I'm using boost version 1.33.1 and am contemplating using a multiIndex container in my application. The held object will be something like: class element { int x; int y; Object *pObject; }; I need 2 ordered_non_unique indices using x and y and one ordered_unique index on pObject. The problem is that the values of x and y will need to be modified during the life of this container. Since the documentation says these indices are implemented using red-black trees, I think I'm heading for trouble. However, the multiIndex container seems to have a "modify_key" method. I can guarantee that the pObject value will not change, so if I obtain an iterator to an element based on this index, will I be able to modify either x or y and expect their related indices to still work?