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  1. #include <iostream>
  2. #include <type_traits>
  3.  
  4. namespace details
  5. {
  6.     template <typename T, typename R, typename = R>
  7.     struct equality : std::false_type {};
  8.  
  9.     template <typename T, typename R>
  10.     struct equality<T, R, decltype(std::declval<T>() == std::declval<T>())> : std::true_type {};
  11. }
  12.  
  13. template<typename T, typename R = bool>
  14. struct equality : details::equality<T, R> {};
  15.  
  16. struct A  {};
  17. struct B  {  bool operator == (B const &); };
  18. struct C  {  short operator == (C const &); };
  19. struct D  {  bool operator == (short); };
  20.  
  21. int main()
  22. {
  23.     std::cout<< "equality<A>::value = " << equality<A>::value << std::endl;
  24.     std::cout<< "equality<B>::value = " << equality<B>::value << std::endl;
  25.     std::cout<< "equality<C>::value = " << equality<C>::value << std::endl;
  26.     std::cout<< "equality<B,short>::value = " << equality<B,short>::value << std::endl;
  27.     std::cout<< "equality<C,short>::value = " << equality<C,short>::value << std::endl;
  28.     std::cout<< "equality<D>::value = " << equality<D>::value << "<====\n";
  29. }
Success #stdin #stdout 0s 3456KB
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stdin
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Standard input is empty
stdout
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equality<A>::value = 0
equality<B>::value = 1
equality<C>::value = 0
equality<B,short>::value = 0
equality<C,short>::value = 1
equality<D>::value = 0<====
https://ideone.com/Yy3ByZ
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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