ClickHouse/libs/libcommon/include/common/singleton.h

#pragma once

/** Пример:
  * 
  *	class Derived : public Singleton<Derived>
  *	{
  *	    friend class Singleton<Derived>;
  *     ...
  *	protected:
  *		Derived() {};
  *	};
  *
  * Или так:
  *
  * class Some
  * {
  *     ...
  * };
  *
  * class SomeSingleton : public Some, public Singleton<SomeSingleton> {}
  */
template<class Subject> class Singleton
{
public:
	static Subject & instance()
	{
		/// Нормально при включенных thread safe statics в gcc (по-умолчанию).
		static Subject instance;
		return instance;
	}

protected:
	Singleton(){};

private:
	Singleton(const Singleton&);
	Singleton& operator=(const Singleton&);
};