Add example of visitor pattern in C++

cpp/patterns/visitor/visitor.hpp

@@ -0,0 +1,63 @@
+
+#ifndef VISITOR_HPP
+#define VISITOR_HPP
+
+#include <string>
+#include <iostream>
+#include <utility>
+
+class PartVisitor;
+
+// Abstract component
+class Part {
+public:
+  Part(std::string name_, const float &price_) :
+      name(std::move(name_)), price(price_) {}
+
+  inline std::string getName() const { return name;}
+  inline float getPrice() const { return price;}
+
+  virtual void accept(PartVisitor *v) = 0;
+private:
+  std::string name;
+  float price;
+};
+
+
+/******************************************************************************/
+// Concrete components
+class Gear : public Part  {
+public:
+  Gear(const float &price_, const float &radius_) :
+      Part("Gear", price_), radius(radius_) {}
+
+  void accept(PartVisitor *v) override;
+  inline float getRadius() const { return radius;}
+
+private:
+  float radius;
+};
+
+class Spring : public Part  {
+public:
+  Spring(const float &price_, const float &elasticity_) :
+      Part("Spring", price_), elasticity(elasticity_) {}
+
+  void accept(PartVisitor *v) override;
+  inline float getElasticity() const { return elasticity;}
+
+private:
+  float elasticity;
+};
+
+
+/******************************************************************************/
+// Concrete visitors
+class PartVisitor {
+public:
+  // Handle visiting different components accordingly
+  virtual void visit(Gear *g);
+  virtual void visit(Spring *g);
+};
+
+#endif // VISITOR_HPP