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  1. #include <iostream>
  2.  
  3. class Visitor;
  4.  
  5. class Base
  6. {
  7.     public:
  8.         virtual ~Base() {}
  9.         virtual void visit(Visitor&) = 0;
  10. };
  11.  
  12. class Derived : public Base
  13. {
  14.     protected:
  15.         int someVar = 2;
  16.  
  17.     public:
  18.         int getSomeVar () {return this->someVar;}
  19.         void visit(Visitor& v) override;
  20. };
  21. class Visitor {
  22.     public:
  23.          void visit(Derived& d) {
  24.               std::cout << d.getSomeVar() << std::endl;
  25.          }
  26. };
  27.  
  28. void Derived::visit(Visitor& v) {
  29.     v.visit(*this);
  30. }
  31.  
  32. int main()
  33. {
  34.     Visitor v;
  35.     // DO NOT USE MANUAL HEAP ALLOCATION IN REAL CODE !!!!!!!!
  36.     Base * b = new Derived;
  37.     b->visit(v);
  38.     delete b;
  39.     return 0;
  40. }
  41.  
Success #stdin #stdout 0s 16064KB
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stdin 
Standard input is empty
stdout 
2
https://ideone.com/rfcO6A
language:
C++ (gcc 8.3)
created:
8 years ago
visibility:
public

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