If you are looking for Bar, it is highly likely that you are already looking specifically for a particular functionality - say, the action - for Bar. As such, it is irrelevant which method you use, both will get you to the function you need.

Conversely, while it is likely you will want to look up all items that implement a particular functionality, it is much less likely you are going to ever need a complete listing of all functionality that an item employs; you will be targeting only one functionality for that item and will have that one functionality as the primary and concrete focus. Ergo, functionality comes first, followed by what item has that functionality.