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  1. #include <cassert>
  2. using namespace std;
  3.  
  4. class Box;
  5. class Rabbit {
  6. public:
  7.     ~Rabbit() { disconnect(); }
  8. 	void connect(Box& box);
  9.     void disconnect();
  10. 	Box* getMyBox() const { return box; }
  11. private:
  12. 	Box* box = nullptr;
  13. };
  14. class Box {
  15. public:
  16.     ~Box() { disconnect(); }
  17. 	void connect(Rabbit& otherRabbit);
  18.     void disconnect();
  19. 	Rabbit* getMyRabbit() const { return rabbit; }
  20. private:
  21. 	Rabbit* rabbit = nullptr;
  22. };
  23.  
  24. inline void Rabbit::connect(Box& otherBox)
  25. {
  26. 	if (box != &otherBox)
  27. 	{
  28. 		disconnect();
  29. 		box = &otherBox;
  30. 	    box->connect(*this);
  31. 	}
  32. }
  33.  
  34. inline void Rabbit::disconnect()
  35. {
  36. 	if (box != nullptr)
  37. 	{
  38. 		Box* oldBox = box;
  39. 		box = nullptr; // do this before calling disconnect on box - otherwise you get infinite recursion...
  40. 		oldBox->disconnect();
  41. 	}
  42. }
  43.  
  44. inline void Box::connect(Rabbit& otherRabbit)
  45. {
  46. 	if (rabbit != &otherRabbit)
  47. 	{
  48. 		disconnect();
  49. 		rabbit = &otherRabbit;
  50. 	    rabbit->connect(*this);
  51. 	}
  52. }
  53.  
  54. inline void Box::disconnect()
  55. {
  56. 	if (rabbit != nullptr)
  57. 	{
  58. 		Rabbit* oldRabbit = rabbit;
  59. 		rabbit = nullptr; // do this before calling disconnect on box - otherwise you get infinite recursion...
  60. 		oldRabbit->disconnect();
  61. 	}
  62. }
  63.  
  64. int main() {
  65. 	Box b1, b2;
  66. 	Rabbit r1;
  67.  
  68. 	b1.connect(r1);	
  69. 	assert(b1.getMyRabbit() == &r1);
  70. 	assert(r1.getMyBox() == &b1);
  71.  
  72. 	r1.connect(b2);
  73. 	assert(b1.getMyRabbit() == nullptr);
  74. 	assert(r1.getMyBox() == &b2);
  75. 	assert(b2.getMyRabbit() == &r1);
  76.  
  77. 	b2.disconnect();
  78. 	assert(b1.getMyRabbit() == nullptr);
  79. 	assert(r1.getMyBox() == nullptr);
  80. 	assert(b2.getMyRabbit() == nullptr);
  81.  
  82. 	{ 
  83. 		Rabbit r2;
  84. 		r2.connect(b1);
  85. 		assert(b1.getMyRabbit() == &r2);
  86. 		assert(r2.getMyBox() == &b1);
  87. 	}
  88. 	assert(b1.getMyRabbit() == nullptr);
  89.  
  90.  
  91. }
Success #stdin #stdout 0s 3452KB
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https://ideone.com/Vh8qoi
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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