best collection object for FIFO and ability to view items by position

Question

I'm looking for a collection object/strategy that can allow for FIFO and lets me view the items in the collection by simply specifying their position. To clarify:

1. I would like this data structure to hold say 100 DTO objects, and then when it gets to 101, I can make room by deleting the first item, etc. (FIFO).

2. I'd like to be able to return the newest x # of these objects when requested.

I tried to use the .Net queue object, however as far as I can tell it does not support #2, although I might be overlooking something there.

Answer 1

It would not be hard to wrap a List and do a RemoveAt(0) when you want to pop an item out of the queue. That would give you FIFO and let you index in anywhere you want. You should probably wrap it to protect the integrity of the queue (FIFO only).

Answer 2

I took a quick look at the .NET docs and I couldn't find anything that fulfils it as you need it. Looks like you need to implement it on your own, though that's not too difficult. I recommend going with an array of the appropriate size, and keep around read and write indices for the current position in the array, and use it as a circular array.

Enqueue would be writing the value to readIndex, then setting readIndex to ((readIndex + 1) % queueSize). Dequeue would throw an exception if readIndex == writeIndex, otherwise get the value at writeIndex, then increment writeIndex by ((writeIndex + 1) % queueSize). Peeking into a queue index (from the top of the queue, that is the item that was queued last) would be returning the item at ((queueSize + (readIndex - index)) % queueSize).