Implementing the Singleton Pattern

1#include <iostream>
2
3class Singleton {
4 private:
5  static Singleton* instance;
6
7  // Private constructor to prevent instantiation
8  Singleton() {}
9
10 public:
11  // Delete copy constructor and assignment operator
12  Singleton(const Singleton&) = delete;
13  Singleton& operator=(const Singleton&) = delete;
14
15  static Singleton* getInstance() {
16    if (instance == nullptr) {
17      instance = new Singleton();
18    }
19    return instance;
20  }
21
22  void someBusinessLogic() {
23    std::cout << "Singleton is doing something.\n";
24  }
25
26  // Use this pointer to provide instance methods
27  Singleton* doSomething() {
28    std::cout << "Did something and "
29      "returning this.\n";
30    return this;  
31  }
32
33  Singleton* doSomethingElse() {
34    std::cout << "Did something else and "
35      "returning this.\n";
36    return this;  
37  }
38};
39
40// Initialize the static member
41Singleton* Singleton::instance = nullptr;
42
43int main() {
44  Singleton* s = Singleton::getInstance();
45  s->someBusinessLogic();
46
47  // Chain method calls using 'this'
48  s->doSomething()->doSomethingElse();
49
50  return 0;
51}