I'd love an easy way to get around weird recursive generics. Here's my use case. The editor actually teases me by saying this is valid code, but the compiler doesn't seem to support it yet: package com.acornui.core import com.acornui.utils.collections.MutableArray /** * @author nbilyk */ public trait ParentᐸC: ChildᐸThisᐳᐳ { protected val children: MutableArrayᐸCᐳ public fun addChild(child: C) { children.add(child) child.setParent(this) } public fun removeChild(child: C) { children.removeValue(child) child.setParent(null) } public fun clearChildren() { for (i in children) { i.setParent(null) } children.clear() } } public trait ChildᐸP: ParentᐸThisᐳᐳ { protected var _parent: P? public fun getParent():P? { return _parent } public fun setParent(parent: P?) { _parent = parent } public fun remove() { if (_parent != null) { _parent!!.removeChild(this) } } } The error I get when I compile (just in case it's supposed to work): Error:Kotlin: [Internal Error] java.lang.IllegalStateException: Error types are not allowed…