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  1. #include <iostream>
  2.  
  3. class B {
  4. protected:
  5.     const int a_;
  6.     int b_;
  7.     B (int b, int a) : a_(a), b_(b) {}
  8. public:
  9.     operator bool () const { return b_ == a_; }
  10. };
  11.  
  12. class D1 : public B {
  13. public:
  14.     D1 (int b = 0, int a = 0) : B(b, a) {}
  15.     operator int () const { return b_; }
  16. };
  17.  
  18. class D2 : public B {
  19. public:
  20.     D2 (int b = 0, int a = 0) : B(b, a) {}
  21.     operator int & () { return b_; }
  22. };
  23.  
  24. int main () {
  25.     if (D1 d1a = D1('a', 'a')) std::cout << "d1a\n";
  26.     if (D1 d1b = D1('b', 'a')) std::cout << "d1b\n";
  27.     if (D2 d2a = D2('a', 'a')) std::cout << "d2a\n";
  28.     if (D2 d2b = D2('b', 'a')) std::cout << "d2b\n";
  29.     return 0;
  30. }
Success #stdin #stdout 0s 2896KB
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Standard input is empty
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d1a
d2a
d2b
https://ideone.com/CpPXZS
language:
C++14 (gcc 8.3)
created:
12 years ago
visibility:
public

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