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  1. #include <cstdio>
  2.  
  3. // External implementation 1
  4. class SomeShape {};
  5. class SomeBody { public: SomeShape *shape; };
  6.  
  7. // External implementation 2
  8. class OtherShape {};
  9. class OtherBody { public: OtherShape *shape; };
  10.  
  11. //////////////
  12.  
  13. class Shape
  14. {
  15. public:
  16.   virtual const char *name() { return "Shape"; }
  17. };
  18.  
  19.  
  20. template<class Shape>
  21. class Body 
  22. {
  23.   Shape *shape; 	
  24. public:
  25.   void setShape(Shape *s) { 
  26.   	shape=s; 
  27.     printf("Setting shape: %s\n", s->name());
  28.   }
  29. };
  30.  
  31. template <class Shape, class Body>
  32. class Factory
  33. {
  34. public:
  35.   Shape *makeShape()
  36.     { return new Shape(); }
  37.   Body *makeBody()
  38.     { return new Body(); }
  39. };
  40.  
  41. //////////////
  42.  
  43. class AShape : public Shape
  44. {
  45. public:
  46.   SomeShape *someShape;
  47.   virtual const char *name() { return "AShape"; }
  48. };
  49.  
  50. class ABody : public Body<AShape>
  51. {
  52. protected:
  53.   SomeBody *someBody;
  54. public:
  55.   ABody() { someBody = new SomeBody; }
  56. };
  57.  
  58.  
  59. //////////////
  60.  
  61. class BShape : public Shape
  62. {
  63. public:
  64.   OtherShape *otherShape;
  65.   virtual const char *name() { return "BShape"; }
  66. };
  67.  
  68. class BBody : public Body<BShape>
  69. {
  70. protected:
  71.   OtherBody *otherBody;
  72. public:
  73.   BBody() { otherBody = new OtherBody; }
  74. };
  75.  
  76. using BFactory = Factory<BShape, BBody>; 
  77. using AFactory = Factory<AShape, ABody>; 
  78.  
  79. int main()
  80. {
  81.   // Of course in a real program we would return
  82.   // a particular Factory from some selection function,
  83.   // this should ideally be the only place the user is
  84.   // exposed to the implementation selection.
  85.   AFactory f1;
  86.   BFactory f2;
  87.  
  88.   // Associate a shape and body in implementation 1
  89.   auto *s1 = f1.makeShape();
  90.   auto *b1 = f1.makeBody();
  91.   b1->setShape(s1);
  92.  
  93.   // Associate a shape and body in implementation 2
  94.   auto *s2 = f2.makeShape();
  95.   auto *b2 = f2.makeBody();
  96.   b2->setShape(s2);
  97.  
  98.   // This should not be possible, compiler error ideally
  99.   //b2->setShape(s1);
  100.  
  101.   return 0;
  102. }
Success #stdin #stdout 0s 3460KB
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Standard input is empty
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Setting shape: AShape
Setting shape: BShape
https://ideone.com/VfYZMq
language:
C++14 (gcc 8.3)
created:
8 years ago
visibility:
public

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