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  1. #include <iostream>
  2. using namespace std;
  3.  
  4.  
  5. struct NoComparable {
  6. };
  7.  
  8. struct ComparableWithItself {
  9. };
  10.  
  11. bool operator == (ComparableWithItself const &lhs, ComparableWithItself const &rhs) {
  12.     return true;
  13. }
  14.  
  15. struct ComparableWithItselfAndOther {
  16.     bool operator == (ComparableWithItselfAndOther const &lhs) const {
  17.         return true;
  18.     }
  19.  
  20.     bool operator == (ComparableWithItself const &lhs) const {
  21.     	return true;
  22.     }
  23. };
  24.  
  25. namespace CHECK  // namespace to let "operator ==" not become global
  26. {
  27.   typedef char no[7];
  28.   template<typename T, typename T2> no& operator == (const T&, const T2&);
  29.  
  30.   template <typename T, typename T2>
  31.   struct opEqualExists // *(T*)(0) can be replaced by *new T[1] also
  32.   {
  33.     enum { value = (sizeof(*(T*)(0) == *(T2*)(0)) != sizeof(no)) };
  34.   };
  35. }
  36.  
  37.  
  38. int main() {
  39.     std::cout << CHECK::opEqualExists<ComparableWithItselfAndOther, ComparableWithItselfAndOther>::value << std::endl;
  40.     std::cout << CHECK::opEqualExists<ComparableWithItself, ComparableWithItself>::value << std::endl;
  41.     std::cout << CHECK::opEqualExists<ComparableWithItselfAndOther, ComparableWithItself>::value << std::endl;
  42.     std::cout << CHECK::opEqualExists<ComparableWithItself, ComparableWithItselfAndOther>::value << std::endl;
  43.     std::cout << CHECK::opEqualExists<NoComparable, NoComparable>::value << std::endl;
  44.  
  45. 	return 0;
  46. }
Success #stdin #stdout 0s 2684KB
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https://ideone.com/a0oBA0
language:
C++ 4.3.2 (gcc-4.3.2)
created:
9 years ago
visibility:
public

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