By virtue of polymorphism, all List implementations use a single ListIterator that hides complexity of actual solution used (eg: ArrayList). To make this possible, each class implementing List needs to come with a ListIterator implementation adapted to the data structure they are using and keep it hidden to end users so they only work with abstractions.
Usage example:
ArrayList<long> list;
list.addToTail(1);
list.addToTail(2);
// This uses ListIterator<long>* for List<long>*, instead of ArrayList<long>
for(auto it = list.begin(); *it!=*(list.end()); ++(*it)) {
std::cout << (*(*it)) << std::endl;
}
Whereas STL equivalent is:
std::vector<long> list;
list.push_back(1);
list.push_back(2);
// This uses iterator for std::vector<long> directly
for(auto it = list.begin(); it!=list.end(); ++it) {
std::cout << (*it) << std::endl;
}
As one can see above, because API iterators are polymorphic, they require an extra pointer compared to those of STL. Unlike STL, currently only forward non-const iterators are supported, but these will be added in the near future!
Forward iterator prototype for List, returned by latter's begin and end methods
template <typename T>
class ListIterator
| Method | Signature | Description |
| ~ListIterator | virtual ~ListIterator () | Virtual destructor used when iterator is deallocated |
| operator* | virtual const T& operator* () = 0 | Dereferencing operator required when accessing current element |
| operator++ | virtual void operator++ () = 0 | Advance operator required when iterating |
| operator!= | bool operator!= (const ListIterator<T>& it) | Difference operator required when iterating |