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  1. #include <cassert>
  2.  
  3. template<typename T>
  4. struct Exactly : T
  5. {
  6.     explicit Exactly(T const& value) : T(value) {}
  7. };
  8.  
  9. class Complex
  10. {
  11.     double re;
  12.     double im;
  13.  
  14. public:
  15.     Complex(double re, double im) : re(re), im(im) {}
  16.  
  17.     // Non-members require either friend access or public getters.
  18.     double real() const { return re; }
  19.     double imag() const { return im; }
  20. };
  21.  
  22. #pragma GCC diagnostic push
  23. #pragma GCC diagnostic ignored "-Wfloat-equal"
  24. bool operator == (Complex const& a, Exactly<Complex> const& b)
  25. {
  26.     return (a.real() == b.real()) && (a.imag() == b.imag());
  27. }
  28. // two more overloads for completeness
  29. bool operator == (Exactly<Complex> const& a, Complex const& b)
  30. {
  31.     return (a.real() == b.real()) && (a.imag() == b.imag());
  32. }
  33. bool operator == (Exactly<Complex> const& a, Exactly<Complex> const& b)
  34. {
  35.     return (a.real() == b.real()) && (a.imag() == b.imag());
  36. }
  37. #pragma GCC diagnostic pop
  38.  
  39. Exactly<Complex> exactlyOne(Complex(1.0, 0.0));
  40.  
  41. template<typename T>
  42. Exactly<T> exactly(T const& value)
  43. {
  44.     return Exactly<T>(value);
  45. }
  46.  
  47. int main()
  48. {
  49.     Complex c(1.0, 0.0);
  50.     // assert( c == c ); // error (no match):
  51.     assert( c == exactlyOne );
  52.     assert( exactly(Complex(1.0, 0.0)) == c );
  53.     assert( exactlyOne == exactlyOne );
  54. }
Success #stdin #stdout 0s 15240KB
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https://ideone.com/drMJJH
language:
C++14 (gcc 8.3)
created:
7 years ago
visibility:
secret

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