TuttleOFX/libraries/tuttle/src/tuttle/common/patterns/Singleton.hpp

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#ifndef Singleton_HPP
#define Singleton_HPP

/**
 * @brief Singleton<ClassSingleton> Can transform a class into Singleton (by inheriting this class)
 *
 * @par Purpose
 * Forcing (limit) the presence of a single instance of a class
 *
 * @par Usage
 * The class T, to use as Singleton, must derive from this class (: public Singleton <T>).
 * The macro MAKE_SINGLETON (T) create necessary elements (including constructors).
 */
template <class T>
class Singleton
{
private:
        static T* inst;

        Singleton( const Singleton& ) {}
        Singleton& operator=( const Singleton& ) {}

protected:
        Singleton() {}
        virtual ~Singleton() = 0;

public:
        /**
         * @brief return the unique instance of Singleton<T> class
         * @return T the unique instance of Singleton<T> class
         */
        static T& instance()
        {
                if( !inst )
                        inst = new T;
                return *inst;
        }

        /**
         * @brief destroy the unique instance of Singleton<T> class
         */
        static void destroy()
        {
                delete inst;
                inst = NULL;
        }

};

template <class T>
T * Singleton<T>::inst = NULL;

template <class T>
Singleton<T>::~Singleton() {}

///macro to implement singleton. Use it in derived class declaration
#define MAKE_SINGLETON( Class ) \
        public: \
                friend class Singleton < Class >; \
        private: \
                Class() {} \
                ~Class() {}

///macro to implement singleton. Use it in derived class declaration
#define MAKE_SINGLETON_WITHCONSTRUCTORS( Class ) \
        public: \
                friend class Singleton < Class >; \
        private: \
                Class(); \
                ~Class();

#endif