I have a need for a "container" that acts like the following. It has 2 subcontainers, called A and B, and I need to be able to iterate over just A, just B, and A and B combined. I don't want to use extra space for redundant data, so I thought of making my own iterator to iterate over A and B combined. What is the easiest way to make your own iterator? Or, what is another way to do this?
EDIT Ultimately, I don't think it was good design. I have redesigned the entire class heirarchy. +1 for refactoring. However, I did solve this problem sufficiently. Here's an abbreviated version of what I did, for reference; it uses boost::filter_iterator. Let T be the type in the container.
enum Flag{ A_flag, B_flag};class T_proxy{public: T_proxy(const T& t, Flag f) : t_(t), flag_(f) {} operator T() const {return t_;} Flag flag() const {return flag_;} class Compare { public: Compare(Flag f) : matchFlag_(f) {} operator() (const T_proxy& tp) {return tp.flag() == matchFlag_;} private: Flag matchFlag_; };private: T t_; Flag flag_;};class AB_list{public: typedef T_proxy::Compare Compare; typedef vector<T_proxy>::iterator iterator; typedef boost::filter_iterator<Compare, iterator> sub_iterator; void insert(const T& val, Flag f) {data_.insert(T_proxy(val, f));} // other methods... // whole sequence iterator begin() {return data_.begin();} iterator end() {return data_.end();} // just A sub_iterator begin_A() {return sub_iterator(Compare(A_flag), begin(), end()); sub_iterator end_A() {return sub_iterator(Compare(A_flag), end(), end()); // just B is basically the sameprivate: vector<T_proxy> data_;};// usageAB_list mylist;mylist.insert(T(), A_flag);for (AB_list::sub_iterator it = mylist.begin_A(); it != mylist.end_A(); ++it){ T temp = *it; // T_proxy is convertible to T cout << temp;}