Idiomatic way to check if some (not all) properties of two objects equal in Kotlin

Let's assume i have a class with two instances:

class Car(val id: Int, val color: Color, val pistons: Int, val spoiler: Boolean)

val audi = Car(1234, Color.BLUE, 8, false)
val bmw = Car(4321, Color.WHITE, 6, false)

Now i'd like to check equality for some properties (not all -> i'd use a data class in that case)

fun looksSimilar(a: Car, b: Car) = a.color == b.color && a.spoiler == b.spoiler

I'm now looking for a method which does comparison:

• for more generic objects T and their properties
• more idiomatic: no-one wants to read tons of equals-checks
• similarly fast

I've come up with the following proposal:

fun <T> Pair<T, T>.equalIn(vararg arguments: (T) -> Any?) =
    arguments.toList().all { it(first) == it(second) }

which allows me to write the above check as

val looksSimilar = (audi to bmw).equalIn({it.color}, {it.spoiler})

Does anyone know a better (e.g. cleaner/faster) solution?

My usecase is the following:

I'm writing an Android App with multiple RecyclerView's (= fancy view to display lists)

Each RecyclerView has a ListAdapter (responsible for the underlying list)

Each ListAdapter requires a DiffUtil.ItemCallback (for comparing old & new Items & initiating appropiate changes in the view)

val callback = object : DiffUtil.ItemCallback<Car>() {

    override fun areItemsTheSame(oldItem: Car, newItem: Car): Boolean
    // usually checks for id, e.g. oldItem.id == newItem.id

    override fun areContentsTheSame(oldItem: Car, newItem: Car): Boolean
    // checks if two items look the same.
    // Used for fancy enter/exit animations afaik.
    // e.g. (oldItem to newItem).equalIn({it.color}, {it.spoiler})
}