Completed all design patterns in c++

Author: Ehsan Gazar

behavioral/state.cpp

@@ -0,0 +1,26 @@
+#include <iostream>
+
+class Mood
+{
+public:
+        virtual ~Mood() { }
+        virtual void talk()=0;
+};
+
+class Happy : public Mood
+{
+public:
+        void talk() { std::cout << "Hello world!" << std::endl; }
+};
+
+void hello_world(Mood & mood)
+{
+        mood.talk();
+}
+
+int main()
+{
+        Happy mood;
+        hello_world(mood);
+        return 0;
+}

behavioral/strategy.cpp

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+#include <iostream>
+#include <string>
+
+class Strategy
+{
+public:
+        virtual ~Strategy() { }
+        virtual std::string format(const std::string &, const std::string &) const=0;
+};
+
+class Formatter : public Strategy
+{
+public:
+        std::string format(const std::string & s1, const std::string & s2) const
+        {
+                return s1 + " " + s2 + "!";
+        }
+};
+
+void hello_world(const Strategy & strategy)
+{
+        std::cout << strategy.format("Hello", "world") << std::endl;
+}
+
+int main()
+{
+        hello_world(Formatter());
+        return 0;
+}

behavioral/template-method.cpp

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+#include <string>
+#include <iostream>
+
+class HelloWorld
+{
+public:
+        virtual ~HelloWorld() { }
+        void output()
+        {
+                write_string("Hello world!");
+                write_endl();
+        };
+        virtual void write_string(const std::string &)=0;
+        virtual void write_endl()=0;
+};
+
+class HelloWorldImpl : public HelloWorld
+{
+public:
+        void write_string(const std::string & str)
+        {
+                std::cout << str;
+        }
+        void write_endl() 
+        { 
+                std::cout << std::endl; 
+        }
+};
+
+void hello_world(HelloWorld & hw)
+{
+        hw.output();
+}
+
+int main()
+{
+        HelloWorldImpl hw;
+        hello_world(hw);
+        return 0;
+}

behavioral/visitor.cpp

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+#include <vector>
+#include <string>
+#include <iostream>
+
+class Visitor
+{
+public:
+        virtual ~Visitor() { }
+        virtual void on_recipient(const std::string &)=0;
+};
+
+class Recipients
+{
+        std::vector<std::string> recipients;
+public:
+        void add_recipient(const std::string & recipient)
+        {
+                recipients.push_back(recipient);
+        }
+        void visit(Visitor & visitor) const
+        {
+                for(std::vector<std::string>::const_iterator recipient = recipients.begin();
+                        recipient != recipients.end(); 
+                        ++recipient)
+                {
+                        visitor.on_recipient(*recipient);
+                }
+        }
+};
+
+class PrintHello : public Visitor
+{
+public:
+        void on_recipient(const std::string & recipient)
+        {
+                std::cout << "Hello " << recipient << "!" << std::endl;
+        }
+};
+
+void hello_world(Visitor & visitor)
+{
+        Recipients recipients;
+        recipients.add_recipient("world");
+        recipients.visit(visitor);
+}
+
+int main()
+{
+        PrintHello visitor;
+        hello_world(visitor);
+        return 0;
+}

structural-patterns/null_object.cpp

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+#include <iostream>
+#include <string>
+
+class Recipient
+{
+public:
+        virtual ~Recipient() { }
+        virtual std::string name() const=0;
+};
+
+class NullRecipient : public Recipient
+{
+public:
+        std::string name() const { return "nobody"; }
+};
+
+class World : public Recipient
+{
+public:
+        std::string name() const { return "world"; }
+};
+
+void hello_world(const Recipient & recipient = NullRecipient())
+{
+        std::cout << "Hello " << recipient.name() << "!" << std::endl;
+}
+
+int main()
+{
+        hello_world(World());
+        return 0;
+}