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  1. #include <iostream>
  2. #include <type_traits>
  3.  
  4. struct UserType{};
  5. struct LibType1{};
  6. struct LibType2{};
  7.  
  8. namespace def {
  9.     struct NoOp {};
  10.  
  11.     template <typename T>
  12.     NoOp operator ^ (T, LibType2)
  13.     {
  14.         static_assert(sizeof(T) == 0, "Don't do that.");
  15.     }
  16. }
  17.  
  18. // try commenting this out
  19. LibType1 operator ^ (UserType, LibType2)
  20. {
  21.     return {};
  22. }
  23.  
  24. void doIt(UserType ut)
  25. {
  26.     using namespace def;
  27.     LibType2 lt2;
  28.     ut ^ lt2;
  29. }
  30.  
  31. template <typename T>
  32. bool exists()
  33. {
  34.     using namespace def;
  35.     return !std::is_same<decltype(std::declval<T>() ^ std::declval<LibType2>()), NoOp>::value;
  36. }
  37.  
  38. int
  39. main(void)
  40. {
  41.     std::cout << exists<UserType>() << std::endl;
  42.     return 0;
  43. }
Success #stdin #stdout 0s 15240KB
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1
https://ideone.com/eYs7bU
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
public

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