template <typename T>
class Client
{
    private:
        Client(...) {}
        ~Client()   {}

        template <typename U>
        friend class Client<T>& initialize(...);
};


template <typename T>
Client<T> initialize(...)
{
      Client<T> client = new Client<T>(...);
}

template <typename T>
class Client
{
private:
    Client() {} // Note private constructor
public:
    ~Client() {} // Note public destructor

    // Note friend template function syntax
    template<typename U>
    friend Client<U> initialize();
};


template<typename T>
Client<T> initialize()
{
      /* ... */
}

int main()
{
    Client<int> client = initialize<int>();
}

template <typename U> friend Client<U> initialize(.....);

template <typename T>
class Client
{
    private:
        Client() {}
        ~Client() {}

        template <typename U>
        friend Client<U> *initialize();

        template <typename U>
        friend void destroy( Client<U> * );
};


template <typename T>
Client<T> *initialize()
{
  return new Client<T>();
}

template <typename T>
void destroy( Client<T> *client )
{
  delete client;
}

int main()
{
  auto client = initialize<int>();

  destroy( client );

  return 0;
}

template <typename T>
class MyClass {
   template <typename U>
   friend MyClass<U> f();
};

// Forward declarations
template <typename T>
class MyClass;
template <typename T>
MyClass<T> f();

// Definition of class template
template <typename T>
class MyClass {
   friend MyClass<T> f<T>();
};

// Definition of friend function
template <typename T>
MyClass<T> f() { ... }

template <typename T>
class MyClass {
    friend MyClass<T> f() { ... } // define inline
};