[STATE]: Added sample code for State pattern.

Author: MericLuc

behavioral-patterns/state/state.cpp

@@ -0,0 +1,54 @@
+/*!
+ * From https://github.com/pezy/DesignPatterns/blob/master/State/main.cpp
+ */
+
+#include <iostream>
+#include <string>
+#include <algorithm>
+#include <memory>
+
+class IWritingState {
+public:
+    virtual void Write(std::string p_words) = 0;
+};
+
+class UpperCase : public IWritingState {
+    void Write(std::string p_words) override {
+        std::transform(p_words.begin(), p_words.end(), p_words.begin(), ::toupper);
+        std::cout << p_words << std::endl;
+    }
+};
+
+class LowerCase : public IWritingState {
+    void Write(std::string p_words) override {
+        std::transform(p_words.begin(), p_words.end(), p_words.begin(), ::tolower);
+        std::cout << p_words << std::endl;
+    }
+};
+
+class Default : public IWritingState {
+    void Write(std::string p_words) override { std::cout << p_words << std::endl; }
+};
+
+class TextEditor {
+public:
+    TextEditor(const std::shared_ptr<IWritingState>& p_state): m_state(p_state) {}
+    void SetState(const std::shared_ptr<IWritingState>& p_state) { m_state = p_state; }
+    void Type(const std::string& p_words) { m_state->Write(p_words); }
+private:
+    std::shared_ptr<IWritingState> m_state;
+};
+
+int main()
+{
+  TextEditor editor(std::make_shared<Default>());
+  editor.Type("First line");
+
+  editor.SetState(std::make_shared<UpperCase>());
+  editor.Type("Second line");
+  editor.Type("Third line");
+
+  editor.SetState(std::make_shared<LowerCase>());
+  editor.Type("Fourth line");
+  editor.Type("Fifth line");
+}