Hi John, 2012/1/11 John M. Dlugosz <mpbecey7gu@snkmail.com>:
Consider something like this:
themap_type::iterator search_for (int val) { return boost::find_if (themap|map_values, my_predicate(val)); }
... Is there a good reason why the filtered iterator can't give up the inner original iterator? How do you use range adaptors in these situations?
I think this situation's better way is wrap by function template and use boost::optional. example: #include <iostream> #include <map> #include <boost/optional.hpp> #include <boost/range/adaptor/map.hpp> #include <boost/range/algorithm/find_if.hpp> template <class Range, class Predicate> boost::optional<typename boost::range_value<Range>::type> search_for(const Range& r, Predicate pred) { auto it = boost::find_if(r, pred); if (it == boost::end(r)) return boost::none; return *it; } template <class MapRange, class Predicate> boost::optional<typename MapRange::mapped_type> map_search_for(const MapRange& r, Predicate pred) { return search_for(r | boost::adaptors::map_values, pred); } bool is_alice(const std::string& name) { return name == "Alice"; } int main() { std::map<int, std::string> m = {{3, "Alice"}, {1,"Bob"}, {4, "Carol"}}; if (boost::optional<std::string> name = map_search_for(m, is_alice)) { std::cout << "found:" << name.get() << std::endl; } else { std::cout << "not found" << std::endl; } } Thanks,
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