/**/#include "defs.H"const int DEFAULT_LIST_CAPACITY = 100;template <class Item> class Iterator;/**/template <class Item>class List {public:    List(long size = DEFAULT_LIST_CAPACITY);/**/    Iterator<Item>* CreateIterator() const;/**/    long Count() const;    Item& Get(long index) const;    // ...};/**/template <class Item>class Iterator {public:    virtual void First() = 0;    virtual void Next() = 0;    virtual bool IsDone() const = 0;    virtual Item CurrentItem() const = 0;protected:    Iterator();};/**/template <class Item>class ListIterator : public Iterator<Item> {public:    ListIterator(const List<Item>* aList);    virtual void First();    virtual void Next();    virtual bool IsDone() const;    virtual Item CurrentItem() const;/**/private:    const List<Item>* _list;    long _current;};/**/template <class Item>ListIterator<Item>::ListIterator (    const List<Item>* aList) : _list(aList), _current(0) {}/**/template <class Item>void ListIterator<Item>::First () {    _current = 0;}/**/template <class Item>void ListIterator<Item>::Next () {    _current++;}/**/template <class Item>bool ListIterator<Item>::IsDone () const {    return _current >= _list->Count();}/**///class IteratorOutOfBounds;#define throw ///**/template <class Item>Item ListIterator<Item>::CurrentItem () const {    if (IsDone()) {        throw IteratorOutOfBounds;    }    return _list->Get(_current);}/**/template <class Item>class ReverseListIterator : public Iterator<Item> {public:    ReverseListIterator(const List<Item>* aList);    virtual void First();    virtual void Next();    virtual bool IsDone() const;    virtual Item CurrentItem() const;};/**/class Employee {  public:    void Print();};/**/void PrintEmployees (Iterator<Employee*>& i) {    for (i.First(); !i.IsDone(); i.Next()) {        i.CurrentItem()->Print();    }}/**/template <class Item>class SkipList : public List<Item> {    public:};template <class Item>class SkipListIterator : public ListIterator<Item> {public:    SkipListIterator(const List<Item>* aList);    void First();    void Next();    bool IsDone() const;    Item CurrentItem() const;};void dummy () {/**/List<Employee*>* employees;// ...ListIterator<Employee*> forward(employees);ReverseListIterator<Employee*> backward(employees);PrintEmployees(forward);PrintEmployees(backward);/**/}/**/void dummy2 () {/**/SkipList<Employee*>* employees;// ...SkipListIterator<Employee*> iterator(employees);PrintEmployees(iterator);/**/}/**/template <class Item>class AbstractList {public:    virtual Iterator<Item>* CreateIterator() const = 0;    // ...};/**/template <class Item>Iterator<Item>* List<Item>::CreateIterator () const {    return new ListIterator<Item>(this);}/**/void dummy3() {/**/// we know only that we have an AbstractListAbstractList<Employee*>* employees;// ...Iterator<Employee*>* iterator = employees->CreateIterator();PrintEmployees(*iterator);delete iterator;/**/}/**/template <class Item>class IteratorPtr {public:    IteratorPtr(Iterator<Item>* i): _i(i) { }    ~IteratorPtr() { delete _i; }/**/    Iterator<Item>* operator->() { return _i; }    Iterator<Item>& operator*() { return *_i; }private:    // disallow copy and assignment to avoid    // multiple deletions of _i:    IteratorPtr(const IteratorPtr&);    IteratorPtr& operator=(const IteratorPtr&);private:    Iterator<Item>* _i;};/**/void dummy4 () {/**/AbstractList<Employee*>* employees;// ...IteratorPtr<Employee*> iterator(employees->CreateIterator());PrintEmployees(*iterator);/**/}/**/template <class Item>class ListTraverser {public:    ListTraverser(List<Item>* aList);    bool Traverse();protected:    virtual bool ProcessItem(const Item&) = 0;private:    ListIterator<Item> _iterator;};/**/template <class Item>ListTraverser<Item>::ListTraverser (    List<Item>* aList) : _iterator(aList) { }/**/template <class Item>bool ListTraverser<Item>::Traverse () {    bool result = false;    for (        _iterator.First();        !_iterator.IsDone();        _iterator.Next()    ) {        result = ProcessItem(_iterator.CurrentItem());/**/        if (result == false) {            break;        }    }    return result;}/**/class PrintNEmployees : public ListTraverser<Employee*> {public:    PrintNEmployees(List<Employee*>* aList, int n) :        ListTraverser<Employee*>(aList),        _total(n), _count(0) { }/**/protected:    bool ProcessItem(Employee* const&);private:    int _total;    int _count;};/**/bool PrintNEmployees::ProcessItem (Employee* const& e) {    _count++;    e->Print();    return _count < _total;}/**/void dummy5 () {/**/List<Employee*>* employees;// ...PrintNEmployees pa(employees, 10);pa.Traverse();/**/ListIterator<Employee*> i(employees);int count = 0;/**/for (i.First(); !i.IsDone(); i.Next() ) {    count++;    i.CurrentItem()->Print();/**/    if (count >= 10) {        break;    }}/**/}/**/template <class Item>class FilteringListTraverser {public:    FilteringListTraverser(List<Item>* aList);    bool Traverse();protected:    virtual bool ProcessItem(const Item&) = 0;    virtual bool TestItem(const Item&) = 0;private:    ListIterator<Item> _iterator;};/**/template <class Item>void FilteringListTraverser<Item>::Traverse () {    bool result = false;/**/    for (        _iterator.First();        !_iterator.IsDone();        _iterator.Next()    ) {        if (TestItem(_iterator.CurrentItem())) {            result = ProcessItem(_iterator.CurrentItem());/**/            if (result == false) {                break;            }        }    }    return result;}/**/