Add factory example

cpp/patterns/factory/factory.cpp

@@ -0,0 +1,42 @@
+
+#include <iostream>
+
+#include "factory.hpp"
+
+Part* GearFactory::requestPart() {
+  // Create a new part
+  Part * newPart = makePart();
+  // Increment the QTY for part in AbstractFactory::inventory base class
+  // + If the item is not in the inventory map, this will also add it first.
+  inventory[newPart->getName()]++;
+  // Make the requested part
+  return newPart;
+}
+
+Part* GearFactory::requestPart(std::string partName, float price)
+{
+  Part * newPart = makePart(partName, price);
+  inventory[newPart->getName()]++;
+  return newPart;
+}
+
+void GearFactory::showStock() const
+{
+  for (const auto &item : inventory) {
+    if (item.first.empty()) continue; // Don't show an empty item
+    std::cout << item.first << " QTY in stock: " << item.second << std::endl;
+  }
+}
+
+
+/*****************************************************************************/
+// Gear
+
+Part* GearFactory::makePart() {
+  return new Gear();
+}
+
+Part* GearFactory::makePart(std::string name, float price)
+{
+  return new Gear(name, price);
+}