Added decorator example source code.

examples/structural/decorator.cpp

@@ -0,0 +1,118 @@
+#include <iostream>
+#include <memory>
+#include <string>
+
+class Coffee
+{
+  public:
+    typedef std::shared_ptr<Coffee> ptr_t;
+    virtual float getPrice(void) = 0;
+    virtual std::string getDescription(void) = 0;
+};
+
+class SimpleCoffee : public Coffee
+{
+  public:
+    float getPrice(void)
+    {
+      return 3;
+    }
+
+    std::string getDescription(void)
+    {
+      return "Simple coffee";
+    }
+};
+
+class MilkCoffee : public Coffee
+{
+  public:
+    MilkCoffee(Coffee::ptr_t coffee)
+        : coffee_(coffee)
+    {
+    }
+
+    float getPrice(void)
+    {
+      return coffee_->getPrice() + 0.5;
+    }
+
+    std::string getDescription(void)
+    {
+      return coffee_->getDescription() + ", milk";
+    }
+
+  private:
+    Coffee::ptr_t coffee_;
+};
+
+class WhipCoffee : public Coffee
+{
+  public:
+    WhipCoffee(Coffee::ptr_t coffee)
+        : coffee_(coffee)
+    {
+    }
+
+    float getPrice(void)
+    {
+      return coffee_->getPrice() + 2;
+    }
+
+    std::string getDescription(void)
+    {
+      return coffee_->getDescription() + ", whip";
+    }
+
+  private:
+    Coffee::ptr_t coffee_;
+};
+
+class VanillaCoffee : public Coffee
+{
+  public:
+    VanillaCoffee(Coffee::ptr_t coffee)
+        : coffee_(coffee)
+    {
+    }
+
+    float getPrice(void)
+    {
+      return coffee_->getPrice() + 1;
+    }
+
+    std::string getDescription(void)
+    {
+      return coffee_->getDescription() + ", vanilla";
+    }
+
+  private:
+    Coffee::ptr_t coffee_;
+};
+
+int main()
+{
+  Coffee::ptr_t simple = std::make_shared<SimpleCoffee>();
+  // Output: 3
+  std::cout << simple->getPrice() << std::endl;
+  // Output: Simple coffee
+  std::cout << simple->getDescription() << std::endl;
+
+  Coffee::ptr_t milk = std::make_shared<MilkCoffee>(simple);
+  // Output: 3.5
+  std::cout << milk->getPrice() << std::endl;
+  // Output: Simple coffee, milk
+  std::cout << milk->getDescription() << std::endl;
+
+  Coffee::ptr_t whip = std::make_shared<WhipCoffee>(milk);
+  // Output: 5.5
+  std::cout << whip->getPrice() << std::endl;
+  // Output: Simple coffee, milk, whip
+  std::cout << whip->getDescription() << std::endl;
+
+  Coffee::ptr_t vanilla = std::make_shared<VanillaCoffee>(whip);
+  // Output: 6.5
+  std::cout << vanilla->getPrice() << std::endl;
+  // Output: Simple coffee, milk, whip, vanilla
+  std::cout << vanilla->getDescription() << std::endl;
+}