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POMake a c++ iterator that traverses 2 containers
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  1. POMake a c++ iterator that traverses 2 containers
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    copied!<p>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?</p> <p><strong>EDIT</strong> 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.</p> <pre><code>enum Flag { A_flag, B_flag }; class T_proxy { public: T_proxy(const T&amp; 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&amp; tp) {return tp.flag() == matchFlag_;} private: Flag matchFlag_; }; private: T t_; Flag flag_; }; class AB_list { public: typedef T_proxy::Compare Compare; typedef vector&lt;T_proxy&gt;::iterator iterator; typedef boost::filter_iterator&lt;Compare, iterator&gt; sub_iterator; void insert(const T&amp; 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 same private: vector&lt;T_proxy&gt; data_; }; // usage AB_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 &lt;&lt; temp; } </code></pre>
 

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