MagicIterator
MagicIterator
MagicIterator
class cont_iter
: public boost::iterator_adaptor<
cont_iter // Derived
, std::list<Container::Item>::iterator // Base
, IInterface* // Value
, boost::forward_traversal_tag // CategoryOrTraversal
, IInterface* // Reference :)
>
{
public:
cont_iter()
: cont_iter::iterator_adaptor_() {}
explicit cont_iter(const cont_iter::iterator_adaptor_::base_type& p)
: cont_iter::iterator_adaptor_(p) {}
private:
friend class boost::iterator_core_access;
IInterface* dereference() { return this->base()->pObject->GetInterface(); }
};
namespace detail {
template<typename T, typename U>
struct constify;
template<typename T, typename U>
struct constify<T*, U*> {
typedef T * type;
};
template<typename T, typename U>
struct constify<T*, U const*> {
typedef T const * type;
};
}
template<typename DstType,
typename Container,
typename InputIterator>
struct MagicIterator;
class Container
{
private:
struct Item
{
Object* pObject;
};
std::list<Item> m_items;
public:
// required by every Container for the iterator
typedef std::list<Item> iterator;
typedef std::list<Item> const_iterator;
// convenience declarations
typedef MagicIterator< IInterface*, Container, iterator >
item_iterator;
typedef MagicIterator< IInterface*, Container, const_iterator >
const_item_iterator;
item_iterator Begin();
item_iterator End();
};
template<typename DstType,
typename Container = Container,
typename InputIterator = typename Container::iterator>
struct MagicIterator :
// pick either const T or T, depending on whether it's a const_iterator.
std::iterator<std::input_iterator_tag,
typename detail::constify<
DstType,
typename InputIterator::value_type*>::type> {
typedef std::iterator<std::input_iterator_tag,
typename detail::constify<
DstType,
typename InputIterator::value_type*>::type> base;
MagicIterator():wrapped() { }
explicit MagicIterator(InputIterator const& it):wrapped(it) { }
MagicIterator(MagicIterator const& that):wrapped(that.wrapped) { }
typename base::value_type operator*() {
return (*wrapped).pObject->GetInterface();
}
MagicIterator& operator++() {
++wrapped;
return *this;
}
MagicIterator operator++(int) {
MagicIterator it(*this);
wrapped++;
return it;
}
bool operator==(MagicIterator const& it) const {
return it.wrapped == wrapped;
}
bool operator!=(MagicIterator const& it) const {
return !(*this == it);
}
InputIterator wrapped;
};
// now that the iterator adepter is defined, we can define Begin and End
inline Container::item_iterator Container::Begin() {
return item_iterator(m_items.begin());
}
inline Container::item_iterator Container::End() {
return item_iterator(m_items.end());
}
for(MagicIterator<IInterface*> it = c.Begin(); it != c.End(); ++it) {
// ...
}
template<typename T>
class IteratorImplementation
{
public:
virtual ~IteratorImplementation() = 0;
virtual T &operator*() = 0;
virtual const T &operator*() const = 0;
virtual Iterator<T> &operator++() = 0;
virtual Iterator<T> &operator--() = 0;
};
template<typename T>
class Iterator
{
public:
Iterator(IteratorImplementation<T> * = 0);
~Iterator();
T &operator*();
const T &operator*() const;
Iterator<T> &operator++();
Iterator<T> &operator--();
private:
IteratorImplementation<T> *i;
}
Iterator::Iterator(IteratorImplementation<T> *impl) :
i(impl)
{
}
Iterator::~Iterator()
{
delete i;
}
T &Iterator::operator*()
{
if(!impl)
{
// Throw exception if you please.
return;
}
return (*impl)();
}
// etc.
class ObjectContainer
{
public:
void insert(Object *o);
// ...
Iterator<Object *> begin();
Iterator<Object *> end();
private:
class CustomIteratorImplementation :
public IteratorImplementation<Object *>
{
public:
// Re-implement stuff here.
}
};
Iterator<Object *> ObjectContainer::begin()
{
CustomIteratorImplementation *impl = new CustomIteratorImplementation(); // Wish we had C++0x's "var" here. ;P
return Iterator<Object *>(impl);
}
template<typename T>
class MagicIterator
{
public:
MagicIterator(std::vector<T>::const_iterator i)
{
vector_const_iterator = i;
}
// Reimplement similarly for more types.
MagicIterator(std::vector<T>::iterator i);
MagicIterator(std::list<T>::const_iterator i);
MagicIterator(std::list<T>::iterator i);
// Reimplement operators here...
private:
std::vector<T>::const_iterator vector_const_iterator;
std::vector<T>::iterator vector_iterator;
std::list<T>::const_iterator list_const_iterator;
std::list<T>::iterator list_iterator;
};
// C++0x
template<typename T>
class Iterator :
public T::iterator
{
using T::iterator::iterator;
};
for(Iterator<Container> i = c.begin(); i != c.end(); ++i)
{
// ...
}