namespace Org.DictionaryExtensions =
    type Dictionary<'T> with
     member x.get(key,defaultValue) = 
       match x.TryGetValue(key) with
       | (true,val) -> val
       | (false,_) -> defaultValue

There fixed that for you, now you can do, dict.get("foo","defaultvalue") in whatever CLR language you like. :)

As for fast and knocking .NET you're not seriously suggesting python are you? Runtime method lookup is not exactly what I think when thinking fast.