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  1. #include <iostream>
  2. class Visitor;
  3.  
  4. class Element{ 
  5. public : 
  6.   virtual void Accept(Visitor&) = 0;
  7. protected : 
  8.   Element() {};   
  9.   int num;
  10. };
  11.  
  12. class Visitor {
  13. public: 
  14.   void Visit(Element* pe) { std::cout << getNum(pe) << '\n'; }
  15.   int getNum(Element* pe)
  16.   { 
  17.     struct ElementNumAccessor : private Element
  18.     {
  19.       ElementNumAccessor(Element const& e) : Element(e) {}   
  20.       int getNum() { return num; }
  21.  
  22.       void Accept(Visitor&);
  23.     };
  24.  
  25.     ElementNumAccessor ea(*pe);
  26.     return ea.getNum();
  27.   }
  28. };
  29.  
  30.  
  31.          class ElementA : public Element{
  32.                  public : ElementA() { num = 5; }; 
  33.                  void Accept(Visitor& v) {v.Visit(this);}
  34.          };
  35.  
  36.          class ElementB : public Element{
  37.                  public : ElementB() { num = 6; }; 
  38.                  void Accept(Visitor& v) {v.Visit(this);}
  39.          };
  40.  
  41.  
  42. int main()
  43. {
  44.     ElementA ea;
  45.     ElementB eb;
  46.     Visitor v;
  47.     ea.Accept(v);
  48.     eb.Accept(v);
  49.  
  50. }
Success #stdin #stdout 0s 2896KB
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https://ideone.com/e1chSX
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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