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  1. #include<iostream>
  2.  
  3. namespace CHECK
  4. {
  5.   class No { bool b[2]; };
  6.   template<typename T, typename Arg> No operator== (const T&, const Arg&);
  7.  
  8.   bool Check (...);
  9.   No& Check (const No&);
  10.  
  11.   template <typename T, typename Arg = T>
  12.   struct EqualExists
  13.   {
  14.     enum { value = (sizeof(Check(*(T*)(0) == *(Arg*)(0))) != sizeof(No)) };
  15.   };  
  16. }
  17.  
  18.  
  19. struct A 
  20. { 
  21.   bool operator == (A const &);
  22. };
  23.  
  24. struct B 
  25. {
  26.   short operator == (B const &); 
  27. };
  28.  
  29. struct C {};
  30.  
  31. struct D
  32. {
  33.   short operator == (short);
  34. };
  35.  
  36. int main()
  37. {
  38.   std::cout<< "A::operator== () exists: " << CHECK::EqualExists<A>::value << std::endl;
  39.   std::cout<< "B::operator== () exists: " << CHECK::EqualExists<B>::value << std::endl;
  40.   std::cout<< "C::operator== () exists: " << CHECK::EqualExists<C>::value << std::endl;
  41.   std::cout<< "C::operator== (short) exists: " << CHECK::EqualExists<D, short>::value << std::endl;
  42. }
  43.  
Success #stdin #stdout 0s 3412KB
comments (?)
stdin 
Standard input is empty
stdout 
A::operator== () exists: 1
B::operator== () exists: 1
C::operator== () exists: 0
C::operator== (short) exists: 1
https://ideone.com/cTjEHt
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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