A modern programming language that makes developers happier.

kotlinlang

is it possible to configure an object in a sealed class to execute some behavior any time it is accessed? e.g.

```sealed class ErrorStates {
    object ThingsAreBadNow {
        onAccess {
            Logger.log("A bad thing happened")
        }
    }
}```
The `init` block can be used for data classes. Is there something I can do to get a similar behavior for objects?

`init` can be used in any class, not just data classes. Just change `object` to `class` and have its usages create new instances instead of being a singleton

the issue is you have to override `equals` and then `hashMap` for a stateless class  in a sealed class. adds a lot of unnecessary code

Instead of your app doing true equality checks, doing type-checks might be better in this case. Instead of `if (error == ThingsAreBadNow)`, do `if (error is ThingsAreBadNow)`. No need to override equals/hashCode, and you get better type support with smart-casting or exhaustive `when` expressions

i tend to do type checks for sealed classes in general anyway. i thought it was a compiler error to have a stateless class in a sealed class, but turns out it’s just a warning

For most cases, it’s preferable to use an `object` for stateless subclasses since they will be always be the same, so you’d get fewer allocations. If you need to do something on accessing them, then it’s reasonable to want to create a new instance to trigger an `init` block and ignore the warning. Although, doing any logic on object-creation is generally discouraged, and you might actually be best off just having a wrapper function to protect access to the object itself.

```sealed class ErrorStates {
    private object ThingsAreBadNow : ErrorStates()

    companion object {
        fun thingsAreBadNow() : ErrorStates {
            Logger.log("A bad thing happened")
            return ThingsAreBadNow
        }
    }
}```