What is the correct way to add an abstract private getter and a public setter?

Question

I have an interface where I want a property that can be modified innside the class, but not outside. I cannot use val because it needs to be mutable and the var keyword can not have a specified private setter since this is in an interface.

In Java I would have done this:

public <T> getMyProperty();

I can use the same approach in kotlin and just write the getter function dirrectly, but this does not seem like a kotlinlike approach. Is there a better way to achieve the same as this?

fun getMyProperty()

Answer 1

In Kotlin, you can actually override a val with a var, so, I think, what you want can be expressed as follows:

interface Iface {
    val foo: Foo
}

class Impl : Iface {
     override var foo: Foo
         get() = TODO()
         private set(value) { TODO() } 
}

Or you can override the val with a property with a backing field and default accessors:

class ImplDefaultGetter : Iface {
    override var foo: Foo = someFoo
        private set
}

In both cases, the mutability and the presence of a private setter become an implementation detail of the classes and are not exposed through the interface.