Kotlin overriding supertype variables

Question

Consider two classes:

abstract class ParentRepository {}

class ChildRepository : ParentRepository {}

abstract class ParentClass {
    protected abstract var repository: ParentRepository
}

class ChildClass : ParentClass {
    override var repository: ChildRepository
}

The last part won't work:

override var repository: ChildRepository

It will complain:

Type of 'repository' doesn't match the type of the overridden var-property 'protected abstract var repository: ParentRepository

I understand the problem, but I don't see the reason why this shouldn't work – ChildRepository is an instance of ParentRepository and this is a common thing I am used to from Java.

Answer 1

You have to declare repository as val. You can still override it as var:

protected abstract val repository: ParentRepository

override var repository: ChildRepository