var ivar = [:]

ivar.className // __NSDictionaryI

var i = 1

i.className // error: 'Int' does not have a member named 'className'

If you want to get the type of a primitive, you have to use bridgeToObjectiveC().
Example:

var i = 1


i.bridgeToObjectiveC().className // __NSCFNumber








println("\(object_getClassName(now))");