How can I implement Collection/List interface or abstract class in Kotlin?

Question

I'm having trouble implementing the iterator and get set functions. (Edit: By trouble I mean that I don't know how to do it and I need help)

In the past, I've inherited from ArrayList even though I need a fixed-size collection. I've also used an Array property in my class and added a get and a set operator funcions, but these two solutions just feel like unnecessary workarounds.

Edit: I just found out that Kotlin itself doesn't have a List implementation yet (it uses ArrayList instead), So maybe I'm not supposed to be able to Implement it. I'm going to keep this open just in case.

Answer 1

There is a very neat feature in Kotlin that allows you to easily implement the List interface by Delegation. Just use the by operator on a list property, then the class will delegate all methods of the List interface to that property. So, for example, instead of,

class Cars {
    private val cars = ArrayList<Car>()
}

you write:

class Cars(
    private val cars: MutableList<Car> = ArrayList<Car>()
): MutableList<Car> by cars

Now Cars implements List, and can be used just as such:

val cars = Cars()
cars.add(Car())
for (car in cars)
    car.vroom()