Why ``` object A { sealed class B cla...

# getting-started

[voddan]

Why

object A {
    sealed class B
    
    class C : B()
    class D : B()
}

gives cane be inherited only by nested classes,
but

sealed class B
    
class C : B()
class D : B()

works fine?

[wbertan]

Looking at the bytecodes decompiled:
My example:

object AsasA1 {
    sealed class AsasB1

    class AsasC1 : AsasB1()
    class AsasD1 : AsasB1()
}

sealed class AsasB2

class AsasC2 : AsasB2()
class AsasD2 : AsasB2()

The second case generates:

public abstract class AsasB2 {
   private AsasB2() {
   }

   // $FF: synthetic method
   public AsasB2(DefaultConstructorMarker $constructor_marker) {
      this();
   }
}

while the other one generates:

public abstract static class AsasB1 {
   }

The one inside the object do not generates the constructor. Why? Don't know 😞

[antonis]

The ability to extend sealed classes with not nested classes was added in kotlin 1.1

[antonis]

you can still do this the old way

[antonis]

class A {
sealed class B {
class C : B()
class D : B()
}
}

[voddan]

I am on 1.3

[antonis]

something obviously is not working as expected…

[antonis]

why do you need to defined the sealed class hierarchy inside a singleton?

[antonis]

https://kotlinlang.org/docs/reference/whatsnew11.html#sealed-and-data-classes

[antonis]

quote: “Now you can define subclasses of a top-level sealed class on the top level in the same file, and not just as nested classes of the sealed class”

[antonis]

so what you are trying to achieve can only be done in top-level classes

[antonis]

object A {
sealed class B {
class C : B()
class D : B()
}
}

[antonis]

the workaround is to use nested classes inside your sealed class

[voddan]

So it is probably a bug?

[antonis]

it’s a documented feature, check link above

[antonis]

😛

[ilya.gorbunov]

It's a known limitation that we're considering to lift later:
https://youtrack.jetbrains.com/issue/KT-13495

[voddan]

Thanks, voted!