[SOLVED] kotlin declaring Object within sealed class and initialized

kotlin declaring Object within sealed class and initialized

sealed class StockLabel : Label() {
  object OutOfStockLabel : StockLabel()
}

I know sealed class in kotlin is implicitly abstract and we will get compile error if doing so. But I saw the usage of the code above, the 'OutOfStockLabel' is declared within the 'StockLabel' sealed class also with 'StockLabel()', the 'StockLabel()' I think should be the type for 'OutOfStockLabel' but is it here for initialization or?

Need some help to understand the code case here.

Solution

Although the syntax looks similar, this code:

object OutOfStockLabel : StockLabel()

is the syntax for defining a class, not creating an instance of the abstract class. You are declaring a subclass (an object in this case) whose primary constructor (which is implicit for an object) calls the abstract class's constructor. This is permitted for abstract classes. If you couldn't, it would be impossible to create any subclasses of an abstract class.