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  1. #include <type_traits>
  2. #include <cstdint>
  3.  
  4. #define DEFINE_HAS_SIGNATURE(traitsName, funcName, signature)               \
  5.     template <typename U>                                                   \
  6.     class traitsName                                                        \
  7.     {                                                                       \
  8.     private:                                                                \
  9.         template<typename T, T> struct helper;                              \
  10.         template<typename T>                                                \
  11.         static std::uint8_t check(helper<signature, &funcName>*);           \
  12.         template<typename T> static std::uint16_t check(...);               \
  13.     public:                                                                 \
  14.         static                                                              \
  15.         constexpr bool value = sizeof(check<U>(0)) == sizeof(std::uint8_t); \
  16.     }
  17.  
  18. DEFINE_HAS_SIGNATURE(has_X, T::X, bool (T::*)());
  19. DEFINE_HAS_SIGNATURE(has_Y, T::Y, bool (T::*)());
  20.  
  21. template <typename T>
  22. typename std::enable_if<has_X<T>::value && has_Y<T>::value, bool>::type
  23. func(T a)
  24. {
  25.   if(a.X())
  26.     return a.Y();
  27.   return false;
  28. }
  29.  
  30. template <typename T>
  31. typename std::enable_if<!has_X<T>::value || !has_Y<T>::value, bool>::type
  32. func(T /*a*/)
  33. {
  34.     return false;
  35. }
  36.  
  37. struct A {
  38.     bool X() {return true;}
  39.     bool Y() {return true;}
  40. };
  41.  
  42. struct B {
  43. };
  44.  
  45. int main()
  46. {
  47.     func<A>(A{});
  48.     func<B>(B{});
  49.  
  50.     return 0;
  51. }
  52.  
Success #stdin #stdout 0s 3292KB
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https://ideone.com/XmjQY8
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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