id 1763622392

CMakeLists.txt

@@ -100,6 +100,7 @@ set(APP_SOURCES
     "src/patterns/structural/Decorator.cpp"
     "src/patterns/behavioral/ChainOfCommand.cpp"
     "src/patterns/behavioral/Command.cpp"
+    "src/patterns/behavioral/Iterator.cpp"
 )
 
 # Test files

src/patterns/behavioral/Iterator.cpp

@@ -0,0 +1,239 @@
+// Iterator is a behavioral design pattern that lets you traverse elements of a collection without exposing its underlying representation (list, stack, tree, etc.).
+// Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.
+// Appicability:
+// (*)   when your collection has a complex data structure under the hood, but you want to hide its complexity from clients (either for convenience or security reasons).
+// (**)  reduce duplication of the traversal code across your app.
+// (***) when you want your code to be able to traverse different data structures or when types of these structures are unknown beforehand.
+
+// UML: docs/uml/patterns_behavioral_iterator.drawio.svg
+
+#include <iostream>
+#include <string>
+#include <vector>
+#include <list>
+#include <iterator>
+
+namespace
+{
+    namespace Iterator
+    {
+        class DataModel
+        {
+        private:
+            int m_value;
+
+        public:
+            explicit DataModel(int value) : m_value{value} {}
+
+            void setValue(int v)
+            {
+                m_value = v;
+            }
+
+            int getValue() const { return m_value; }
+        };
+
+        /**
+         * Iterator interface: declares the operations required for traversing a collection: fetching the next element, retrieving the current position, restarting iteration, etc.
+         */
+        template <typename T>
+        class IIterator
+        {
+        public:
+            virtual bool hasNext() const = 0;
+            virtual const T *next() = 0;
+            virtual ~IIterator() = default;
+        };
+
+        /**
+         * Aggregate interface: declares one or multiple methods for getting iterators compatible with the collection.
+         * Note that the return type of the methods must be declared as the iterator interface so that the concrete collections can return various kinds of iterators.
+         */
+        template <typename T>
+        class IAggregate
+        {
+        public:
+            virtual IIterator<T> *createIterator() = 0;
+            virtual ~IAggregate() = default;
+        };
+
+        /**
+         * Concrete Iterator: implement specific algorithms for traversing a collection.
+         * The iterator object should track the traversal progress on its own. This allows several iterators to traverse the same collection independently of each other.
+         */
+        template <typename T>
+        class VectorConcreteIterator : public IIterator<T>
+        {
+        private:
+            const std::vector<T> &m_data;
+            size_t m_currentIndex{0};
+
+        public:
+            explicit VectorConcreteIterator(const std::vector<T> &data) : m_data{data} {}
+
+            bool hasNext() const override
+            {
+                return m_currentIndex < m_data.size();
+            }
+
+            const T *next() override
+            {
+                if (hasNext())
+                {
+                    return (T *)&m_data[m_currentIndex++];
+                }
+                else
+                {
+                    return nullptr;
+                }
+            }
+        };
+
+        template <typename T>
+        class ListConcreteIterator : public IIterator<T>
+        {
+        private:
+            const std::list<T> &m_data;
+            typename std::list<T>::const_iterator m_it;
+
+        public:
+            explicit ListConcreteIterator(const std::list<T> &data)
+                : m_data(data), m_it(m_data.begin()) {}
+
+            bool hasNext() const override
+            {
+                return m_it != m_data.end();
+            }
+
+            const T *next() override
+            {
+                if (!hasNext())
+                    return nullptr;
+                const T *ptr = &(*m_it);
+                ++m_it;
+                return ptr;
+            }
+        };
+
+        /**
+         * Concrete Aggregate: return new instances of a particular concrete iterator class each time the client requests one.
+         */
+        template <typename T>
+        class ListConreteAggregate : public IAggregate<T>
+        {
+        private:
+            std::list<T> m_data;
+
+        public:
+            void add(const T &i)
+            {
+                m_data.push_back(i);
+            }
+
+            IIterator<T> *createIterator() override
+            {
+                return new ListConcreteIterator<T>(m_data);
+            }
+        };
+
+        template <typename T>
+        class VectorConcreteAggregate : public IAggregate<T>
+        {
+        private:
+            std::vector<T> m_data;
+
+        public:
+            void add(const T &i)
+            {
+                m_data.push_back(i);
+            }
+
+            IIterator<T> *createIterator() override
+            {
+                return new VectorConcreteIterator<T>(m_data);
+            }
+        };
+
+        /**
+         * The Client works with both collections and iterators via their interfaces. 
+         * This way the client isn’t coupled to concrete classes, allowing you to use various collections and iterators with the same client code.
+         */
+        namespace Client
+        {
+
+            void clientCode(IAggregate<int> *collection)
+            {
+                IIterator<int> *iterator = collection->createIterator();
+
+                if (iterator != nullptr)
+                {
+                    while (iterator->hasNext())
+                    {
+                        std::cout << "int: " << *(iterator->next()) << "\n";
+                    }
+                }
+
+                delete iterator;
+            }
+
+            void clientCode(IAggregate<DataModel> *collection)
+            {
+                IIterator<DataModel> *iterator = collection->createIterator();
+
+                if (iterator != nullptr)
+                {
+                    while (iterator->hasNext())
+                    {
+                        std::cout << "data: " << iterator->next()->getValue() << "\n";
+                    }
+                }
+                delete iterator;
+            }
+        }
+
+        void run()
+        {
+            std::cout << "\nVectorConcreteAggregate\n";
+            VectorConcreteAggregate<int> intCollection;
+            for (int i = 0; i < 10; ++i)
+            {
+                intCollection.add(i);
+            }
+            Client::clientCode(&intCollection);
+            std::cout << "\n";
+            VectorConcreteAggregate<DataModel> dataCollection;
+            for (int i = 0; i < 10; ++i)
+            {
+                dataCollection.add(DataModel(i * 10));
+            }
+            Client::clientCode(&dataCollection);
+
+            std::cout << "\nListConreteAggregate\n";
+            ListConreteAggregate<int> intCollection2;
+            for (int i = 0; i < 10; ++i)
+            {
+                intCollection2.add(i);
+            }
+
+            Client::clientCode(&intCollection2);
+            std::cout << "\n";
+            ListConreteAggregate<DataModel> dataCollection2;
+            for (int i = 0; i < 10; ++i)
+            {
+                dataCollection2.add(DataModel(i * 10));
+            }
+            Client::clientCode(&dataCollection2);
+        }
+    }
+}
+
+struct IteratorAutoRunner
+{
+    IteratorAutoRunner()
+    {
+        std::cout << "\n--- Iterator Pattern Example ---\n";
+        Iterator::run();
+    }
+};
+
+static IteratorAutoRunner instance;