility>
  4. #include <type_traits>
  5.  
  6. using namespace std;
  7.  
  8. struct has
  9. {
  10. 	void operator()(int const&);	
  11. };
  12.  
  13. struct hasNot1
  14. {
  15. 	void operator()(int);	
  16. };
  17.  
  18. struct hasNot2
  19. {
  20. 	void operator()();	
  21. };
  22.  
  23. struct hasNot3
  24. {
  25. 	void operator()(float);	
  26. };
  27.  
  28. struct hasNot4
  29. {
  30. };
  31.  
  32. template<typename T, typename EDT>
  33. struct is_callable_oper
  34. {
  35.       private:
  36.                     typedef char(&yes)[1];
  37.                     typedef char(&no)[2];
  38.  
  39.                     template <typename U, void (U::*)(EDT const &)> struct
  40.                                                                         Check;
  41.                     template<typename>
  42.                     static yes test(...);
  43.  
  44.                     template <typename U>
  45.                     static no
  46.                             test(Check<U, &U::operator()>*);
  47.  
  48.                 public:
  49.                     static constexpr bool value = sizeof(test<T>(0))
  50.                                                                 == sizeof(yes);
  51. };
  52.  
  53. int main() {
  54. 	cout << boolalpha << is_callable_oper<has, int&>::value << " " 
  55. 		 << is_callable_oper<has, int>::value << " "
  56. 		 << is_callable_oper<hasNot1, int&>::value << " "
  57. 		 << is_callable_oper<hasNot2, int&>::value << " "
  58. 		 << is_callable_oper<hasNot3, int&>::value << " "
  59. 		 << is_callable_oper<hasNot4, int&>::value << endl;
  60. 	return 0;
  61. }
Success #stdin #stdout 0s 16064KB
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stdin
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Standard input is empty
stdout
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true false true true true true
https://ideone.com/tE49xR
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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