val map: MutableMap<Int, String> = WeakHashMap<Int, String>()

class Hi(val something:String, val filter: (String) -> Boolean = Hi.DefaultFilter) {
    companion object DefaultFilter: (String) -> Boolean {
        override fun invoke(p1: String) = true
    }
}

===

val DEFAULT: (String) -> Boolean = { true }
class Hi(val filter: (String) -> Boolean = DEFAULT) {
  fun foo() {
    val isDefaultFilter = filter === DEFAULT
  }
}