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  1. #include <iostream>
  2.  
  3. class IdProvider {
  4.  static int count;
  5. private:
  6.   IdProvider(){}
  7. public:
  8.   static IdProvider& Instance() {
  9.     static IdProvider instance;
  10.     return instance;
  11.   }
  12.  
  13.   int Next() {
  14.     return ++count;
  15.   }
  16. };
  17.  
  18. int IdProvider::count = 0;
  19.  
  20. template <typename T> class TracingValue {
  21.  
  22. private:
  23.   T m_Val;
  24.   int m_Id;
  25.  
  26. private:
  27.   void LogStackTrace() {}
  28.  
  29. public:
  30.   int Id() const { return m_Id; }
  31.  
  32.   TracingValue &operator=(const TracingValue &other) {
  33.     LogStackTrace();
  34.     m_Val = other.m_Val;
  35.     std::cout << "id: " << this->Id() << " new value: " << m_Val
  36.               << " from id: " << other.Id() << std::endl;
  37.     return *this;
  38.   }
  39.  
  40.   TracingValue &operator=(const T &val) {
  41.     LogStackTrace();
  42.     m_Val = val;
  43.     std::cout << "id: " << this->Id() << " new value: " << m_Val << std::endl;
  44.     return *this;
  45.   }
  46.  
  47.   TracingValue(const T &val):m_Id(IdProvider::Instance().Next()),m_Val(val) {
  48.     std::cout << "id: " << this->Id() << " constructed with value: " << val << std::endl;
  49.     LogStackTrace();
  50.   }
  51.  
  52.   TracingValue(const TracingValue &other):TracingValue(other.m_Val) {
  53.     std::cout << "id: " << this->Id() << " constructed from id: " << other.Id() << std::endl;
  54.   }
  55.  
  56.   TracingValue():TracingValue(T()) { LogStackTrace(); }
  57.  
  58.   operator T() const { return m_Val; }
  59. };
  60.  
  61. int main() {
  62. TracingValue<double> d;
  63. d = 3.;
  64. d = 42.;
  65. double x = d - 2.;
  66. std::cout << x << std::endl;
  67. TracingValue<double> other_d(d);
  68.  
  69. TracingValue<double> another_d;
  70. another_d = other_d;  
  71. }
  72.  
Success #stdin #stdout 0s 3344KB
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stdin
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Standard input is empty
stdout
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id: 1 constructed with value: 0
id: 1 new value: 3
id: 1 new value: 42
40
id: 2 constructed with value: 42
id: 2 constructed from id: 1
id: 3 constructed with value: 0
id: 3 new value: 42 from id: 2
https://ideone.com/5J8R9m
tracing a value
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
secret

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