Building More Flexible Types with Mixins

Listing 2

template<typename T>
class ConcreteStack : AbstractStack {
public:
  ~ConcreteStack() { while (!IsEmpty()) Pop(); }
  void Push(std::auto_ptr<Item> x) { m.push_back(x.release()); }
  std::auto_ptr<Item> Pop() { std::auto_ptr<Item> x = m.top(); m.pop_back(); return m; }
  bool IsEmpty() { return m.IsEmpty(); }
private:
  std::vector<Item*> m;
};