demo.kt

val newX = x.copy(
  a = if (fields.contain("a")) x.a else y.a
  b = if (fields.contain("b")) x.b else y.b
  c = if (fields.contain("c")) x.c else y.c
)

// Is there a nicer way that i could do:
val newX = x.copy(a = getCorrect("a"), b = getCorrect("b'), c = getCorrect("c"))