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  1. #include <iostream>
  2.  
  3. // Base class for entities
  4. class entity
  5. {
  6.     public:
  7.     virtual void do_walk() { std::cout << "I like walking" << std::endl; };
  8. };
  9.  
  10. // A class property for healer characters
  11. class healer
  12. {
  13.     public:
  14.     // interface
  15.     virtual void do_heal() = 0;
  16. };
  17.  
  18. // A class property for healer npcs
  19. class merchant
  20. {
  21.     public:
  22.     // interface
  23.     virtual void do_sell() = 0;
  24. };
  25.  
  26. // implementation of the healer property
  27. class healer_implementation : public healer
  28. {
  29.     public:
  30.     virtual void do_heal() { std::cout << "I heal people" << std::endl; }
  31. };
  32.  
  33.  
  34.  
  35. // implementation of the healer property
  36. class merchant_implementation : public merchant
  37. {
  38.     public:
  39.     virtual void do_sell() { std::cout << "I sell things" << std::endl; }
  40. };
  41.  
  42. // To deduce the implementation of a property, we'll use the template property which will be specialized for each property and reference an implementation
  43. template<typename T>
  44. class property
  45. {};
  46.  
  47. template<>
  48. class property<merchant>
  49. {
  50. public: typedef merchant_implementation implementation;
  51. };
  52.  
  53. template<>
  54. class property<healer>
  55. {
  56. public: typedef healer_implementation implementation;
  57. };
  58.  
  59.  
  60. // This class is a class helper to deduce the right class type from a list of property for an entity
  61. template<class... Property>
  62. class factory
  63. {
  64. public:
  65.     class custom : public property<Property>::implementation..., public entity {};
  66.  
  67. };
  68.  
  69. int main()
  70. {
  71.     entity* bob = new factory<healer, merchant>::custom();
  72.  
  73.     // bob will try to sell things
  74.     merchant* m = dynamic_cast<merchant*>(bob);
  75.     if (m)
  76.         m->do_sell();
  77.  
  78.     // bob will try to heal people
  79.     healer* h = dynamic_cast<healer*>(bob);
  80.     if (h)
  81.         h->do_heal();
  82.  
  83.     // and as an entity, bob can walk
  84.     bob->do_walk();
  85.  
  86.     entity* frank = new factory<healer>::custom();
  87.  
  88.     // frank will try to sell things
  89.     m = dynamic_cast<merchant*>(frank);
  90.     if (m)
  91.         m->do_sell();
  92.  
  93.     // frank will try to heal people
  94.     h = dynamic_cast<healer*>(frank);
  95.     if (h)
  96.         h->do_heal();
  97.  
  98.     // and as an entity, frank can walk
  99.     frank->do_walk();
  100. }
Success #stdin #stdout 0s 3232KB
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Standard input is empty
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I sell things
I heal people
I like walking
I heal people
I like walking
https://ideone.com/StrKo3
language:
C++14 (gcc 8.3)
created:
9 years ago
visibility:
public

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