On Feb 16, 10:03 ¨Βν¬ ΆΓθςιστοπθες ΔιγεμωΌγνδιγ®®®ΐηναιμ®γονΎ χςοτεΊ > Since the main use is lookup by reference, and hash is designed for > keyed access, hash would seem to be the natural container to use. I'm > not sure I quite get what you are saying about iterating through a > singleton instead, could you explain a little more? [...] There's one set of rooms, which may have sub-sets, of course. But, for the set of rooms you may want to iterate through each room for whatever reason. Putting the rooms into a Singleton allows such iteration in an inherently thread-safe way. Admittedly, I don't really understand Hash that well. -Thufir