generics - Setter for field is removed by type projection -

i have following sscce:

class foo(val bars: map<int, bar<*>>) {      fun <baz> qux(baz: baz) {         val bar2 = bars[2]!!         bar2.bazes += baz     }      interface bar<baz> {         var bazes: mutablelist<baz>     } } 

this seems fine me, compiler complains that:

error:(5, 9) kotlin: setter 'bazes' removed type projection 

i have no idea means, less how correct it. what's going on here , how around it?

there's couple little issues. temporarily using bars[2]!! bar<baz>,

w: (4, 20): unchecked cast: foo.bar<any?> foo.bar<baz> e: (5, 20): assignment operators ambiguity:  public operator fun <t> collection<baz>.plus(element: baz): list<baz> defined in kotlin.collections @inlineonly public operator inline fun <t> mutablecollection<in baz>.plusassign(element: baz): unit defined in kotlin.collections 

kotlin doesn't know whether handle bar2.bazes = bar2.bazes.plus(baz) or bar2.bazes.plusassign(baz). if change var2.bazes.add(baz) or val bazes ambiguity goes away.

fixing , removing unsafe cast brings up

e: (5, 20): out-projected type 'mutablelist<out any?>' prohibits use of 'public abstract fun add(element: e): boolean defined in kotlin.collections.mutablelist' 

the question of can safely done type projection. gets treated out any?, can read list, in nothing, means can't add list.

it's unclear example why you're using *. if doesn't cause other issues, perhaps lift out <baz> parameter, e.g.

class foo<baz>(val bars: map<int, bar<baz>>)