initial matador ng commit

include/matador/utils/singleton.hpp

@@ -0,0 +1,45 @@
+#ifndef SINGLETON_HPP
+#define SINGLETON_HPP
+
+namespace matador::utils {
+
+/**
+ * @class singleton
+ * @brief Provides only one instance of a type.
+ * @tparam T The type of the singleton.
+ * 
+ * This class implements the singleton pattern.
+ * It ensures that only one instance of a class
+ * exists.
+ * @note The derived class must add a friend declaration
+ * for the concrete singleton type.
+ */
+template < typename T >
+class singleton
+{
+public:
+  typedef T value_type; /**< Shortcut for the singletons type */
+
+  /**
+   * @brief Access the instance of the class.
+   * 
+   * The static instance method provides
+   * the access to the one instance of the
+   * concrete class.
+   * 
+   * @return The one instance of the class.
+   */
+  static value_type& instance ()
+  {
+    static value_type instance_;
+    return instance_;
+  }
+  virtual ~singleton() = default;
+
+protected:
+  singleton() = default;
+};
+
+}
+
+#endif /* SINGLETON_HPP */