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  1. #include <iostream>
  2. using namespace std;
  3.  
  4. class A {
  5. public:
  6.     int x;
  7.  
  8.     A(int x = 0) : x(x) {}
  9.  
  10.     struct Cmp {
  11.         const A *ptr;
  12.         mutable bool val;
  13.  
  14.         operator bool() const {
  15.             return val;
  16.         }
  17.  
  18.         const Cmp &operator == (const A &other) const {
  19.             return other == *this;
  20.         }
  21.     };
  22.  
  23.     bool isEqualTo (const A &other) const {
  24.     	return x == other.x;
  25.     }
  26.  
  27.     Cmp operator == (const A &other) const {        
  28.         return {this, isEqualTo(other)};
  29.     }
  30.  
  31.     const Cmp &operator == (const Cmp &other) const {
  32.         //other.val = other.val && (*this == *other.ptr).val;
  33.         other.val &= other.ptr->isEqualTo(*this);
  34.         return other;
  35.     }
  36. };
  37.  
  38. int main() {
  39.     cout << (A(10) == A(10) == A(10)) << endl;
  40.     cout << (A(10) == A(9) == A(10)) << endl;
  41.  
  42.     return 0;
  43. }
Success #stdin #stdout 0s 3412KB
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https://ideone.com/ZrvsHh
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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