is there any way to simplify this?

update( B(firstField = objA.name, secondField = objB.surname) )

into something similar to this? (it doesn’t work)

update( ::objA )

given that the two classes have the same structure but just different property names? so that I don’t need to manually specify each field?

val objA = A("John", "Walker")

fun update(obj : B) {
    ...
}

data class A (
    val name : String
    val surname : String
)

data class B (
    val firstField : String
    val secondField : String
)

N.B. I cannot modify the classes definition, by extending or implementing interfaces

My question is, if this was possible to make work what would you expect to happen if someone flips the order of B's or A's properties?

yes, true, I was just wondering if Kotlin provides something like that, based on the property order, but I guess not

afaik not, and even if it did - it's not a good idea, property order changes, boom whole thing stops working and you wouldn't even see what went wrong

yes, I see your point, but in some cases, this would be very handy

is this a good idea? no.

definitely not a very concise code, but interesting to see, thanks!