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  1. #include <bits/stdc++.h>
  2. #include <memory>
  3. #include <iostream>
  4.  
  5. template <typename T>
  6. class SingletonBase {
  7. public:
  8.     static std::shared_ptr<T> m_Instance;
  9.  
  10.     SingletonBase() {
  11.         std::cout << "Calling base constructor" << std::endl;
  12.     }
  13.  
  14.     static std::shared_ptr<T> GetInstance() {
  15.         std::cout << "Calling GetInstance" << std::endl;
  16.  
  17.         if (m_Instance == nullptr) {
  18.             m_Instance = std::shared_ptr<T>(new T);
  19.         }
  20.  
  21.         return m_Instance;
  22.     }
  23.  
  24.     void Init() {
  25.         if (m_Instance) {
  26.             std::cout << "Init called" << std::endl;
  27.         } else {
  28.             std::cout << "Init not called" << std::endl;
  29.         }
  30.     }
  31. };
  32.  
  33. template <typename T>
  34. std::shared_ptr<T> SingletonBase<T>::m_Instance = nullptr;
  35.  
  36. class Derived : public SingletonBase<Derived> {
  37. public:
  38.     Derived() {
  39.         std::cout << "Calling Derived constructor" << std::endl;
  40.     }
  41. };
  42.  
  43. class Derived2 : public SingletonBase<Derived2> {
  44. public:
  45.     Derived2() {
  46.         std::cout << "Calling Derived2 constructor" << std::endl;
  47.     }
  48. };
  49.  
  50. using namespace std;
  51.  
  52. int main() {
  53.     std::shared_ptr<Derived> d1; 
  54.     d1 = Derived::GetInstance();
  55.     d1->Init();
  56.  
  57.     std::shared_ptr<Derived2> d2;  
  58.     d2 = Derived2::GetInstance();
  59.     d2->Init();
  60.     std::cout << " -         ------";
  61.     std::shared_ptr<Derived2> d3;  
  62.     d3 = Derived2::GetInstance();
  63.     d3->Init();
  64.     return 0;
  65. }
Success #stdin #stdout 0.01s 5288KB
comments (?)
stdin
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45
stdout
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Calling GetInstance
Calling base constructor
Calling Derived constructor
Init called
Calling GetInstance
Calling base constructor
Calling Derived2 constructor
Init called
 -         ------Calling GetInstance
Init called
https://ideone.com/fWNjBz
language:
C++14 (gcc 8.3)
created:
8 days ago
visibility:
public

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