I was thinking about improving array performance, and was wondering if a transactional model would work well. You would keep a base copy of the array, and any writes would be written to a delta style transaction list. A reference to the array would be the list plus the base array. Different references to the same array would just reference different points in the delta list. The garbage colector would eat the delta list from the tail, merging writes into the base array once references to that part of the list are discarded. Writes would be very fast - just the time to add a delta to the transaction list. Reads would slow down as the transaction list grows, but the list would only be as long as the oldest reference, so providing references to very old copies of the array are not required, the transaction list would remain short. It would be even more efficient if the 'liveness' of references could be checked when writing the array - at the cost of a slight slowdown in write performance. I would be interested in any comments... I suspect somebody has done this before, but I havent looked for any papers yet. Regards Keean Schupke.