fork download 
  1. #include <iostream>
  2. #include <unordered_map>
  3. #include <map>
  4. #include <cinttypes>
  5.  
  6. class MyClass
  7. {
  8.     typedef std::unordered_map<uint32_t, MyClass> Instances;
  9.     friend Instances;
  10.     friend std::pair<uint32_t, MyClass>;
  11.     friend std::pair<const uint32_t, MyClass>;
  12.   public:
  13.     static const MyClass& getObject(uint32_t key) { return instances_[key] = 2 * key; }
  14.     ~MyClass() {}
  15.     int n() const { return n_; }
  16.   private:
  17.     MyClass() : n_(-1) { }
  18.     MyClass& operator=(int n) { n_ = n; return *this; }
  19.     int n_;
  20.     static Instances instances_;
  21. };
  22.  
  23. MyClass::Instances MyClass::instances_;
  24.  
  25. int main() {
  26. 	const MyClass& m20 = MyClass::getObject(20);
  27. 	const MyClass& m21 = MyClass::getObject(21);
  28. 	std::cout << m20.n() << ' ' << m21.n() << '\n';
  29. }
Success #stdin #stdout 0s 3432KB
comments (?)
stdin 
Standard input is empty
stdout 
40 42
https://ideone.com/HVvI08
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

Share or Embed source code

Discover > Sphere Engine API

The brand new service which powers Ideone!

Discover > IDE Widget

Widget for compiling and running the source code in a web browser!