Does an iterator iterate through boost::unordered_set or boost::unordered_map in the same order as long as the set or the map is unchanged?
Some implementations of a hash map will reorder the items that hash to the same bin, putting the most recently accessed item at the front of a list, as an optimization. This would change the order. I'm not aware that boost::unordered_map does this, but in the future you might end up substituting std::unordered_map and it will all depend on your compiler's implementation.