key_iterator.hpp

template<typename TMapIterator>
class key_iterator : public TMapIterator
{
public:
    typedef typename TMapIterator::value_type::first_type key_type;

    key_iterator() : TMapIterator() { }
    key_iterator(TMapIterator iter) : TMapIterator(iter) { }

    key_type* operator->()
    {
        return &this->TMapIterator::operator->()->first;
    }

    key_type& operator*()
    {
        return this->TMapIterator::operator*().first;
    }
};

template<typename TMapIterator>
key_iterator<TMapIterator> make_key_iterator(TMapIterator iter)
{
    return key_iterator<TMapIterator>(iter);
}