Add example of visitor pattern in C++

cpp/patterns/CMakeLists.txt

@@ -23,3 +23,4 @@ add_subdirectory(prototype)
 add_subdirectory(abstract-factory)
 add_subdirectory(state)
 add_subdirectory(observer)
+add_subdirectory(visitor)

cpp/patterns/visitor/CMakeLists.txt

@@ -0,0 +1,20 @@
+###############################################################################
+## Author: Shaun Reed                                                        ##
+## Legal: All Content (c) 2021 Shaun Reed, all rights reserved               ##
+## About: A project for practicing the visitor C++ design pattern            ##
+##                                                                           ##
+## Contact: shaunrd0@gmail.com  | URL: www.shaunreed.com | GitHub: shaunrd0  ##
+##############################################################################
+#
+cmake_minimum_required(VERSION 3.15)
+project(
+    #[[NAME]]   Visitor
+    VERSION     1.0
+    DESCRIPTION "An example of the visitor design pattern in C++"
+    LANGUAGES   CXX
+)
+add_compile_options("-Wall")
+
+add_library(visitor "visitor.cpp")
+add_executable(visitor-test "main.cpp")
+target_link_libraries(visitor-test visitor)

cpp/patterns/visitor/main.cpp

@@ -0,0 +1,16 @@
+
+#include <iostream>
+
+#include "visitor.hpp"
+
+int main(const int argc, const char * argv[])
+{
+  Gear *newGear = new Gear(1.5f, 1.0f);
+  PartVisitor *newVisitor = new PartVisitor;
+  // Test visiting the Gear concrete component with PartVisitor
+  newGear->accept(newVisitor);
+
+  // Testing a Spring concrete component on the same visitor
+  auto *newSpring = new Spring(2.5f, 5.0f);
+  newSpring->accept(newVisitor);
+}

cpp/patterns/visitor/visitor.cpp

@@ -0,0 +1,32 @@
+
+#include "visitor.hpp"
+
+
+/******************************************************************************/
+// Concrete components
+
+void Gear::accept(PartVisitor *v)
+{
+  v->visit(this);
+}
+
+void Spring::accept(PartVisitor *v)
+{
+  v->visit(this);
+}
+
+
+/******************************************************************************/
+// Concrete visitors
+
+void PartVisitor::visit(Gear *g)
+{
+  std::cout << g->getName() << " is price " << g->getPrice() << " with radius of "
+            << g->getRadius() << std::endl;
+}
+
+void PartVisitor::visit(Spring *g)
+{
+  std::cout << g->getName() << " is price " << g->getPrice()
+            << " with elasticity of " << g->getElasticity() << std::endl;
+}

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