What's the type of an object expression?


This works:

class X(n: Int) {
  val foo = object {
    val bar = n * 2

This does not work:

class X(n: Int) {
  val foo = object {
    val bar = n * 2
  fun y() = foo.bar // bar can't be resolved

If this is expected, is there another way to declare a foo namespace inside X (with access to X’s instance state)? Would be very handy in some cases, e.g. to group related properties in a class.


Yes, this is expected. Properties declared in a class need to have a non-anonymous type, so if you’re not explicitly specifying the supertype of object, the type of foo in the second example will be Any.

For grouping related members of the class, I think it’s best to use features that don’t impact the runtime behavior of a class, such as folding regions in the IDE.


What I’m looking for is a grouping that’s visible at call sites, e.g. metrics.foo, metrics.bar, metrics.baz with two-stage auto-completion.


Can you use named objects?


That was my initial hope, but as far as I can tell, named objects cannot access instance state (or at least constructor arguments) of the enclosing class, as in my example.


Have you tried using an inner class?


That would work, but declaring a private named inner class, creating a single instance, and assigning it to a private property feels a bit too indirect/verbose for my needs. I just wanted to make sure that I’m not missing a way to achieve this with object expressions or a similar language feature, given that object { val foo = 1 }.foo actually works.

I think it’s safe to say by now that there is no easier way than an inner class. Thanks for the suggestion!