I'd like to propose adding collection_keys and collection_values to iterators library. ======== Motivation ======== I find myself very often having to iterate over all keys or values of a map (or multimap). The best I can do is to use BOOST_FOREACH to iterate over the collection value_type pairs and then work with .first or .second. That makes for awkward and unclear code. BOOST_FOREACH( const foo_bar_map_t::value_type &foo_bar_pair, my_map ) { baz(foo_bar_pair.second); } Instead, I'd like to do something like: BOOST_FOREACH( const bar_t &bar, collection_values(my_map) ) { baz(bar); } BOOST_FOREACH( const foo_t &foo, collection_keys(my_map) ) { baz(foo); } ======== Proposal ======== Add this to iterators library as collection_iterators.hpp Thanks, - Igor #ifndef .... #define .... #include <boost/iterator/transform_iterator.hpp> namespace boost { namespace detail { template<typename CollectionT> struct key_function : public std::unary_function<const typename CollectionT::value_type&, const typename CollectionT::key_type&> { typename key_function::result_type operator()(typename key_function::argument_type p) const { return p.first; } }; template<typename CollectionT> struct value_function : public std::unary_function<const typename CollectionT::value_type&, const typename CollectionT::mapped_type&> { typename value_function::result_type operator()(typename value_function::argument_type p) const { return p.second; } }; template<typename CollectionT, typename AdapterF> class collection_adapter { const CollectionT &c; public: typedef boost::transform_iterator<AdapterF, typename CollectionT::const_iterator> const_iterator; typedef const_iterator iterator; collection_adapter(const CollectionT &c) : c(c) {} const_iterator begin() const { return boost::make_transform_iterator(c.begin(), AdapterF()); } const_iterator end() const { return boost::make_transform_iterator(c.end(), AdapterF()); } }; } // Adapter for map-like collection -> iterable keys collection template<typename CollectionT> const detail::collection_adapter<CollectionT, detail::key_function<CollectionT> > collection_keys(const CollectionT &c) { return detail::collection_adapter<CollectionT, detail::key_function<CollectionT> >(c); } // Adapter for map-like collection -> iterable values collection template<typename CollectionT> const detail::collection_adapter<CollectionT, detail::value_function<CollectionT> > collection_values(const CollectionT &c) { return detail::collection_adapter<CollectionT, detail::value_function<CollectionT> >(c); } } // namespace boost #endif // ....