scala - Map.contains with a super-type of key type -

i have case where

trait eventlike trait event extends eventlike  trait api {   private var map = map.empty[event, any]    def contains(e: eventlike): boolean = map.contains(e) } 

this doesn't work because of invariance in map's key type:

<console>:58: error: type mismatch;  found   : eventlike  required: event              def contains(e: eventlike): boolean = map.contains(e)                                                                 ^ 

what work-around minimum performance penalty. is, don't want introduce terrible thing:

  def contains(e: eventlike): boolean = e match {     case e1: event => map.contains(e1)     case _ => false   } 

is there different map implementation (may mutable thread local) use?

you can declare map map[eventlike, any]:

trait api {   private var map = map.empty[eventlike, any]   def contains(e: eventlike): boolean = map.contains(e)    def add(e:event): unit = {     map += (e -> ???)   } } 

you can still populate map event keys only, while searching both event , eventlike.

upd

if don't mind using java mutable collections, can use hashmap, accepts object argument of contains regardless of type parameters of map:

trait api {   private val map = new java.util.hashmap[event, any]   def contains(e: eventlike): boolean = map.containskey(e) }