IntMap and LongMap are completely similar except for the fact that LongMap does not have firstKey and lastKey. I am not sure if these collections are going to stay in the collections library in the long run, but if so it would be very helpful to add firstKey and lastKey to LongMap (just copy the code from IntMap).

I need this to check if a collection is continuous (c.lastKey-c.firstKey+1 == c.size), because that allows me to do some optimizations. I know I could use c.keys.head and c.keys.last, but that is very inefficient since c.keys.last requires a full traversal of the collection.