#include <iostream>
#include <vector>
using namespace std;

template<class Item>
class Iterator
{
public:
    virtual void first() = 0;
    virtual void next() = 0;
    virtual Item *currentItem() = 0;
    virtual bool isDone() = 0;
    virtual ~Iterator() {}
};

template<class Item>
class ConcreteAggregate;

template<class Item>
class ConcreteIterator : public Iterator<Item>
{
public:
    ConcreteIterator(ConcreteAggregate<Item> *aggr, int idx=0) :_aggr(aggr), _idx(idx) {}
    virtual void first()
    {
        _idx = 0;
    }

    virtual void next()
    {
        if (!isDone())
            ++_idx;
    }

    virtual  Item *currentItem()
    {
        if (isDone())
            return nullptr;
        return &(*_aggr)[_idx];
    }

    virtual bool isDone()
    {
        return _idx == _aggr->size();
    }
    
private:
    ConcreteAggregate<Item> *_aggr;
    int _idx;
};

template<class Item>
class Aggregate
{
public:
    virtual Iterator<Item> *createIteator() = 0;
    virtual void addItem(const Item &i) = 0;
    virtual ~Aggregate() {}
};

template<class Item>
class ConcreteAggregate : public Aggregate<Item>
{
public:
    ConcreteAggregate()
    {
        _data.clear();
    }

    ~ConcreteAggregate()
    {
        _data.clear();
    }

    virtual void addItem(const Item &i) override
    {
        _data.push_back(i);
    }

    virtual Iterator<Item> * createIteator() override
    {
        return new ConcreteIterator<Item>(this);
    }

    Item & operator[](int idx)
    {
        return _data[idx];
    }

    int size()
    {
        return _data.size();
    }
private:
    vector<Item> _data;
};


void test()
{
    Aggregate<int> *aggr = new ConcreteAggregate<int>();
    aggr->addItem(10);
    aggr->addItem(20);
    aggr->addItem(30);
    
    Iterator<int> *it = aggr->createIteator();
    it->first();
    while (!it->isDone())
    {
        cout << *(it->currentItem()) << endl;
        it->next();
    }

　  delete aggr;
　  delete it;

}

int main()
{
    test();
    cin.get();
    return 0;
}