fork(1) download
copy 
  1. #include <iostream>
  2. #include <memory>
  3.  
  4. class trigger
  5. {
  6. public:
  7.     trigger() : m_flag(true) {}
  8.     bool get() const { return m_flag; }
  9.  
  10.     friend class trackable;
  11.  
  12. private:
  13.     void set(bool flag) { m_flag = flag; }
  14.     bool m_flag;
  15. };
  16.  
  17. typedef std::shared_ptr<trigger> spy_type;
  18.  
  19. class trackable
  20. {
  21. public:
  22.     trackable(const trackable &)
  23.         : spy(std::make_shared<trigger>())
  24.     {}
  25.  
  26.     trackable()
  27.         : spy(std::make_shared<trigger>())
  28.     {}
  29.  
  30.     trackable &operator=(const trackable &) { return *this; }
  31.  
  32.     ~trackable() { spy->set(false); }
  33.     spy_type spy;
  34. };
  35.  
  36.  
  37. struct SomeObject : public trackable
  38. {
  39.     //...
  40. };
  41.  
  42. struct SomeClient
  43. {
  44.     SomeObject * m_Object;
  45.  
  46.     bool objectIsValid() const { return (spy) ? spy->get() : false; }
  47.  
  48.     void setObject(SomeObject * obj)
  49.     {
  50.         m_Object = obj;
  51.         spy = obj->spy;
  52.     }
  53.  
  54. private:
  55.     spy_type spy;
  56. };
  57.  
  58.  
  59. int main()
  60. {
  61.     SomeClient Client;
  62.  
  63.     std::cout << std::boolalpha << Client.objectIsValid() << std::endl;
  64.  
  65.     SomeObject * Object = new SomeObject();
  66.  
  67.     Client.setObject(Object);
  68.  
  69.     std::cout << Client.objectIsValid() << std::endl;
  70.  
  71.     delete Object;
  72.  
  73.     std::cout << Client.objectIsValid() << std::endl;
  74.  
  75.     return 0;
  76. }
Success #stdin #stdout 0s 15240KB
comments (?)
stdin
copy 
Standard input is empty
stdout
copy 
false
true
false
https://ideone.com/q3IbxF
language:
C++14 (gcc 8.3)
created:
5 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!