add Prototype pattern

prototype/Prototype.cpp

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+/*
+ * C++ Design Patterns: Prototype
+ * Author: Jakub Vojvoda [github.com/JakubVojvoda]
+ * 2016
+ *
+ * Source code is licensed under MIT licence
+ * (for more details see LICENCE)
+ *
+ */
+
+#include <iostream>
+
+/*
+ * Prototype
+ * declares an interface for cloning itself
+ */
+class Prototype {
+public:
+  virtual Prototype *clone() = 0;
+  virtual std::string type() = 0;
+  // ...
+};
+
+/*
+ * Concrete Prototype A and B
+ * implement an operation for cloning itself
+ */
+class ConcretePrototypeA : public Prototype {
+public:
+  Prototype *clone() {
+    return new ConcretePrototypeA;
+  }
+  std::string type() {
+    return "type A";
+  }
+  // ...
+};
+
+class ConcretePrototypeB : public Prototype {
+public:
+  Prototype *clone() {
+    return new ConcretePrototypeB;
+  }
+  std::string type() {
+    return "type B";
+  }
+  // ...
+};
+
+/*
+ * Client
+ * creates a new object by asking a prototype to clone itself
+ */
+class Client {
+public:
+  static Prototype* make(int index) {
+    return types[index]->clone();
+  }
+  // ...
+
+private:
+  static Prototype* types[2];
+};
+
+Prototype* Client::types[] =
+{
+  new ConcretePrototypeA,
+  new ConcretePrototypeB
+  // ...
+};
+
+
+int main()
+{
+  Prototype* prototype;
+
+  prototype = Client::make(0);
+  std::cout << "Prototype: " << prototype->type() << std::endl;
+
+  prototype = Client::make(1);
+  std::cout << "Prototype: " << prototype->type() << std::endl;
+
+  return 0;
+}

prototype/README.md

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+## Prototype
+
+Specify the kinds of objects to create using a prototypical instance, and create 
+new objects by copying this prototype. Pattern has creational purpose and deals 
+with object relationships, which are more dynamic. The pattern hides the complexities
+of making new instances from the client.
+
+### When to use
+
+* when the classes to instantiate are specified at run-time
+* to avoid building a class hierarchy of factories that parallels the class hierarchy of products
+* when instances of a class can have one of only a few different combinations of state