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  1. #include<iostream>
  2. #include<type_traits>
  3.  
  4. namespace CHECK
  5. {
  6.   struct No {}; 
  7.   template<typename T, typename Arg> No operator== (const T&, const Arg&);
  8.  
  9.   template<typename T, typename Arg = T>
  10.   struct EqualExists
  11.   {
  12.     enum { value = !std::is_same<decltype(*(T*)(0) == *(Arg*)(0)), No>::value };
  13.   };  
  14. }
  15.  
  16. struct A 
  17. { 
  18.   bool operator == (A const &);
  19. };
  20.  
  21. struct B 
  22. {
  23.   short operator == (B const &); 
  24. };
  25.  
  26. struct C {};
  27.  
  28. struct D
  29. {
  30.   short operator == (short);
  31. };
  32.  
  33. int main()
  34. {
  35.   std::cout<< "A::operator== () exists: " << CHECK::EqualExists<A>::value << std::endl;
  36.   std::cout<< "B::operator== () exists: " << CHECK::EqualExists<B>::value << std::endl;
  37.   std::cout<< "C::operator== () exists: " << CHECK::EqualExists<C>::value << std::endl;
  38.   std::cout<< "C::operator== (short) exists: " << CHECK::EqualExists<D, short>::value << std::endl;
  39. }
  40.  
Success #stdin #stdout 0s 3456KB
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stdin
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Standard input is empty
stdout
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A::operator== () exists: 1
B::operator== () exists: 1
C::operator== () exists: 0
C::operator== (short) exists: 1
https://ideone.com/pldMrr
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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