I just tried again. I think it's just with

fun getCount() = aCollection.count()

.

size

works correctly in all cases EDIT Updated snippet above. Error is consistent To reproduce: Create extension function

x

on

SomeClass

. Create a class

Bar

extending a java interface with

getX

. Override

getX

like

fun getX() = someClassInstance.x()

Can be fixed by specifying type explicitly like

fun getX(): ReturnType = someClassInstance.x()

Looks like a compiler bug