scala - Why do some collection classes have an "empty" instance method additionally to the class method? -

both exist example here:

map.empty[int, int] map(1 -> 41).empty  set().empty set.empty 

but here class methods existing:

list.empty        //ok list(1,2,3).empty //doesn't exist  array.empty       //ok array("a").empty  //doesn't exist 

isn't empty perfect case class method (and shouldn't instance method empty deprecated therefore)?

or should empty instance method added classes missing it?

is there language point of view makes difficult having empty class method (e. g. type inference, higher-kinded types, ...).

ps: suggested maps default values harder achieve without instance method empty:

map[int, int](1->2, 21->42).withdefault(_*2).empty 

what think?

that's true, empty method on class instance. reason why it's required sets , maps because implement builders using method. guess reason why wasn't included elsewhere because wasn't typical use case.