That you'll better ask the dictionary implementors at Redmond :). I was a bit surprised by this myself some time ago. Just create a little test yourself and probably you will be more than surprised by the result...
There are some articles out there describing it better than I probably can... http://www.safnet.com/writing/tech/archives/2007/07/performance_3_c.html http://blogs.msdn.com/shawnhar/archive/2007/07/02/twin-paths-to-garbage-collector-nirvana.aspx http://beardseye.blogspot.com/2007/08/nuts-enum-conundrum.html From: [email protected] [mailto:[email protected]] On Behalf Of Ayende Rahien Sent: den 6 februari 2009 15:45 To: [email protected] Subject: [nhibernate-development] Re: IDictionary<entitymode, xxx> Ha? Why would there be boxing involved at all? On Fri, Feb 6, 2009 at 3:46 PM, Roger <[email protected]<mailto:[email protected]>> wrote: Hi EntityModeToTuplizerMapping holds a dic keyed by entitymode internally. From a perf perspective, it's a bad thing to do - enum as a key will cause a lot of boxing internally in dictionary operations. And in (large) resultsets these dictionary items in it will be retrieved _a lot_. I just made a quick test and changed this dictionary to be keyed by an int instead (casting the enum to int when added), some extreme queries (=fast query, big resultset) run approx 10% faster in total. I'll be glad to send this little patch. However, I would say a better solution would be to change this enum to a class instead (I don't really like enums at all :)). I can provide a patch for this as well, but this type has a lot of dependencies. In short words - before spending some hours doing this, I would like to see if you have any opinions on this? Whatever you think, I would strongly suggest that get rid of often used dictionaries keyed by enums. Keep up the great work! Regards Roger
