Nice article. While I've gotten a corresponding example to work based upon your example, I haven't been able to get one to work where the collection key is itself a class (I've been experimenting with key class containing two longs).

I'm fairly sure I need to override the indexer
(public TItem this[ Tkey key ] {get;})
but I don't see what needs to be put into the accessor for efficient access, other than some kind of for loop (which seemed like it would defeating the purpose of an efficient lookup). Could you point out what I'm missing?

Thanks in advance.