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  1. #include <iostream>
  2. #include <memory>
  3.  
  4. struct Visitor;
  5.  
  6. struct Shape {
  7.     virtual void accept(std::unique_ptr<Visitor> v) = 0;
  8. };
  9.  
  10. struct Circle : Shape { void accept(std::unique_ptr<Visitor> v) override; };
  11. struct Triangle : Shape { void accept(std::unique_ptr<Visitor> v) override; };
  12. struct Square : Shape { void accept(std::unique_ptr<Visitor> v) override; };
  13.  
  14. struct Point {
  15.     Point(float x, float y) {}   
  16. };
  17.  
  18. struct Visitor {
  19.     virtual void visit(Circle   &c) const = 0;
  20.     virtual void visit(Triangle &t) const = 0;
  21.     virtual void visit(Square   &s) const = 0;
  22. };
  23.  
  24.  
  25. void Circle::accept(std::unique_ptr<Visitor> v) {
  26.         v->visit(*this);
  27. }
  28. void Triangle::accept(std::unique_ptr<Visitor> v) {
  29.         v->visit(*this);
  30. }
  31. void Square::accept(std::unique_ptr<Visitor> v) {
  32.         v->visit(*this);
  33. }
  34.  
  35.  
  36. struct SnapToPoint : Visitor {
  37.     SnapToPoint(float x, float y) : _point(x, y) {}
  38.  
  39.     void visit(Circle   &c) const override { std::cout << "Snapped a Circle\n"; }
  40.     void visit(Triangle &t) const override { std::cout << "Snapped a Triangle\n"; }
  41.     void visit(Square   &s) const override { std::cout << "Snapped a Square\n"; }
  42.  
  43. private:
  44.     Point _point;
  45. };
  46.  
  47. struct ShapeOperationFactory {
  48.     virtual std::unique_ptr<Visitor> snapToPoint(float x, float y) const = 0;
  49. };
  50.  
  51. struct MyShapeOpFactory : ShapeOperationFactory {
  52.     std::unique_ptr<Visitor> snapToPoint(float x, float y) const override {
  53.         return std::unique_ptr<Visitor>(new SnapToPoint(x, y));
  54.     }
  55. };
  56.  
  57. int main() {
  58.  
  59.    Shape *pShape = new Circle;
  60.    ShapeOperationFactory *pFactory = new MyShapeOpFactory;
  61.  
  62.    pShape->accept(pFactory->snapToPoint(4.0f, 7.0f));
  63.  
  64.    delete pFactory;
  65.    delete pShape;
  66.    return 0;
  67. }
Success #stdin #stdout 0s 3472KB
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Standard input is empty
stdout
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Snapped a Circle
https://ideone.com/sI1SGD
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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