class Clam
{
public:
  Clam();
  ~Clam();
private:
  class Self; // декларируем сторонний класс
  Self* self;
};

class Clam::Self
{
  // private things (pearls?) here
};

Clam::Clam()
{
  self = new Clam::Self();
}

Clam::~Clam()
{
  delete self;
}