Add example of visitor pattern in C++

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;
+}