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  1. #include <memory>
  2. #include <vector>
  3. #include <functional>
  4. #include <iostream>
  5. #include <algorithm>
  6.  
  7. template<class T>
  8. class observer_ptr;
  9.  
  10. template <typename T>
  11. class observable_delete {
  12. 	std::vector<observer_ptr<T>*> notifyList;
  13. public:
  14. 	void remove_observable(observer_ptr<T>* remove_this);
  15. 	void add_observable(observer_ptr<T>* add_this);
  16. 	void operator()(T* obj) const;
  17. };
  18.  
  19. template <typename T>
  20. class observer_ptr {
  21. 	T* pt = nullptr;
  22. 	observable_delete<T>* deleter;
  23. 	bool has_callback;
  24. 	std::function<void (T*)> callback;
  25. public:
  26. 	observer_ptr(const observer_ptr<T> &other) : pt(other.pt), deleter(other.deleter), has_callback(other.has_callback), callback(other.callback) {
  27. 		deleter->add_observable(this);
  28. 	}
  29. 	observer_ptr(observer_ptr<T> &&other) : pt(other.pt), deleter(other.deleter), has_callback(other.has_callback), callback(std::move(other.callback)) {
  30. 		deleter->remove_observable(&other);
  31. 		other.pt = nullptr; //flags temporary as expired.
  32. 		deleter->add_observable(this);
  33. 	}
  34. 	observer_ptr<T> operator=(const observer_ptr<T> &other) = delete;
  35.  
  36. 	observer_ptr(std::unique_ptr<T, observable_delete<T>>* observed) : pt(observed->get()), deleter(&observed->get_deleter()), has_callback(false) {
  37. 		deleter->add_observable(this);
  38. 	}
  39.  
  40. 	observer_ptr(std::unique_ptr<T, observable_delete<T>>* observed, const std::function<void(T*)> &callback) : pt(observed->get()), deleter(&observed->get_deleter()), callback(callback), has_callback(true) {
  41. 		deleter->add_observable(this);
  42. 	}
  43.  
  44. 	~observer_ptr() {
  45. 		if (!expired()) {
  46. 			deleter->remove_observable(this);
  47. 		}
  48. 	}
  49.  
  50. 	void observed_has_died() {
  51. 		if (has_callback) {
  52. 			callback(pt);
  53. 		}
  54. 		pt = nullptr;
  55. 	}
  56.  
  57. 	bool expired() const {
  58. 		return pt == nullptr;
  59. 	}
  60.  
  61. 	T* operator->() const { return pt; }
  62. 	T& operator*() const { return *pt; }
  63. };
  64.  
  65. template <typename T>
  66. void observable_delete<T>::remove_observable(observer_ptr<T>* remove_this) {
  67. 	auto found = std::find(notifyList.begin(), notifyList.end(), remove_this);
  68. 	if (found != notifyList.end()) {
  69. 		notifyList.erase(found);
  70. 	}
  71. }
  72.  
  73. template <typename T>
  74. void observable_delete<T>::add_observable(observer_ptr<T>* add_this) {
  75. 	notifyList.push_back(add_this);
  76. }
  77.  
  78. template <typename T>
  79. void observable_delete<T>::operator()(T* obj) const {
  80. 	for (auto&& item : notifyList) {
  81. 		try {
  82. 			item->observed_has_died();
  83. 		} catch (...) {
  84. 			delete obj;
  85. 			throw;
  86. 		}
  87. 	}
  88. 	delete obj;
  89. }
  90.  
  91. template<typename T, typename... Args>
  92. std::unique_ptr<T, observable_delete<T>> make_observable_unique(Args&&... args) {
  93. 	return std::unique_ptr<T, observable_delete<T>>(new T(std::forward<Args>(args)...));
  94. }
  95.  
  96. template<typename T>
  97. observer_ptr<T> make_observer(std::unique_ptr<T, observable_delete<T>> &observed) {
  98. 	return observer_ptr<T>(&observed);
  99. }
  100.  
  101. template<typename T, typename F>
  102. observer_ptr<T> make_observer(std::unique_ptr<T, observable_delete<T>> &observed, const F &callback) {
  103. 	return observer_ptr<T>(&observed, callback);
  104. }
  105.  
  106. int main() {
  107. 	auto uniquePtrValue = make_observable_unique<int>(5);
  108. 	auto observer = make_observer(uniquePtrValue, [](int *value) { std::cout << "We're destroying it! " << *value << std::endl; });
  109. 	std::cout << (!observer.expired() ? *observer : -1) << std::endl;
  110. 	uniquePtrValue.reset();
  111. 	std::cout << (!observer.expired() ? *observer : -1) << std::endl;
  112. 	return 0;
  113. }
Success #stdin #stdout 0s 3416KB
comments (?)
stdin 
Standard input is empty
stdout 
5
We're destroying it! 5
-1
https://ideone.com/MbKfRJ
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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